Would like to build simple volume control or attenuator

[Barry R]

I have a Sony AV-Receiver (about 100 watts per channel). It is hooked up to a Niles speaker selector. My main speakers are Boston Acoustics A100s. There are two add'l pair of Satellite speakers in other rooms (which have their own attenuators). All are 8 ohms (I think). The A100s are much louder than the other speakers so I'd like to use either a potentiometer or fixed resistor (which I'll switch on or off) to lower the volume of the A100s when I'm using multiple speakers. Can anyone help me figure out how to do this?

I'm not sure how many dbs I need to attenuate. Subjectively, the volume on the main speakers is moderately too loud, not blasting (I'd probably want to drop it by 30-50%.
Sorry if I'm lacking enough of the technical details.
I'm looking for a quick and easy fix as I won't be using it in this mode all that often.

Thanks.

[Barry R]

Should I have posted this to a different forum?
Suggestions?

[bobhayes]

You're going to need large high power aluminium cased resistors mounted on heatsinks to persue this approach. However, if your A100's are nominally 8 ohms, connect a 25watt 8.2 ohm resistor across the speaker terminals (parallel), and a 50watt 3.9 ohm resistor in one of the connecting wires (series). This will maintain 8 ohms for your amp, but attenuate S.P.L. by 6dB (half the volume).
The resistors will have some inductance which will probably attenuate the treble output and make your speakers sound dull, which is why you'de be better off running a seperate amp for your main speakers, with a seperate volume control.
Don't underestimate the cost of high power resistors.
Maybe someone could suggest a better approach?

[Barry R]

Thanks.
It is obviously not worth doing it the way I thought. I'll probably either by an impedence-matching attenuator or live with it the way it is!

[bobhayes]

An circuit I described is an impedance matching attenuator.
Normally the variable types you can buy commercially are usually used to attenuate the more sensitive tweeter in multi way loudspeakers, to maintain 8 ohms for the crossover. There is substantially less power being fed to the tweeter than the woofer but you wish to attenuate the whole signal. I believe that high power models are available, but your talking big bucks. A second amp may work out cheaper!