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#1
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
A previous poster stated that the Heathkit AR1500 and AR3a are a poor
combination. This is true if you listen at any level other than quiet. A couple of years after introduction, the AR1500's output amplifiers were updated and the AR1500A was born. The AR1500A has specific circuits that limit clipping and other distortion when it is driving low imperance speakers at high levels. It is possible to modify the AR1500's output amplifiers to include this improvement; you'd have to go to a Heathkit users groups to obtain that information. Driving AR3a's hard with an unmodified AR1500 produces a lot of "clipped sine waves" that will blow the mid-range driver. If you don't want to burnout the mid-range, but want to turn the volume up, add a 1 ohm resistor in series with each mid-range. This will change the mid-range balance, but that's better than burning out the driver. The AR3a was sold in kit form as the Heathkit AS103a. Let me know if you have any questions. |
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#2
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
wrote in message ...
A previous poster stated that the Heathkit AR1500 and AR3a are a poor combination. This is true if you listen at any level other than quiet. Rolf, I have an AR-3a and an AR1500 and they seem to work together fairly well. I don't know about "quiet" as that is a relative term. My den is quite small and my normal listening level is less than 1 watt, but occasionally I'll listen at levels higher. A couple of years after introduction, the AR1500's output amplifiers were updated and the AR1500A was born. The AR1500A has specific circuits that limit clipping and other distortion when it is driving low imperance speakers at high levels. It is possible to modify the AR1500's output amplifiers to include this improvement; you'd have to go to a Heathkit users groups to obtain that information. Rolf, any chance you have the schematic for the power amp on the "a" version. If I could see the "a", I could document the differences. I would think you'd really have to to be driving the speakers hard to get anywhere near clipping. My guess is the heavy current drain forces the rail voltages way down, and this allows even modest signals to clip. Only real solution is to "beef up" the power supply. Driving AR3a's hard with an unmodified AR1500 produces a lot of "clipped sine waves" that will blow the mid-range driver. If you don't want to burnout the mid-range, but want to turn the volume up, add a 1 ohm resistor in series with each mid-range. This will change the mid-range balance, but that's better than burning out the driver. Well, Rolf, I've done just the opposite. I've taken all the pots out of the AR-3a circuit and this significantly INCREASES the sensitivity of the mid-range and tweeter. (Frankly, I'm a little surprised that the mid is most susceptible to clipping damage. People on the AR forum worry far more about the tweeters.) In any event, "clipping" is no longer an issue for me. I'm now bi-amping my AR-3a's. My AR1500 drives only the woofers. I have a nice little 30 watt Kenwood powering the mid-range and tweeter. The Kenwood has rail voltages of 40 volts! With the pots out AND the fundamentals greatly reduced, it's hard to get peak voltages of 3 volts going to the mid-range and tweeter. I mean, at 3 volts I can barely stand the volume. Now, there is no question that at the same time that I have 3 volt peaks in the Kenwood, the peak voltages in the AR1500 are much, much higher. I can't see any clipping, but even if there were some, the mid and tweeter are totally isolated from that amp. The AR3a was sold in kit form as the Heathkit AS103a. Let me know if you have any questions. Rolf, if you have an AR1500 and a set of AR-3a's, I'd strongly recommend you try a bi-amping experiment. Not only will you protect your mids and tweeters, but there is a significant tightening of the bass that results. Regards, Jerry |
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#3
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Jerry wrote:
wrote in message ... A previous poster stated that the Heathkit AR1500 and AR3a are a poor combination. This is true if you listen at any level other than quiet. Rolf, I have an AR-3a and an AR1500 and they seem to work together fairly well. I don't know about "quiet" as that is a relative term. My den is quite small and my normal listening level is less than 1 watt, but occasionally I'll listen at levels higher. A couple of years after introduction, the AR1500's output amplifiers were updated and the AR1500A was born. The AR1500A has specific circuits that limit clipping and other distortion when it is driving low imperance speakers at high levels. It is possible to modify the AR1500's output amplifiers to include this improvement; you'd have to go to a Heathkit users groups to obtain that information. Rolf, any chance you have the schematic for the power amp on the "a" version. If I could see the "a", I could document the differences. I would think you'd really have to to be driving the speakers hard to get anywhere near clipping. My guess is the heavy current drain forces the rail voltages way down, and this allows even modest signals to clip. Only real solution is to "beef up" the power supply. Driving AR3a's hard with an unmodified AR1500 produces a lot of "clipped sine waves" that will blow the mid-range driver. If you don't want to burnout the mid-range, but want to turn the volume up, add a 1 ohm resistor in series with each mid-range. This will change the mid-range balance, but that's better than burning out the driver. Well, Rolf, I've done just the opposite. I've taken all the pots out of the AR-3a circuit and this significantly INCREASES the sensitivity of the mid-range and tweeter. (Frankly, I'm a little surprised that the mid is most susceptible to clipping damage. People on the AR forum worry far more about the tweeters.) In any event, "clipping" is no longer an issue for me. I'm now bi-amping my AR-3a's. My AR1500 drives only the woofers. I have a nice little 30 watt Kenwood powering the mid-range and tweeter. The Kenwood has rail voltages of 40 volts! With the pots out AND the fundamentals greatly reduced, it's hard to get peak voltages of 3 volts going to the mid-range and tweeter. I mean, at 3 volts I can barely stand the volume. Now, there is no question that at the same time that I have 3 volt peaks in the Kenwood, the peak voltages in the AR1500 are much, much higher. I can't see any clipping, but even if there were some, the mid and tweeter are totally isolated from that amp. The AR3a was sold in kit form as the Heathkit AS103a. Let me know if you have any questions. Rolf, if you have an AR1500 and a set of AR-3a's, I'd strongly recommend you try a bi-amping experiment. Not only will you protect your mids and tweeters, but there is a significant tightening of the bass that results. Regards, Jerry October 5, 2005 update from Rolf: Both versions of the AR1500's output amplifier have a current limiting circuit to protect the amplifier's power transistors (Motorola MJ802's) from burning out. For the original AR1500, the circuit limited the current too soon when driving low impedance speaker like the AR3a. The AR1500A added a modification (resistors and capacitors only) that limited the response time of the current limiters. In effect, the new current limit circuit let short high-current transients through (which don't heat up the MJ802's enough to cause trouble) and only limited the current for non-transients. With the original AR1500 power amplifier, the too fast-acting current limiting circuit introduced "harmonics" not in the original signal; at high sound levels these harmonics have enough energy to burn-out the mid-range drivers. I have both versions of the AR1500, a pair of AR3a's (the kit version Heathkit sold as AS103) and a pair of AS101's (the kit version of the Altec Lansing Valencia). (The AR1500 and AR3a's were my dad's.) I modified the power amplifier of the original AR1500 many years ago, and unforunately no longer have the instructions. The only problem I've had with the AR1500A was the need to replace the front panel bulbs more frequently than I want to. I added silicone grease into the bulbs' sockets, and the bulbs now last much longer (due to better heat transfer away from the bulbs). I also spray painted the inside of the AR1500A's cabinet flat black, this reduces the internal heat of the receiver. |
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#4
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Jerry wrote:
My den is quite small and my normal listening level is less than 1 watt, but occasionally I'll listen at levels higher. Jerry: There are a lot of misconception to do with "volume", and especially as it relates to "watts". At one watt average, with moderately dynamic source, you will need at least a 100-watt amp to get clean peaks absolutely without clipping. But you already know this. Put another way, a speaker with an 86dB @ 1-watt SPL, a 30-watt amp simply will not cut it, even bi-amped at anything above a very moderate volume. Agreed, mostly one listens at a very moderate volume. But not always. Components of the vintage of your Heath more-or-less send straight DC into the speaker when driven to clipping. And depending on the source (where, as it usually happens most of the signal is at the mid-range), that could be a lot of the time and pretty rapidly fatal to your speakers. Again, put another way, it is (Very typical of vintage SS amps) amplifiers of low power that burn speakers, not high power. Almost any well-made speaker can handle normal signal at very high power, well beyond their nominal ratings, for brief periods. Even the very best conventional PM speakers will fry in short order when fed DC. I think this is what the OP was trying to convey. Those of us who dabble in tube equipment tend to ignore this simple truth as output transformers will not pass DC, so clipping is much softer and relatively harmless (to the speaker, that is). Also why those of us who have high-powered amps (tube or SS) also tend to ignore this as there is enough headroom in any case to minimize consequences from clipping. Bi-Amping, even as you have applied it will create some advantages if very carefully managed. But the real-world difference between a 30 watt amp and two 30-watt amps split is limited in this *particular* application given that at any given moment about 75% of your signal will be at/within the midrange, and if you include the tweeter, that goes to about 90%, at least as it applies to the need for headroom. I would very strongly suggest that you make it your mission in Audio to beg, borrow or steal a well-made high-powered amplifier (200W/RMS/CH @ 4 ohms or better) and re-evaluate your position. Enjoy the results in any case. Peter Wieck Wyncote, PA |
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#5
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Peter Wieck wrote:
Some misconceptions: There are a lot of misconception to do with "volume", and especially as it relates to "watts". At one watt average, with moderately dynamic source, you will need at least a 100-watt amp to get clean peaks absolutely without clipping. A peak-to-average ratio of 20 dB: moderate?? Components of the vintage of your Heath more-or-less send straight DC into the speaker when driven to clipping. Some pathological cases do, the vast majority don't. Again, put another way, it is (Very typical of vintage SS amps) amplifiers of low power that burn speakers, not high power. This has been pretty thoroughly debunked elsewhere, check out Rane's application notes on apolifier clipping and tweeter life. Those of us who dabble in tube equipment tend to ignore this simple truth as output transformers will not pass DC, so clipping is much softer and relatively harmless That tubes clip more softwly has almost nothing whatsoever to do with the fact that the output transformers do not pass DC. The clipping is software for two reasons: 1. The upper end gain transfer characteristics of the tube do not change as abruptly when limiting is reached, 2. The conbination of the tube's HF bandwidth, the transformer's HF bandwidth and the overall circuit's HF bandwidth can suppress some of the higher harmonics resulting from clipping. |
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#6
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
"Peter Wieck" wrote in message
... Jerry wrote: My den is quite small and my normal listening level is less than 1 watt, but occasionally I'll listen at levels higher. Jerry: There are a lot of misconception to do with "volume", and especially as it relates to "watts". At one watt average, with moderately dynamic source, you will need at least a 100-watt amp to get clean peaks absolutely without clipping. But you already know this. Put another way, a speaker with an 86dB @ 1-watt SPL, a 30-watt amp simply will not cut it, even bi-amped at anything above a very moderate volume. Agreed, mostly one listens at a very moderate volume. But not always. Peter, please remember that the 30 watt amp is driving strictly the mid and tweeter. Further, this amp sees greatly reduced fundamentals, so the voltage swings are NOTHING like what a single amp would experience. When playing music at levels I can just barely stand (somewhere around 10 -20 watts), PEAK output voltages in this amp are LESS than 7 volts. Now, one reason for that low output voltage is that I removed those blasted pots from the AR xover circuit. This netted a huge gain in sensitivity on just those drivers. So I must compensate by reducing volume or the mid/tweeter will overpower the woofer. To give you a feel ... the average voltage swings in the woofer amp are 5 times higher! Based upon all of the above, there is just no way that peak output voltage could ever get to the 40 volt rails in the mid/tweeter amp. Further, rail drop will be minimal given the low current drain of the mid and tweeter. Peter, please remember that I don't have the fundamentals going through that 30 watt amp and this significantly changes the game and the math. Components of the vintage of your Heath more-or-less send straight DC into the speaker when driven to clipping. And depending on the source (where, as it usually happens most of the signal is at the mid-range), that could be a lot of the time and pretty rapidly fatal to your speakers. Even if this is the case, (and I doubt that because I measured the filter caps and they are just fine), the mid and tweeter will never see the impact of the clipped waves and resulting harmonics in the woofer amp. Further, neither will the woofer as it's internal xover will reject those harmonics. Peter don't forget that the Heath amp sees reduced harmonics as well. Now this reduction is NOT as great as the reduction of fundamentals in the 30 watt amp, but still there is a significantly less harmonics "riding on fundamentals" than what a single amp would see. Again, put another way, it is (Very typical of vintage SS amps) amplifiers of low power that burn speakers, not high power. Almost any well-made speaker can handle normal signal at very high power, well beyond their nominal ratings, for brief periods. Even the very best conventional PM speakers will fry in short order when fed DC. I think this is what the OP was trying to convey. Peter, if we drove this 30 watt amp to the 40 volts rails, clipping would be the least of our problems. Both the mid and the tweeter would be smoking long, long before. With the fundamentals removed, the impact of stacking 40 volt rails on top of 40 volt rails in the Heath is equivalent to a 750 watt amp. Now this is from the vantage point of the mids/tweeters. (The woofer still sees the same 100 watt amp with but even it "goes further" without the harmonics.) Those of us who dabble in tube equipment tend to ignore this simple truth as output transformers will not pass DC, so clipping is much softer and relatively harmless (to the speaker, that is). Also why those of us who have high-powered amps (tube or SS) also tend to ignore this as there is enough headroom in any case to minimize consequences from clipping. Peter, you can ignore it, but the truth is that I have far, far more headroom than you with your "brute" ss amp. You must pass fundamentals with harmonics on top through that amp. Further, you still have the pots "sucking up power" in your AR-3a's and this also contributes to a reduction in headroom. Bi-Amping, even as you have applied it will create some advantages if very carefully managed. But the real-world difference between a 30 watt amp and two 30-watt amps split is limited in this *particular* application given that at any given moment about 75% of your signal will be at/within the midrange, and if you include the tweeter, that goes to about 90%, at least as it applies to the need for headroom. I would very strongly suggest that you make it your mission in Audio to beg, borrow or steal a well-made high-powered amplifier (200W/RMS/CH @ 4 ohms or better) and re-evaluate your position. Peter, are you saying that 75% of the signal STRENGTH is going to the mids/tweeters? This is totally incorrect and I have a dual channel scope to prove it. Less than 25% of the voltage swings are going to the mid/tweeter amp. Then if we integrated the signals to compute power, once again the real power is in the woofer amp ... BY A LOT! It's not even close. I have the equivalent of a 750 watt amp (@ 4 ohms - 375 watts @ 8 ohms). Why in heavens name would I want a mere 200 watt amp. That would be going backwards. Regards, Jerry |
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#7
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Jerry wrote:
I have the equivalent of a 750 watt amp (@ 4 ohms - 375 watts @ 8 ohms). Why in heavens name would I want a mere 200 watt amp. That would be going backwards. Jerry: Pulling the pots from the AR3(a) is about the first thing that should be done, they were barely functional when-new. So we are 100% agreed there. But per any of the several web-sites dedicated to these speakers (Layne, Vintage, et.al.) this gives only about a 3dB gain (assuming otherwise good pots) over the pots in the max (theoretically straight-wire) position. And, as to the "equivalent" of a 750 watt amp, _ALL_ I am suggesting is that unless you have tried the brute-force amp and rejected it as being unsatisfactory as compared to your present set-up, you REALLY SHOULD try it. The results may well be revealing. At the very least they will endorse your present position. Yeah, a good part of the stuff I listen to regularly does have a 20dB P/A, the room is fairly large, and I do like to run at a moderately high volume... trumpets like that. And even the solo human voice with an orchestral background likes that. Peter Wieck Wyncote, PA |
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#8
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
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#9
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
John Stone wrote:
I thought all your bi-amping adventures were done with the purpose of not altering the original design of your AR3a's. John, the various mod sites noted emphasize the need for a fixed resistor in place of the pot, simply bypassing the adjustable function. Yes, *maybe* get them out of the circuit, no, do not alter the overall function of the circuit. http://layneaudio.hypermart.net/AR3aXorig.gif shows the OEM crossover arrangement. One may either bypass the wiper directly to the 0-ohms position, or remove the pot inserting a 16-ohm resistor and tying the correct leads at the 0-ohm position. (above link courtesy Layne Audio) Classic Speaker Pages: http://www.classicspeakerpages.net/a...ar-3a/ar3a.htm All sorts of information and suggestions. Peter Wieck Wyncote, PA |
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#10
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Peter Wieck wrote on 10/7/2006:
Jerry wrote: I have the equivalent of a 750 watt amp (@ 4 ohms - 375 watts @ 8 ohms). Why in heavens name would I want a mere 200 watt amp. That would be going backwards. Jerry: Pulling the pots from the AR3(a) is about the first thing that should be done, they were barely functional when-new. So we are 100% agreed there. But per any of the several web-sites dedicated to these speakers (Layne, Vintage, et.al.) this gives only about a 3dB gain (assuming otherwise good pots) over the pots in the max (theoretically straight-wire) position. Hmmm, 3db seems low, but could be right. I should have, but didn't measure before and after. In any event, a 3db reduction in power is equivalant to cutting the power to the mids/tweeters in HALF. That is, I now send half as much power to the mids/tweeters and get the same SPL. This equates to a terriffic gain in headroom and issures clipping in the mid/tweeter amp will never happen. Peter, you never told me you removed the pots from your AR-3a's! You can't do this, Peter, and mainain the proper sound balance UNLESS you compensate with fixed resistance in the xover. So, Peter, what mod did you perform upon your 3a's? And, as to the "equivalent" of a 750 watt amp, _ALL_ I am suggesting is that unless you have tried the brute-force amp and rejected it as being unsatisfactory as compared to your present set-up, you REALLY SHOULD try it. The results may well be revealing. At the very least they will endorse your present position. Alas, I can't do this anymore. With the pots out, there is no way to power my AR with a single amp and maintain any semblance of balance between the energy sent to the woofer and that sent to the mids and tweeters. And I'm NOT putting those pots back in the circuit. I itched for three days the last time I opened those boxes. Peter did you ever look at your audio signal on a scope to see the height of the transients? I look fairly often and I've never seen peak voltages as high as you describe. Regards, Jerry |
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#11
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
John Stone wrote on 10/7/2006:
I thought all your bi-amping adventures were done with the purpose of not altering the original design of your AR3a's. Well, now that you're in there changing things around, I'm wondering if you did anything to compensate for the removal of those pots from the circuit. They place a 16 ohm load across the mid and tweeter crossover circuits, and that load forms part of the filter network. Did you put a fixed 16 ohm resistor in the circuit in their place? If not, you've certainly altered the crossover responses and consequently, the speaker response. (I can't wait to see whether you're going to agree with this). I'm also trying to figure out how you got such a huge gain in sensitivity by removing the pots. Turned all the way up, the mid and tweeter are directly connected to the crossover outputs, so the pot is out of the circuit other than presenting a parallel 16 ohm load. Unless those were the world's most defective pots-and you would have easily been able to tell from the intermittent operation-then I don't see where you're picking up all the sensitivity from. No, John! No pots and no fixed resistors. Pots are removed from the circuit. The real purpose of the pots was to balance the energy going to the more sensitive drivers (mid and tweeters) in relationship to the energy going to the woofers. In short, they were "padding" to bring all the drivers in balance, plus they allowed some minor tweaking. Now most folks have long set the tweeter pot to max as is recommended everywhere. Further, removing the tweeter pot was even suggested by Chuck McShane. See: http://www.classicspeakerpages.net/ar/ar-9/3and9.txt So, John, this leaves just the mid pot and it has a dramatic impact on the balance of music ... no question about it. Any adjustments to this pot dramatically impact the balance of high vs low frequencies. I don't think anyone would argue this as a simple test of moving the pot form end to end results in dramatically different sound. Your question is how can I remove this pot and still maintain the proper balance. Well, for me, John, the pot is redundant. I still have total control over the balance of energy going to the woofers vs the energy going to the mids/tweeters ... only instead of pots, I use volume controls. Yes, the volume controls on the amps that independently power each half of the speaker. I think you'll agree, John, that over time it's far, far easier to maintain low power volume controls than it is to maintain the high power pots in the speakers. As for the improvement in sensitivity, all I can say it's significant and very noticable. That 16 ohms still draws current that produces no sound. If we assume that the impedance of the driver over it's frequency range averages 4 ohms. Then if the pot is set to max increase, approx 25% of the current going through the driver is also flowing through the pot and ... producing zero sound. On top of this, I never had the mid pot set to max. That would be way too "bright" and in my room would NOT be balanced. So when I removed the pots the padding that was going on, is no longer happening. So to balance the speakers, I send significantly less power to the mids and tweeters and my guess is the actual current flowing through them is very similar to what it was when the pots were in the circuits. John, when I removed the pots, I never claimed any change in sound with the minor exception that my left speaker no longer loses mid-range completely any more. I'm also amazed at how much work you've gone through to deviate from the original design intent of the AR3a's. If it was me, I would put them back to stock and sell them. They still bring decent money. Then I would invest in some real DIY loudspeaker building using the much more robust and better performing loudspeaker components that are available today. You could then tweak to your heart's desire without the worry of blowing fragile drivers that are no longer available. You seem like the type that loves to experiment. Why limit yourself to such old technology that will never reach today's performance levels no matter what you do? John, I don't believe that I have changed the intent of the AR3a's. I think they sound terrific and I believe that any amp will drive them better with the complex xover network split. Further these drivers are somewhat unusual. AR made both the mid and tweeter because they could NOT find drivers of comparable quality. The woofer they purchased, but they specified all parameters so that it matched the closed cabinet. Regards, Jerry |
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#12
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Peter Wieck wrote on 8/7/2006:
John Stone wrote: I thought all your bi-amping adventures were done with the purpose of not altering the original design of your AR3a's. John, the various mod sites noted emphasize the need for a fixed resistor in place of the pot, simply bypassing the adjustable function. Yes, *maybe* get them out of the circuit, no, do not alter the overall function of the circuit. http://layneaudio.hypermart.net/AR3aXorig.gif shows the OEM crossover arrangement. One may either bypass the wiper directly to the 0-ohms position, or remove the pot inserting a 16-ohm resistor and tying the correct leads at the 0-ohm position. Peter, if I were going to do this, I'd just solder the lead going to the driver to the top of the pot. This by passes the wiper (which by now is heavily corroded), but it leaves that 16 ohm wire resistor encased in ceramic in the circuit. Current is still flowing through that resistor and I like the fact that while it's inside the box surrounded by all that insulation, that it's encased in ceramic. That's NOT what I did, however. Pots are completely out of my xovers. All I really did was move the function of the pots back to the volume controls on the individual amps. Under a single amp, I don't think "soldering to the top of the pot" would actually work, Peter. I mean that balance would be way off ... far too bright! Regards, Jerry |
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#13
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Jerry wrote:
Peter, if I were going to do this, I'd just solder the lead going to the driver to the top of the pot. This by passes the wiper (which by now is heavily corroded), but it leaves that 16 ohm wire resistor encased in ceramic in the circuit. Current is still flowing through that resistor and I like the fact that while it's inside the box surrounded by all that insulation, that it's encased in ceramic. That's NOT what I did, however. Pots are completely out of my xovers. All I really did was move the function of the pots back to the volume controls on the individual amps. Under a single amp, I don't think "soldering to the top of the pot" would actually work, Peter. I mean that balance would be way off ... far too bright! YIKES!.... Yikes.... Before I completely misunderstand what you did, how did you remove the 3-wire pot from the circuit? OK. Pot is gone, what got connected where? Did you just lump the three wires together? I am (admittedly) boggling at the "far too bright" comment as well, especially as connected to the comment "move the function back to the volume controls". What does the crossover look like when you are done with your mods? Did you replace the various caps? Peter Wieck Wyncote, PA |
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#15
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Peter Wieck wrote 10/8/2006:
Jerry wrote: Under a single amp, I don't think "soldering to the top of the pot" would actually work, Peter. I mean that balance would be way off ... far too bright! YIKES!.... Yikes.... Before I completely misunderstand what you did, how did you remove the 3-wire pot from the circuit? OK. Pot is gone, what got connected where? Did you just lump the three wires together? I am (admittedly) boggling at the "far too bright" comment as well, especially as connected to the comment "move the function back to the volume controls". What does the crossover look like when you are done with your mods? Did you replace the various caps? Peter Wieck Wyncote, PA Ok, my "mod" (and I don't really think of it as a mod as there was essentially zero change in sound) was to remove the pots from the circuit. The pots are still in place, just doing nothing and dissipating zero energy. To implement this, all I did was cut the lead on the pots going to the drivers and the leads at the top of the pot. Twisted these together and soldered. Put on a wire connector and sandwiched between mounds of fiberglass (or whatever that itchy stuff is). The yellow wires are still connected to the pots and from the pots on to the drivers. Everything else is exactly as it was. All the reactive components are intact. Peter, I did not change the caps. They looked good so I measured and they were fine. I expected to see some pretty excessive leakage, but that was fine as well. Next, I ran some tests to see if the current going to the drivers was consistent with the xovers and again it's clear the xovers are performing their job well. For these tests, I sent full signals to each half. And while voltage was applied to the speakers, the xovers effectively "blocked" frequencies not intended for their respective drivers. So, xovers are doing their job, drivers are doing their job and all I have to do is send the appropriate energy to each half of the speaker. Peter, this adjustment is so coarse and impacts so many frequencies that it's pretty hard to be much off. In short, if the balance isn't correct, human voice sounds awful and so do instruments. Under bi-amping the volume controls perform essentially the same function that was performed by the pots ... to balance energy between the drivers. Regards, Jerry |
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#16
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
John Stone wrote 10/8/2006: On 10/7/06 8:40 PM, in article
, "Jerry" Jerry wrote: Now most folks have long set the tweeter pot to max as is recommended everywhere. Further, removing the tweeter pot was even suggested by Chuck McShane. See: http://www.classicspeakerpages.net/ar/ar-9/3and9.txt Yes, I read that. It wasn't Chuck McShane that wrote this, it was his nephew writing what he BELIEVES Chuck McShane said. Hardly authoritative. The context of this post is totally missing, and the meaning of the word "remove" is misleading at best. He could easily have meant removing the L pad aspect of the pots as opposed to removing the pots completely. I find it hard to believe Chuck McShane would have recommended just pulling them out. Well, John, it was published in the AR library and someone would have complained vehemently if it was totally wrong. I think this is the part that is most convincing: "Even wide open, the pot reduces tweeter output by about 1db." So, if the tweeter pot is set to max and the pot opens up, the net change in the tweeter is 1 db. However, if the wiper in the pot is corroded the reduction can be far, far more substantial than 1 db. So, John, this leaves just the mid pot and it has a dramatic impact on the balance of music ... no question about it. Any adjustments to this pot dramatically impact the balance of high vs low frequencies. I don't think anyone would argue this as a simple test of moving the pot form end to end results in dramatically different sound. Your question is how can I remove this pot and still maintain the proper balance. No, my question is NOT how you can remove the pot and still maintain the proper balance. It's how you can remove the pot and still maintain the proper crossover frequency. John, xover frequency is determined primarily by the reactive components. The coils and caps are all still there. The xover for the mid-range is really a band pass and I have tested the xover to see whether it was in fact working. I did this by applying a full frequency signal to the mid/tweeter (did exactly the same for the woofer). So a full frequency and full strength voltage was applied to the mid/tweeter and I measured the current actually going to the drivers. In short, the xovers were performing perfectly. That is, they were "blocking" (little or no current) was flowing for the frequencies NOT intended for the respective drivers. Lastly, John, as you stated in your other post, the net resistance of the 16 ohm pot and the mid-range driver (with the pot at max) is still pretty close to the resistance of the mid-range driver. So, we really can't be that far different from the original design. Well, for me, John, the pot is redundant. Obviously. You do like to make up your own rules, independent of facts or reality. Not my rules. Function of the pots is to balance energy going to the respective drivers to adjust for room conditions and RECORDINGS. I can perform exactly the same function with the volume controls. With a single amp, John, you have no where near the control over sound that I have. And with harmonics riding on fundamentals, you have no where near the headroom that I have. As an aside, John, a totally flat response on AR-3a's is achieved with the pots at max AND a slight increase in the treble volume control. I think you'll agree, John, that over time it's far, far easier to maintain low power volume controls than it is to maintain the high power pots in the speakers. But you say you've left the midrange pots in, so you still have to maintain those. So you really haven't solved the maintenance problem at all. The big issue with the pots is having to take apart the speakers to get to them. Once you're in there, cleaning them is no big deal. All you've done is eliminate the need to clean one of them, which you could have done anyway just by jumpering the wiper to the high side of the pot. Neither pot is in the circuit (both pots are physically attached to the speakers, but doing nothing and dissipating zero power.) From my first post in this thread: "Well, Rolf, I've done just the opposite. I've taken all the pots out of the AR-3a circuit ...." From this point on, I'll only take the speakers apart upon component failure .... NOT for cleaning those blasted pots. As for the improvement in sensitivity, all I can say it's significant and very noticable. That 16 ohms still draws current that produces no sound. If we assume that the impedance of the driver over it's frequency range averages 4 ohms. Then if the pot is set to max increase, approx 25% of the current going through the driver is also flowing through the pot and .... producing zero sound. Jerry, your ignorance of even basic loudspeaker design principles is appalling. If I didn't know better, I'd swear you were joking. The tweeter network in the AR3a consists of a single series element; i.e., a 6uf cap feeding a load consisting of a tweeter and a 16 ohm tapped resistor. For all intents and purposes, when you run the tweeter pot at full, you simply have a tweeter and a 16 ohm resistor in parallel. The crossover frequency is determined by the value of the series cap AND the impedance of the load. Removing that 16 ohm resistor alters the load (increases the impedance), which in turn alters the crossover frequency, moving it downward. I'm quite sure what you've done IS significant, My ignorance, huh? John, you spouted a lot of "facts", but not a single number. Are you lazy, John, or perhaps you don't know how to do the math. Let's just see how significant. DC resistance of tweeter is approx. 3.2 ohms So with the 16 ohm pot full across - net resistance = 2.67 ohms or a difference of .53 ohms Real, real significant, John ... huh?? Now, let's look at the total network near the xover frequency I @ 2 v I @ 2 v Hz Z for Cap Z w/o pot Z with pot w/o pot with pot % diff 3,000 8.8 ohms 12.0 11.5 .166 ..145 12.8% 4,000 6.6 ohms 9.8 9.3 .203 ..179 11.9% 5,000 5.3 ohms 8.5 8.0 .235 ..522 11.1% 6,000 4.4 ohms 7.6 7.1 .656 ..588 10.4% Real significant, John! Maximum difference in current going through the tweeter is 2.2% over this entire range. WOW!! Tell us, John, do you think there is a human anywhere ... that could actually hear this difference? Perhaps your arguments would have some weight, John, if you backed them up with the math. But let's just say that those are quite fragile and you've definitely moved things in the wrong direction regarding the chances of surviving your "improvement". If you still don't get this, here's a link that demonstrates, in simple terms, the relationship between load impedance and crossover frequency: http://www.carstereo.com/help/Articles.cfm?id=1 What in heck are you talking about?? What wrong direction? 0.5% more current at 6000 Hz than at 3000 Hz!! Who cares?? Now, if you are talking about sensitivity in total .... YES, for the same voltage we get approx. 11% more current going through the tweeters. We must absolutely reduce the voltage in the mid/tweeter amp or the sound would be too bright. What in heavens name does that have to do with "fragile"? So to balance the speakers, I send significantly less power to the mids and tweeters and my guess is the actual current flowing through them is very similar to what it was when the pots were in the circuits. Well the only part of this statement I agree with is that you are guessing. How do you dissipate less power through the drivers while keeping the current flow the same? Sorry Jerry, but you cannot change the relationship between SPL and power dissipation through the drivers. If you are getting more output from a driver, it is simply because you are putting more signal into it. End of story. Total nonsense, John. We are NOT talking about SPL out of the drivers. We are talking about SPL out of the speakers. I get more output for the same voltage for two reasons: 1. I'm NOT wasting current flowing through the 16 ohms pot like you do (approx. 11%) 2. Actual waste on the mid-range is much, much higher, because I never set the mid pot to max. In that case the amount of current the mid driver actually sees is greatly reduced. This is really a waste of voltage and headroom. Even though voltage can be significant the current will be low due the voltage divider function that the pot performs. John, when I removed the pots, I never claimed any change in sound with the minor exception that my left speaker no longer loses mid-range completely any more. Now I'm really confused. I thought you said you didn't remove the midrange pots.. Confused I guess you are, because I've been consistent. I've always said I removed ALL pots. John, I don't believe that I have changed the intent of the AR3a's. I think they sound terrific and I believe that any amp will drive them better with the complex xover network split. There's that belief system again. Never let the facts get in the way of what you believe. John, this is getting a little tiring. You have never quote a single fact .... just total supposition. Here is my charts and my graphs and facts : http://www.classicspeakerpages.net/d...ng_type=search You have come to the conclusion that ANY amp will drive them better with split x-over based on what? Using what even you admit is a pretty marginal amp for those speakers? Many here have told you from their own experience that using a single amp of adequate power and stability for these speakers will get as much out of them as they are capable of giving. Look over the impedance charts, John. Then let's see your facts. Your charts. Your experiments ... or do we have an empty bag? As for my amps, after looking over the facts ... I believe I have far, far more voltage headroom than anyone with a single amp. Which brings up another question: If using separate amps gave such a huge improvement, why didn't AR suggest it in the first place? I don't believe at the time that the AR's were developed, people were even experimenting with bi-amping for home use. As time went on and AR continued to develop speakers, they started experimenting with bi-amping. "Satisfactory results were obtained when bi-amping the AR-90" according to AR (see reference on the AR forum). The same exact thing you have done could have been done back in 1968 when they were introduced. Yet nowhere in the owner's manual or the literature is any such arrangement suggested. Why not? Are you saying that the designers never thought of it, or were totally unaware of the capabilities of their own speakers? Strange that they could be so brilliant in designing the speakers, yet so ignorant of their true capabilities. I don't believe back in 1968 ANYBODY was thinking about bi-amping for home use, but please share a reference showing that I am wrong. Quote any article from 1968 or earlier recommending bi-amping in the home. Further these drivers are somewhat unusual. AR made both the mid and tweeter because they could NOT find drivers of comparable quality. The woofer they purchased, but they specified all parameters so that it matched the closed cabinet. Yes, and all of that happened back in 1968. What does any of this have to do with my suggestion of looking at what is going on today in DIY using up-to-date driver technology? I'm not so certain there are comparable drivers available today. It seems that "quality" anything is harder to find. Just look at the products offered today in terms of receiver and speaker systems. Regards, Jerry |
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#17
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Jerry wrote:
To implement this, all I did was cut the lead on the pots going to the drivers and the leads at the top of the pot. Twisted these together and soldered. Put on a wire connector and sandwiched between mounds of fiberglass (or whatever that itchy stuff is). The yellow wires are still connected to the pots and from the pots on to the drivers. Everything else is exactly as it was. All the reactive components are intact. OK, on the schematic (OEM), there is still 16 ohms in parallel with each driver to ground, and 32 ohms across both drivers. If I read you correctly, you have removed the green wire & the output wire from the tweet-pot, joined them, and left them separated from the pot. The pot is now out-of-circuit altogether. On the Mid side (again, if I read you correctly), you have removed the choke wire and the wire to the mid from the pot, joined those and left them separate from the pot. Now that pot is also out-of-circuit, as well as delivering maximum brightness to the mid. So, not only is the resistor gone across the drivers, but also across the pair. This will increase the impedance of the speaker overall, and, of course, the tweet and the mid. It will also send _ALL_ of the energy across the two drivers, dissipating none of it across the two TWENTY-FIVE WATT, 16 ohm fixed resistors (elements of the pots) as they are now out-of-circuit. You are correct (more-or-less) in that it will not affect the frequency performance of the crossover, but it will change its function. Is this correct? On mine, I have soldered the output wire to the 'high side', but I have left the fixed elements of the pots in place electrically. This gains the 1dB - 3dB that the pot-in-place wastes, and with replacement of the caps with 'tighter' caps, makes the speaker a good deal clearer, at least to me. But there could be _A LOT_ of power going into those beasts, I question the wisdom of pulling the pots out of the circuit entirely. Peter Wieck Wyncote, PA |
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#18
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
On 10/9/06 6:38 PM, in article , "Jerry"
wrote: John Stone wrote 10/8/2006: On 10/7/06 8:40 PM, in article , "Jerry" Yes, I read that. It wasn't Chuck McShane that wrote this, it was his nephew writing what he BELIEVES Chuck McShane said. Hardly authoritative. The context of this post is totally missing, and the meaning of the word "remove" is misleading at best. He could easily have meant removing the L pad aspect of the pots as opposed to removing the pots completely. I find it hard to believe Chuck McShane would have recommended just pulling them out. Well, John, it was published in the AR library and someone would have complained vehemently if it was totally wrong. Jerry, AR is long gone. The "AR library", as you put it, is nothing more than a loose collection of posts and articles from DIY folks and others with an interest in and nostalgia for the speakers. There's nothing official about it and while there's lots of good stuff there, there's also some really questionable stuff. Nobody polices it for accuracy, so it should not all be taken as bible. I think this is the part that is most convincing: "Even wide open, the pot reduces tweeter output by about 1db." So, if the tweeter pot is set to max and the pot opens up, the net change in the tweeter is 1 db. However, if the wiper in the pot is corroded the reduction can be far, far more substantial than 1 db. What a novel interpretation! Jerry, the term "wide open" is common terminology to describe a pot being set to maximum, not a pot that is electrically open. The 1dB simply refers to the insertion loss of the pot, operating properly in circuit, at full setting. No, my question is NOT how you can remove the pot and still maintain the proper balance. It's how you can remove the pot and still maintain the proper crossover frequency. John, xover frequency is determined primarily by the reactive components. Any filter network's turnover frequency is calculated through the values of source impedance, the value of reactive components, and the impedance of the load. Don't believe me? Then substitute a 100 ohm resistor for the tweeter and run a sweep of the crossover. I'm sure you'll you'll see a pretty huge change. The coils and caps are all still there. The xover for the mid-range is really a band pass and I have tested the xover to see whether it was in fact working. I did this by applying a full frequency signal to the mid/tweeter (did exactly the same for the woofer). So a full frequency and full strength voltage was applied to the mid/tweeter and I measured the current actually going to the drivers. In short, the xovers were performing perfectly. That is, they were "blocking" (little or no current) was flowing for the frequencies NOT intended for the respective drivers. I have read this paragraph over and over, and for the life of me, I can't figure out what you are talking about. What kind of "full frequency and full strength voltage" are you referring to? How do you accurately measure the crossover response with a "full frequency" signal? Do you have a spectrum analyzer? The simplest way to accurately measure the response is to run a sine sweep and plot the voltage/frequency curve using an rms voltmeter at the driver terminals. Do it with and without the pot in place an you'll get an exact picture of what is happening. You also keep using the term "current". How, and why are you are measuring current (amps)? Lastly, John, as you stated in your other post, the net resistance of the 16 ohm pot and the mid-range driver (with the pot at max) is still pretty close to the resistance of the mid-range driver. ??? I never stated any such thing. Please provide a quote, and please show me where I ever used the term "resistance" in reference to the drivers. Not my rules. Function of the pots is to balance energy going to the respective drivers to adjust for room conditions and RECORDINGS. I can perform exactly the same function with the volume controls. No you can't. You pulled out 2 pots and substituted them with 1 amplifier gain control, driving the entire mid/tweeter section. You have removed one of the pots' key functions, which was to allow shelving of the mid and tweeter levels individually. With a single amp, John, you have no where near the control over sound that I have. And with harmonics riding on fundamentals, you have no where near the headroom that I have. I have no idea what this means. As an aside, John, a totally flat response on AR-3a's is achieved with the pots at max AND a slight increase in the treble volume control. Anybody who has actually measured AR3a's as opposed to just reading the AR literature will tell you this isn't true. Here's an actual real world measurement of the 3a's: http://murphyblaster.com/content.php?f=AR3a.html These measurements are backed up in a post on 8/7 by Dick Pierce to you regarding the frequency response of the AR3a: "No, the reason for this is that Roy Allison and Ed Villchur at AR decided on a balance that resulted in an overall downward trend in the speaker's response toward the high end. That was their choice, for whatever reasons. The midrange efficiency is about 2 db less than the woofer, and the tweeter is another 2-3 dB less efficient than that. That's what the people of AR designed it to be." (end quote) A "slight increase" in the treble control will not achieve a totally flat response as is clear from the actual response measurements. ... Jerry, your ignorance of even basic loudspeaker design principles is appalling. If I didn't know better, I'd swear you were joking. The tweeter network in the AR3a consists of a single series element; i.e., a 6uf cap feeding a load consisting of a tweeter and a 16 ohm tapped resistor. For all intents and purposes, when you run the tweeter pot at full, you simply have a tweeter and a 16 ohm resistor in parallel. The crossover frequency is determined by the value of the series cap AND the impedance of the load. Removing that 16 ohm resistor alters the load (increases the impedance), which in turn alters the crossover frequency, moving it downward. I'm quite sure what you've done IS significant, My ignorance, huh? John, you spouted a lot of "facts", but not a single number. Are you lazy, John, or perhaps you don't know how to do the math. Let's just see how significant. DC resistance of tweeter is approx. 3.2 ohms So with the 16 ohm pot full across - net resistance = 2.67 ohms or a difference of .53 ohms Sorry Jerry, but yes, your ignorance, or perhaps just lack of attention to detail, as again demonstrated above. DC resistance is utterly meaningless to this discussion, as the last time I checked, tweeters required AC to produce sound. Yet you use resistance interchangeably with impedance as if they were one and the same. The "nominal" impedance of a tweeter with 3.2ohm dcr is 4 ohms. If you take that nominal impedance in parallel with the 16 ohm pot (the pot will have an impedance close to 16 ohms given that it is largely non-inductive) the 2 in parallel yield a resulting impedance of 3.2 ohms. With the pot totally out, you shift the impedance up by a minimum of 20%. Real, real significant, John ... huh?? Um, yeah, I'd say by any measure a 20% shift is significant. And in a previous post, you yourself said so: As for the improvement in sensitivity, all I can say it's significant and very noticable. Those are YOUR words, Jerry. So which is it? Significant or not? 20% is way beyond the impedance tolerance AR specified for the drivers alone, so the crossover is indeed operating into a significantly different load than intended, with the resultant shift in xover response as previously stated. More importantly 20% is the MINIMUM shift. In reality, the tweeter (and midrange) impedance curve is nowhere near flat, and deviates considerably with frequency. Given that these drivers use no ferrofluid they will exhibit a fairly high Q at mechanical resonance ( which I'd estimate around 300Hz for the mid and 3kHz for the tweeter), yielding an impedance peak at resonance perhaps double the nominal value. The driver impedance also rises gradually with increased frequency, due to the voice coil inductance. So the pots were there for 2 reasons: provide level adjustment, and to provide a measure of impedance stabilization for the crossover. By removing them, you have changed things a whole bunch. Tell us, John, do you think there is a human anywhere ... that could actually hear this difference? You said you could hear it yourself, so I'd assume others could as well. Perhaps your arguments would have some weight, John, if you backed them up with the math. There's plenty of "math" above. And it least its based on correct parameters (impedance rather than resistance), which makes your "math" less than useful. But let's just say that those are quite fragile and you've definitely moved things in the wrong direction regarding the chances of surviving your "improvement". If you still don't get this, here's a link that demonstrates, in simple terms, the relationship between load impedance and crossover frequency: http://www.carstereo.com/help/Articles.cfm?id=1 What in heck are you talking about?? What wrong direction? 0.5% more current at 6000 Hz than at 3000 Hz!! Who cares?? Now, if you are talking about sensitivity in total .... YES, for the same voltage we get approx. 11% more current going through the tweeters. We must absolutely reduce the voltage in the mid/tweeter amp or the sound would be too bright. What in heavens name does that have to do with "fragile"? Pushing down the crossover frequency puts more strain on the tweeter. Like it or not, those tweeters were notorious for marginal power handling ability. A.75in voice coil on a paper former with no ferrofluid cannot take much power without burning out. John, this is getting a little tiring. You have never quote a single fact ... just total supposition. Jerry, you're the one making all the claims. It's up to you, not me, to back your claims with facts. I and others smarter than me have provided plenty of opposing facts, all of which you have chosen to ignore. And you think you're tired? Here is my charts and my graphs and facts : http://www.classicspeakerpages.net/d...forum=3&topic_ id=10658&mesg_id=10658&listing_type=search Nothing more than the same old stuff you've been saying here for the past few months. I've read it all and there's nothing further to learn from it. You have come to the conclusion that ANY amp will drive them better with split x-over based on what? Using what even you admit is a pretty marginal amp for those speakers? Many here have told you from their own experience that using a single amp of adequate power and stability for these speakers will get as much out of them as they are capable of giving. Look over the impedance charts, John. Then let's see your facts. Your charts. Your experiments ... or do we have an empty bag? Jerry, as others here have told you countless times, nothing is to be gained in your configuration compared to a single amp, as long as the driving amplifier has adequately low output impedance and sufficient undistorted power to drive the speakers to the desired level. Virtually all competent amplifiers act as voltage sources, and within the limit of their power output capability, perform largely independent of the load they see. The AR3a designers knew this and designed the speakers accordingly. You have never provided a shred of proof that your configuration solves any problem that couldn't be solved with a single more powerful amplifier. To now extend this argument to ALL amplifiers, regardless of power, is absurd and based totally on unsubstantiated generalizations about power amplifier behavior. Yes, by using 2 amps, you can now adjust the mid and tweeter outputs to levels above the woofer, but that was never the intent of the original design. As for my amps, after looking over the facts ... I believe I have far, far more voltage headroom than anyone with a single amp. I know what you believe. Now, please explain the basis of this belief. Let's see your experiments or charts showing your "biamp" configuration with ancient low powered amplifiers of dubious quality having far more headroom than a single 250 watt/ch amplifier with total stability down to 2 ohms. Your claim, your proof. Which brings up another question: If using separate amps gave such a huge improvement, why didn't AR suggest it in the first place? I don't believe at the time that the AR's were developed, people were even experimenting with bi-amping for home use. I don't believe back in 1968 ANYBODY was thinking about bi-amping for home use, but please share a reference showing that I am wrong. Quote any article from 1968 or earlier recommending bi-amping in the home. Having lived during that era, I can assure you that biamping was indeed being done in home systems well before 1968. Ever hear of the Marantz 3? It's an electronic crossover from the '50s. In fact, even Heathkit offered one called the XO-1 which also dates back well before 1968. There were others. I'm not so certain there are comparable drivers available today. There aren't. Nobody buying a high quality driver today would accept the performance compromises in power handling, sensitivity, or frequency response. It seems that "quality" anything is harder to find. Just look at the products offered today in terms of receiver and speaker systems. Please look a little more closely. You will find plenty of examples of very high quality loudspeakers that will outperform the AR3a by a wide margin. Contrary to what you seem to believe, advances in loudspeakers did not end in 1968. Jerry, the last word is all yours. I won't be posting any further responses to this thread in the hope that it dies the merciful death it so deserves. Enjoy your speakers. |
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#19
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Peter Wieck wrote on 10/9/2006:
Jerry wrote: To implement this, all I did was cut the lead on the pots going to the drivers and the leads at the top of the pot. Twisted these together and soldered. Put on a wire connector and sandwiched between mounds of fiberglass (or whatever that itchy stuff is). The yellow wires are still connected to the pots and from the pots on to the drivers. Everything else is exactly as it was. All the reactive components are intact. OK, on the schematic (OEM), there is still 16 ohms in parallel with each driver to ground, and 32 ohms across both drivers. If I read you correctly, you have removed the green wire & the output wire from the tweet-pot, joined them, and left them separated from the pot. The pot is now out-of-circuit altogether. Peter, that is exactly correct. Only one wire (yellow wire) is connected to the pot and pot acts as a terminal strip. The other two terminals on the pot are connected to NOTHING! On the Mid side (again, if I read you correctly), you have removed the choke wire and the wire to the mid from the pot, joined those and left them separate from the pot. Now that pot is also out-of-circuit, as well as delivering maximum brightness to the mid. So, not only is the resistor gone across the drivers, but also across the pair. This will increase the impedance of the speaker overall, and, of course, the tweet and the mid. Yes, it does increase the effective impedance of those individual drivers. Let's assume the DC resistance of the drivers is around 3.2 ohms (by themselves). So with the 16 ohms in parallel, the effective resistance would be 2.67 ohms. Pot causes the impedance to be .53 ohms LOWER. Notice, that with the pot across the drivers the impedance is lower in total (some would argue 2.76 ohms is a 'tough' load for any amp), so the speakers draw more current. The sound output (SPL), however, is also lower! It will also send _ALL_ of the energy across the two drivers, dissipating none of it across the two TWENTY-FIVE WATT, 16 ohm fixed resistors (elements of the pots) as they are now out-of-circuit. You are correct (more-or-less) in that it will not affect the frequency performance of the crossover, but it will change its function. Peter, you are correct again! With zero dissipation, the drivers become more sensitive so we must reduce the energy (actually voltage) applied to them. Reducing voltage is trivial as all I do is set the volume control LOWER. Failing to do this results in way, way too much emphasis in the high frequencies. With lower voltage being applied, the headroom (difference between signal voltage and rails) INCREASES. That is, it becomes far, far more difficult to get into clipping on this amp. Then when we significantly reduce the fundamental frequencies, it's just about impossible to reach clipping in that amp. Impossible, of course, UNLESS we "fry" the drivers by over driving. Is this correct? On mine, I have soldered the output wire to the 'high side', but I have left the fixed elements of the pots in place electrically. This gains the 1dB - 3dB that the pot-in-place wastes, and with replacement of the caps with 'tighter' caps, makes the speaker a good deal clearer, at least to me. But there could be _A LOT_ of power going into those beasts, I question the wisdom of pulling the pots out of the circuit entirely. Peter Wieck Wyncote, PA Peter, what you have done is equivalent to setting the pots to Max Increase. This is the correct position for the pots (you also need just a slight increase in the treble control), if you want a totally FLAT response. AR did NOT recommend this setting back in 1968, because at that time all the record companies were enhancing high frequencies to compensate for the poor audio equipment in the general market. Peter, you have accomplished something else, however, which is very good. Specifically, you have totally by-passed the pot wiper!! That wiper because of age and dissimilar metals corrodes and that corrosion reduces effective energy sent to the drivers. You cannot do what I did, Peter, without testing the resulting balance. That is, with the pots out the drivers become so sensitive and that sensitivity is over such a broad band, that you would have a very difficult time bringing the sound back into balance. You could NOT do it with tone controls. You'd have to have a minimum 7 band EQ and even then I have my doubts. Now, with a separate amp powering those drivers, it's trivial maintaining the balance. Peter, this is why I've been trying to get you to try your tube amps on the mid/tweeter. There may be a problem with your tube amps, however. If I'm not mistaken, your tube amps don't tie the shielding on the audio inputs to chassis ground. If I am correct, you cannot use them with an ss amp on the woofers without bring out adding a new terminal on the speakers. In short, I think you are out of luck. Regards, Jerry |
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#20
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
John Stone wrote on 10/11/2006:
John, xover frequency is determined primarily by the reactive components. Any filter network's turnover frequency is calculated through the values of source impedance, the value of reactive components, and the impedance of the load. Don't believe me? Then substitute a 100 ohm resistor for the tweeter and run a sweep of the crossover. I'm sure you'll you'll see a pretty huge change. OK, but in this case (16 ohms across 3.2 ohms) the xover frequency is primarily determined by the reactive components. I did this by applying a full frequency signal to the mid/tweeter (did exactly the same for the woofer). So a full frequency and full strength voltage was applied to the mid/tweeter and I measured the current actually going to the drivers. In short, the xovers were performing perfectly. That is, they were "blocking" (little or no current) was flowing for the frequencies NOT intended for the respective drivers. I have read this paragraph over and over, and for the life of me, I can't figure out what you are talking about. What kind of "full frequency and full strength voltage" are you referring to? How do you accurately measure the crossover response with a "full frequency" signal? Do you have a spectrum analyzer? I have a dual trace scope and a 20Hz to 200KHz sine and square wave generator. With this I can monitor voltage while I'm watching current flowing in the drivers. The simplest way to accurately measure the response is to run a sine sweep and plot the voltage/frequency curve using an rms voltmeter at the driver terminals. Do it with and without the pot in place an you'll get an exact picture of what is happening. You also keep using the term "current". How, and why are you are measuring current (amps)? John, this is really trivial. I put a .4 ohm resistor in series with the mid/tweeter half of the speaker and watch the voltage drop across it. So as I'm scanning the frequency spectrum and watching the voltage, I can simultaneously watch the actual current flowing. Not my rules. Function of the pots is to balance energy going to the respective drivers to adjust for room conditions and RECORDINGS. I can perform exactly the same function with the volume controls. No you can't. You pulled out 2 pots and substituted them with 1 amplifier gain control, driving the entire mid/tweeter section. You have removed one of the pots' key functions, which was to allow shelving of the mid and tweeter levels individually. True, accept I always set the tweeter pot to max increase. Actually to achieve a totally FLAT response both pots should be set to MAX and there should be a slight increase in treble control. So for me the only real control was over the mid range (which I set fairly close to max as well). I still have control over the tweeter using my treble tone control. If I need more I simply turn it up. If I need less, I turn it down. With a single amp, John, you have no where near the control over sound that I have. And with harmonics riding on fundamentals, you have no where near the headroom that I have. I have no idea what this means. As an aside, John, a totally flat response on AR-3a's is achieved with the pots at max AND a slight increase in the treble volume control. Anybody who has actually measured AR3a's as opposed to just reading the AR literature will tell you this isn't true. Here's an actual real world measurement of the 3a's: http://murphyblaster.com/content.php?f=AR3a.html These measurements are backed up in a post on 8/7 by Dick Pierce to you regarding the frequency response of the AR3a: We have asbolutley no idea how the pots were set in this dude's experiments. Nor do we know how well or what he did when he "restored" his AR-3a's. I can't believe anyone takes this guy's stuff seriously. And on top of all that, he mentions a problem in the mid-highs that the pots would actually help correct. I much prefer the folks at AR who really knew how to test speakers. Further, I don't consider this advertising literatu http://www.classicspeakerpages.net/a...ember_1968.jpg "No, the reason for this is that Roy Allison and Ed Villchur at AR decided on a balance that resulted in an overall downward trend in the speaker's response toward the high end. That was their choice, for whatever reasons. Urban legend. Simply not true. Per Ken Kantor: "Quantifying the high frequency response of a speaker, any speaker, is a much more complex subject than (almost) anyone wants to think about. Short sounds can evoke a perceptually different response than longer tones. Distance from the speaker can have a profound effect, as can placement, listening position and room acoustics. Even more subtly, the whole idea that there is one uniquely "correct" frequency response is unjustifiable, as comforting as it may be. (I believe it to be a residue of the Logical Positivism that arose in the 1960's as an over-reaction to the magical thinking of 1950's High End subjectivism. Kind of like now...) To this day, there is little agreement even between very experienced professionals about how to properly characterize what "flat" response is. AR had their methods, (which evolved over the years.) Within the limitations of those methodologies, AR always tried to make accurate speakers, at least near the top of their line. " Further, if you read the other reference, you can see that AR recommended that folks set the pots at mid point to correct for what the record companies were doing in 1968. The midrange efficiency is about 2 db less than the woofer, and the tweeter is another 2-3 dB less efficient than that. That's what the people of AR designed it to be." (end quote) A "slight increase" in the treble control will not achieve a totally flat response as is clear from the actual response measurements. So you are saying that the pots should be at flat and we need a more than a slight increase in treble?? OK, so? Jerry, your ignorance of even basic loudspeaker design principles is appalling. If I didn't know better, I'd swear you were joking. The tweeter network in the AR3a consists of a single series element; i.e., a 6uf cap feeding a load consisting of a tweeter and a 16 ohm tapped resistor. For all intents and purposes, when you run the tweeter pot at full, you simply have a tweeter and a 16 ohm resistor in parallel. The crossover frequency is determined by the value of the series cap AND the impedance of the load. Removing that 16 ohm resistor alters the load (increases the impedance), which in turn alters the crossover frequency, moving it downward. I'm quite sure what you've done IS significant, My ignorance, huh? John, you spouted a lot of "facts", but not a single number. Are you lazy, John, or perhaps you don't know how to do the math. Let's just see how significant. DC resistance of tweeter is approx. 3.2 ohms So with the 16 ohm pot full across - net resistance = 2.67 ohms or a difference of .53 ohms Sorry Jerry, but yes, your ignorance, or perhaps just lack of attention to detail, as again demonstrated above. DC resistance is utterly meaningless to this discussion, as the last time I checked, tweeters required AC to produce sound. Yet you use resistance interchangeably with impedance as if they were one and the same. The "nominal" impedance of a tweeter with 3.2ohm dcr is 4 ohms. Yep, the reactive component combined with the resistive componet yields an "effective" Z. Z= 3.2 +jwL But the resistance components will respond exactly as I stated. There is no reactive component in the pot. If you take that nominal impedance in parallel with the 16 ohm pot (the pot will have an impedance close to 16 ohms given that it is largely non-inductive) the 2 in parallel yield a resulting impedance of 3.2 ohms. With the pot totally out, you shift the impedance up by a minimum of 20%. Real, real significant, John ... huh?? Um, yeah, I'd say by any measure a 20% shift is significant. And in a previous post, you yourself said so: John, what are you talking about?? Now whose ignorance is showing? With the pots out, naturally LESS current flows ... all of the time. So what?? The end result of that is the speakers have increased in sensitivity. Your issue was that we have significantly altered the xover frequency. That is, taking the pots out causes current to flow MORE at some frequencies than at others. That is we have a frequency altering impact. (This is awful trying to create any tables in Usenet, but let's try again and I'll even use your numbers.) Here we show the current flowing through the high frequency driver under both conditions: Z Z I @ 2 v I @ 2 v Hz Z for Cap w/o pot with pot w/o pot with pot % diff 3,000 8.8 ohms 12.8 12.0 .156 .132 14.7% 4,000 6.6 ohms 10.6 9.8 .188 .163 13.5% 5,000 5.3 ohms 9.3 8.5 .215 .188 12.5% 6,000 4.4 ohms 8.4 7.6 .238 .210 11.6% John, if we look at the last column, we see that the difference in current varies by 3% between 3000Hz and 6000Hz As for the improvement in sensitivity, all I can say it's significant and very noticable. Those are YOUR words, Jerry. So which is it? Significant or not? 20% is way beyond the impedance tolerance AR specified for the drivers alone, so the crossover is indeed operating into a significantly different load than intended, with the resultant shift in xover response as previously stated. Yes, the speakers (not drivers) are more sensitive and it is significant. The change in xover frequency is INSIGNIFICANT! See the table above and show us your proof that this is incorrect (I even used your numbers for impedance). More importantly 20% is the MINIMUM shift. Minimum shift in what? Current doesn't change by 20%. From my table there is 14.7% more current at 3000 Hz and 11.6% more current flowing at 6,000 for the same applied voltage. Over the frequency range of where the tweeter operates, my guess is the average increase in current through the driver will be around 10%. And, YES, that will make the driver put out more SPL. In reality, the tweeter (and midrange) impedance curve is nowhere near flat, and deviates considerably with frequency. Given that these drivers use no ferrofluid they will exhibit a fairly high Q at mechanical resonance ( which I'd estimate around 300Hz for the mid and 3kHz for the tweeter), yielding an impedance peak at resonance perhaps double the nominal value. The driver impedance also rises gradually with increased frequency, due to the voice coil inductance. So the pots were there for 2 reasons: provide level adjustment, and to provide a measure of impedance stabilization for the crossover. By removing them, you have changed things a whole bunch. John, I don't agree with your conclusion at all. I even calculated the current flow through the tweeter at 3000Hz both ways. At 3000 Hz there is a 14.7% difference .... @ 4000 hz the difference is 13.5% .... @ 5000 hz the difference is 12.5% ... @ 6000 hz 11.6% What the pots did is "pad" the output of these drivers to bring them closer in line with the woofer. With the pots gone the output is higher. Tell us, John, do you think there is a human anywhere ... that could actually hear this difference? You said you could hear it yourself, so I'd assume others could as well. Perhaps your arguments would have some weight, John, if you backed them up with the math. There's plenty of "math" above. And it least its based on correct parameters (impedance rather than resistance), which makes your "math" less than useful. I re-did the math using your numbers (even though I don't agree with them) and the result is still the same. No significant change in frequency dependent current. Pushing down the crossover frequency puts more strain on the tweeter. Like it or not, those tweeters were notorious for marginal power handling ability. A.75in voice coil on a paper former with no ferrofluid cannot take much power without burning out. John, your argument bears weight if I removed the pots and single amped. I don't! I adjust the voltage delivered to the mid/tweeter section with my voilume controls. This half of the AR-3a's are NOW more sensitive, so I send LESS voltage. The speakers simply require less voltage and that's part of where I get more headroom. Double check my math if you like, John, but there is simply is NO significant change in frequency dependent current flowing. There is a change that varies by 3% over the range of 3000 to 6000 hz. I don't consider that significant and I don't believe there is a human on this earth that can hear that difference. Jerry, as others here have told you countless times, nothing is to be gained in your configuration compared to a single amp, as long as the driving amplifier has adequately low output impedance and sufficient undistorted power to drive the speakers to the desired level. It's possible that no such amplifier exists. Some could better than others, but the AR-3a has a very complex impedance map. I don't know if any amplifier can perform over the entire range ... as well as an amp over a much narrower, easier and better behave impedance range. Further, the amp driving the mid/tweeter is operating at a completely different level in terms of both voltage and current. In addition, it isn't burdened at all with fundamentals. Whenever we mix fundamentals with harmonics we create the opportunity for IM distortion. When these frequencies are NOT mixed that opportunity is greatly reduced. Virtually all competent amplifiers act as voltage sources, and within the limit of their power output capability, perform largely independent of the load they see. I don't believe that for a minute. One requires enormous "faith" to assume the simply because an amp can produce a nice wave form open loop, it will perform the same when driving a dynamic speaker system. I believe that much is going on inside an amp under continually varying loads and very complex music signals. I believe they are anything, but pure voltage sources. The AR3a designers knew this and designed the speakers accordingly. You have never provided a shred of proof that your configuration solves any problem that couldn't be solved with a single more powerful amplifier. To now extend this argument to ALL amplifiers, regardless of power, is absurd and based totally on unsubstantiated generalizations about power amplifier behavior. Yes, by using 2 amps, you can now adjust the mid and tweeter outputs to levels above the woofer, but that was never the intent of the original design. I've demonstrated that the impedance seen by two amps is radically different than the impedance seen by a single amp. The impedance seen by two amps is much, much more stable. In an single map with widely varying impedance by frequency, we'll see widely fluctuating current flows over the frequency range ... at the same voltage. This "instability" just has to have ramifications. Each amp in a bi-amp of the AR-3a's just has a much, much easier job to do and in my opinion, will always out perform a single amp. Now at the same time that I say this, I want to go on the record that I don't believe this is the case with every speaker system. I have bi-amped a fairly efficient JBL system and while I can hear some minor difference, they are minor. I believe the AR-3a benefits greatly from bi-amping because of the very difficult frequency dependent load it presents to any single amp. I've demonstrated that enormous headroom can be gained in the mid-tweeter amp. Then others have argued that even if clipping occurs in the woofer amp, the "harmful" harmonics are totally isolated from the mid-range and tweeter. As for adjusting the mid/tweeter above the woofer, I never claimed that as a benefit. It's true I can, but I don't. As for my amps, after looking over the facts ... I believe I have far, far more voltage headroom than anyone with a single amp. I know what you believe. Now, please explain the basis of this belief. Let's see your experiments or charts showing your "biamp" configuration with ancient low powered amplifiers of dubious quality having far more headroom than a single 250 watt/ch amplifier with total stability down to 2 ohms. Your claim, your proof. First of all, I don't believe any claims of stable down to 2 ohms. I have some pretty large 2 ohm resistors. Wanna burn out your amp? Next, my typical voltage on the mid/tweeter amp is around 2 volts for fairly loud music. My rails are at 40 volts. Now look at the the voltages of your amp with fundamentals and see what your real headroom is. Which brings up another question: If using separate amps gave such a huge improvement, why didn't AR suggest it in the first place? I don't believe at the time that the AR's were developed, people were even experimenting with bi-amping for home use. I don't believe back in 1968 ANYBODY was thinking about bi-amping for home use, but please share a reference showing that I am wrong. Quote any article from 1968 or earlier recommending bi-amping in the home. Having lived during that era, I can assure you that biamping was indeed being done in home systems well before 1968. Ever hear of the Marantz 3? It's an electronic crossover from the '50s. In fact, even Heathkit offered one called the XO-1 which also dates back well before 1968. There were others. I never heard of any of this and was a Heathkit customer, so I can't imagine it was very popular. Regards, Jerry |
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#21
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Jerry:
I keep a 10-band equalizer, but at the same time I question the value of installing such a unit in other than extreme cases, especially to replace a function that is both effective and already in place, the OEM crossover. Also, keep in mind that that OEM crossover was developed over some 20 years of production of this particular speaker and its children. (3, 3a, LST, 11, 10pi) and does a pretty good job. Note also that none of the aftermarket 'acquired wisdom' on these speakers suggests that the pots should be removed from the circuit, a couple of contributors even caution against it. Apart from all that, I used the term "more-or-less" when I mentioned crossover function. There is some marked effect on its response, making your balance yet more "tetchy"(but not impossible). Once again, I urge you to borrow, beg, steal a brute-force amp and try it with the pots bypassed but the fixed elements LEFT IN PLACE. This adds back the element of protection that the pots provided, brings back the full response of the crossover to its original intention, and still allows you to play with the overall response with your pre-amp tone controls and/or an equalizer. On a purely techical level, I also question your contention that by simply turning down the Volume Control (and therefore reducing the potential for clipping), you are increasing headroom to the mid/tweet. You are increasing both the simple resistance across the voice-coil and the overall impedance (of course). This means that you will require _more_ energy out of the amplifier to make the same voltage at the speakers (watts drop as nominal load increases for most solid-state devices). So what you gain at one end, you lose at the other. However in this case, the speaker VCs are now acting as the system fuse... Pre Ferro-Fluid AR domes are not so good at that... allow me to rephrase: they are very good at being fuses, and blowing. Energy Dissipation: You may think that the most energy going into a speaker goes into the woofer. Not really. Take a simple operatic piece, one of my favorites: Handel's "Let the Bright Seraphim" and the test-piece I used for my biamping experiments. Although there is _some_ bass on that piece (kettledrums, and so forth), even those elements are mostly above the crossover point to the woofer. The P/A on that piece is well over 10dB, approaching 20dB. So at some of the loudest passages, at least 70% (probably more) of the total energy delivered to the speakers is above the crossover point to the woofers. I am not saying that you are going to clip, but I am saying that you are sending a bunch of energy (heat) into those speakers with all the designed-in protections removed, such as they were. Bi-amped or otherwise. Not that I am arguing with your scope and other instruments, but just do a simple band-pass reading of the amp(s) output and see where the frequencies (and associated energy levels) are. Just some thoughts. What you have done seems to work for you, but as much as you have urged me to try things, I also urge you to do the same. I also really hope you have fused your speakers, the AR factory had quite a bit of literature on fusing, and specified quite-expensive low-loss fuses, not the little glass-bits that most use. Peter Wieck Wyncote, PA |
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#22
Posted to rec.audio.high-end
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Jerry wrote:
John Stone wrote on 10/11/2006: John, xover frequency is determined primarily by the reactive components. Any filter network's turnover frequency is calculated through the values of source impedance, the value of reactive components, and the impedance of the load. Don't believe me? Then substitute a 100 ohm resistor for the tweeter and run a sweep of the crossover. I'm sure you'll you'll see a pretty huge change. OK, but in this case (16 ohms across 3.2 ohms) the xover frequency is primarily determined by the reactive components. False. Completely false, for several reasons. First, especially in the case of the high-pass function for the tweeter crossover and the low-pass function for the midrange crossover, these are first-order networks, and the crossover frequency is an equal function of BOTH the series reactance AND the driver impedance. Second, you keep making a simplifying assumption that the drivers are essentially equivalent to these 3.2 ohm resistors, and the most assuredly ARE NOT. Take, for instance, the fact that the tweeter impedance shows a significant rise above it's DC resistance at the fundamental mechanical resonance, which is around 2500 Hz. The impedance reaches, IIR, a high of about 9-10 ohms at that frequency. Under this circumstance, the presence or absence of that 16 ohm shunt resistance makes a SUBSTANTIAL difference in the response of the crossover output below cutoff, and that has an equally substantial effect on the amount of signal fed to the tweeter below cutoff. This changes the frequency response of the speaker as a whole, increases the distortion output of the tweeter and reduces its overall power handling. More specifically, the impedance presented to the tweeter crossover at about 2.5 kHz with and without the shunt resistance of the pot is 6 ohms vs about 9.5 ohms. Thirdly, you keep focusing on one VERY narrow aspect of the crossover response, the "crossover frequency" while ignoring totally the much BIGGER issue of the overall crossover transfer function. IN just the case of the tweeter, not only is the crosover frequency changed rather substantially (assuming the "crossover frequency, you mean the -3dB re passband level frequency, which is moved DOWN by a third of an octave), but you have also substantially changed the shape of the crossover response. Among other things, you have introduced a substantial hump in the response around 2.5 kHz, leading to the problems outlined above. No you can't. You pulled out 2 pots and substituted them with 1 amplifier gain control, driving the entire mid/tweeter section. You have removed one of the pots' key functions, which was to allow shelving of the mid and tweeter levels individually. True, accept I always set the tweeter pot to max increase. Actually to achieve a totally FLAT response both pots should be set to MAX and there should be a slight increase in treble control. So for me the only real control was over the mid range (which I set fairly close to max as well). I still have control over the tweeter using my treble tone control. If I need more I simply turn it up. If I need less, I turn it down. With a single amp, John, you have no where near the control over sound that I have. And with harmonics riding on fundamentals, you have no where near the headroom that I have. I have no idea what this means. As an aside, John, a totally flat response on AR-3a's is achieved with the pots at max AND a slight increase in the treble volume control. Anybody who has actually measured AR3a's as opposed to just reading the AR literature will tell you this isn't true. Here's an actual real world measurement of the 3a's: http://murphyblaster.com/content.php?f=AR3a.html These measurements are backed up in a post on 8/7 by Dick Pierce to you regarding the frequency response of the AR3a: We have asbolutley no idea how the pots were set in this dude's experiments. Nor do we know how well or what he did when he "restored" his AR-3a's. I can't believe anyone takes this guy's stuff seriously. And on top of all that, he mentions a problem in the mid-highs that the pots would actually help correct. I much prefer the folks at AR who really knew how to test speakers. Further, I don't consider this advertising literatu http://www.classicspeakerpages.net/a...ember_1968.jpg "No, the reason for this is that Roy Allison and Ed Villchur at AR decided on a balance that resulted in an overall downward trend in the speaker's response toward the high end. That was their choice, for whatever reasons. Urban legend. Simply not true. Per Ken Kantor: "Quantifying the high frequency response of a speaker, any speaker, is a much more complex subject than (almost) anyone wants to think about. Short sounds can evoke a perceptually different response than longer tones. Distance from the speaker can have a profound effect, as can placement, listening position and room acoustics. Even more subtly, the whole idea that there is one uniquely "correct" frequency response is unjustifiable, as comforting as it may be. (I believe it to be a residue of the Logical Positivism that arose in the 1960's as an over-reaction to the magical thinking of 1950's High End subjectivism. Kind of like now...) To this day, there is little agreement even between very experienced professionals about how to properly characterize what "flat" response is. AR had their methods, (which evolved over the years.) Within the limitations of those methodologies, AR always tried to make accurate speakers, at least near the top of their line. " Nowhere in this quote does Mr. Kantor in any way refute what I said, nor does Mr. Kantor sdtate or even infer that the AR3a's had anechoically flat response. Indeed, the AR3a literature to which you refer show clearly THEY DID NOT HAVE ANECHOICALLY flat response and never did they claim that it did. Further, if you read the other reference, you can see that AR recommended that folks set the pots at mid point to correct for what the record companies were doing in 1968. The midrange efficiency is about 2 db less than the woofer, and the tweeter is another 2-3 dB less efficient than that. That's what the people of AR designed it to be." (end quote) A "slight increase" in the treble control will not achieve a totally flat response as is clear from the actual response measurements. So you are saying that the pots should be at flat and we need a more than a slight increase in treble?? OK, so? Jerry, your ignorance of even basic loudspeaker design principles is appalling. If I didn't know better, I'd swear you were joking. The tweeter network in the AR3a consists of a single series element; i.e., a 6uf cap feeding a load consisting of a tweeter and a 16 ohm tapped resistor. For all intents and purposes, when you run the tweeter pot at full, you simply have a tweeter and a 16 ohm resistor in parallel. The crossover frequency is determined by the value of the series cap AND the impedance of the load. Removing that 16 ohm resistor alters the load (increases the impedance), which in turn alters the crossover frequency, moving it downward. I'm quite sure what you've done IS significant, My ignorance, huh? John, you spouted a lot of "facts", but not a single number. Are you lazy, John, or perhaps you don't know how to do the math. Let's just see how significant. DC resistance of tweeter is approx. 3.2 ohms So with the 16 ohm pot full across - net resistance = 2.67 ohms or a difference of .53 ohms Sorry Jerry, but yes, your ignorance, or perhaps just lack of attention to detail, as again demonstrated above. DC resistance is utterly meaningless to this discussion, as the last time I checked, tweeters required AC to produce sound. Yet you use resistance interchangeably with impedance as if they were one and the same. The "nominal" impedance of a tweeter with 3.2ohm dcr is 4 ohms. Yep, the reactive component combined with the resistive componet yields an "effective" Z. Z= 3.2 +jwL But the resistance components will respond exactly as I stated. There is no reactive component in the pot. You utterly and completely failed or igored what he said. The simply point is that the drivers DO NOT present a resistive load equal to the DC resistance of the voice coils to the crossover, and any conclusion based on this assumption are simply incorrect. With the pots out, naturally LESS current flows ... all of the time. So what?? The end result of that is the speakers have increased in sensitivity. False, the SENSITIVITY, as defined by the loudspeaker industry IS THE SAME. Your issue was that we have significantly altered the xover frequency. No, his issues, and your problem, is that you have changed THE CROSSOVER RESPONSE. The crossover frequency is merely one aspect of that repsonse. You have chosen, at your peril, to ignore the bigger issue. is, taking the pots out causes current to flow MORE at some frequencies than at others. That is we have a frequency altering impact. If you want to play in the realm of loudspeaker engineering, how about using the proper terminology and concepts, please? You HAVE change the transfer function of the network by what you did. You HAVE altered the frequency response as a result. This is true whether you want to admit it or know it or not. Yes, the speakers (not drivers) are more sensitive and it is significant. The change in xover frequency is INSIGNIFICANT! THE CROSSOVER FREQUENCY IS NOT THE ISSUE! YOU HAVE CHANGED THE OVERALL REPONSE OF THE CROSSOVER, EVEN IF THE CROSSOVER FREQUENCY REMAINS THE SAME. Minimum shift in what? Current doesn't change by 20%. From my table there is 14.7% more current at 3000 Hz and 11.6% more current flowing at 6,000 for the same applied voltage. Over the frequency range of where the tweeter operates, my guess is the average increase in current through the driver will be around 10%. STOP LOOKING AT THE NARROW ISSUE OF CURRENT AND CROSSOVER FREQUENCY. Try this: Jerry, youy're staring at a single tree. Are you aware there's a bug forest that you have igored? In reality, the tweeter (and midrange) impedance curve is nowhere near flat, and deviates considerably with frequency. Given that these drivers use no ferrofluid they will exhibit a fairly high Q at mechanical resonance ( which I'd estimate around 300Hz for the mid and 3kHz for the tweeter), yielding an impedance peak at resonance perhaps double the nominal value. The driver impedance also rises gradually with increased frequency, due to the voice coil inductance. So the pots were there for 2 reasons: provide level adjustment, and to provide a measure of impedance stabilization for the crossover. By removing them, you have changed things a whole bunch. John, I don't agree with your conclusion at all. I even calculated the current flow through the tweeter at 3000Hz both ways. At 3000 Hz there is a 14.7% difference .... @ 4000 hz the difference is 13.5% .... @ 5000 hz the difference is 12.5% ... @ 6000 hz 11.6% Once again, you ignored what he said, and you ignored the physical reality of what's going on with the drivers. You failed completely to address his point: "In reality, the tweeter (and midrange) impedance curve is nowhere near flat, and deviates considerably with frequency. Given that these drivers use no ferrofluid they will exhibit a fairly high Q at mechanical resonance ( which I'd estimate around 300Hz for the mid and 3kHz for the tweeter), yielding an impedance peak at resonance perhaps double the nominal value. The driver impedance also rises gradually with increased frequency, due to the voice coil inductance. Perhaps your arguments would have some weight, John, if you backed them up with the math. He did. You chose, perhaps conveniently, to ignore it. It's possible that no such amplifier exists. They do. They're quite common and affrodable. The Heath AR1500 most assuredly isn't one of them. Some could better than others, And almost all are better than what you're using, with all due respect, but you've reduced your experiment to one based on the lowest common denominator of 30 years ago. You have an obvious problem with your am,plifier, and you've done absolutely everything EXCEPT fix the problem: the amplifier. but the AR-3a has a very complex impedance map. No, it most assuredly does not. It's impedance is low, to be sure, but it is largely resistive in nature. Above its low-frequency resonance of about 43 Hz, the impedance is, in fact, quite tame. The fact that YOU have decided to stick with an amplifier that seems to be uniquely incapable of handling one of the more common speakers of the era is no reason to assume that the faults and warts or your AR1500 is generally applicable. I don't know if any amplifier can perform over the entire range You should get out a lot more. THere are literally hundreds of such that will do what you are trying to do with your ancient AR1500 MUCH better than the AR1500 ever good on its best day. Further, the amp driving the mid/tweeter is operating at a completely different level in terms of both voltage and current. In addition, it isn't burdened at all with fundamentals. Whenever we mix fundamentals with harmonics we create the opportunity for IM distortion. When you mix fundamentals with harmonics AND they generate intermodulation products, those products ARE AT THE SAME FREQUENCIES AS THE FUNDAMENTAL AND HARMONICS. When these frequencies are NOT mixed that opportunity is greatly reduced. But, even in your scheme, they are, because you have completely failed to priovide a sufficiently sharp crossover to eliminate one from the other. Further, the largest producer of distortion products is the woofer, and it will produce them whether or not you've multi amped or not. Virtually all competent amplifiers act as voltage sources, and within the limit of their power output capability, perform largely independent of the load they see. I don't believe that for a minute. One requires enormous "faith" to assume the simply because an amp can produce a nice wave form open loop, it will perform the same when driving a dynamic speaker system. Uh, no. An audio amplifier without a load IS NOT 'OPEN LOOP." Please learn what the terminology measn before you bandy it about so. I believe that much is going on inside an amp under continually varying loads and very complex music signals. I believe they are anything, but pure voltage sources. My, god, Jerry, do you really NOT have any idea what "pure voltage source" means. Are you at all familiar with the concept of Thevenin equivalents? Mr. Stone is talking about fundamental concepts of electrical engineering which you are twisting into so much gobbledygook. The impedance seen by two amps is much, much more stable. No, the impedance is NOT more or less "stable." Please define what "stable impedance" mean, in your view. In an single map with widely varying impedance by frequency, we'll see widely fluctuating current flows over the frequency range ... at the same voltage. This "instability" just has to have ramifications. No, it does not. Your fundamental premise is highly flawed. Each amp in a bi-amp of the AR-3a's just has a much, much easier job to do and in my opinion, will always out perform a single amp. That's your opinion, and you're entitled to it. But no matter how strongly held, your opinion is still opinion and not fact. There have been a number of people involved in this conversation, any one of whom has DECADES more professionial experiuence than you have, yet you have chosen to simply plow forward, ignoring facts, ignoring reality, and stating your opinions as fact. I believe the AR-3a benefits greatly from bi-amping because of the very difficult frequency dependent load it presents to any single amp. NO, IT PRESENTS A DIFFICULT LOAD TO YOUR AR1500, WHICH CAN'T GET OUT OF ITS OWN WAY. If your amp is BUSTED, which you have provided ample evidence that it is, the solution is to REPLACE THE AMP. I've demonstrated that enormous headroom can be gained in the mid-tweeter amp. Then others have argued that even if clipping occurs in the woofer amp, the "harmful" harmonics are totally isolated from the mid-range and tweeter. No, you have misread, misconstrued, mirunderstood and misrepresented that they are "totally" isolate. They most assuredly ARE NOT, and your particular "solution" is about as far from what you are claiming as one could imagine. I know what you believe. Now, please explain the basis of this belief. Let's see your experiments or charts showing your "biamp" configuration with ancient low powered amplifiers of dubious quality having far more headroom than a single 250 watt/ch amplifier with total stability down to 2 ohms. Your claim, your proof. First of all, I don't believe any claims of stable down to 2 ohms. I have some pretty large 2 ohm resistors. The wide disparity between your beliefs and opinions and physical reality have been noted a plenty elsewhere. Wanna burn out your amp? Bring it on. I have amplifiers here that are UNDCONDITIONALLY stable into ANY load, resistive or reactive. ANY load. Your AR1500 seems to have problems driving one of the more common speakers of its era. Sorry about that, but the world has LONG since moved on. Maybe you should, too. Which brings up another question: If using separate amps gave such a huge improvement, why didn't AR suggest it in the first place? I don't believe at the time that the AR's were developed, people were even experimenting with bi-amping for home use. I don't believe back in 1968 ANYBODY was thinking about bi-amping for home use, but please share a reference showing that I am wrong. Quote any article from 1968 or earlier recommending bi-amping in the home. Having lived during that era, I can assure you that biamping was indeed being done in home systems well before 1968. Ever hear of the Marantz 3? It's an electronic crossover from the '50s. In fact, even Heathkit offered one called the XO-1 which also dates back well before 1968. There were others. I never heard of any of this and was a Heathkit customer, so I can't imagine it was very popular. So, once again, YOUR opinon is the same as reality? What about the Marantz 3, which was sold a decade before your time frame? What about the Heat XO-1? What about products from DeCoursey, Crown and others. What about the AR1-W? which was late '50's/early '60's which was SPECIFICALLY designed for multi-amped systems? A VERY common high-end setup at the time was KLH-9's with AR1W's using the McIntosh electronic crossovers. The fact that you never heard of them doesn't mean they didn't exist. You are either unaware of or have deliberately chosen to ignore an enormous body of act that contradicts your world view. Unfortunately, no matter how much you might ignore or be unaware of, the real worls is still out there, and your continued tilting against it has done little but squander any credibility you might have enjoyed. I mean no insult by this, none whatseoevere, and only use it necause it is a convenient metaphor, but Mr. Stone (who has been in the loudspeaker business for a LONG time) myself (who also enhoys a long and successful career in the business) and other have been egaging in an excercise akin to teaching a pig to sing: It's a long, frustrating and fruitless endeavor, and it only serves to **** off the pig. There is SO much to learn and know and enjoy about how loudspeakers work, and you have done yourself a huge disservice by staking out such a narrowly constructed, poorly supported and largely technically incorrect position. The facts and realities of loudspeaker physics are so much more varied and nuanced and powerful than what your opinions and what you are unaware of aloow you to experience. If that satisfies you, then, well, fine, have at it. But while you are sitting there with your AR1500 and your VERY narrowly limited experience and view, the rest of the world has moved on. Decades ago. |
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#23
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AR3a/AS103a speakers and the Heathkit AR1500 receiver
Peter Wieck wrote on 10/12/2006:
Jerry: On a purely techical level, I also question your contention that by simply turning down the Volume Control (and therefore reducing the potential for clipping), you are increasing headroom to the mid/tweet. You are increasing both the simple resistance across the voice-coil and the overall impedance (of course). This means that you will require _more_ energy out of the amplifier to make the same voltage at the speakers (watts drop as nominal load increases for most solid-state devices). Peter, it's a little confusing (actually it can be a LOT confusing), even though the impedance without the pots goes UP, the actual current flowing through the driver goes UP. Please remember that the pots "steal current" yet produce no sound. So for exactly the same voltage (with and without pots), there is more current flowing through the driver when the pots are completely removed. Since Watts = I * I * R Power consumed in the driver is approx 25% higher and it follows with more power we get more SPL. So for the same voltage, we get approx 25% more SPL and this would make the sound far, far too bright. So we must reduce the voltage coming out of the amp by turning down the volume. Lower voltage for the same sound gets us further away from the rail voltages ..... hence more headroom. So what you gain at one end, you lose at the other. There is NO losss only a gain in sensitivity of the speakers (the sensitivity of the raw drivers, of course, remains unchanged). However in this case, the speaker VCs are now acting as the system fuse... Pre Ferro-Fluid AR domes are not so good at that... allow me to rephrase: they are very good at being fuses, and blowing. Ok, for the same voltage we have approximately 25% more power dissipated in the voice coil. Over driving is easier ... admittley, but that's why I use a quality, low power amp (approx. 30 -35 watts). This amp has no where near the power of the AR1500, but even at 30 watts, it could still easily fry the mid and the tweeter. However to achieve that kind of power requires the volume control to be way, way over on the right hand side. I rarely advance beyond 9 o'clock. Energy Dissipation: You may think that the most energy going into a speaker goes into the woofer. Not really. Take a simple operatic piece, one of my favorites: Handel's "Let the Bright Seraphim" and the test-piece I used for my biamping experiments. Although there is _some_ bass on that piece (kettledrums, and so forth), even those elements are mostly above the crossover point to the woofer. The P/A on that piece is well over 10dB, approaching 20dB. So at some of the loudest passages, at least 70% (probably more) of the total energy delivered to the speakers is above the crossover point to the woofers. Peter, I seriously doubt your numbers. It's more complicated than just the ratio of frequencies. The low frequencies require far, far more power to reproduce, so even though you don't hear much low frequency, what you do hear requires plenty of power. Peter, the only way to understand this better is to watch the current flowing to the respective halves. You'd be surprised by how much current goes to woofer ... even for instruments we consider "altos". I am not saying that you are going to clip, but I am saying that you are sending a bunch of energy (heat) into those speakers with all the designed-in protections removed, such as they were. The pots really aren't protection, Peter. Yes, they siphon off 25% of the current, but you can still over drive. Their real function is "padding" to bring the SPL from the various drivers somewhat "in line". Bi-amped or otherwise. Not that I am arguing with your scope and other instruments, but just do a simple band-pass reading of the amp(s) output and see where the frequencies (and associated energy levels) are. I have and the vast majority of energy goes to the woofer ... by a lot! Just some thoughts. What you have done seems to work for you, but as much as you have urged me to try things, I also urge you to do the same. I also really hope you have fused your speakers, the AR factory had quite a bit of literature on fusing, and specified quite-expensive low-loss fuses, not the little glass-bits that most use. Peter Wieck Wyncote, PA My amp has fuses, however, I doubt they'd protect the drivers. The AR literature is OK, except I would have to reduce everything by approx. 12%. Regards, Jerry |
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