JBL Stage Series A120P 12" 500W Subwoofer - 32hz to 150hz, this ones running for top honours
Taga Harmony
BIC America F12 - the lowest it goes is 25hz which indicates it runs out of steam much earlier
Polk Audio XT12 - So good they didn't bother with its frequency response
Polk Audio HTS12 - -3db @ 28hz and 22hz lowest, its fallen asleep before the svs reaches -3db @ 19hz not to mention the 320watts of headroom the svs has at peak power
All subs go below 20Hz question is how will you experience that? Our ears are not meant to perceive sound below 20Hz. You will have to be in physical contact with the subwoofer. As far as audio is concerned I think 25Hz is enough for a subwoofer if it produces that well. Ported subs will never go near 20Hz as you will keep the volume level accoridng to the tuning frequency and any frequency below that will give very slight effect.