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Old 6th October 2004, 07:35 AM   #1
mike.e is offline mike.e  New Zealand
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Default THD measurement method

Hi all
Topic i havent seen much solid info on
Im keen on measuring woofer distortion both baffled and unbaffled.-linkwitzlabs style,steady state sine and impulse.

Mainly consisting of THD and IMD measurements
Ive seen the site listed below-but its not highly useful due to different drive voltages used!

Questions
1-Is the FFT in cooledit accurate enough?Can do quite high FFT size,ive heard of people using it for specialist uses.

2-If i was to keep one thing constant-should it be drive voltage/power OR SPL

3-program to use hobbybox4/praxis demo/winmls etc

4-Baffle size when used? IEC size? Im only considering the bass frequencies so i think this isnt such an issue at all

RS SPL meter->cooledit recording line in-inspection of wave files with FFT tool

Il only consider outside measurements to keep it simple and not get into MLS/gated stuff.

Im keen on seeing the resonant effects of ported box vs horn vs IB etc!

-Hopefully my eyes will show what i hear

Apparently the TCsounds 2+ matches the XLS12 driver distortionwise!

When i overlay the two graphs to have the same fundamental amplitude-
xls seems to have more distortions(+10db) at 4th and 5th harmonic.

Cheers!
Mike.e



tc2+ vs xls www.mfk-projects.com
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Old 6th October 2004, 09:03 AM   #2
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did you try http://www.cetaceanresearch.com/analysis.html spectralab?
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Old 6th October 2004, 04:24 PM   #3
mike.e is offline mike.e  New Zealand
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No,ive vaguely heard of that one il check it out!

Im mainly looking for something thats user friendly but still pretty accurate and can compensate for nonlinear soundcards

Thanks!
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Old 6th October 2004, 04:35 PM   #4
mike.e is offline mike.e  New Zealand
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Ok ive got a list of software now

Speaker workshop(especially since its free)
Winmls
Clio
Praxis ...
Spectralab

What il do is download all of those-Do the measurements all at once,and see what i get!Compare results and see what works and whats hard to use...

And once chosen i could jump in and buy the one most suitable + a better mic than RS spl meter

Cheers!
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Old 6th October 2004, 05:32 PM   #5
jdybnis is offline jdybnis  United States
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let us know what you decide on
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Old 6th October 2004, 06:38 PM   #6
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Default Re: THD measurement method

Quote:
Originally posted by mike.e
Hi all
Topic i havent seen much solid info on
Im keen on measuring woofer distortion both baffled and unbaffled.-linkwitzlabs style,steady state sine and impulse.

Mainly consisting of THD and IMD measurements
Ive seen the site listed below-but its not highly useful due to different drive voltages used!

Questions
1-Is the FFT in cooledit accurate enough?Can do quite high FFT size,ive heard of people using it for specialist uses.
[....]


The FFT in CoolEdit is quite accurate, far better than any sound card out there. I used it recently to debug a nasty aliasing problem for $DAYJOB.


Francois.
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Old 7th October 2004, 02:20 AM   #7
mike.e is offline mike.e  New Zealand
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My dad even used the FFT in cooledit2000 for Radio repeater fault diagnosis once! i told him it had a good looking FFT function,and he found a problem and solved it hehe

Il tell you guys what happens! Cheers
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