B&W 602 goes under the knife (pics and measurements) - Page 2 - diyAudio
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Old 3rd September 2009, 09:59 AM   #11
sangram is offline sangram  India
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Good work, I'd surely like to see more of this stuff.

I seem to remember Zaph once saying that for HD measurements all you needed was a signal gen and a spectrum analyser, but I wouldn't know how it would work with swept as opposed to single tones.

So, since you constructed the mic yourself, could you tell us a bit about it?

Also, I don't know that the level you tested at is high enough - but I guess someone else will chip in. I think the reference standard is 1m at 2.83V/1KHz, but not 100% sure of that. For HD measurements one would look at slightly higher levels - 90dB or so?

Last edited by sangram; 3rd September 2009 at 10:01 AM.
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Old 3rd September 2009, 10:36 AM   #12
Dr_EM is offline Dr_EM  United Kingdom
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Interesting stuff! I have DM602 S3 (your freind has S2 it appears). Differences on S3 I can see are different (more flush) woofer mounting, whole front baffle is gently curved and the "golf ball" texture on the reflex ports, intended to reduce air turbulence.

I am building a 3-way active system which will ultimately replace them, but I do still wonder if I'd have been just as pleased adding a good subwoofer to my DM602s, they are pretty decent really
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Old 3rd September 2009, 11:49 AM   #13
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Very enlightening,......AGAIN!!!..........AGAIN!!!..... ....

Mick.
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Old 3rd September 2009, 04:52 PM   #14
tresch is offline tresch  United States
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Quote:
Originally Posted by sangram View Post
So, since you constructed the mic yourself, could you tell us a bit about it?

Also, I don't know that the level you tested at is high enough - but I guess someone else will chip in. I think the reference standard is 1m at 2.83V/1KHz, but not 100% sure of that. For HD measurements one would look at slightly higher levels - 90dB or so?
I've said about all there is to say, really, it's a Panasonic WM-61A capsule microphone attached to the end of a metal rod My sound card is providing the voltage bias.

As far as levels there's two reasons that I'm not cranking up the volume. One is that in the same measurement session I was getting data for the current set of speakers I'm building, which is an MTM using a MarkAudio Alpair5 as a mid-tweet. I wanted to get full-spectrum response graphs on the alpair5 without damaging it.

The second, and really the main reason, is that since I have NOT done the Linkwitz mod to my microphone, it will supposedly only handle something like 86db before starting to distort, and I wanted to steer well clear of that.

By the next set of tests I'm sure I'll have either modified the mic to handle more power (insert Tim Allen grunt here), or I'll have bought one of these:
http://www.parts-express.com/pe/psho...number=390-801
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Old 3rd September 2009, 05:19 PM   #15
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Quote:
Originally Posted by sangram View Post
Good work, I'd surely like to see more of this stuff.

I seem to remember Zaph once saying that for HD measurements all you needed was a signal gen and a spectrum analyser, but I wouldn't know how it would work with swept as opposed to single tones.

So, since you constructed the mic yourself, could you tell us a bit about it?

Also, I don't know that the level you tested at is high enough - but I guess someone else will chip in. I think the reference standard is 1m at 2.83V/1KHz, but not 100% sure of that. For HD measurements one would look at slightly higher levels - 90dB or so?
The ARTA set of programs will measure distortion for you.
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Old 3rd September 2009, 06:28 PM   #16
tresch is offline tresch  United States
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Quote:
Originally Posted by 5th element View Post
The ARTA set of programs will measure distortion for you.
well, so does HOLMImpulse, which I'm already using. What I don't know is how sensitive harmonic distortion measurements are to:

a) microphone quality
b) reflections, and
c) ambient noise

If I measure outside I get a decent amount of ambient noise (crickets, people mowing their lawns, etc). If I measure in the garage I get really really nasty reverberation. Does one truly need a proper anechoic chamber to get decent HD measurements? As far as the microphone... do microphones produce their own discernible harmonic distortion that would affect the measurements? These are my curiosities! Perhaps I will make another thread about this topic
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Old 3rd September 2009, 06:52 PM   #17
tresch is offline tresch  United States
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and I did!

http://www.diyaudio.com/forums/showt...09#post1915009

Please direct any HD discussion there!
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Old 3rd September 2009, 07:11 PM   #18
Key is offline Key  United States
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Good stuff. Can you do off axis FR? You don't have to do a bunch of angles or anything for my benefit just maybe 90 degrees off axis. A little curious. Thanks
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Old 3rd September 2009, 09:20 PM   #19
paulfx is offline paulfx  United States
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Hey There tresch!
I need to measure my project and I want to copy your setup. I want to do frequency response first and then get into distortion like in your other thread - - I have a Gen I Mighty Mike and some multimeters. You are using this application HOLMImpulse along with a particular PC sound card, is that right? Where can I get these?
Thanks,
Paul
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Old 3rd September 2009, 09:27 PM   #20
ra7 is offline ra7  United States
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Very very good work! I always thought the B&W 602 was a great speaker. It does very few things offensive.

I've been playing around with doing measurements too. Please continue the fantastic work!

Thanks a mil!
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