Two Subs in Normal Mode vs Cardioid
In open space, two boxes in normal mode will provide more output up front than one in cardioid. BUT — if a reflection from a wall behind the subs cancels the primary output, then placing one cabinet in cardioid mode to mitigate that reflection could result in higher SPL in front of the two boxes.
In other words, you can use cardioid mode with just 2 boxes to good effect when it's called for.
When Cardioid Mode Pays Off
Cardioid mode uses the output of one box (turned to face backwards) to deliberately phase out the sound going backwards behind the stack. If that backwards-traveling sound hits a wall and comes forward again, it can cancel the forward-traveling sound.
If you cancel the backwards-traveling sound before it hits the wall, it won't have the energy to do any cancelling out front.
How to Use It
Place one sub facing forward, one facing backward directly behind it. Both are connected, but the rear-facing sub uses a cardioid preset to invert polarity and apply the correct delay. The result: bass energy is focused forward, rear wall reflections are suppressed.
This is particularly effective in venues where the DJ setup is near a rear wall, or where strong rear-wall reflections are audibly canceling low frequencies at the listening position.
