The problem with putting a speaker on its side is that you end up with a different horizontal location for different frequency ranges, which mucks up the imaging.

When the speaker is vertical all the drivers are in line.

The only reason centers don't have this problem is that they religiously use symmetrical driver layouts, eg. WTW or TWWWT. If you have two identical drivers side by side they act roughly the same as a single driver at the midpoint between them -- so if you look at any center speaker and replace symmetrical pairs with a single driver at the midpoint you end up with all the drivers at the midpoint.

Try that with a normal speaker on its side and it falls apart -- a woofer and a tweeter don't cover the same frequency ranges so you can't treat them as a single driver at the midpoint.


M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8