Subwoofer Array Delay

Two or more subs are placed front-to-back and the front box is delayed by spacing divided by the speed of sound (343 m/s). The delayed front output arrives in step with the rear box going forwards, so they add, but arrives out of step going backwards, so they partly cancel. The result is more level out front and less on stage.

A cardioid array reverses the polarity of the rear-facing box and adds a small delay so the array radiates forward and rejects roughly 10 to 15 dB behind it. It keeps low end off the stage and out of nearby neighbours.

Sound travels about a metre every 2.9 milliseconds, so the physical spacing between boxes becomes a timing offset. Matching that offset with electronic delay is what steers the array, so getting the spacing and delay right is the whole trick.