hey on the FI Q how low should i set the subsonic level?? and exacly what is subsonic level mean?? i got sealed box 2.3cf The sub-sonic filter removes bass frequencies that are too low to be heard by the human ear, hence the term sub-sonic, the main purpose of a SSF is to cut out low freq. to prevent damage to your sub when in a ported enclosure. If you enclosure is tuned to...say 32Hz...this means you are producing 32Hz at 0dB...as the scale drops below 0dB the sub has the potential of reaching an over excursion limit (cone will move more than it is made to) and in result you will damage you sub. The enclosure can not supply enough back pressure to support the suspension of the sub below its tuning freq. For sealed box, it is not so important, but for basreflex boxes it is, because speaker excursion goes rapidly up under vent tuning frequency. So you can blow your 1000W speaker with 200 Watts easily without smoke. The voice coil can hit the backplate of magnetic assembly or speaker cone can leave the basket and fly somewhere...; so if you want to have 30Hz in your music, you should tune your bassreflex box to 30-35Hz and cut it somewhere around 30Hz, because if 20Hz tone come, your speaker is going to crash when fully powered.