Pwest if you are a crafty guy, grab the;
Parts Express / Dayton 1cu^ft Subwoofer box Parts Express / Dayton 500w RMS BASH Sub Amp TC-Sounds TC-1000 12in sub
In a sealed enclosure you will get anechoic fs of 20-22Hz 92dB and dive as deep as 15Hz no problems.
It will cost about $463 after shipping to do this.
~Bob