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Woofer compliance sample variation [message #48210] Wed, 16 November 2005 16:00 Go to next message
Paul C. is currently offline  Paul C.
Messages: 218
Registered: May 2009
Master
I had read posts where fellows said they would measure their particular drivers and use those figures to try to fine tune their speakers/ports.

I remembered reading an AES paper by Pat Snyder (with Speakerlab at that time). It was presented at AES convention in Nov of '77, Preprint No. 1307, "Simple Formulas and Graphs for Design of Vented Loudspeaker Systems".

He goes though the standard definition of terms, and T-S stuff, and in the end, gives a set of low end response curves. We now generate these curves easily with various programs on the market, so I won't go into all of that. I am sure these programs use these formulas.

BUT what was really intersting was an observation by Pat, and he showed this mathematically, that driver compliance, Vas, had very little to do with the low end response.

"Keele observed that drive compliance Vas has relatively little effect on system frequency response. (Ref 3) I also know that of the woofer physical parameters--compliance, cone mass, magnet strength, and so on--compliance is the one that varies the most in production."

Pat goes on to combine some formulas and shows that Q and resonant frequency both contain the Vas, and that when Vas varies, so do Q and resonant frequency. He shows how compliance factors out of the equations.

I would love to reproduce all of that here, but don't know how to make the various symbols required. Anyway, anyone who wants a pdf of this portion of the paper need only email me.

What he shows happens is that when Vas is off, these other parameters are off in such a way that the completed speaker still functions as designed.

I had read on another forum where a fellow did various speaker measurements before and after "break in". Presumably after "break in" a speaker's compliance changes, it becomes loosened up, so to speak. Yet when you put the real woofer in a real box, and measured response before and after "break in" no difference could be observed.

So, I think the lesson is, don't get too upset if your actual measurements vary from the manufacturers' specs. Go on and design your box and vent, put the speaker together, and enjoy the music.

Re: Woofer compliance sample variation [message #48211 is a reply to message #48210] Wed, 16 November 2005 18:24 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18792
Registered: January 2001
Illuminati (33rd Degree)

Thanks for posting that, Paul. If you'd like, I can put the PDF file on a sever so you can link to it and make it available for download.


Re: Woofer compliance sample variation [message #48212 is a reply to message #48211] Wed, 16 November 2005 19:08 Go to previous messageGo to next message
Paul C. is currently offline  Paul C.
Messages: 218
Registered: May 2009
Master
Yes, please do so.

Thanks, Wayne!

Re: Woofer compliance sample variation [message #48217 is a reply to message #48212] Thu, 17 November 2005 11:04 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 18792
Registered: January 2001
Illuminati (33rd Degree)

Will do.


Re: Woofer compliance sample variation [message #48237 is a reply to message #48217] Thu, 17 November 2005 19:50 Go to previous message
Paul C. is currently offline  Paul C.
Messages: 218
Registered: May 2009
Master
Wayne has put this on his server here:

http://www.audioroundtable.com/misc/Spkr_Pat_Snyder.pdf


Thanks, Wayne.


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