Setting my subwoofer cutoff frequency

Most HT receivers have bass management of some kind. For most low/mid-fi receivers that I've played with, the cutoff frequency was fixed by the receiver at 80 or 100hz. If you have your receiver setup set to SUB=yes/on, it is likely that the receiver is "fixing" the low pass filter for the sub/LFE out port.

If this is true, changing the cutoff frequency at the sub will have no affect. Most manufacturers suggest setting the sub cutoff freq. to max. in this configuration. Since the receiver is controlling the cutoff, there is no reason to set it at the sub. Just set it to max (125hz?) and forget about it.

TIC

Typically, the subwoofer's crossover knob only has an effect if you are deriving the subwoofer info. Which is to say, running the main L and R signals through the sub then into the L and R speakers.

Most subs have an alternate method of hookup, the "LFE" mode. In this case, as mentioned above, the crossover is handled by the receiver/processor. The crossover knob on the sub is disabled. This appears to be what you are running into. Dig into the owners manual of your Denon to see if you can tweak this. Typically in that type of receiver (not higher end), you cannot adjust the crossover. If it's really bugging you, you can purchase external crossovers from companies like Paradigm.

I have the same sort of situation you have, Steve, although I don't use a receiver. I run a separate line-out signal to the sub(Velodyne 1500R) and can adjust the crossover frequency to suit my taste. The sub is not tied to my main speakers (ADS 1590's). Admittedly, there could be some bass overlap here if you get the crossover too high, so let your ears be your guide. Good luck.