i listen to all kinds of music from heavy bass line stuff to low signal stregth mp3's of random other shit....so i have a large range to know when to adjust to every time.
here's the trick. you'll notice as you turn the gain up (HU at 75%-80%) the sub will get louder until it starts reaching it's mechanical limits. if you turn up the gain any more, it'll seem like it's only getting only very slightly louder (which is clipping territory).you have to train your ears to recognize the sound intensity of where that plateau starts at. if you turn up the gain and notice the amount of output your getting isnt increasing very much, vs. the amount you're continuing turn the gain up....then you know to you have found that plateau, and bring back the gain just a hair.
when you get comfortable enough with the sound of your woofer, you can have the remote knob act as your full gain range, and tune specific per song. that being said, be careful when the track changes and the new song has a more intense bass line or you might piss off your subs...
