@noble100 wrote: "But my main reason for posting is to ask about your quote above.
Was " and time-delay it such that it cancels the signal from the front wall when it arrives." accurate and not a typo?"
That’s what I meant to write.
My understanding is that the idea is to arrange four subs in a centered, half-the wall’s-scale pattern on the front wall. So if the front wall is 18 feet wide by 8 feet tall, then the subs would be at the corners of a rectangle 9 feet wide by 4 feet tall, centered on the middle of the wall. This mimics the best four-sub geometry Todd Welt found in his study of symmetrical sub arrays, but it’s on the wall instead of on the floor. If the wall reflections cooperate, they should cancel out standing waves in the vertical and side-to-side dimensions.
To cancel out standing waves in the front-to-back dimension, the idea is to use active cancellation based on an identical array on the rear wall. This array is in reverse polarity, with a time delay that corresponds to the length of the room.
So the subs in the front of the room to create a planar wave that moves to the back of the room and then disappears as the active cancellation array cancels it when it gets to the back wall. The "no bass" you mentioned happens at the rear wall, not out in the room, or so the theory goes.
I do not know how well this would work in practice. The answer is probably some variation on "it depends". Nor do I know whether it would sound better than a distributed multi-sub system. I haven’t really investigated it and will never build anything like it myself, but it MIGHT be a competitive "cost no object" approach.
Duke