Joe:

True re room effects. But interestingly enough, neither the M2i nor the NHT M5 I had on hand exhibited these effects. The reason I was in a sense looking at this issue rather closely is that the layout of the VP150 is very unusual (in fact no other manufacturer has picked up on it) and seems prone to comb filtering which is what I think I was hearing and measuring. But I'm sure Ian knows a lot more than I do about speaker design!