On Tue, 11 Oct 2005 19:25:02 -0700, "ScottW"
wrote:

I don't think you want to invert the feeds. Take two amps set at identical
gain with a common feed, tie the grounds of each amp together (neg speaker
terminal) and connect the positive output of one amp to the + speaker
terminal, the positive of the other amp to the negative speaker terminal.
The speaker will only "play" the difference of the amps.

Seems to me if you invert the polarity to one amp you will always have a
difference.

I can't see how this method would be very revealing. Maybe if you took the
difference signal and ran it through a 3rd amp to get some gain on it.

Yes, of course, you are right and I was not thinking it through.

Kal