From: Randy Dawson
Subject: Re: volume control at speaker location
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Date: Sun, 13 Oct 2002 20:41:03 -0500
NNTP-Posting-Date: Sun, 13 Oct 2002 21:42:48 EDT
On Thu, 26 Sep 2002 20:26:42 +0100, John Woodgate
>I read in sci.electronics.design that N. Thornton
>wrote (in ) about
>'volume control at speaker location', on Thu, 26 Sep 2002:
>>> I read in sci.electronics.design that Benoit Provost
>>> about 'volume control at speaker location', on Tue, 24 Sep 2002:
>>> > My sound system is in my living room, and I am installing speakers in the
>>> >basement, wired to "Speakers B" on the amplifier. I would like to know if
>>> >there is a simple (passive) way to adjust the volume at the speakers in the
>>> >basement. The simplest way to do this is of course to put a potentiometer in
>>Use a variable resistor in series. It is the easiest way to do it. You
>>won't get a linear scale as you say, but I don't see how that is a
>>problem to be honest. It still works perfectly.
>That's what he did, AIUI, and he DIDN'T like it, which doesn't surprise
>me. Adding series resistance changes the frequency response, because the
>loudspeaker impedance varies with frequency, often by large amounts.
>Consider an 8 ohm loudspeaker, which is really 8ohms (resistive) at say
>400 Hz (typical), but is 32 ohms (resistive) at 100 Hz (also typical).
>To reduce the sound level by 10 dB at 400 Hz, we need 16 ohms in series.
>But at 100 Hz, the level goes down by only 3.5 dB.
>You might argue that it's a desirable effect, because it provides
>automatic 'loudness compensation' at low sound levels, and some people
>might agree with you. But now consider the case of a 2-way system, where
>the impedance is 32 ohms at 2 kHz as well. That is NOT going to sound
>right to anyone!
The correct thing to use is called a T-Pad, the one I have is made by
Clarostat, but I am sure there are others. It presents a constant
impeadence to the amp, and a variable attenuated signal to the
speaker. Mine is wire wound, and can probably handle 50W or more.