Sub speakers are omni-directional in sound, which isn’t always ideal at your event. Cardioid sub arrays can make a huge difference in making low sound frequencies reach your audience, without spilling in every direction.
Cardioid arrangement of subs are a way of directing the sound from your subs towards your audience and eliminating spill of sound in all other directions.
As mentioned, sound waves emitted from subs are omni-directional (equal in all directions). This means that energy caused by the soundwaves is expelled out of the back of the speakers into any stages and walls behind, or simply outside of your licensed area.
Cardioid sub arrays are positioned with 1 in every 2 subs facing backwards, or with one sub positioned behind another.
In the first instance, because the backwards sub is out of phase with the forward (audience) facing subs, it can absorb the soundwave energy from the forward facing subs. This is known as a rear facing cardioid array. As the driver in this backwards sub is not in line with the front facing subs, this can be delayed to match them, ensuring clarity of sound.
The second instance, an end-fire cardioid array works by setting the behind sub out of phase, reversing the sound wave, cancelling out the soundwaves emitted from the back of the front sub.
Sub speakers can cause disturbance with onstage mics, vinyl decks, and your performers hearing on stage as well as potentially other stages/audiences in the surrounding area. Cardioid sub arrays can reduce this interference, making the sound on stage easier to engineer. Solid objects behind your speakers, or a strict sound limit also benefit from cardioid sub arrays, as the output is more directional, and in the case of solid objects, does not feed back and create cancellations at the front of your subs.