Don’t know much about THX myself, but according to this site it’s 24 dB. Not saying that’s gospel; it’s just the first thing I hit when I Googled “thx high pass.”Please correct me if I am wrong. Is the THX HPF (80Hz and up) not a 12dB/oct slope? Is the design not to work with the acoustic roll-off of THX speakers at 80Hz (typically 12dB/oct for sealed box) to become a 24dB slope?
I think it probably would be at audible. Anytime you cascade two filters on top of each other, the roll-out slopes combine for a steeper slope. I don’t see how it could be any different if one of the “filters” is acoustic. After all, the speaker can’t “ignore” the effect of the electronic filter.Prof's room (like my own) is small. I am not sure how the difference between 80Hz (HPF'd) and a natural acoustic roll off is so night and day.
In any event, actual extension with the speakers set for small vs. large would be easy enough to check with a sine wave at something like 80 Hz or perhaps a bit lower, and an SPL meter. If there is no change in a small vs. large reading, then the filter is having no audible effect.
Theoretically, if move the crossover point far enough beyond the speaker’s actual bass output, the effect should be inaudible.I wonder if Prof experimented with lowering the crossover from the THX 80Hz default back to 50Hz, rather than bi-pass HPF'ing altogether?