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Path: utzoo!linus!philabs!cmcl2!seismo!umcp-cs!cvl!umd5!don
From: don@umd5.UUCP
Newsgroups: net.audio
Subject: Speaker Physics
Message-ID: <464@umd5.UUCP>
Date: Sun, 7-Apr-85 16:52:49 EST
Article-I.D.: umd5.464
Posted: Sun Apr  7 16:52:49 1985
Date-Received: Tue, 9-Apr-85 01:12:36 EST
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Organization: U of Md, CSC, College Park, Md
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[]
The vote has been tallied .. My calculations are off by 10^6 as the speed
of sound is about 330 meters per second, and I mistakenly used the speed
of light which is about 300,000 KILOmeter per second. So the REAL cutoff
frequency of the waveguide model of a speaker is 693 Hz -- a reasonable
number. (I guess then that is why PA systems use a whole bunch of big
speakers -- LARGE effective diameter pushes the cutoff freq. higher)
   So I can't sail the Nimitz through the holes in Phil's explanation,
(that's OK Phil, when all else fails call me "stupid"!) but I can still
possibly paddle a canoe through the holes (I've always been suspicious
of anyone who doesn't sprinkle in a little math to backup their argument,
so why don't you call me a "Doubting Thomas" instead?)
   The waveguide model is now ruled out since wvaguides become VERY lossy
when operated above cutoff. Most speakers have woofer crossovers at 1,000 Hz.
Given the above and that (330 m/s) divided by (0.254 m) = 1,300 Hz, how is
the dispersal mechanism going to affect anything ? The woofer power will
already be decreased at the supposed limiting frequency of the speaker.
   I have speakers whose tweeters are 0.064 meter in diameter. They work
quite well out to 16,000 Hz, but by what Phil said they shouldn't even
work at all beyond 5,200 Hz !! [(330 m/s) / (0.064 m) = 5,200 Hz; "speakers
cannot reproduce wavelengths shorter than their diameter ..."]
   Please, someone (or Phil) clear this up....


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