Good HZ for a Ported Box

The "subsonic" filter should be set just below Fb in a ported enclosure.  If it is set above Fb, you will never achieve max SPL from the enclosure.  You do not want to drive a woofer too hard below Fb, however, as the speaker is unloaded below that frequency and is basically running in free-air.  If your enclosure is tuned to 36 Hz, the "subsonic" filter should be at least 18db/octave and set around 30Hz, in my opinion.Support the12volt.com

Which I will agree with as usual and add to it that 36hz is a great tuning frequency, for that matter so is 31.75 and you will probably never be able to hear the difference as it is less than 1/2 octave down in frequency. A noticeable difference in tuning frequencies for the most part (not all the time) will come when you are tuning by a full octave in bandwidth. So if you a tuning point of 36hz, a new tuning point of 18hz would be one full octave down and produce a noticeable difference provided the amp can provide the current to drive the sub with enough amplitude for you to hear it.Top Secret, I can tell you but then my wife will kill me.