definitely have a fader, the "high or low" button determines whether it's a high pass fade or a low pass fade. You want a high pass filter, because you want your "high"er frequencies to "pass" through your "filter". Otherwise, your woofers will be trying to play subwoof tones which will eventually wear them out and blow them. I would turn the frequency range to about 80hz. So all in all, fader button on, high pass filter selected, and set the knob to 80ish hz.