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#1
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Help measuring frequency response for a speaker system
I have some speaker systems and I want to test their frequency
response. I'm not a sound engineer or anything and I don't really know much about audio. But I assumed I could do this in the following way. I found a test clip on the net which has several frequencies in the audible range 20 Hz - 20 kHz, each playing for 2 seconds. I open it in Nero Wave Editor and it shows that it has the same level from start to finish. Then I take my mic and place it close to a speaker, I mute the other speaker and playback this file, recording with the microphone. I then save the recording uncompressed and open it in Nero Wave Editor to see how loud/quiet each frequency is. My understanding is that the recording should be as close as possible to the test file that I use as input. I did this with two different speaker sets and you can see the results below: http://img224.echo.cx/my.php?image=t...esponse7xo.png http://img224.echo.cx/my.php?image=o...esponse8hv.png Original test file (downloaded recording): http://img156.echo.cx/my.php?image=testclip7ci.png Is this lousy frequency response or what? Am I doing something wrong with my testing method? |
#2
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On 28 Jun 2005 13:40:54 GMT, "Pink_isn't_well"
wrote: I have some speaker systems and I want to test their frequency response. I'm not a sound engineer or anything and I don't really know much about audio. But I assumed I could do this in the following way. I found a test clip on the net which has several frequencies in the audible range 20 Hz - 20 kHz, each playing for 2 seconds. I open it in Nero Wave Editor and it shows that it has the same level from start to finish. Then I take my mic and place it close to a speaker, I mute the other speaker and playback this file, recording with the microphone. I then save the recording uncompressed and open it in Nero Wave Editor to see how loud/quiet each frequency is. My understanding is that the recording should be as close as possible to the test file that I use as input. I did this with two different speaker sets and you can see the results below: http://img224.echo.cx/my.php?image=t...esponse7xo.png http://img224.echo.cx/my.php?image=o...esponse8hv.png Original test file (downloaded recording): http://img156.echo.cx/my.php?image=testclip7ci.png Is this lousy frequency response or what? Am I doing something wrong with my testing method? What you are trying to do here is really difficult, even for experts with many years of experience. You are suffering from a few specific problems. First trying to do it in a normal room instead of an anechoic chamber; I know you are trying to mitigate the effects by close miking, but that doesn't help - a speaker is not designed to be flay close up. Then you are using tones; this is virtually impossible with speakers. You need to use filtered noise, perhaps a third of an octave wide. This is to provide some averaging of the residue of the room's effects. Lastly, you have overdriven the sound card with the mic signal, causing clipping. I'm sorry to have to tell you this, but unless you are prepared to get really serious, give up with this plan. d Pearce Consulting http://www.pearce.uk.com |
#3
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"Pink_isn't_well" wrote in message ... Is this lousy frequency response or what? Can't say; it depends on the frequency response of the microphone you're using. Tim |
#4
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Pink_isn't_well wrote:
I have some speaker systems and I want to test their frequency response. I'm not a sound engineer or anything and I don't really know much about audio. But I assumed I could do this in the following way. I found a test clip on the net which has several frequencies in the audible range 20 Hz - 20 kHz, each playing for 2 seconds. I open it in Nero Wave Editor and it shows that it has the same level from start to finish. Then I take my mic and place it close to a speaker, I mute the other speaker and playback this file, recording with the microphone. I then save the recording uncompressed and open it in Nero Wave Editor to see how loud/quiet each frequency is. My understanding is that the recording should be as close as possible to the test file that I use as input. I did this with two different speaker sets and you can see the results below: http://img224.echo.cx/my.php?image=t...esponse7xo.png http://img224.echo.cx/my.php?image=o...esponse8hv.png It may not be as bad as it seems. One problem is that the amplitude scale is given in percentage, when frequency response is usually plotted on a dB scale. For example, 50% on your FR curve is only 6 dB down from the peak level, and 10% is only 20 dB down. +/- 10 dB frequency response is not all that bad, but it shows up as 10% - 100% on your chart. Original test file (downloaded recording): http://img156.echo.cx/my.php?image=testclip7ci.png Is this lousy frequency response or what? Hard to say. Am I doing something wrong with my testing method? For sure. As Don Pearce says, measuring the FR of speakers correctly is a tall order, and your methodology is very simplistic. If you want to see a better job of FR testing, try downloading this softwa http://audio.rightmark.org/downloads/rmaa55.exe You also need a better microphone. About the cheapest one I can recommend is this one: http://www.zzounds.com/item--BEHECM8000 To interface it to your PC, you need this mic preamp or something like it: http://www.music123.com/Rolls-MP13-M...p-i11840.music If you want better measurement softwa http://www.etfacoustic.com/ |
#5
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Pink_isn't_well wrote: I have some speaker systems and I want to test their frequency response. Before we get into the specifics of your case, let me ask you, in all seriousness, why do you want to do this? Let's assume for the moment your methods are correct and your data is good. What are you going to do with this data? How are you going to act on it? That's real important in determining WHAT data you need to get. Do you want to know the frequency response becuas you're just curious or because you need to make design changes? Very different sorts of data are needed. That being said, let's proceed... I'm not a sound engineer or anything and I don't really know much about audio. But I assumed I could do this in the following way. I found a test clip on the net which has several frequencies in the audible range 20 Hz - 20 kHz, each playing for 2 seconds. I open it in Nero Wave Editor and it shows that it has the same level from start to finish. First problem: "several frequencies." Do you mean stepped sine waves? Narrow band pink noise? What? All of these have their advantages and disadvantages and require appropriate techniques to gather useful data. Then I take my mic Second problem, what kind of mic? This has a profound influence over the usability of the results. For reliable results, just any ol' microphone won't do. Different microphones that may be suitable different vocal or musical applications are generally highly unsuitable for measurement purposes. and place it close to a speaker, Third problem: depending upon what you mean by "close," your results are going to be severely skewed by a number of proximity effects that make such measurements suspect under a number of conditions. Fourth problem: under what acoustical conditions are you measuring? The existance of noise plus the influence of nearby reflective boundaries and room-reletaed resonance can have a tremendous influsence over such measurements. I mute the other speaker and playback this file, recording with the microphone. I then save the recording uncompressed and open it in Nero Wave Editor to see how loud/quiet each frequency is. Fifth problem: such a display yells you nothing about frequency response. Assuming the data you recorded is useable, a linear display of amplitude is next to useless. FOr example, take the differenence beween the loudest possible signal and one half as loud: that's 1/4 of the height of the graph and corresponds to a level difference of 6db between those to levels. But that smae 1/4 height difference could correspond to a difference of 10 db, if it's netween 25% and 75%, or it could correspond to a difference of 34 dB if that 1/4 height is between 1% and 51%! My understanding is that the recording should be as close as possible to the test file that I use as input. No, not necessarily. Is this lousy frequency response or what? It's worse than that: it's a useless frequency response. Because of all the problems outlined above, your data is invalid. This is not to say your speakers do or do not have a bad frequency response: it's just that there is no way of knowing that from the data you're presented. Am I doing something wrong with my testing method? Yes, regrettably, just about everything fundamental is wrong with your method. Start first with answering my first question: why do you want to do this? |
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wrote on Tue, 28 Jun 2005 15:32:59 GMT in
rec.audio.tech: Before we get into the specifics of your case, let me ask you, in all seriousness, why do you want to do this? Well, I got myself some speakers recently and they sounded like they had too much bass. That's what I thought. I did find a review of them on tomshardware which had a frequency response graph and it showed no particular problem with the bass, it was roughly the same as the treble. So I got curious and thought maybe I'll try something like that myself and see what comes out. I knew that I wasn't going to get the most accurate results, but I thought the results would be interesting, particularly checking against other speakers I have laying around here. First problem: "several frequencies." Do you mean stepped sine waves? Narrow band pink noise? I used this: http://www.dogstar.dantimax.dk/testwavs/3stepoct.zip Second problem, what kind of mic? This has a profound influence over the usability of the results. For reliable results, just any ol' microphone won't do. Well, I knew of course that my mic is a cheap one, but I have to admit that the recorded file sounded the same as what my ears were telling me, and that's all that matters I guess. I used the same mic on the other set of speakers, too. and place it close to a speaker, Third problem: depending upon what you mean by "close," your results are going to be severely skewed by a number of proximity effects that make such measurements suspect under a number of conditions. Why? What could those effects be? Fourth problem: under what acoustical conditions are you measuring? The existance of noise plus the influence of nearby reflective boundaries and room-reletaed resonance can have a tremendous influsence over such measurements. Under my normal listening conditions, close to my computer. I did turn off the AC though. Fifth problem: such a display yells you nothing about frequency response. Assuming the data you recorded is useable, a linear display of amplitude is next to useless. FOr example, take the differenence beween the loudest possible signal and one half as loud: that's 1/4 of the height of the graph and corresponds to a level difference of 6db between those to levels. But that smae 1/4 height difference could correspond to a difference of 10 db, if it's netween 25% and 75%, or it could correspond to a difference of 34 dB if that 1/4 height is between 1% and 51%! Ah, and this is one reason why I posted here, so I could get help. What software would give more useful displays? My understanding is that the recording should be as close as possible to the test file that I use as input. No, not necessarily. Why? Thanks for the reply, I'm not trying to say that my method is perfect or anything, just to learn some stuff and maybe evaluate my speakers (or my ears) better. |
#7
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#8
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Pink_isn't_well wrote: (Don Pearce) wrote on Tue, 28 Jun 2005 14:03:54 GMT in rec.audio.tech: I'm sorry to have to tell you this, but unless you are prepared to get really serious, give up with this plan. So there is absolutely no way I can get an idea of my speakers' FR without spending thousands and moving them to some sort of professional chamber? Well, not THOUSANDS, but around about a kilobuck if you want reliable, consistent, repeatable results. Do a web search for something called ClioWin, which is a purpose-built measurement system for Windows including a very reasonable microphone. There are other packages which can be had cheaper, but require more care and knowledge using them. |
#9
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Pink_isn't_well wrote: wrote on Tue, 28 Jun 2005 15:32:59 GMT in rec.audio.tech: Before we get into the specifics of your case, let me ask you, in all seriousness, why do you want to do this? Well, I got myself some speakers recently and they sounded like they had too much bass. That's what I thought. I did find a review of them on tomshardware which had a frequency response graph and it showed no particular problem with the bass, it was roughly the same as the treble. So I got curious and thought maybe I'll try something like that myself and see what comes out. I knew that I wasn't going to get the most accurate results, but I thought the results would be interesting, particularly checking against other speakers I have laying around here. Fine, but you still need to address the question, what are you going to do with the results? Second problem, what kind of mic? This has a profound influence over the usability of the results. For reliable results, just any ol' microphone won't do. Well, I knew of course that my mic is a cheap one, but I have to admit that the recorded file sounded the same as what my ears were telling me, and that's all that matters I guess. I used the same mic on the other set of speakers, too. But the mic is one of the most important links in the chain. and place it close to a speaker, Third problem: depending upon what you mean by "close," your results are going to be severely skewed by a number of proximity effects that make such measurements suspect under a number of conditions. Why? What could those effects be? There are a number of such effects, depending upon the distance. I'm hardly going to take the time to catalog and explain them all, but consider, for example, close-miking a woofer, with the result that there are significant differences in the distances to different parts of the driver, with the result that cancellations occur at some frequencies. These cancellations will not be present in the far field. Fourth problem: under what acoustical conditions are you measuring? The existance of noise plus the influence of nearby reflective boundaries and room-reletaed resonance can have a tremendous influsence over such measurements. Under my normal listening conditions, close to my computer. I did turn off the AC though. Fine, but did you attempt, at all, to account for the influence of the room boundaries and such? Fifth problem: such a display yells you nothing about frequency response. Assuming the data you recorded is useable, a linear display of amplitude is next to useless. FOr example, take the differenence beween the loudest possible signal and one half as loud: that's 1/4 of the height of the graph and corresponds to a level difference of 6db between those to levels. But that smae 1/4 height difference could correspond to a difference of 10 db, if it's netween 25% and 75%, or it could correspond to a difference of 34 dB if that 1/4 height is between 1% and 51%! Ah, and this is one reason why I posted here, so I could get help. What software would give more useful displays? Software thatv is more suited to measuring frequency response. what you picked is uttewrly unsuitable to the task, as you're discovering. Check out some of the references given. My understanding is that the recording should be as close as possible to the test file that I use as input. No, not necessarily. Why? Because of all the problems you have encountered. Because the speaker may not have been designed that way, on purpose. Because you may not be measuring on the preferred axis of the system, at a sufficient distance, and more. |
#10
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Well, I got myself some speakers recently and they sounded like
they had too much bass. Do they have a volume control for the "sub-woofer" speaker? That's what I thought. I did find a review of them on tomshardware which had a frequency response graph and it showed no particular problem with the bass, it was roughly the same as the treble. Did you reveal what speakers you are talking about? I've never seen reviews on TomsHardware for anything except plastic toy "computer" speakers. Nothing against plastic toy computer speakers, they have their place. I use them myself. But they will never be something that one would expect any kind of accurate frequency response from. |
#11
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"Richard Crowley" wrote on Wed, 29 Jun
2005 17:58:49 GMT in rec.audio.tech: Did you reveal what speakers you are talking about? I've never seen reviews on TomsHardware for anything except plastic toy "computer" speakers. http://www6.tomshardware.com/consume..._audio-05.html Well, yes, I'm talking about "toy" speakers (why would they be toy?). Of course you can connect them to any kind of device, not just computers. |
#12
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#13
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"Pink_isn't_well" wrote ...
"Richard Crowley" wrote : Did you reveal what speakers you are talking about? I've never seen reviews on TomsHardware for anything except plastic toy "computer" speakers. http://www6.tomshardware.com/consume..._audio-05.html Well, yes, I'm talking about "toy" speakers (why would they be toy?). Of course you can connect them to any kind of device, not just computers. If you are really concerned enough about audio quality to go to the trouble of trying to run frequency response curves, you likely will not be sataisfied with ANY of those speakers that are sold to the computer crowd. They're OK for playing games or listening to internet radio, etc. but I wouldn't trust them for any kind of qualitative audio mixing, processing etc. I'd think that the minimum for any kind of quality would be some of the powered monitors sold for the home recording crowd. Something like M-Audio or Behringer or Roland, etc. This kind of stuff.... http://www.musiciansfriend.com/srs7/g=rec/search?c=4901 If you aren't doing serious audio processing, but just curious about your computer speakers, maybe you'd be happier not knowing. :-) |
#14
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For a while, Cool Edit Pro was available as a demo version. Now that
they're no longer making it (I believe Adobe bought it out), you might have to do some digging. "Pink_isn't_well" wrote in message ... wrote on Tue, 28 Jun 2005 15:32:59 GMT in rec.audio.tech: Fifth problem: such a display yells you nothing about frequency response. Assuming the data you recorded is useable, a linear display of amplitude is next to useless. Any free software I can use to open my waves and have them on a dB scale? |
#15
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"Pink_isn't_well" wrote ...
Any free software I can use to open my waves and have them on a dB scale? Audacity? GoldWave? likely others? But it doesn't really mean anything unless you are interested in the combined frequency response of the speakers AND the microphone. And even if you had a flat instrumentation mic, you can get any curve you wish by moving the mic a fraction of an inch in any direction in your "measurement environment". |
#16
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Pink_isn't_well wrote: wrote on Tue, 28 Jun 2005 15:32:59 GMT in rec.audio.tech: Fifth problem: such a display yells you nothing about frequency response. Assuming the data you recorded is useable, a linear display of amplitude is next to useless. Any free software I can use to open my waves and have them on a dB scale? Why? The data you have is probably useless. Displaying useless data in the proper format is still pretty useless. Do you remember all the other problems we discussed? The issue of the display format is probably the easiest to solve and the least useful of the bunch. It's not going to make your data any more valid. And it's been revealed that the epseakers you're measuring are so-called "computer speakers." Almost without exception, these sorts of things range from plain awful to truly, miserably dreadful. They aren't toys, they're worse than toys. The designers of these things (and I've had the misfortune of working with some of them) are required to shoehorn as much pizzazz and sparkle and over-hyped specifications into the absolute cheapest package possible, and about the LAST thing on their mind is reasonable acoustic performance. A fair number of them are, in fact, made in a number of far east companies whose main product line is high-volume (as in millions) injection-molded products ranging anywhere from plastic forks and spoons to telephone cases. They know next to nothing about loudspeakers, only how to make a whole bunch of anything at the lowest possible price. One of my clients makes a computer-based system and has to supply speakers with it. Their customer expects the speakers to be worth on the order of $100-$150 a pair, and the client had a devil of a time finding speakers at OEM pricing for any more tha $20 the pair! They're junk. They measure like junk, they sound, as you said, like junk. Why bother? |
#17
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wrote in message oups.com... One of my clients makes a computer-based system and has to supply speakers with it. Their customer expects the speakers to be worth on the order of $100-$150 a pair, and the client had a devil of a time finding speakers at OEM pricing for any more tha $20 the pair! Surely you told them they are looking in the wrong spot? They should be checking out the cheaper near field monitors available from the pro audio manufacturers. MrT. |
#18
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"Pink_isn't_well" wrote in message ... wrote on Tue, 28 Jun 2005 15:32:59 GMT in rec.audio.tech: Fifth problem: such a display yells you nothing about frequency response. Assuming the data you recorded is useable, a linear display of amplitude is next to useless. Any free software I can use to open my waves and have them on a dB scale? You may have got some suitable software with your sound card. Otherwise, you can download Goldwave - it's not free, but you can use it first and decide whether to pay later. You can also use Goldwave to generate test signals. The test signal you are using starts with a lot of LF sound, from 20Hz to 40Hz, which is below the LF range of your speakers, You will have a problem with the microphone ... most microphones are designed to be less responsive to low frequencies below about 70Hz, and I believe it's the LF region you are most concerned with.. You have another problem with the microphone, in that it won't have a flat response in the mid-and HF region. Again, most microphones are deliberately designed that way. What you could try is measure your speakers, measure another pair which you think sound normal, and compare the results. If your speakers are over-responsive in part of the frequency range, this might help show where. Anyway, it's well worth doing, because it's fun and educational.. Tim |
#19
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#20
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"Pink_isn't_well" wrote ...
dpierce wrote : They know next to nothing about loudspeakers, only how to make a whole bunch of anything at the lowest possible price. I see. Is this true even for the more expensive systems, ranging $300 - $500? Or just for the cheap systems like mine? Define "more expensive systems". As far as I have seen ANYTHING intended for the "computer speaker market" suffers from this problem regardless of selling price. "Computer speakers" as a class are held in low regard in these circles. I've never seen any that even aspired to having a decent frequency response. Glitz, thump, and number of channels/speakers seems far more important than audio quality. Even historically prestigious names in audio history like Altec have been sold off to the highest bidder and are now put on toy plastic computer speakers. How the mighty have fallen. James B Lansing just be spinning in his grave. |
#21
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" wrote:
Do you want to know the frequency response becuas you're just curious or because you need to make design changes? Very different sorts of data are needed. Sounds mostly like he wants to have some 'fancy looking pictures' to prove/disprove whatever his theory might be. His methodology however looks to be pretty dodgy. |
#22
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Pink_isn't_well wrote:
Michael Conzo wrote on Fri, 01 Jul 2005 04:06:46 GMT in rec.audio.tech: Sounds mostly like he wants to have some 'fancy looking pictures' to prove/disprove whatever his theory might be. No. You could've read the previous postings before you write this, couldn't you? Ummm, Usenet, ...free advice, ...you get what you paid for. ~quityourbitchin~ Later... Ron Capik cynic in training -- |
#23
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Ron Capik wrote on Fri, 01 Jul 2005
13:37:28 GMT in rec.audio.tech: Ummm, Usenet, ...free advice, ...you get what you paid for. I've gotten lots of good advice here already. |
#24
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"Pink_isn't_well" wrote ...
Michael Conzo wrote : Sounds mostly like he wants to have some 'fancy looking pictures' to prove/disprove whatever his theory might be. No. You could've read the previous postings before you write this, couldn't you? OK, then what ARE you trying to do? I didn't think Mr. Conzo's characterization was that far from the mark. Sounds like all you need is some way to balance your subwoofer, (and you never responded to the obvious questions about setting the subwoofer level). But then you got off on trying to actually measure the frequency response without knowing what a huge can of worms it is and how far in over your head you are. If it were me, I would just play some pink noise and tune the subwoofer level in-situ by ear. That is ultimately what counts, after all. |
#25
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"Richard Crowley" wrote on Fri, 01 Jul
2005 16:07:17 GMT in rec.audio.opinion: If it were me, I would just play some pink noise and tune the subwoofer level in-situ by ear. That is ultimately what counts, after all. Yeah, you're very smart. The problem is that bass level is too high even with the subwoofer turned off. |
#26
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"Pink_isn't_well" wrote in message
"Richard Crowley" wrote on Fri, 01 Jul 2005 16:07:17 GMT in rec.audio.opinion: If it were me, I would just play some pink noise and tune the subwoofer level in-situ by ear. That is ultimately what counts, after all. Yeah, you're very smart. The problem is that bass level is too high even with the subwoofer turned off. Sounds like room resonance problems. Here's a potential solution: http://www.realtraps.com/ |
#27
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"Arny Krueger" wrote in message ... "Pink_isn't_well" wrote in message "Richard Crowley" wrote on Fri, 01 Jul 2005 16:07:17 GMT in rec.audio.opinion: If it were me, I would just play some pink noise and tune the subwoofer level in-situ by ear. That is ultimately what counts, after all. Yeah, you're very smart. The problem is that bass level is too high even with the subwoofer turned off. Sounds like room resonance problems. Here's a potential solution: http://www.realtraps.com/ Or maybe the subwoofer level adjustment is broken. Doesn't seem to have an actual hardware pot. Uses some kind of remote control(?) |
#28
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"Richard Crowley" wrote on Fri, 01 Jul
2005 22:50:43 GMT in rec.audio.tech: Or maybe the subwoofer level adjustment is broken. Doesn't seem to have an actual hardware pot. Uses some kind of remote control(?) Wired control. It works, if I turn it up the effect is even worse. I guess they make them that way so they can give stronger effects with games and movies. |
#29
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Pink_isn't_well wrote: "Richard Crowley" wrote on Fri, 01 Jul 2005 22:50:43 GMT in rec.audio.tech: Or maybe the subwoofer level adjustment is broken. Doesn't seem to have an actual hardware pot. Uses some kind of remote control(?) Wired control. It works, if I turn it up the effect is even worse. I guess they make them that way so they can give stronger effects with games and movies. I don't know how many systems use compensation, but the one I have on my computer obviously has some form of loudness or automatic control of the bass driver, a 3 piece unit. The response depends on the volume. I could never get it right by any adjustmet or positioning, always too much low bass, or I should say too much upper bass. It sounds like it would be much easier if you were back in the 70's, with all those spectrum analyzers that were available back then. They came with a mic, and with pink noise or warble tones, you could get a rough look at what your looking for. They are still there on Ebay. greg |
#30
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wrote in message
oups.com It sounds like it would be much easier if you were back in the 70's, with all those spectrum analyzers that were available back then. Just because they aren't in the same form as they were then, doesn't mean that they don't exist. They came with a mic, and with pink noise or warble tones, you could get a rough look at what your looking for. Modern stuff does more and has far higher resolution. Much of it is computer-based. |
#31
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"Arny Krueger" wrote in message ... wrote in message oups.com It sounds like it would be much easier if you were back in the 70's, with all those spectrum analyzers that were available back then. Just because they aren't in the same form as they were then, doesn't mean that they don't exist. They came with a mic, and with pink noise or warble tones, you could get a rough look at what your looking for. Modern stuff does more and has far higher resolution. Much of it is computer-based. You won't need much resolution since the damn speakers have no midrange or treble. I can get pretty good generalized response curves off my old Audio Control and its cheap measurement mic. As far as te anechoic chamber, that is not actually required. You can make measurements in the back yard and get fairly good cures for speaker design problems such as box tuning and beaming. its a good way to measure free air resonance also |
#32
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"Carl Valle" wrote in message
m "Arny Krueger" wrote in message ... wrote in message oups.com It sounds like it would be much easier if you were back in the 70's, with all those spectrum analyzers that were available back then. Just because they aren't in the same form as they were then, doesn't mean that they don't exist. They came with a mic, and with pink noise or warble tones, you could get a rough look at what your looking for. Modern stuff does more and has far higher resolution. Much of it is computer-based. You won't need much resolution since the damn speakers have no midrange or treble. That makes no sense at all. If speakers have response problems, we need our ears and our test equipment to determine what the problem is. Bad speakers aren't a justification for having poor test equipment. I can get pretty good generalized response curves off my old Audio Control and its cheap measurement mic. You get something, but how accurate is it? Here's an independent critical look at the Audio Control RTA: http://www.hometheaterhifi.com/volum...equalizer.html "For one thing, a simple spectrum analyzer cannot capture information in the time domain, and therefore cannot differentiate between direct sound and reflected sound. So, what the spectrum analyzer shows is the average of the two. Because of this, if adjusted solely by the RTA, an EQ alters both the direct and indirect sound so that the two sum flat, although neither may be so individually. Human hearing works in a much more complex manner, so that although we may not hear the two (direct and indirect sound) as distinctly separate in most home environments, altering one to correct the other won't always work very well. One of the best examples of this is to get a dipolar speaker, which usually has a horrible pink noise response due to a high ratio of delayed, reflected sound from the rear wall. "If you adjust an EQ to compensate for the RTA reading, you often get sliders shoved all over the place, and a very weird tonality. This is because the process of hearing somewhat compensates for the environment, and takes much of the comb filtering effects of reflected/direct sound interaction which skew the tonality of continuous pink noise, and puts it to use with impulsive signals to derive spatial cues about the environment. That's why bipolar/dipolar speakers tend to do such a great job providing a "they are here" presentation. Tangent aside, even though an equalizer can slightly compensate for room problems, if the room's broken, you're best off fixing the room. "Secondly, a spectrum analyzer, especially a 10 band, 1 octave jobbie, has limited frequency resolution, looking only across relatively broad sections. For instance, the frequency response may vary 10 dB up and down, but so long as it averages within that octave, appears perfectly flat on the analyzer. The corollary is that an equalizer with similar resolution cannot effectively compensate for narrow band response peaks or dips caused either by loudspeaker problems or extreme room modes. As far as the anechoic chamber, that is not actually required. You can make measurements in the back yard and get fairly good cures for speaker design problems such as box tuning and beaming. its a good way to measure free air resonance also. Actually, a RTA is a very poor means for measuring woofer free air resonance. A signal generator a resistor and a AC voltmeter are the classic means which yields excellent results. Since I have a highly accurate computer-based speaker impedance-measuring facility, that's what I use. The technology of acoustic measurements has made dramatic improvements in performance and convenience in the last 5-10 years. The key component has been the computer with an apporpriate audio interface. |
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In article , "Arny Krueger" wrote:
"Carl Valle" wrote in message om "Arny Krueger" wrote in message ... wrote in message roups.com It sounds like it would be much easier if you were back in the 70's, with all those spectrum analyzers that were available back then. Just because they aren't in the same form as they were then, doesn't mean that they don't exist. They came with a mic, and with pink noise or warble tones, you could get a rough look at what your looking for. Modern stuff does more and has far higher resolution. Much of it is computer-based. You won't need much resolution since the damn speakers have no midrange or treble. That makes no sense at all. If speakers have response problems, we need our ears and our test equipment to determine what the problem is. Bad speakers aren't a justification for having poor test equipment. I can get pretty good generalized response curves off my old Audio Control and its cheap measurement mic. You get something, but how accurate is it? Here's an independent critical look at the Audio Control RTA: http://www.hometheaterhifi.com/volum...equalizer.html "For one thing, a simple spectrum analyzer cannot capture information in the time domain, and therefore cannot differentiate between direct sound and reflected sound. So, what the spectrum analyzer shows is the average of the two. Because of this, if adjusted solely by the RTA, an EQ alters both the direct and indirect sound so that the two sum flat, although neither may be so individually. Human hearing works in a much more complex manner, so that although we may not hear the two (direct and indirect sound) as distinctly separate in most home environments, altering one to correct the other won't always work very well. One of the best cut This is all very interesting. I suppose one could go on and on about measuring speakers and also comparing this to listening to speakers. I do know delayed sound is not as loud to the ear,. Perhaps that sort of diminishes its importance in measuring response. I have used my trusty cheap BSR display unit with remarkable results over time. I have come to trust its readings for the most part, except for the lowest and highest frequency ranges. Even if its off, its interesting to compare different responses of various speakers. greg |
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"Arny Krueger" wrote in message ... The technology of acoustic measurements has made dramatic improvements in performance and convenience in the last 5-10 years. The key component has been the computer with an apporpriate audio interface. Whilst I agree with your other points, computer controlled measurement systems have been used for over 30 years. Obviously they have steadily improved, but I see no radical developments that have only occurred in the last 5 years, or even 10. Maybe you mean the cost is now within the range of many amateurs? Unfortunately though, the concept of measurement uncertainty doesn't seem to have trickled down along with the technology. MrT. |
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"Mr.T" wrote ...
Whilst I agree with your other points, computer controlled measurement systems have been used for over 30 years. Obviously they have steadily improved, but I see no radical developments that have only occurred in the last 5 years, or even 10. Maybe you mean the cost is now within the range of many amateurs? Unfortunately though, the concept of measurement uncertainty doesn't seem to have trickled down along with the technology. And computer-aided trickery can go only so far to cheat the physical/acoustical facts of life. (i.e. measurement environment, etc.) |
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"Mr.T" MrT@home wrote in message
"Arny Krueger" wrote in message ... The technology of acoustic measurements has made dramatic improvements in performance and convenience in the last 5-10 years. The key component has been the computer with an apporpriate audio interface. Whilst I agree with your other points, computer controlled measurement systems have been used for over 30 years. Cars have been used for over 100 years, doesn't mean that they haven't involved over that time. Obviously they have steadily improved, but I see no radical developments that have only occurred in the last 5 years, or even 10. I'm speaking in the context of measurements by enthusiasts and listeners. Maybe you mean the cost is now within the range of many amateurs? Yes. Unfortunately though, the concept of measurement uncertainty doesn't seem to have trickled down along with the technology. What do you mean by that? |
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In rec.audio.tech and rec.audio.opinion, On Fri, 8 Jul 2005 06:21:30
-0400, "Arny Krueger" wrote: "Mr.T" MrT@home wrote in message u "Arny Krueger" wrote in message ... The technology of acoustic measurements has made dramatic improvements in performance and convenience in the last 5-10 years. The key component has been the computer with an apporpriate audio interface. ... Maybe you mean the cost is now within the range of many amateurs? Yes. Unfortunately though, the concept of measurement uncertainty doesn't seem to have trickled down along with the technology. What do you mean by that? I understood him to mean that high-quality measurement equipment is now inexpensive, but many people who can afford it and will buy it don't know how to effectively use it or interpret the results. ----- http://www.mindspring.com/~benbradley |
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Ben Bradley said to the Krooborg: Unfortunately though, the concept of measurement uncertainty doesn't seem to have trickled down along with the technology. What do you mean by that? I understood him to mean that high-quality measurement equipment is now inexpensive, but many people who can afford it and will buy it don't know how to effectively use it or interpret the results. Please spare Arnii your peacock's tail of superior knowledge. Arnii is a grunt's grunt. |
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"Ben Bradley" wrote in message ... Unfortunately though, the concept of measurement uncertainty doesn't seem to have trickled down along with the technology. What do you mean by that? I understood him to mean that high-quality measurement equipment is now inexpensive, but many people who can afford it and will buy it don't know how to effectively use it or interpret the results. Yes. Access to a million dollar + lab is usually only for those with measurement experience, understanding of proper procedures, calibration requirements, and how to interpret the test results and uncertainty. Having access to a computer, soundcard and microphone requires none of those things. Yet many still think their results are beyond reproach. MrT. |
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"Mr.T" MrT@home wrote in message
"Ben Bradley" wrote in message ... Unfortunately though, the concept of measurement uncertainty doesn't seem to have trickled down along with the technology. What do you mean by that? I understood him to mean that high-quality measurement equipment is now inexpensive, but many people who can afford it and will buy it don't know how to effectively use it or interpret the results. Yes. Access to a million dollar + lab is usually only for those with measurement experience, understanding of proper procedures, calibration requirements, and how to interpret the test results and uncertainty. Having access to a computer, soundcard and microphone requires none of those things. Yet many still think their results are beyond reproach. Chauvenism aside, the results one gets with intelligent procedures, intelligent equipment choices, and the use of a computer, soundcard and microphone does serve one's technical interests a whole lot better than a 10-band audio analyzer. |
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