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Speakers testing
Sure, happy to comment:
1- "20 to 20K." I'm not exactly sure what the underlying question is here. Is isn't particularly difficult to reliably measure 20 Hz speaker output, especially using near-field techniques. It takes a good mic and preamp, and the ability to examine the spectrum in order to understand what is fundamental and what is harmonic distortion. Measuring very long wavelengths is in many ways easier than measuring shorter ones, provided you are not concerned with understanding room effects. 2- "Multiples." Though the question of what "efficiency" properly refers to is perpetually ellusive, there is no doubt that more radiating area increases low frequency efficiency. "...it should be mentioned again that the radiating efficiency of a direct-radiator loudspeaker can be increased at low frequencies by mounting several units side by side in a single baffle. The mutual interaction among the radiating units serves to increase the radiation resistance of each unit substantially. For example, two identical direct-radiators very near each other in an infinitely large plane baffle, and vibrating in phase, will produce four times the intensity on the principle axis as will one of them alone." Beranek, "Acoustics," 1st Ed., 1954, p259. -k ow (Goofball_star_dot_etal) wrote in message ... Hi Ken, Care to comment over on rec.audio.tech on either thread "20hz to 20Khz , yea right!" or "Speaker sensitivity and fs in multiples." ? I would like it resolved, whether I am right or wrong. It is your field and Dick does not seem to want to play. Regards, David. |
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On Sun, 07 Dec 2003 08:36:07 -0000, Rich Andrews
wrote: "...it should be mentioned again that the radiating efficiency of a direct-radiator loudspeaker can be increased at low frequencies by mounting several units side by side in a single baffle. The mutual interaction among the radiating units serves to increase the radiation resistance of each unit substantially. For example, two identical direct-radiators very near each other in an infinitely large plane baffle, and vibrating in phase, will produce four times the intensity on the principle axis as will one of them alone." Beranek, "Acoustics," 1st Ed., 1954, p259. -k I think that rule goes awry when multiple tweeters are involved in a column. I do know that the 6db rule does not apply to an array of tweeters in a column. This is interesting. What assumptions are being made above regarding the power supplied to each speaker? Specifically, when you go from one speaker to two in the above example, is the original amount of power now being divided between two speakers, or do both speakers receive power equal to what the solo speaker had? Getting 6dB of increase by doubling the number of speakers AND the power provided makes sense to me, but if the 6dB increase is coming solely from doubling the number of speakers, I confess I'm confused. Also, do the speakers have to share the same enclosure volume for the above paragraph to apply? How about the following three scenarios? 1) One speaker, being supplied 1000 Watts. 2) Two speakers in separate enclosures, each being supplied 500 Watts 3) Two speakers, sharing an enclosure that's twice the size of a single enclosure, each being supplied 500 Watts. Which of these three would produce the highest intensity? From the "Acoustics" quote above, I think it would be #3, with #1 and #2 being about equal. The reason I'm curious is that in car audio, two subwoofers in a box is a fairly common arrangement, but the boxes are usually constructed such that the two subs don't share the same enclosure volume. If there's an extra 3dB to be had just by having the subs share the same enclosure volume, I'd think more boxes would be designed this way. Scott Gardner |
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Speakers testing
On Sun, 07 Dec 2003 08:36:07 -0000, Rich Andrews
wrote: "...it should be mentioned again that the radiating efficiency of a direct-radiator loudspeaker can be increased at low frequencies by mounting several units side by side in a single baffle. The mutual interaction among the radiating units serves to increase the radiation resistance of each unit substantially. For example, two identical direct-radiators very near each other in an infinitely large plane baffle, and vibrating in phase, will produce four times the intensity on the principle axis as will one of them alone." Beranek, "Acoustics," 1st Ed., 1954, p259. -k I think that rule goes awry when multiple tweeters are involved in a column. I do know that the 6db rule does not apply to an array of tweeters in a column. This is interesting. What assumptions are being made above regarding the power supplied to each speaker? Specifically, when you go from one speaker to two in the above example, is the original amount of power now being divided between two speakers, or do both speakers receive power equal to what the solo speaker had? Getting 6dB of increase by doubling the number of speakers AND the power provided makes sense to me, but if the 6dB increase is coming solely from doubling the number of speakers, I confess I'm confused. Also, do the speakers have to share the same enclosure volume for the above paragraph to apply? How about the following three scenarios? 1) One speaker, being supplied 1000 Watts. 2) Two speakers in separate enclosures, each being supplied 500 Watts 3) Two speakers, sharing an enclosure that's twice the size of a single enclosure, each being supplied 500 Watts. Which of these three would produce the highest intensity? From the "Acoustics" quote above, I think it would be #3, with #1 and #2 being about equal. The reason I'm curious is that in car audio, two subwoofers in a box is a fairly common arrangement, but the boxes are usually constructed such that the two subs don't share the same enclosure volume. If there's an extra 3dB to be had just by having the subs share the same enclosure volume, I'd think more boxes would be designed this way. Scott Gardner |
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Speakers testing
On Sun, 07 Dec 2003 08:36:07 -0000, Rich Andrews
wrote: "...it should be mentioned again that the radiating efficiency of a direct-radiator loudspeaker can be increased at low frequencies by mounting several units side by side in a single baffle. The mutual interaction among the radiating units serves to increase the radiation resistance of each unit substantially. For example, two identical direct-radiators very near each other in an infinitely large plane baffle, and vibrating in phase, will produce four times the intensity on the principle axis as will one of them alone." Beranek, "Acoustics," 1st Ed., 1954, p259. -k I think that rule goes awry when multiple tweeters are involved in a column. I do know that the 6db rule does not apply to an array of tweeters in a column. This is interesting. What assumptions are being made above regarding the power supplied to each speaker? Specifically, when you go from one speaker to two in the above example, is the original amount of power now being divided between two speakers, or do both speakers receive power equal to what the solo speaker had? Getting 6dB of increase by doubling the number of speakers AND the power provided makes sense to me, but if the 6dB increase is coming solely from doubling the number of speakers, I confess I'm confused. Also, do the speakers have to share the same enclosure volume for the above paragraph to apply? How about the following three scenarios? 1) One speaker, being supplied 1000 Watts. 2) Two speakers in separate enclosures, each being supplied 500 Watts 3) Two speakers, sharing an enclosure that's twice the size of a single enclosure, each being supplied 500 Watts. Which of these three would produce the highest intensity? From the "Acoustics" quote above, I think it would be #3, with #1 and #2 being about equal. The reason I'm curious is that in car audio, two subwoofers in a box is a fairly common arrangement, but the boxes are usually constructed such that the two subs don't share the same enclosure volume. If there's an extra 3dB to be had just by having the subs share the same enclosure volume, I'd think more boxes would be designed this way. Scott Gardner |
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(Scott Gardner) wrote in message ...
On 7 Dec 2003 10:39:16 -0800, (Svante) wrote: 1) One speaker, being supplied 1000 Watts. That would give a level of x dB (given that it is mounted in a box of y litres). 2) Two speakers in separate enclosures, each being supplied 500 Watts The level would now be x + 3 dB, if each box is y litres. 3) Two speakers, sharing an enclosure that's twice the size of a single enclosure, each being supplied 500 Watts. The level would still be x + 3 dB, if the box is 2*y litres. Which of these three would produce the highest intensity? From the "Acoustics" quote above, I think it would be #3, with #1 and #2 being about equal. The reason I'm curious is that in car audio, two subwoofers in a box is a fairly common arrangement, but the boxes are usually constructed such that the two subs don't share the same enclosure volume. If there's an extra 3dB to be had just by having the subs share the same enclosure volume, I'd think more boxes would be designed this way. No, the gain is on the acoustic side, not inside the box. Two drivers (each receiving the same power as the single driver) would double the sound pressure, and quadruple the acoustic power. Again, read the other thread in this group, I beleive this will save you some thinking. Thanks, but I'm not really interested in being "saved" from thinking. Sounds sound... :-) I enjoy the discussion. What you explained was pretty much what I've always thought, I was just confused by the paragraph from "Acoustics" above. For one, it mentions a four-fold increase in SPL without explicitly mentioning the fact that he's doubling amplifer power as well as the number of speakers, and the part about mounting multiple speakers "side by side" in a "single baffle" makes it sound like that's a requirement to get the efficiency increase from multiple speakers. From your response to my three scenarios, it sounds like that's not the case after all. I think the baffle (could just as well have been a box) is put there just to remove the radiation from the back side of the membrane. The effect would have been similar with loudspeaker elements in free air, but it saves some thinking :-) to put them in the baffle. |
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Speakers testing
(Scott Gardner) wrote in message ...
On 7 Dec 2003 10:39:16 -0800, (Svante) wrote: 1) One speaker, being supplied 1000 Watts. That would give a level of x dB (given that it is mounted in a box of y litres). 2) Two speakers in separate enclosures, each being supplied 500 Watts The level would now be x + 3 dB, if each box is y litres. 3) Two speakers, sharing an enclosure that's twice the size of a single enclosure, each being supplied 500 Watts. The level would still be x + 3 dB, if the box is 2*y litres. Which of these three would produce the highest intensity? From the "Acoustics" quote above, I think it would be #3, with #1 and #2 being about equal. The reason I'm curious is that in car audio, two subwoofers in a box is a fairly common arrangement, but the boxes are usually constructed such that the two subs don't share the same enclosure volume. If there's an extra 3dB to be had just by having the subs share the same enclosure volume, I'd think more boxes would be designed this way. No, the gain is on the acoustic side, not inside the box. Two drivers (each receiving the same power as the single driver) would double the sound pressure, and quadruple the acoustic power. Again, read the other thread in this group, I beleive this will save you some thinking. Thanks, but I'm not really interested in being "saved" from thinking. Sounds sound... :-) I enjoy the discussion. What you explained was pretty much what I've always thought, I was just confused by the paragraph from "Acoustics" above. For one, it mentions a four-fold increase in SPL without explicitly mentioning the fact that he's doubling amplifer power as well as the number of speakers, and the part about mounting multiple speakers "side by side" in a "single baffle" makes it sound like that's a requirement to get the efficiency increase from multiple speakers. From your response to my three scenarios, it sounds like that's not the case after all. I think the baffle (could just as well have been a box) is put there just to remove the radiation from the back side of the membrane. The effect would have been similar with loudspeaker elements in free air, but it saves some thinking :-) to put them in the baffle. |
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Speakers testing
You are very welcome.
It's been done, but it in common use. Why not? Because external near-field techniques work well, and are much more direct and convenient. -k ow (Goofball_star_dot_etal) wrote in message ... On 7 Dec 2003 00:01:45 -0800, (Ken Kantor) wrote: Quite a lot of fuss is made at times of the difficulty of measuring low frequency response, particularly in an ordinary room. Perhaps it is easy when you know how. I was wondering if the "in speaker" method Svante and I described was in common use and if not, why not? |
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Speakers testing
You are very welcome.
It's been done, but it in common use. Why not? Because external near-field techniques work well, and are much more direct and convenient. -k ow (Goofball_star_dot_etal) wrote in message ... On 7 Dec 2003 00:01:45 -0800, (Ken Kantor) wrote: Quite a lot of fuss is made at times of the difficulty of measuring low frequency response, particularly in an ordinary room. Perhaps it is easy when you know how. I was wondering if the "in speaker" method Svante and I described was in common use and if not, why not? |
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Speakers testing
You are very welcome.
It's been done, but it in common use. Why not? Because external near-field techniques work well, and are much more direct and convenient. -k ow (Goofball_star_dot_etal) wrote in message ... On 7 Dec 2003 00:01:45 -0800, (Ken Kantor) wrote: Quite a lot of fuss is made at times of the difficulty of measuring low frequency response, particularly in an ordinary room. Perhaps it is easy when you know how. I was wondering if the "in speaker" method Svante and I described was in common use and if not, why not? |
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Speakers testing
ow (Goofball_star_dot_etal) wrote in message ...
On 7 Dec 2003 00:01:45 -0800, (Ken Kantor) wrote: Quite a lot of fuss is made at times of the difficulty of measuring low frequency response, particularly in an ordinary room. Perhaps it is easy when you know how. I was wondering if the "in speaker" method Svante and I described was in common use and if not, why not? (Ken Kantor) wrote in message . com... You are very welcome. It's been done, but it in common use. Why not? Because external near-field techniques work well, and are much more direct and convenient. Having seen the difference between near-field measurements in a studio environment and the in-box method I feel I should add this: 1. The in-box method is in agreement with simulations well down to 10 Hz for the system we measure on (a butterworth bass-reflex box designed for -3dB at 35Hz). We see some extra sloping of towards low frequencies, probaly due to the microphone and the electronics. 2. SNR is great inside the box. The level easily reaches 120-140dB and room noise at low frequencies is typically reach 50-70dB. This still gives 50 dB SNR. That will NOT happen outside the box. Try to demonstrate the slope of 24 dB/octave of a bass-reflex system below the helmholtz frequency with near field measurements. Environmental noise will disturb this measurement a lot. 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". 4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. I would guess that the reason that the method is not widely used is the counter-intuitivity (is that proper english?!?) of the method, the need to tilt the response by 12dB/octave and the fact that the method is not well known. But it is great for LF! |
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ow (Goofball_star_dot_etal) wrote in message ...
On 7 Dec 2003 00:01:45 -0800, (Ken Kantor) wrote: Quite a lot of fuss is made at times of the difficulty of measuring low frequency response, particularly in an ordinary room. Perhaps it is easy when you know how. I was wondering if the "in speaker" method Svante and I described was in common use and if not, why not? (Ken Kantor) wrote in message . com... You are very welcome. It's been done, but it in common use. Why not? Because external near-field techniques work well, and are much more direct and convenient. Having seen the difference between near-field measurements in a studio environment and the in-box method I feel I should add this: 1. The in-box method is in agreement with simulations well down to 10 Hz for the system we measure on (a butterworth bass-reflex box designed for -3dB at 35Hz). We see some extra sloping of towards low frequencies, probaly due to the microphone and the electronics. 2. SNR is great inside the box. The level easily reaches 120-140dB and room noise at low frequencies is typically reach 50-70dB. This still gives 50 dB SNR. That will NOT happen outside the box. Try to demonstrate the slope of 24 dB/octave of a bass-reflex system below the helmholtz frequency with near field measurements. Environmental noise will disturb this measurement a lot. 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". 4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. I would guess that the reason that the method is not widely used is the counter-intuitivity (is that proper english?!?) of the method, the need to tilt the response by 12dB/octave and the fact that the method is not well known. But it is great for LF! |
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ow (Goofball_star_dot_etal) wrote in message ...
On 7 Dec 2003 00:01:45 -0800, (Ken Kantor) wrote: Quite a lot of fuss is made at times of the difficulty of measuring low frequency response, particularly in an ordinary room. Perhaps it is easy when you know how. I was wondering if the "in speaker" method Svante and I described was in common use and if not, why not? (Ken Kantor) wrote in message . com... You are very welcome. It's been done, but it in common use. Why not? Because external near-field techniques work well, and are much more direct and convenient. Having seen the difference between near-field measurements in a studio environment and the in-box method I feel I should add this: 1. The in-box method is in agreement with simulations well down to 10 Hz for the system we measure on (a butterworth bass-reflex box designed for -3dB at 35Hz). We see some extra sloping of towards low frequencies, probaly due to the microphone and the electronics. 2. SNR is great inside the box. The level easily reaches 120-140dB and room noise at low frequencies is typically reach 50-70dB. This still gives 50 dB SNR. That will NOT happen outside the box. Try to demonstrate the slope of 24 dB/octave of a bass-reflex system below the helmholtz frequency with near field measurements. Environmental noise will disturb this measurement a lot. 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". 4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. I would guess that the reason that the method is not widely used is the counter-intuitivity (is that proper english?!?) of the method, the need to tilt the response by 12dB/octave and the fact that the method is not well known. But it is great for LF! |
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Svante wrote:
4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. You can not call it measurement with an unlinear microphone, so do not overload it. I would guess that the reason that the method is not widely used is the counter-intuitivity (is that proper english?!?) of the method, the need to tilt the response by 12dB/octave and the fact that the method is not well known. But it is great for LF! Ad notam. Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
#30
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Svante wrote:
4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. You can not call it measurement with an unlinear microphone, so do not overload it. I would guess that the reason that the method is not widely used is the counter-intuitivity (is that proper english?!?) of the method, the need to tilt the response by 12dB/octave and the fact that the method is not well known. But it is great for LF! Ad notam. Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
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Svante wrote:
4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. You can not call it measurement with an unlinear microphone, so do not overload it. I would guess that the reason that the method is not widely used is the counter-intuitivity (is that proper english?!?) of the method, the need to tilt the response by 12dB/octave and the fact that the method is not well known. But it is great for LF! Ad notam. Kind regards Peter Larsen -- ************************************************** *********** * My site is at: http://www.muyiovatki.dk * ************************************************** *********** |
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"Svante" wrote in message om... 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". Exactly how the two fields (or 3 or even 4 for a vented D'Appolito design) actually combine in the far field, is something routinely ignored by many when making near field measurements. But the error will be less when combining woofer and port outputs, compared to a dual woofer set up at slightly higher frequencies. TonyP. |
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"Svante" wrote in message om... 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". Exactly how the two fields (or 3 or even 4 for a vented D'Appolito design) actually combine in the far field, is something routinely ignored by many when making near field measurements. But the error will be less when combining woofer and port outputs, compared to a dual woofer set up at slightly higher frequencies. TonyP. |
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"Svante" wrote in message om... 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". Exactly how the two fields (or 3 or even 4 for a vented D'Appolito design) actually combine in the far field, is something routinely ignored by many when making near field measurements. But the error will be less when combining woofer and port outputs, compared to a dual woofer set up at slightly higher frequencies. TonyP. |
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"Tony Pearce" wrote in message . au...
"Svante" wrote in message om... 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". Exactly how the two fields (or 3 or even 4 for a vented D'Appolito design) actually combine in the far field, is something routinely ignored by many when making near field measurements. But the error will be less when combining woofer and port outputs, compared to a dual woofer set up at slightly higher frequencies. It should not be THAT hard to add the two signals, given that phase and amplitude is taken into account. Of course that depends on what you mean with "near field"; if the microphone is put VERY close to the membrane/port, then the effective distance (ie the amplitude) may be hard to estimate correctly. On the other hand, the "inside-the-box" method elegantly adds up the two volume flows automatically. |
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"Tony Pearce" wrote in message . au...
"Svante" wrote in message om... 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". Exactly how the two fields (or 3 or even 4 for a vented D'Appolito design) actually combine in the far field, is something routinely ignored by many when making near field measurements. But the error will be less when combining woofer and port outputs, compared to a dual woofer set up at slightly higher frequencies. It should not be THAT hard to add the two signals, given that phase and amplitude is taken into account. Of course that depends on what you mean with "near field"; if the microphone is put VERY close to the membrane/port, then the effective distance (ie the amplitude) may be hard to estimate correctly. On the other hand, the "inside-the-box" method elegantly adds up the two volume flows automatically. |
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"Tony Pearce" wrote in message . au...
"Svante" wrote in message om... 3. A bass-reflex box is hard to measure near-field if the port and speaker is separated by some distance. Half-way between the speaker and port is maybe not "near-field". Exactly how the two fields (or 3 or even 4 for a vented D'Appolito design) actually combine in the far field, is something routinely ignored by many when making near field measurements. But the error will be less when combining woofer and port outputs, compared to a dual woofer set up at slightly higher frequencies. It should not be THAT hard to add the two signals, given that phase and amplitude is taken into account. Of course that depends on what you mean with "near field"; if the microphone is put VERY close to the membrane/port, then the effective distance (ie the amplitude) may be hard to estimate correctly. On the other hand, the "inside-the-box" method elegantly adds up the two volume flows automatically. |
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Peter Larsen wrote in message ...
Svante wrote: 4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. You can not call it measurement with an unlinear microphone, so do not overload it. I think that was my point, that this method is NOT suited for distorsion measurement, since the microphine itself will contribute more to the distorsion than the loudspeaker itself. Frequency response, however, works great. FR is essentially a small-signal measurement. Just drop the level sufficiently, and the distorsion will be low (even from the microphone) and will thus not affect the frequency response. |
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Peter Larsen wrote in message ...
Svante wrote: 4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. You can not call it measurement with an unlinear microphone, so do not overload it. I think that was my point, that this method is NOT suited for distorsion measurement, since the microphine itself will contribute more to the distorsion than the loudspeaker itself. Frequency response, however, works great. FR is essentially a small-signal measurement. Just drop the level sufficiently, and the distorsion will be low (even from the microphone) and will thus not affect the frequency response. |
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Peter Larsen wrote in message ...
Svante wrote: 4. Distorsion cannot, however be measured inside the box due to the high SPL. There will be a lot of distorsion from the microphone. You can not call it measurement with an unlinear microphone, so do not overload it. I think that was my point, that this method is NOT suited for distorsion measurement, since the microphine itself will contribute more to the distorsion than the loudspeaker itself. Frequency response, however, works great. FR is essentially a small-signal measurement. Just drop the level sufficiently, and the distorsion will be low (even from the microphone) and will thus not affect the frequency response. |
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