I use LPF on my amp, And the HPF setting on my head unit if thats what your referring to. And if you look in the first page of this thread, their is a picture of my amp. It doesnt allow you to set the LPF frequency. The only option I have is 80hz LPF, Off, and HPF on my amp. And on the headunit I dont have the LPF setting I have a HPF setting. ??