Hey Big Red,

Yep, it's called the Hafler effect or Out Of Phase Stereo or OOPS.

Never tried it with a keyboard setup but I use to do this in my cars. Back in the old days when they still put a center speaker in the middle of the front dash. My first car, a 69 Olds Cutlass, I had a Craig PowerPlay 8-track, Big Boomers in the rear deck and then I would wire the front speaker by sending just the '+' sides to the front speaker.

Nice little trick. Some folks think it was better sounding than using fancy electronics to get the same effect.

mike