How do I know what to set my SSF to?

The Fs of my sub is 36.4Hz

Box is 2 cubes tuned to 38Hz

FS of my truck is 37Hz

I can give you any T/S params you need, or you can get them from here:

http://www.mtx.com/caraudio/products/subwo...ta_T9512-44.pdf (PDF file, 693KB)

A direct answer of what to set it to is fine, but I would like to know how to calculate it, or at least a "rule of thumb" to go by when setting the cutoff frequency.

Normally you want it set right around the tuning freq, there is no formula for figuring it out. Below tuning the enclosure will actually push and pull the speaker farther than it would travel on its own. This can lead to damage to the sub as the limits of the suspension are quickly reached at really low frequencies. The purpose of a susbsonic filter is to keep these frequencies from getting to the sub.

Normally you want it set right around the tuning freq, there is no formula for figuring it out. Below tuning the enclosure will actually push and pull the speaker farther than it would travel on its own. This can lead to damage to the sub as the limits of the suspension are quickly reached at really low frequencies. The purpose of a susbsonic filter is to keep these frequencies from getting to the sub.

In my many years of designing enclosures I have found that 5Hz below tuning frequency is about right for any given enclosure---the -3dB roll-off should be around 5-10Hz below tuning frequency anyway---so 5-10Hz below tuning for the sub-sonic filter should be ok.

Thanks. I think I'll set it at 30Hz. Nothing below 30 sounds good anyways. Will I be ok with a 12db/octave rolloff, or should I go with 18?

set it where the sub over extends and the tone is below your hearing range,