Thanks for the input, all.

I have listened to special bass test tones that go in and out of
phase, but that only demonstrates if left and right speakers are in or
out of phase. It's useless for judging if a pair of woofers in just
the left side or just the side are in/out phase. The only way is to
use your ears, or my RTA.

Speaking of which, my RTA indicates the right set of 3-way speakers
has 15db higher bass response around the 75-150hz region than the left
set. And the left set actually has a nasty 15hz dip centered around
90hz that I can NOT remove using internal or external EQ's in my
system. That indicates an out of phase woofer set to me.

I found the following item on Monster Cable's site:

http://www.monstercable.com/productPage.asp?pin=534

This would be an invaluable tool for home audiophiles and especially
good car audio shops (which is why none around here have one!). But
it's $150.00, which is a steep price to pay just to prove my shop
****ed up my install. Anyone use this device, and if so, is it worth
it? Supposedly it can even check TWEETER phasing, which i've never
been able to pull off with batteries or listening.

Hell, I can't even find a car audio shop that has an RTA!!! What has
this pathetic world come to?!?!??! "Duhhhh... can you put some big
beats into my Cadillac??? Duhhhhh"