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Old 14th March 2002, 04:19 AM   #1
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Join Date: Apr 2001
Location: Melbourne, Australia
Default Need an anechoic Freq Response Test System

Hi All,

I have been experimenting for some time with the Audua labs "Speaker Workshop" and a DIY microphone for doing psuedo anechoic frequency response testing with mixed success. The system is not very accurate, often gives spurious results and I don't have a lot of faith in the measured responses.

I have decided to bite the bullet and purchase/build a professional FR test setup so that I can measure the performance of my speaker designs in near real time anechoic conditions. I have a small testing room which I plan to coat with anechoic tiles but I need the test system.

All I want to do is on and off axis FR testing and I want the results to be repeatable and the system relatively easily to operate. I don't need super accuracy or precise calibration as most of the testing is of a relative nature anyway, ie eliminating peaks and dips in the crossover performance.

Can anyone suggest a test setup (inc microphone)? I have contacted Bruel & Kjaer Sound and Vibration here in Australia but their basic system is $15,000 - a little out of my budget!

Thanks

Marcus

www.theloudspeakerkit.com
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Old 14th March 2002, 05:06 PM   #2
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Join Date: Feb 2002
Location: Roy, WA
Default Sound level meter

Hi

I use a std PC running some freeware that does an FFT(gram42.zip). I've found that the ordinary "Microsoft windows" ISA sound card has a good 'n flat response, 20 - 20K. You can get 'em for $5 -

For a microphone, I'm lucky enough to have a GenRad sound level meter, which I openly trust to deliver the goods...

Notice I said GenRad. I dont know if I'd "openly trust" a similar unit from "Radio Shack".

To get the same unit as I have, see http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1713182995

I also have a white/pink noise source, which works great for testing crossover anomalies. Mine is an IVIE. For a genrad source, check out http://cgi.ebay.com/ws/eBayISAPI.dll...tem=1712836248

I dont test in a room; you can just test outside (if it's not raining)
Since the FFT can average over time, intermittent outside noises arent a problem and the only combing you'll get is from a reflection off the ground. At 1M or so, these shouldnt be much of a problem. You also can always point straight up!

I set you up for ~$150, provided you win the items and have a PC with a known flat response sound card installed.

Good luck!
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Old 14th March 2002, 11:55 PM   #3
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Join Date: Apr 2001
Location: Melbourne, Australia
Joe,

This setup looks to be about the same or even a little less professional as the Audua software and I really need something more suited to production development of speakers.

I've found the LMS product from LinearX and although at $3300AUD it's a bit more realistic than the B&K setup it's still pricey.

Does anyone have first hand experience with LMS?

Marcus
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