Correct me if im wrong on this theory.

HPF = High pass filter = Sends high frequency signals out to your speaker
LPF = Low Pass Filter = Usually for Sub, sends low frequencies to your sub/low
Bandpass = Mixed of the above

Before u fiddle with that, Know your speakers response range. If you put it too low you can risk spoiling a voice coil. too high and it will distort. If you still keep your manual for your speakers, then u can play around but never go below its FS.

Sifu here can correct me if im wrong. I also budak baru belajar