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From: John Woodgate
Subject: Re: Cancel speaker resistance?
Date: Tue, 17 Sep 2002 03:43:53 +0100
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Tue, 17 Sep 2002 06:54:39 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Chuck Simmons
wrote (in <3D868192.F61269AB@webaccess.net>)
about 'Cancel speaker resistance?', on Tue, 17 Sep 2002:
>The first two peaks are mechanical.
The URL shows the impedance curve of a 2-way system, not a single
> The first peak is the first
>principle mode of the diaphragm and suspension.
>Very small speakers
>don't have the second peak which I suspect is due to the second
>principle mode of the diaphragm.
In the URL curve, the second peak is due to the crossover network not
being a constant-impedance filter.
>The third appears to be electrical
>rather than mechanical because it is present in voice coils not
>attached to diaphragms.
There is no third peak as such; the rising impedance at high frequencies
is simply due to the inductance of the tweeter voice-coil.
>A voice coil with a stiff mass load and a spring
>suspension has only two peaks corresponding to the spring mass resonance
>and to the self resonance of the coil and stray capacitance.
That second resonance doesn't appear within the audio-frequency range
for most loudspeakers. Even a 10 mH voice-coil needs 6nF of stray to
resonate at 20 kHz. Not likely.
There IS a second resonance, which almost all drivers show, but it is
the *series* resonance of the voice-coil inductance with the
(capacitive) motional impedance, and occurs typically between 200 and
600 Hz. It is responsible for the impedance *minimum* (purely resistive)
in that mid-range frequency band.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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