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[Paul Miller]

So the theater that I am loosely affiliated with has their L'Acoustics SB28 subs arranged in two stacks of four, on either side of the stage. The stacks are tucked into nooks with minimal space behind them and angled slightly in. The bottom sub in each stack is turned around, suggesting a cardioid configuration. See attached pic.

My question is, will there actually be any usable cancellation occurring on stage with this arrangement? I'm thinking there won't be, as there is not enough room directly behind the subs for those opposing wavelengths to cancel much (if at all) before getting reflected back into the room. And therefore, in theory it would be better if the bottom subs were turned back around and run conventionally.

[Gordon Brinton]

You are correct. In order for this type of array to work, there must be at least 1/2 wavelength of free space behind the stack for adequate cancellation to occur. (For 60Hz, that might be roughly 10 feet.) The wall behind the stack is clearly interfering by reflecting the reversed polarity sound waves forward.

You might do better to face all 8 subs forward and install thick sound absorbing panels on three sides of the stack. I'm talking very heavy, like maybe 8 inches of rockwool. Make them even heavier between the stack and stage wings.

Good luck.

EDIT: But make sure that the cabinets can still get ventilation.

[ProSoundWeb Community]