It is actually a high pass filter for your subs. If you are running a ported enclosure it is extremely helpful to keep the destructive low frequencies that are below your tuned frequency away from your driver(s). It also increases your overall power handling and allows the amp to run more efficiently by reducing the power robbing low frequencies that can be produced in alot of today's music. You won't hear much difference because the frequencies it is cutting are usually low enough to not be heard. if you set the subsonic(infrasonic, same thing) to let's say, 40hz, then you will have 12db less at 20hz. That is if it is a 12db per octave slope. Can really save your system if used properly. Hope this helps.
ok so how i set it meaning what postion to turn the dial yes it is an ported box, i have the dial turn down.
Does the filter (dial) have any markings as to what frequency it is working at? And if you know what your enlcosure is tuned to that will help. Otherwise I would just turn it up all the way or damn close and listen to it. Most filters don't go very high. I would say to keep it below 35 hz unless you are tuned higher than that. then move it up some.
