My Ultimax 15 is sealed so it drops off below 25hz pretty rapidly in my listening room. It wouldn't even occur to me worry about filtering frequencies below 25 hz.. It probably goes lower in a vented enclosure depending on your room. Since I use my system at normal listening levels I can't even see cone excursion from across the room. It sounds very powerful and looks like it is hardly working. I use a 300 watt plate amp in mine which has proven to be overkill. I can't help but think you are worried about things that shouldn't worry you.