My comments about two Bose L1's being better than one ONLY applies to the sound of a stereo piano sample and not to any other instrument. This is because piano samples are "recorded" as stereo from each end of the acoustic piano keyboard, just like your ears are hearing different ends of the piano while you are sitting on the bench to play. All other instrument sounds are emitted from a point source so they never exist as stereo. If you combine the left and right electronically before your ears have the chance to hear them, not only is stereo effect lost but some of the left/right sounds interfere with each other (phase cancellation) and the overall sound quality is degraded. You can hear the same difference when you use the mono output jack on the keyboard which sums to mono inside the keyboard.

I agree that the stereo effect is lost except for a few people in the perfect position but the issue (for piano sounds) is about avoiding sound quality degradation NOT maintaining the stereo separation. The reason that two Bose are so good is due to the "spatial" sound pattern that is very even for everyone in the audience.

I used to be active on the Bose forum and this issue was debated and researched for months on end. Some people (including me) conducted exhaustive tests with different keyboards, one or two L1's and different instrument sounds. The overwhelming conclusions were that
1)Stereo piano sounds are much better through two L1's - assuming you keep the channels separate.
2)It didn't apply to other instruments
3)It didn't matter which make of keyboard you used.

The difference to my ears while playing is dramatic so even if you are still doubtful that it makes any difference to many people in the audience don't we all play better when we sound better to our own ears?

Tony