⚙️ ENGINEER LEVEL: Dipole Cancellation and Room Interaction
Multiple Subwoofer Placement Theory
In a vehicle, the cabin is small relative to bass wavelengths. Subwoofer placement strongly affects the modal response — which modes are excited and at what level.
Two subwoofers in phase:
If both subs are near the same wall:
SPL_total = SPL_single + 6 dB (coherent addition)
If subs are separated (opposite ends of vehicle): - At low frequencies (λ >> separation): still +6 dB - At frequencies where separation = λ/2: cancellation at some positions, addition at others - Creates spatial variation — good for some seats, bad for others
Cardioid subwoofer arrangement:
Two identical subs, one facing forward and one facing backward, with a delay equal to their separation distance applied to the forward-facing one:
Delay = L/c
Where L = physical separation.
This creates a cardioid radiation pattern — strong output forward, cancellation backward. Used in some professional car audio installs to reduce reflections from rear window and tailgate. Complex to implement but reduces certain modal problems.