Sound travels about 13500 inches per second. So if your dipoles are 4 feet out from the wall, the backwave's arrival is delayed by roughly (4*12*2)/13500 = 7.1 milliseconds relative to the frontwave, not factoring in angles.
I prefer diffusion of the backwave rather than absorption, unless your room is extremely live, and/or unless you are forced to place the speakers very close to the wall behind them.
My understanding is that a round-trip path length for the backwave energy sufficient to impose about 10 milliseconds time delay is desirable from a psychoacoustics standpoint. But this isn't a hard and fast rule; if you can't achieve that much delay, still get as much as you can.
In my experience if you are unable to place dipoles more than about two and a half feet out from the wall, absorption of the backwave (or switching to monopoles) starts to make sense.
Duke
daler/manufacturer
I prefer diffusion of the backwave rather than absorption, unless your room is extremely live, and/or unless you are forced to place the speakers very close to the wall behind them.
My understanding is that a round-trip path length for the backwave energy sufficient to impose about 10 milliseconds time delay is desirable from a psychoacoustics standpoint. But this isn't a hard and fast rule; if you can't achieve that much delay, still get as much as you can.
In my experience if you are unable to place dipoles more than about two and a half feet out from the wall, absorption of the backwave (or switching to monopoles) starts to make sense.
Duke
daler/manufacturer