How to make 150-dB ++ with only four-subwoofer 12 inch subs.

1. Make small box and fill it with a 12inch (prefers that use for competition)
2. Place it in the car which the real box will stand
3. Use bass mechanics disc to found your resonance (in my car is 53 Hz)
4. With box programs like Blaubox, etc make count the box which in that frequency is the loudest.(in my car is 4 cufeet each sub and ported in 45 Hz)
5. Make the box the larger your car can take the better results. Make that box total (if one subs need 4 cufeets use 16 cufeets for four subs)
6. Use 3 inch PnR port (flange port) use as many as you can (in my car I use 18 3inch port) and you must use the shortest possible (in my box I use 4 inch)
7. In the car test once more with Bass mechanics CD.( in my car the frequency is move to 56 Hz)
8. Retune your Box (with new frequency I use 16 3inch PnR port)
9. In my car with that steps I can hit 156 db with only 1 power
10. I use Crossfire DB12 DVC and 1 Hifonics Zeus Series 7