butt-woofer 

subwoofer located underneath the butt

see also booty-buzzer for feminine version

I was looking at an ad in the newspaper for one of those game rockers with the speakers in the headrest & all - then I noticed it said 'built-in subwoofer' and I thought "Now just where exactly would they put that particular item?" and might there be another word for it that would leave no doubt as to the nature of this feature. 'Built-in subwoofer' my ..., it's a

*BUTT-WOOFER*

butt-woofer by 1OO1 December 9, 2008