techdeveloper wrote:
I recall reading an article which described a test that allowed 2
amps to be connected to a single speaker. If and only if there were
differences between the 2 would the speaker make any sound at all.

Anyone know of this test?

Yes, of course.

I don't know what it's "called" in various circles, but it's a
"differential test". The test shows up the difference between not only
the signals but the difference between the errors. You can try it
between two ams in a stereo unit, or between two different amps. The
main problem is you have to PRECISELY match the gain of the two amps.

It is the same connection as driving the amps in x-bridged mode but the
second signal is not inverted. Of course the gain-matching has to be done at
a particular frequency i.e. 1kHz. Then we can not only compare the frequency
response but also the phase response. If there are different treble cut.off
frequencies, phase differences will show up in the audio range making a
trebelish output, the same is true for the low frequencies with a rumblish
sound. Only if both amps perform identical and are not overdriven, we will
get silence. We can do this test also with one amp only and comparing the
left and right channels in the same way.
--
ciao Ban
Bordighera, Italy