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millwood 10th July 2004 01:25 AM

speaker distortion
 
we bought a pro audio company last year (one of the largest in the world) and they are doing some competitive testing of amps and speakers. here is a particular speaker (by a well known high-end brand name) and its thd figures:

2nd harmonic:
100hz: about 10%;
1000hz: about 0.5%;
10Khz: about 5%

3rd harmonic:
100hz: about 10%;
1khz: about 0.2%;
10khz: about 0.5%.

who said they could hear 0.00001% thd?

:)

sss 10th July 2004 01:37 AM

how do u test a speakers THD?

SY 10th July 2004 01:48 AM

Those numbers are kind of meaningless without reference to drive and SPL.

sss: One easy way is to drive the speaker with a sine wave, look at the acoustic output with a mike and preamp, then either take an FFT to determine harmonic content (an apodization is necessary!) or use a plain vanilla distortion analyzer or wave analyzer.

sss 10th July 2004 02:02 AM

what about the distortion of the mic used?
anyways i think that even humidity in the air will change speakers distortion

till 10th July 2004 02:04 AM

to me these numbers look like THD at rated maximum power. What SPL at what distance?

SY 10th July 2004 03:41 AM

Quote:

Originally posted by sss
what about the distortion of the mic used?
anyways i think that even humidity in the air will change speakers distortion

Yeah, you can't just use any old mike. But some of the cheap ones like the Panasonic do pretty well. A B&K is definitely better!

Humidity is a big issue for paper cones and cloth surrounds/spiders.

cunningham 10th July 2004 08:25 AM

Quote:

Originally posted by SY




Humidity is a big issue for paper cones and cloth surrounds/spiders.


A-MEN:yes: :yes: :yes:

also typically you can almost eliminate speaker distortion by never exceeding 60% or so of rated RMS power.:rolleyes:

classd4sure 10th July 2004 08:59 AM

Hi,

Please know (this will soon become very obvious) I'm completely ignorant in this matter (most others too)...but anyway,

Would some form of velocity sensor coupled to the cone be better than a Mic?

millwood 10th July 2004 03:34 PM

Quote:

Originally posted by SY
Those numbers are kind of meaningless without reference to drive and SPL.
yes, SY. when the Mars and Pluto are exactly lined, and Saturn's 3rd and 7th satellites are exactly perpenticular to the earth, you cannot observe any speaker distortion. :)

I don't have all the specifics, but the measurements are done in a sound chamber with the mic placed 1m from the speaker center.

But doesn't that make the measurement totally useless? since no one listens to their speakers in a sound chamber.

:)

till 10th July 2004 06:18 PM

you did not get the point. At what input power, and whats the rated input power.


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