Originally Posted by BSHuff
Would the AVR not provide a high pass filter/crossover if using the subwoofer out port? I would agree if you were trying to send full frequency to the sub could cause a lot of problems. The DSP would provide it with a lot more options and tune ability, but if you were using a decent AVR should it not have a crossover on the sub out outputs?
I think you're confusing High Pass with Low Pass.
Low Pass passes everything lower than its setting
and attenuates higher frequencies, usually set to roll off somewhere like 60-120 Hz. Your AVR should be able to do that. A High Pass works the other way. It passes everything higher than its setting
and attenuates the lower frequencies, usually frequencies below 30 Hz, and in Home Theater setups can work much lower.
A ported subwoofer will unload below its tuning frequency and can be damaged with very little power. If you have a ported box tuned to 25 Hz, you should set a High Pass to attenuate or cut everything below that.
In the first graph, excursion is plotted with a 25 HZ tune. Note that with no High Pass filter in place, excursion shoots upward past Xmax below about 20 Hz. Some movies have content below 20 Hz which can damage the driver.
In the second graph, a High Pass filter set at 22 Hz attenuates the signal below that setting (thereby reducing excursion), and keeps the driver safe below tune (as safe at it would be at any other frequencies, as it can still be damaged by too much power).