What does a subsonic filter do? How does it work? I was told to ask you that you would know. Also I heard that JBL amps don't have any. Is that true? Thanks alot Glasswolf
corrent the JBL BP series amps have no integrated SSF.
a subsonic filter is a high-pass filter that blocks frequencies below a specified point, usually a little below the tuned port frequency of a ported box. The purpose for this is twofold. 1: the SSF prevents the amp from trying to reproduce frequencies you can't hear anyway, and thus wasting otherwise useful power from the amplifier. 2: in a ported box, if you try to reproduce frequencies below that of the port's tuned frequency, you lose the damping factor of the enclosure, and by doing so, the sub can over-excurse (go past it's mechanical Xmax) and damage the sub easily. The SSF prevents the amp from sending frequencies below that point to the sub(s) and thus protects them when used in a ported box.
In a sealed box, this isn't a factor, and the SSF isn't necessary. A sealed box in a vehicle has a flat response down to about 9Hz after you factor it transfer point and cabin gain.