I use the FDeck (Francis Deck) HPF III all of the time. Literally. It removes the mud and boom from my bass tone, regardless of room dynamics. It saves my speakers from over-excursion. It is likely the best audio-related purchase I have ever made. Thanks, Francis!
PS learn all about it here: Review of new pre-amp/high-pass filter
Fdeck Hpf-pre Series 3
High-pass filter for bass amps