Re: QSC KW181 stacking (placement) - NEED ADVICE!
Put full-range audio into both the KW181 and the tops. The KW181 has a built-in, full-time 100 Hz low-pass filter. Set the tops to "EXT SUB," which will engage a 100 Hz high-pass filter that complements the sub's filter.
Putting subs on each side gives you the proverbial "Bass Alley" right up the middle (i.e., equidistant between them, where their sound is in-phase at all frequencies) and varying bass response off to the sides. If it's possible to put them tight together, whether side-by-side or stacked, do so. Sometimes, though, physical constraints of the venue require doing left and right subs, and you have to make do with that situation.
