SVS is probably the only manufacturer using a HPF on their subs. I don’t know about that. The Klipsch RP-1600SW James reviewed recently also appears to have a HPF. Its rolloff is certainly steeper than 24dB/octave. The RBH SX 1212P/R and XTZ 3X12 measured by Josh Ricci also used HPFs. If a disc contains tracks with extremely loud passages at frequencies below 15 hz, that could create a problem but this would not be a really audible musical signal. Who said anything about audible musical signals? Movie soundtracks can and occasionally do contain some crazy stuff.
