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Old November 7th 19, 08:39 PM posted to
Trevor Wilson[_3_]
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Posts: 127
Default Motional feedback in speakers

On 8/11/2019 6:31 am, Peter Wieck wrote:
> Take the (permanent magnet) speaker as a linear motor.
> Now, for illustrative purposes, obtain a small DC brush-type motor. Spin it with your fingers. Now, short the leads to the motor. Now, try spinning it again with your fingers.
> Not so easy.
> That is the function of "damping factor" - As a way to prevent a PM speaker from wobbling like a spring when it is released.

**No. It doesn't work like that. In a PROPERLY designed enclosure,
so-called "damping" is not dependent on amplifier output impedance.
Damping is supplied by the enclosure itself.

However, the poor output impedance exhibited by the vast majority of
valve amplifiers and some SS amplifiers can lead to significant
frequency response aberrations in line with the impedance variations
exhibited by most speaker systems.

Again, I refer you to a couple of curves published by Stereophile:

Note the 3.5dB peaks at 65Hz and 1.5kHz.

Now here is the curve of a 'perfect' amplifier driving the same,
simulated, speaker load:

Note the differences between resistive loads and reactive loads.

And, of course, here is a rather more modestly priced 'perfect' amplifier:

And, once mo "Damping factor" is a misnomer. It is a misleading and
incorrect term to use. Output impedance (preferably quoted from 20Hz ~
20kHz) is vastly more preferable. A PROPERLY designed speaker system
already has adequate damping. Amplifier damping is not relevant, BUT
output impedance is.

Trevor Wilson