Subwoofer Coupling Breakdown

In order to achieve optimum performance you will require power that will offer an addition +3 dB to your loudspeakers.
1000 watts: 0 dB
1000 watts – 2000 watts: +3 dB
2000 watts – 4000 watts: + 3 dB (+6 dB)
4000 watts – 8000 watts: + 3 dB (+9 dB)
8000 watts – 16000 watts: + 3 dB (+ 12 dB)

To achieve + 3 dB from your loudspeakers the same principal applies.
1 sub: 0 dB
2 subs: +3 dB
4 subs: + 6 dB
8 subs: + 9 dB

You will achieve an additional +3 dB once the subwoofers are coupled together. 1 sub: + 0 dB
2 subs: +3 dB compared to 1 sub
4 subs: + 3 dB compared to 2 subs
8 subs: + 3 dB compared to 4 subs