From: DPierce@TheWorld.com (Richard D Pierce)
Subject: Re: Cancel speaker resistance?
Sender: email@example.com (Mr Usenet Himself)
Date: Mon, 16 Sep 2002 19:41:00 GMT
Organization: Professional Audio Development
X-Newsreader: trn 4.0-test72 (19 April 1999)
In article ,
John Woodgate wrote:
>I read in sci.electronics.design that Richard D Pierce
> wrote (in ) about
>'Cancel speaker resistance?', on Mon, 16 Sep 2002:
>>One can easily construct an amplifier that has a net negative
>>output impedance, thus resulting in a net reduction in the
>>total loop resistance of the amplifier/speaker circuit.
>The voice-coil gets hot, and its resistance thus changes. To preserve
>bridge balance (and combined positive and negative feedback involves a
>bridge), that has to be allowed for, and it is not easy to do.
I presume you mean that "under normal operation, the voice coil
can get hot. Since the voice coil winding has a non-zero
temperature coefficient of resistance, any scheme that attempts
to eliminate the effects of the voice coil resistance must
either compensate for this or, at best, be an approximation at
all but some arbitrarily chosen average drive level."
If THAT'S what you mean, yes, that's absolutely true. It might
be argued that, on first glance, a scheme that reduces the
effect of the resistance, if not taking this effect into
account, will suffer MORE from the thermal effects on resistance
than a more ordinary scheme might because, if uncompensated,
the realtively small changes that would occur under normal
operations would have a more profound effect when the expected
resistance is small or zero, than if they are simply a few
percent of the total normal resistance.
I think these sorts of secondary effects are simply another
complication to a solution, it seems, that is searching for a
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