Perhaps I misunderstood what comb filtering is. What do you call it when you walk across the room, playing a single tone, and you can hear the volume go up and down. Also measurable with a sound meter. If you stay in one place, the tone is constant, but moving just an inch one way or the other causes the volume to change. Walking at a slow steady pace is like a ripple effect.
Yeah. Was this when you had "your wall of speakers" hooked in series with each other? If so it could have been the bad acoustical interference which why it was so noticeable with the test tones.