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#81
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20hz to 20Khz , yea right!
So-called (actually, mis-named) 'isobarik' systems are a way of
obtaining a given response in half the volume, since the arrangement results in half the total equivalent compliance volume and thus requires half the enclosure volume for the same response function. My Isobric has been constructed to improve LF ouput (it seems) not reduces size as i can tell as it has a ~12 cubic foot cubed primary with a ~ 6 cubic secondary, I guess that they have decided that the cone mass of an 8 inch drive in isobaric has advantages over that of an 12 inch driver (at the size of the brute it could easily use a 12 inch drive, one thing did occur to me is that perhaps due to its age that duel VC speakers were not avalible and the only method of getting a phase and anti phase driver easily was to use two drivers. As to "true hifi response," such a term needs definition to be anything but meaningless jargon, in precisely the same way that a "specification" like "20Hz-20kHz" is meaningless without qualification. I guess what I desire is a reasonably flat response fro 32 Hz to 15Khz with gradual roll off above and below. If that is 'hi fi' or not is questionable. I spent some time years ago analysing CD's to find usual and lowest frequency's (plus HF, lots of CD's have significant output above 15Khz (components up to 25Khz+ can be present) but at my age thats starting to get above what I can easily here!) LF it seems stops round the ~30 Hz, few instraments produce much less than this (yes I know that alot can) a lot of the very LF on disk is artificial (1/2 frequency echo and its that it is possibly added to give 'space' to the recordings) unless you are a pipe organ freak under 30Hz seems to unused (but not in Dolby Prologic, ES or such as the LF in these type video recordings is huge it seems (and unnatural in my books) ) THe fundamental efficiency/enclosure volume/cutoff frequency equation will ALWAYS rule. But, interestingly enough, driver diameter simply does not enter into that relation. Specifically, the relation: n0 = kn Vb F3^3 where n0 is reference efficiency, Vb is enclosure volume, F3 is is low frequency cutoff and kn is the efficiency constant has NO term in it in any way depedent upon driver diameter. This directly refutes your assertion that it's not possible to get your "unqualified" 'hifi response from an 8 inch driver. One needs to simply balance the three terms of efficiency, enclosure volume and cutoff frequency and you're there. You seem to intimate that low efficiency is incompatible with 'hifi response," for example, an unjustifiable viewpoint in light of the lack of qualification of 'hifi response.' kn = efficiency constant derived from driver (this figure will improve with driver diameter, thus a large driver will allow a a small enclosue to produce the same output at the same frequency with less power - correct me if wrong) However in order to get usable (at say 32Hz) levels the enclosure volume (8 inch) will become so large as to be impactical in a lot of cases. This equates to the 'You can put an airplane engine in a submarine' but who wants too? An enclose that is over 32 cubic feet will meet significant resistance when placed in the home! (Test this by asking you wife if you can shift 2 small fridges into the lounge!) I tend to deal with and try and work in what can be achieved reasonably easily in real world situations, absolutes and what is theoretically possible don't fit! (But are well worth knowing and considering (Hey I own a leak stereo 30 once discribed as all the power a home stereo would ever need and enough th have your neighbours complaining! This we all know not to be true!)) As a side issue I see that companies are producing very large (24 inch diametre) woofers now. how well do these work and are they worth the premiums being asked for them? |
#82
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20hz to 20Khz , yea right!
Peter,
Good comments. Thanks. --Ethan |
#83
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20hz to 20Khz , yea right!
Peter,
Good comments. Thanks. --Ethan |
#84
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20hz to 20Khz , yea right!
"The Flash" wrote in message ...
So-called (actually, mis-named) 'isobarik' systems are a way of obtaining a given response in half the volume, since the arrangement results in half the total equivalent compliance volume and thus requires half the enclosure volume for the same response function. My Isobric has been constructed to improve LF ouput (it seems) not reduces size as i can tell as it has a ~12 cubic foot cubed primary with a ~ 6 cubic secondary, I guess that they have decided that the cone mass of an 8 inch drive in isobaric has advantages over that of an 12 inch driver (at the size of the brute it could easily use a 12 inch drive, one thing did occur to me is that perhaps due to its age that duel VC speakers were not avalible and the only method of getting a phase and anti phase driver easily was to use two drivers. That's NOT what an "isobarik" is for, more to the point, that's NOT what the primary advantage to an isobarik is. By using two drivers one behind the other in close proximity and coupled in-phase both acoustically and electrically, the effective moving mass is doubled, the Bl product is doubled, all of your Q figures remain the same and, most significantly, you effective compliance is halved. The result is a driver that will have the same low frequency performance in an enclosure 1/2 the volume required for a single driver. There will be the attendant change in reference efficiency resulting from the fact that the effective radiating area remain constant. If that's not what your system is doing, it is not a so-called "isobarik" system. As to "true hifi response," such a term needs definition to be anything but meaningless jargon, in precisely the same way that a "specification" like "20Hz-20kHz" is meaningless without qualification. I guess what I desire is a reasonably flat response fro 32 Hz to 15Khz with gradual roll off above and below. If that is 'hi fi' or not is questionable. I spent some time years ago analysing CD's to find usual and lowest frequency's (plus HF, lots of CD's have significant output above 15Khz (components up to 25Khz+ can be present) Really? On a CD? If you are seeing components at "25KkHz+", then you have a broken CD player. instraments produce much less than this (yes I know that alot can) a lot of the very LF on disk is artificial (1/2 frequency echo and its that it is possibly added to give 'space' to the recordings) There is no such thing as "1/2 frequency echo" in any linear system. unless you are a pipe organ freak under 30Hz seems to unused (but not in Dolby Prologic, ES or such as the LF in these type video recordings is huge it seems (and unnatural in my books) ) In fact, having been involved in not an inconsiderable amount of both organ building, recording and analysis, it's something of unsubstantiated myth that organs have some unique amount of very low frequency content. They simply do not. THe fundamental efficiency/enclosure volume/cutoff frequency equation will ALWAYS rule. But, interestingly enough, driver diameter simply does not enter into that relation. Specifically, the relation: n0 = kn Vb F3^3 where n0 is reference efficiency, Vb is enclosure volume, F3 is is low frequency cutoff and kn is the efficiency constant has NO term in it in any way depedent upon driver diameter. This directly refutes your assertion that it's not possible to get your "unqualified" 'hifi response from an 8 inch driver. One needs to simply balance the three terms of efficiency, enclosure volume and cutoff frequency and you're there. You seem to intimate that low efficiency is incompatible with 'hifi response," for example, an unjustifiable viewpoint in light of the lack of qualification of 'hifi response.' kn = efficiency constant derived from driver (this figure will improve with driver diameter, thus a large driver will allow a a small enclosue to produce the same output at the same frequency with less power - correct me if wrong) Well, you're right and you're wrong. One cannot arbitrarily increase the radiating area of the driver without having some other effects. For example, while the area goes as the suqare of the diameter, and one might think that the efficiency would go up accordingly, the moving mass ALSO increases at least as the square of the diameter, and thus what you might think you gain in increased area, you lose in increased mass, as far as efficiency is concerned. And, indeed, the effect is often working against you, since larger cones are heavier in excess to the propoerion of the simple square of diameter, since they also are generally thicker as well. Thus we find, in a completely practical sense, that all other things being equal, increased diameter DOES NOT increase efficiency. Larger drivers are more efficiency NOT because they have larger cones, but because they have larger voice coils that have more wire in the larger magnet gaps and thus larger Bl products. Look at the correlation, for example, between diameter and Bl product: it's ALMOST a linear relationship: it's not uncommon for a typical high-quality 8" woofer to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A. The correlation between the numbers, as uncanny as it may seem, is merely a coincidence of mixing English (inches) and metric (Newtons per Amp) units, but the trend is clear. However in order to get usable (at say 32Hz) levels the enclosure volume (8 inch) will become so large as to be impactical in a lot of cases. No, or the efficiency has to be appropriate. For example, you can get 30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed enclosure is ENTIRELY possible if you're willing to tolerate a sensitivity on the order of 82 dB/watt. On the other hand, if you want a system with the same cutoff frequency with an efficiency of 90 dB/watt, you are fiorever condemned to an enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER WHAT SIZE DRIVER YOU USE. This equates to the 'You can put an airplane engine in a submarine' but who wants too? Well, actually, airplane engines work rather well in submarines, given that there exist submarines with Allison V16 diesels, an engine also found in some fighters. An enclose that is over 32 cubic feet will meet significant resistance when placed in the home! (Test this by asking you wife if you can shift 2 small fridges into the lounge!) But, clearly, you're simply not willing to entertain the notion that you have SEVERAL variables to play with in the efficiency/volume cuitoff frequency equation. As a side issue I see that companies are producing very large (24 inch diametre) woofers now. They've been around, actualy, for a number of decades. EV, for example, had a 30" woofer in the 60's and 70's, and the Hartley 24" was also available in the 1970's how well do these work and are they worth the premiums being asked for them? Well, of the two I site above, both are pretty awful woofers, having quite high resonances due to their crude and stiff suspensions. Low frequency systems built with more conventional woofers that are designed to work well instead of look impressive perform FAR better. |
#85
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20hz to 20Khz , yea right!
"The Flash" wrote in message ...
So-called (actually, mis-named) 'isobarik' systems are a way of obtaining a given response in half the volume, since the arrangement results in half the total equivalent compliance volume and thus requires half the enclosure volume for the same response function. My Isobric has been constructed to improve LF ouput (it seems) not reduces size as i can tell as it has a ~12 cubic foot cubed primary with a ~ 6 cubic secondary, I guess that they have decided that the cone mass of an 8 inch drive in isobaric has advantages over that of an 12 inch driver (at the size of the brute it could easily use a 12 inch drive, one thing did occur to me is that perhaps due to its age that duel VC speakers were not avalible and the only method of getting a phase and anti phase driver easily was to use two drivers. That's NOT what an "isobarik" is for, more to the point, that's NOT what the primary advantage to an isobarik is. By using two drivers one behind the other in close proximity and coupled in-phase both acoustically and electrically, the effective moving mass is doubled, the Bl product is doubled, all of your Q figures remain the same and, most significantly, you effective compliance is halved. The result is a driver that will have the same low frequency performance in an enclosure 1/2 the volume required for a single driver. There will be the attendant change in reference efficiency resulting from the fact that the effective radiating area remain constant. If that's not what your system is doing, it is not a so-called "isobarik" system. As to "true hifi response," such a term needs definition to be anything but meaningless jargon, in precisely the same way that a "specification" like "20Hz-20kHz" is meaningless without qualification. I guess what I desire is a reasonably flat response fro 32 Hz to 15Khz with gradual roll off above and below. If that is 'hi fi' or not is questionable. I spent some time years ago analysing CD's to find usual and lowest frequency's (plus HF, lots of CD's have significant output above 15Khz (components up to 25Khz+ can be present) Really? On a CD? If you are seeing components at "25KkHz+", then you have a broken CD player. instraments produce much less than this (yes I know that alot can) a lot of the very LF on disk is artificial (1/2 frequency echo and its that it is possibly added to give 'space' to the recordings) There is no such thing as "1/2 frequency echo" in any linear system. unless you are a pipe organ freak under 30Hz seems to unused (but not in Dolby Prologic, ES or such as the LF in these type video recordings is huge it seems (and unnatural in my books) ) In fact, having been involved in not an inconsiderable amount of both organ building, recording and analysis, it's something of unsubstantiated myth that organs have some unique amount of very low frequency content. They simply do not. THe fundamental efficiency/enclosure volume/cutoff frequency equation will ALWAYS rule. But, interestingly enough, driver diameter simply does not enter into that relation. Specifically, the relation: n0 = kn Vb F3^3 where n0 is reference efficiency, Vb is enclosure volume, F3 is is low frequency cutoff and kn is the efficiency constant has NO term in it in any way depedent upon driver diameter. This directly refutes your assertion that it's not possible to get your "unqualified" 'hifi response from an 8 inch driver. One needs to simply balance the three terms of efficiency, enclosure volume and cutoff frequency and you're there. You seem to intimate that low efficiency is incompatible with 'hifi response," for example, an unjustifiable viewpoint in light of the lack of qualification of 'hifi response.' kn = efficiency constant derived from driver (this figure will improve with driver diameter, thus a large driver will allow a a small enclosue to produce the same output at the same frequency with less power - correct me if wrong) Well, you're right and you're wrong. One cannot arbitrarily increase the radiating area of the driver without having some other effects. For example, while the area goes as the suqare of the diameter, and one might think that the efficiency would go up accordingly, the moving mass ALSO increases at least as the square of the diameter, and thus what you might think you gain in increased area, you lose in increased mass, as far as efficiency is concerned. And, indeed, the effect is often working against you, since larger cones are heavier in excess to the propoerion of the simple square of diameter, since they also are generally thicker as well. Thus we find, in a completely practical sense, that all other things being equal, increased diameter DOES NOT increase efficiency. Larger drivers are more efficiency NOT because they have larger cones, but because they have larger voice coils that have more wire in the larger magnet gaps and thus larger Bl products. Look at the correlation, for example, between diameter and Bl product: it's ALMOST a linear relationship: it's not uncommon for a typical high-quality 8" woofer to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A. The correlation between the numbers, as uncanny as it may seem, is merely a coincidence of mixing English (inches) and metric (Newtons per Amp) units, but the trend is clear. However in order to get usable (at say 32Hz) levels the enclosure volume (8 inch) will become so large as to be impactical in a lot of cases. No, or the efficiency has to be appropriate. For example, you can get 30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed enclosure is ENTIRELY possible if you're willing to tolerate a sensitivity on the order of 82 dB/watt. On the other hand, if you want a system with the same cutoff frequency with an efficiency of 90 dB/watt, you are fiorever condemned to an enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER WHAT SIZE DRIVER YOU USE. This equates to the 'You can put an airplane engine in a submarine' but who wants too? Well, actually, airplane engines work rather well in submarines, given that there exist submarines with Allison V16 diesels, an engine also found in some fighters. An enclose that is over 32 cubic feet will meet significant resistance when placed in the home! (Test this by asking you wife if you can shift 2 small fridges into the lounge!) But, clearly, you're simply not willing to entertain the notion that you have SEVERAL variables to play with in the efficiency/volume cuitoff frequency equation. As a side issue I see that companies are producing very large (24 inch diametre) woofers now. They've been around, actualy, for a number of decades. EV, for example, had a 30" woofer in the 60's and 70's, and the Hartley 24" was also available in the 1970's how well do these work and are they worth the premiums being asked for them? Well, of the two I site above, both are pretty awful woofers, having quite high resonances due to their crude and stiff suspensions. Low frequency systems built with more conventional woofers that are designed to work well instead of look impressive perform FAR better. |
#86
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20hz to 20Khz , yea right!
Mark wrote:
In article , says... I have had no luck in measuring speaker response at low frequency's, Then you may not be using the right tools. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. Because they (or you) are not providing all the information. It isn't enough to say 20-20k, you must also include (for the measurement to have Any validity) what the +/- dB range is across the band. I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know at what frequec(ies) does the reponse vary most from 'flat'. e.g., is there a 3 dB hump or depression somewhere in the midrange, or is it just at the tail ends of the spectrum? Is there anything implied in the common 'range +/- dB' spec about where the variation occurs? -- -S. "They've got God on their side. All we've got is science and reason." -- Dawn Hulsey, Talent Director |
#87
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20hz to 20Khz , yea right!
Mark wrote:
In article , says... I have had no luck in measuring speaker response at low frequency's, Then you may not be using the right tools. Almost any speaker system sold today claims 20Hz to 20Kz response yet this is so far from the truth I cannot understand how they dare claim such figures. Because they (or you) are not providing all the information. It isn't enough to say 20-20k, you must also include (for the measurement to have Any validity) what the +/- dB range is across the band. I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know at what frequec(ies) does the reponse vary most from 'flat'. e.g., is there a 3 dB hump or depression somewhere in the midrange, or is it just at the tail ends of the spectrum? Is there anything implied in the common 'range +/- dB' spec about where the variation occurs? -- -S. "They've got God on their side. All we've got is science and reason." -- Dawn Hulsey, Talent Director |
#88
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20hz to 20Khz , yea right!
Dick Pierce wrote:
As a side issue I see that companies are producing very large (24 inch diametre) woofers now. They've been around, actualy, for a number of decades. EV, for example, had a 30" woofer in the 60's and 70's, and the Hartley 24" was also available in the 1970's At least recently Fostex had a 30" woofer on their menu, quite well sounding, Ole Lund Christensen here in Copenhagen has built some different custom monitor systems based on it. I have heard the system DR has in a control room, maily used for popular and jazz music, and it does a good job. Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
#89
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20hz to 20Khz , yea right!
Dick Pierce wrote:
As a side issue I see that companies are producing very large (24 inch diametre) woofers now. They've been around, actualy, for a number of decades. EV, for example, had a 30" woofer in the 60's and 70's, and the Hartley 24" was also available in the 1970's At least recently Fostex had a 30" woofer on their menu, quite well sounding, Ole Lund Christensen here in Copenhagen has built some different custom monitor systems based on it. I have heard the system DR has in a control room, maily used for popular and jazz music, and it does a good job. Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
#90
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20hz to 20Khz , yea right!
In article ,
Steven Sullivan wrote: I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know at what frequec(ies) does the reponse vary most from 'flat'. Is there anything implied in the common 'range +/- dB' spec about where the variation occurs? 50Hz is -3dB from the average, which is relevant in determining whether you need a sub-woofer and where you'd want to cross one over. Otherwise nothing useful is implied. Variations may be dips/peaks than span a small set of frequencies or only affect the on-axis response so they aren't noticeable, or long trends that will be perceived as a significant coloration. -- a href="http://www.poohsticks.org/drew/"Home Page/a Life is a terminal sexually transmitted disease. |
#91
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20hz to 20Khz , yea right!
In article ,
Steven Sullivan wrote: I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know at what frequec(ies) does the reponse vary most from 'flat'. Is there anything implied in the common 'range +/- dB' spec about where the variation occurs? 50Hz is -3dB from the average, which is relevant in determining whether you need a sub-woofer and where you'd want to cross one over. Otherwise nothing useful is implied. Variations may be dips/peaks than span a small set of frequencies or only affect the on-axis response so they aren't noticeable, or long trends that will be perceived as a significant coloration. -- a href="http://www.poohsticks.org/drew/"Home Page/a Life is a terminal sexually transmitted disease. |
#92
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20hz to 20Khz , yea right!
Peter Larsen wrote in message ...
Rusty Boudreaux wrote: I just downloaded the pdf. The stated response is 15Hz-20kHz but no dB qualifier. The magnitude plot shows essentially flat down to 60Hz but no data below. However, they do show response to 30kHz...down 10dB. My incomplete understanding is that there is no reason why that type of microphone should roll off early other than series capacitance. Plenty of reasons. A pressure microphone works because of pressure differences betwen the front and the rear of the diaphragm. Assume, for the moment, that the rear chamber of the microphone is perfectly sealed. What's now going to happen is that any changes in barometric pressure is going to change the position of the diaphragm. So, for that reason alone, you want to put a leak in the back chamber to allow for equalization of pressure. The problem that you then face is how big a leak. Make it too small a leak, and you haven't solved the problem. Make it too big, and it "leaks" at too high a frequency. One reason why laboratory mics are expensive is that the manufacturing of such involves VERY careful attention to such matters: the leak is a high-precision hole drilled through the backplate, and they essentially guarantee the time constant of that leak to within a fairly tight margin. (There are other factors, such as quartz rear insulators to ensure both very high isolation resistance and very stable mechanical dimensions with temperature, and so on). Take a microphone that is made from a $2.00 mass-produced electret condensor capsule, where there is little or no attention paid in manufacturing to the time constant of the equalization leak and other factors, and you'll actually find very large variations in the low-frequency cutoff of the capsule, simply because the capsule was NEVER intended, designed or manufactured for precision, low frequency use. These microphones and their variants are good as far as they go: they have reasonable high frequency response, reasonably flat response through the midband, reasonable though not remarkable temperature stability, sensitivity matching is a little, well, variable AND inconsitent low frequency performance. And, they're cheap. As always, you get what you pay for. I have quite a few of these things in my lab, and I use them not for any broadband measurements, but for moderate-sized arrays to measure moderately wide-band power response. They're not very rugged, but, what the hell, if I break 2 or 3 or 20, who cares? For less than a moderately priced German wine, I can replace them ALL. For any real measurements, out comes one of the B&K's. |
#93
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20hz to 20Khz , yea right!
Peter Larsen wrote in message ...
Rusty Boudreaux wrote: I just downloaded the pdf. The stated response is 15Hz-20kHz but no dB qualifier. The magnitude plot shows essentially flat down to 60Hz but no data below. However, they do show response to 30kHz...down 10dB. My incomplete understanding is that there is no reason why that type of microphone should roll off early other than series capacitance. Plenty of reasons. A pressure microphone works because of pressure differences betwen the front and the rear of the diaphragm. Assume, for the moment, that the rear chamber of the microphone is perfectly sealed. What's now going to happen is that any changes in barometric pressure is going to change the position of the diaphragm. So, for that reason alone, you want to put a leak in the back chamber to allow for equalization of pressure. The problem that you then face is how big a leak. Make it too small a leak, and you haven't solved the problem. Make it too big, and it "leaks" at too high a frequency. One reason why laboratory mics are expensive is that the manufacturing of such involves VERY careful attention to such matters: the leak is a high-precision hole drilled through the backplate, and they essentially guarantee the time constant of that leak to within a fairly tight margin. (There are other factors, such as quartz rear insulators to ensure both very high isolation resistance and very stable mechanical dimensions with temperature, and so on). Take a microphone that is made from a $2.00 mass-produced electret condensor capsule, where there is little or no attention paid in manufacturing to the time constant of the equalization leak and other factors, and you'll actually find very large variations in the low-frequency cutoff of the capsule, simply because the capsule was NEVER intended, designed or manufactured for precision, low frequency use. These microphones and their variants are good as far as they go: they have reasonable high frequency response, reasonably flat response through the midband, reasonable though not remarkable temperature stability, sensitivity matching is a little, well, variable AND inconsitent low frequency performance. And, they're cheap. As always, you get what you pay for. I have quite a few of these things in my lab, and I use them not for any broadband measurements, but for moderate-sized arrays to measure moderately wide-band power response. They're not very rugged, but, what the hell, if I break 2 or 3 or 20, who cares? For less than a moderately priced German wine, I can replace them ALL. For any real measurements, out comes one of the B&K's. |
#94
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20hz to 20Khz , yea right!
Dick Pierce wrote:
Plenty of reasons. .... Thanks! Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
#95
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20hz to 20Khz , yea right!
Dick Pierce wrote:
Plenty of reasons. .... Thanks! Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
#96
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20hz to 20Khz , yea right!
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#97
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20hz to 20Khz , yea right!
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#98
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20hz to 20Khz , yea right!
Dick,
Great explanation. You're turning me into a fan. I especially liked: the leak is a high-precision hole --Ethan |
#99
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20hz to 20Khz , yea right!
Dick,
Great explanation. You're turning me into a fan. I especially liked: the leak is a high-precision hole --Ethan |
#100
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20hz to 20Khz , yea right!
"Ian" wrote in message ... "Tony Pearce" wrote in message u... No mention of what the maximum SPL Vs distortion level is at 30 Hz though, I see. Simply disregard these and you can easily get 30 Hz from a single 4 inch driver. Of course you can't actually HEAR it :-) Tony, please note I said "bandpass enclosure". Some of the excursion/output relations change. Yes but the laws of physics still apply. You provide no actual figures. You (perhaps) cannot "hear" 30Hz, although that depends ;-) You certainly can hear 30 Hz if the level is loud enough. Check the Fletcher/Munsen curves for the required levels. Remember if the distortion is high enough (comon with small speakers), you will probably be hearing the distortion generated, not the 30Hz, since the ear is more sensitive at the higher harmonic frequencies. Re-read what I actually wrote. Maximum SPL vs distortion level is just fine for reasonable levels in a reasonable (UK) size room. As long as you think so, that is all that matters for you anyway :-) TonyP. |
#101
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20hz to 20Khz , yea right!
"Ian" wrote in message ... "Tony Pearce" wrote in message u... No mention of what the maximum SPL Vs distortion level is at 30 Hz though, I see. Simply disregard these and you can easily get 30 Hz from a single 4 inch driver. Of course you can't actually HEAR it :-) Tony, please note I said "bandpass enclosure". Some of the excursion/output relations change. Yes but the laws of physics still apply. You provide no actual figures. You (perhaps) cannot "hear" 30Hz, although that depends ;-) You certainly can hear 30 Hz if the level is loud enough. Check the Fletcher/Munsen curves for the required levels. Remember if the distortion is high enough (comon with small speakers), you will probably be hearing the distortion generated, not the 30Hz, since the ear is more sensitive at the higher harmonic frequencies. Re-read what I actually wrote. Maximum SPL vs distortion level is just fine for reasonable levels in a reasonable (UK) size room. As long as you think so, that is all that matters for you anyway :-) TonyP. |
#105
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20hz to 20Khz , yea right!
ow (Goofball_star_dot_etal) wrote in message ...
On 24 Nov 2003 00:24:57 -0800, (Svante) wrote: Our students in electroacoustics use this method in a lab on loudspeakers. I hope you teach them "inverted thinking" at the same time. :-) Well, some of them have a hard time with the 12 db tilt... :-) There must be some restrictions on the accuracy of this method but the only one I can think off at the moment is that the wavelength must be large compared to the internal dimensions of the speaker. The meaasurement includes the effect of any port and of the enclosure flexing. There is probably an assumption that the air is compressed adiabatically. The pressures involved are, of course, small if the mic is not to be overloaded. No, the pressures involved are HUGE, typically there is no problems reaching 140 dB inside the box at low frequencies. So keep the levels low in order to avoid overloading the microphone. Or did I perhaps misunderstand your statement?) Yes I should have been more clear. I am economical with words to the point of recklessness. I should have warned that it is possible to damage the microphone, which is a good reason to use a cheap one to perfect the setup. What I meant was that when the levels are adjusted so that the mic. is operating linearly then it follows that the physics will be right - the pressure changes inside the box will be linear with volume displacement. It is a small signal measurement with large mic signals. . . You may have to fit an attenuator (with low output impedance between amp and speaker. The actual compression/expansion will be somewhere between adiabatic and isothermal and since isothermal involves heat exchange with the mass of any stuffing I might expect the degree to which it tends towards isothemal to change somewhat with frequency. Hmmm, yes, the "adiabaticness" of the volume will affect the compliance of the box, but not very much. I have noticed a few times when measuring the impedance curve of loudspeakers, that the only way to match the simlated impedance curve with reality is to use a larger volume than the physical in the simulation. The simulation assumes adiabatic compression in this case. But the magnitude of this has been like 135 litres instead of the physical 130 litres, so i don't think this gives raise to any large errors. This error, would be about 20*log(130/135)=-0.3 dB (since box pressure is inversively proportional to box volume). Even more, in order to affect the frequency response (neglecting a pure scale factor) the "adiabaticness" would have to vary with frequency, and this effect would be even smaller. My students use no stuffing in the box, so obviously I have not seen this effect there. Once in a while I throw a sweater into the box to demonstrate the effect on the standing waves, but I can't recall seeing that the apparent volume of the box changes. So in order for the "adiabaticness" to have any significant effect on the response curve, one would have to have A LOT of stuffing material and its "adiabaticness" would also have to be frequency dependant. Maybe someone could prove such an effect, but until then I feel confident that the method is OK. Actually the response curves we measure match the predicted behaviour so well that we beleive that they are far more accurate than measurements in the anechoic chamber (that we don't have any more, sigh...). And... About overloading the microphone; Yes it is easy to overload the microphone, in fact it has proven impossible to measure distorsion inside the box. The distorsion simply originates from the microphone. But on the other hand the microphone (Sennheiser MKE2) has proven robust in the sense that it is not DAMAGED by high pressures. We have been running this lab for some 7 years now, and for sure the box pressure has been high on occasions (I would assume up to 150-160 dB) but the mic is still OK. |
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20hz to 20Khz , yea right!
Hey Dickie
You need to get a life! You are still the annoying fraud you always were. I have this image of you huddled over your PC scouring this NG looking for any posting to which you can latch onto and then act superior, frantically typing, and fuming inside, stop being so silly and get some fresh air now and again. |
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20hz to 20Khz , yea right!
Hey Dickie
You need to get a life! You are still the annoying fraud you always were. I have this image of you huddled over your PC scouring this NG looking for any posting to which you can latch onto and then act superior, frantically typing, and fuming inside, stop being so silly and get some fresh air now and again. |
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20hz to 20Khz , yea right!
By using two drivers one behind the other in close proximity and coupled in-phase both acoustically and electrically, the effective moving mass is doubled, the Bl product is doubled, all of your Q figures remain the same and, most significantly, you effective compliance is halved. The result is a driver that will have the same low frequency performance in an enclosure 1/2 the volume required for a single driver. There will be the attendant change in reference efficiency resulting from the fact that the effective radiating area remain constant. There is no such thing as "1/2 frequency echo" in any linear system. In fact, having been involved in not an inconsiderable amount of both organ building, recording and analysis, it's something of unsubstantiated myth that organs have some unique amount of very low frequency content. They simply do not. Well, you're right and you're wrong. One cannot arbitrarily increase the radiating area of the driver without having some other effects. For example, while the area goes as the suqare of the diameter, and one might think that the efficiency would go up accordingly, the moving mass ALSO increases at least as the square of the diameter, and thus what you might think you gain in increased area, you lose in increased mass, as far as efficiency is concerned. And, indeed, the effect is often working against you, since larger cones are heavier in excess to the propoerion of the simple square of diameter, since they also are generally thicker as well. Thus we find, in a completely practical sense, that all other things being equal, increased diameter DOES NOT increase efficiency. Larger drivers are more efficiency NOT because they have larger cones, but because they have larger voice coils that have more wire in the larger magnet gaps and thus larger Bl products. Look at the correlation, for example, between diameter and Bl product: it's ALMOST a linear relationship: it's not uncommon for a typical high-quality 8" woofer to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A. The correlation between the numbers, as uncanny as it may seem, is merely a coincidence of mixing English (inches) and metric (Newtons per Amp) units, but the trend is clear. No, or the efficiency has to be appropriate. For example, you can get 30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed enclosure is ENTIRELY possible if you're willing to tolerate a sensitivity on the order of 82 dB/watt. On the other hand, if you want a system with the same cutoff frequency with an efficiency of 90 dB/watt, you are fiorever condemned to an enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER WHAT SIZE DRIVER YOU USE. They've been around, actualy, for a number of decades. EV, for example, had a 30" woofer in the 60's and 70's, and the Hartley 24" was also available in the 1970's how well do these work and are they worth the premiums being asked for them? Well, of the two I site (cite?) above, both are pretty awful woofers, having quite high resonances due to their crude and stiff suspensions. Low frequency systems built with more conventional woofers that are designed to work well instead of look impressive perform FAR better. Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! |
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20hz to 20Khz , yea right!
By using two drivers one behind the other in close proximity and coupled in-phase both acoustically and electrically, the effective moving mass is doubled, the Bl product is doubled, all of your Q figures remain the same and, most significantly, you effective compliance is halved. The result is a driver that will have the same low frequency performance in an enclosure 1/2 the volume required for a single driver. There will be the attendant change in reference efficiency resulting from the fact that the effective radiating area remain constant. There is no such thing as "1/2 frequency echo" in any linear system. In fact, having been involved in not an inconsiderable amount of both organ building, recording and analysis, it's something of unsubstantiated myth that organs have some unique amount of very low frequency content. They simply do not. Well, you're right and you're wrong. One cannot arbitrarily increase the radiating area of the driver without having some other effects. For example, while the area goes as the suqare of the diameter, and one might think that the efficiency would go up accordingly, the moving mass ALSO increases at least as the square of the diameter, and thus what you might think you gain in increased area, you lose in increased mass, as far as efficiency is concerned. And, indeed, the effect is often working against you, since larger cones are heavier in excess to the propoerion of the simple square of diameter, since they also are generally thicker as well. Thus we find, in a completely practical sense, that all other things being equal, increased diameter DOES NOT increase efficiency. Larger drivers are more efficiency NOT because they have larger cones, but because they have larger voice coils that have more wire in the larger magnet gaps and thus larger Bl products. Look at the correlation, for example, between diameter and Bl product: it's ALMOST a linear relationship: it's not uncommon for a typical high-quality 8" woofer to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A. The correlation between the numbers, as uncanny as it may seem, is merely a coincidence of mixing English (inches) and metric (Newtons per Amp) units, but the trend is clear. No, or the efficiency has to be appropriate. For example, you can get 30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed enclosure is ENTIRELY possible if you're willing to tolerate a sensitivity on the order of 82 dB/watt. On the other hand, if you want a system with the same cutoff frequency with an efficiency of 90 dB/watt, you are fiorever condemned to an enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER WHAT SIZE DRIVER YOU USE. They've been around, actualy, for a number of decades. EV, for example, had a 30" woofer in the 60's and 70's, and the Hartley 24" was also available in the 1970's how well do these work and are they worth the premiums being asked for them? Well, of the two I site (cite?) above, both are pretty awful woofers, having quite high resonances due to their crude and stiff suspensions. Low frequency systems built with more conventional woofers that are designed to work well instead of look impressive perform FAR better. Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! |
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20hz to 20Khz , yea right!
BoredSilly wrote:
Hey Dickie You need to get a life! You are still the annoying fraud you always were. I have this image of you huddled over your PC scouring this NG looking for any posting to which you can latch onto and then act superior, He doesn't act, he is. Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
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20hz to 20Khz , yea right!
BoredSilly wrote:
Hey Dickie You need to get a life! You are still the annoying fraud you always were. I have this image of you huddled over your PC scouring this NG looking for any posting to which you can latch onto and then act superior, He doesn't act, he is. Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
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20hz to 20Khz , yea right!
From: "BoredSilly"
Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! braindead, But you added no meaningful comment. From Mr. Pierce, I've learned several important concepts, the physics behind them, and their proper application to the field of sound reproduction. From you, I see nothing but childish name calling. If you have an issue with something that Mr.Pierce has stated here, then: 1. Show your real name. Mr. Pierce does, I do, and so do others. Without your real name, your words are nothing but the empty rantings of a deranged internet troll. 2. If you really do have an issue with any statement made by Mr. Pierce, then state it, and it can then be discussed by the group in a mature and intelligent manner. If you, or anyone else, can't see the benefits of such an approach, then I suggest that you find somewhere else to vent your anger. Stuart Welwood http://members.aol.com/StuWelwood |
#113
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20hz to 20Khz , yea right!
From: "BoredSilly"
Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! braindead, But you added no meaningful comment. From Mr. Pierce, I've learned several important concepts, the physics behind them, and their proper application to the field of sound reproduction. From you, I see nothing but childish name calling. If you have an issue with something that Mr.Pierce has stated here, then: 1. Show your real name. Mr. Pierce does, I do, and so do others. Without your real name, your words are nothing but the empty rantings of a deranged internet troll. 2. If you really do have an issue with any statement made by Mr. Pierce, then state it, and it can then be discussed by the group in a mature and intelligent manner. If you, or anyone else, can't see the benefits of such an approach, then I suggest that you find somewhere else to vent your anger. Stuart Welwood http://members.aol.com/StuWelwood |
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20hz to 20Khz , yea right!
"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! Well, it should be very easy for Mr. BoredSilly to show this is the case. All he need do is simply cite the text book and quote the paragraphs he is accusing me of making word-for-sord copies of. How about it, Bored (or is it just Silly?), care to step up to the plate? Nah, let's make it at least sporting. How about betting some real money on it? Just show us the paragraphs from the text book that I copied, as you say "word-for-word." Anyone else want to join in on the bet? |
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20hz to 20Khz , yea right!
"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! Well, it should be very easy for Mr. BoredSilly to show this is the case. All he need do is simply cite the text book and quote the paragraphs he is accusing me of making word-for-sord copies of. How about it, Bored (or is it just Silly?), care to step up to the plate? Nah, let's make it at least sporting. How about betting some real money on it? Just show us the paragraphs from the text book that I copied, as you say "word-for-word." Anyone else want to join in on the bet? |
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20hz to 20Khz , yea right!
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20hz to 20Khz , yea right!
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#118
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20hz to 20Khz , yea right!
On Mon, 01 Dec 2003 00:07:33 GMT, ow
(Goofball_star_dot_etal) wrote: On 30 Nov 2003 15:58:13 -0800, (Dick Pierce) wrote: "BoredSilly" wrote in message ... Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! Well, it should be very easy for Mr. BoredSilly to show this is the case. All he need do is simply cite the text book and quote the paragraphs he is accusing me of making word-for-sord copies of. How about it, Bored (or is it just Silly?), care to step up to the plate? Nah, let's make it at least sporting. How about betting some real money on it? Just show us the paragraphs from the text book that I copied, as you say "word-for-word." Anyone else want to join in on the bet? This post is not my style, Dick, in case you are speculating. Sounds like Bob the Moron, to me. And of course Dick's posts *read* like text books, because they all quote the *same* laws of physics. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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20hz to 20Khz , yea right!
On Mon, 01 Dec 2003 00:07:33 GMT, ow
(Goofball_star_dot_etal) wrote: On 30 Nov 2003 15:58:13 -0800, (Dick Pierce) wrote: "BoredSilly" wrote in message ... Dickie, you poured over the text books and some of your paragraphs are word-for-word copies! Well, it should be very easy for Mr. BoredSilly to show this is the case. All he need do is simply cite the text book and quote the paragraphs he is accusing me of making word-for-sord copies of. How about it, Bored (or is it just Silly?), care to step up to the plate? Nah, let's make it at least sporting. How about betting some real money on it? Just show us the paragraphs from the text book that I copied, as you say "word-for-word." Anyone else want to join in on the bet? This post is not my style, Dick, in case you are speculating. Sounds like Bob the Moron, to me. And of course Dick's posts *read* like text books, because they all quote the *same* laws of physics. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
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20hz to 20Khz , yea right!
Drew Eckhardt wrote:
In article , Steven Sullivan wrote: I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know at what frequec(ies) does the reponse vary most from 'flat'. Is there anything implied in the common 'range +/- dB' spec about where the variation occurs? 50Hz is -3dB from the average, which is relevant in determining whether you need a sub-woofer and where you'd want to cross one over. Is the lower limit of the range determined by the -3dB point in the measuremnts , i.e., 50 Hz was the highest frequency below 20 kHz at which output was down 3 dB? Is the same implied for the other end of the stated range (20 kHz)? I.e., is the resposne down 3 dB from average at 20 kHz too? -- -S. "They've got God on their side. All we've got is science and reason." -- Dawn Hulsey, Talent Director |
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