Thats what subsonic filters are for






Set your subsonic filter a little lower than your boxes tuning frequency (I usually go about 10-15ish hz under what my box is tuned to) and your usually safe from having the sub bottom out on low frequencies when you have the volume cranked.

Ive seen way to many mechanically damaged woofers due to ported boxes and no subsonic filters.
I hate installing setups for people who go buy a generic ported box (usually tuned way to high) and use an amp with no subsonic filter. Those are usually the people that just relentlessly crank their chit too. Tell them not to crank it on low low chit and even show them what to listen for, but I still see some of them driving around with that godawful 'clankclankclankclank' when it bottoms out