Breaking in a new sub?

You could have your amp gain all the way down and it could still clip. The gain on an amp IS NOT a volume control.

Turn the gain all the way down.  While playing one of your favorite CD's, continually turn up the HU until the volume, instead of increasing with clarity, instead starts to sound slurred.  That's distortion creeping in.  So then turn the HU volume back down a notch until the sound is clear again.  Make a note of the volume setting, because that will be the max from this point on.

note, if the amp is only powering a sub, you will have to find the distortion level of the HU using the other speakers instead.  The power of the HU may not be strong enough to hear distortion just from the sub.

Leave the HU setting where it is, and slowly adjust the amp gain up until the same thing as before happens (except now it will be LOUD).  Once you hear that distortion out of the subs, then turn the amp gain back down a little until it is clear again.  At this point the music is maxxed out, so you see why you would want to break in the woofer for awhile before setting gains.

The gain has been properly set, and you can nnow turn the HU volume down before your eardrums burst.

Note, when setting more than one gain (2 amps, 4 channel amp, etc.), you unplug the inputs of all but the gain that you are setting.

Make a note of the HU max setting, and don't let anyone turn it up past that number!