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Old 2nd November 2009, 06:32 PM   #1
PMA is offline PMA  Europe
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Default Measurement of speaker distortion

Hello,

I would like to contribute with my short study on loudspeaker distortion

Measurement of speaker distortion

Cheers,
Pavel
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Old 2nd November 2009, 07:15 PM   #2
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First of all, thanks for your efforts!

Do you have an estimate spl level for 0.6 Vrms (my guess would be < 85 dB for your speaker, which is rather low for speaker testing). The 2 Vrms are more representative.

Can the surprising 19 kHz + 20 kHz measurement be hampered by the extension of your measurement mic?
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Old 2nd November 2009, 07:24 PM   #3
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Hi Taco,

thanks for your reply. You are right, 2Vrms is more realistic, but frankly speaking I do not listen at higher levels. The speaker has above 90dB/2.83Vrms/1m sensitivity.

I was surprised by the 19+20kHz result for the reason that I expected much higher distortion (we can see 1kHz 2nd harmonic product and 18kHz 3rd harmonic product about 60dB below basic level, which is 6dB above 19 and 20kHz spectral line).

The decaying shape of spectrum background is a 1/f noise of microphone and microphone preamp.
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Old 2nd November 2009, 07:38 PM   #4
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Even 85 dB is pretty loud.

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Old 2nd November 2009, 07:41 PM   #5
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Quote:
Originally Posted by PMA View Post
Hello,

I would like to contribute with my short study on loudspeaker distortion

Measurement of speaker distortion

Cheers,
Pavel
Hi Pavel

You made a huge error in your asumptions. The form of the nonlinearity for an amplifier may be completely different than for a loudspeaker, resulting in a situation where .1 % THD in the amp is audible on a loudspeaker with 10% THD. This makes it very difficult to draw any conclusions from you tests.
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Old 2nd November 2009, 07:54 PM   #6
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Hi Earl,

there might be a misunderstanding, I agree with you. I wanted to say that distortion of a current speaker may be quite low (and low order, as shown). There are many amplifiers, especially 'exotic' designs, that distort much more, and it is audible (like SE triode power amp - very very audible with philharmonic orchestra, though appreciated by many).

The system I use for measurement (and listening) has all the distortion components below -100dB at 2Vrms. Power amplifier is no global NFB, 1A idle current design.

Regards,
Pavel
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Old 2nd November 2009, 08:50 PM   #7
gedlee is offline gedlee  United States
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Quote:
Originally Posted by PMA View Post
Hi Earl,

there might be a misunderstanding, I agree with you. I wanted to say that distortion of a current speaker may be quite low (and low order, as shown). There are many amplifiers, especially 'exotic' designs, that distort much more, and it is audible (like SE triode power amp - very very audible with philharmonic orchestra, though appreciated by many).

The system I use for measurement (and listening) has all the distortion components below -100dB at 2Vrms. Power amplifier is no global NFB, 1A idle current design.

Regards,
Pavel
But isn't the point simply that the numbers don't mean anything?
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Old 2nd November 2009, 09:06 PM   #8
cuibono is offline cuibono  United States
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Thanks Pavel for sharing - I'm not surprised by your results - having non-linear distortion down 60dB is not too hard to do for modern drivers, particularly at the levels you've driven them at.

I agree with a general statement that nonlinear distortion is less audible in loudspeakers than many people assume. Toole's recent book has an interesting analysis of nonlinear distortion in loudspeakers. The upshot is that auditory masking limits our ability to hear harmonic tones. I would also add that any natural instrument has many harmonics that are just as loud as the fundamental, and would mask nonlinear distortion in loudspeakers, up to a point.

Stored energy and crossover distortion are areas that may matter more, but that is still a fairly gray area IMO.
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Old 2nd November 2009, 09:37 PM   #9
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Quote:
Originally Posted by gedlee View Post
But isn't the point simply that the numbers don't mean anything?
Partly, IMO. They should not be completely overlooked or ignored. And we are not speaking numbers, but spectra. They are just a part of a whole issue.
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Old 2nd November 2009, 09:43 PM   #10
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Quote:
Originally Posted by PMA View Post
There are many amplifiers, especially 'exotic' designs, that distort much more, and it is audible (like SE triode power amp - very very audible with philharmonic orchestra, though appreciated by many).
Do you have a sample of an SE to try? Based on dim memories of the form of transfer functions which generate 2nd I never saw an obvious reason for discounting the possibility of second order cancellation between electronics and speakers. If you're set up it would make an interesting experiment. An option is to pre-distort the test signal with different percentages of second and graph the results.
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