Originally Posted by superair502
No idea man I am asking. Actually I think it was 60 it's at
Absolutely no lower than 80 Hz (and I like higher) and here is why.....
Placing a sub in a sealed box raises the 'Q' (damping) and raises the resonance (peak in impedance). A 12" sub in a sealed box might realistically have a -3 dB down point (half acoustic power) around 40 Hz. That means it begins to slowly roll-off well above 40 Hz. At the other extreme the output is at about half power at the active crossover frequency and that means it has begun to roll off a little lower than that. You want, at minimum, a full octave of relatively flat subwoofer output. Otherwise you have generated no more than a narrow peak response. So you should place the crossover at least a full octave above the sub/box - 3 dB point. Also, the meat (most perceived energy) of the bass material is from 50 to 80 Hz. You would like to see the subwoofer capturing that span in its entirety.
Properly tuning a system is complex and the frequencies will change from boat to boat, system to system, and gear to gear. There is NO one set of tuning parameters that fits all....only a fixed prescription. But the above should give you a good beginning.