Originally Posted by cel4145
I've had a chance to think about this some more, and this method will never work well with the reasoning you are using (I'm ignoring everyone else's objections at the moment) unless someone has all identical speakers in a 5.1 or 7.1 setup.
Most people have front L/R speakers that are lower in frequency response than the rest of the speakers in their setup. So by setting the sub crossover to match the roll off of the front speakers, the sub is no longer producing frequencies above that. Thus, every other speaker in the surround setup will have a dip or hole in frequency response between say the -3db roll off of the front L/R and what the other speakers' -3db roll off is. For most people, that would be very undesirable in comparison to simply using the internal bass management of the receiver.
Right, but you haven't thought it through entirely. There are 2 ways to try and accomplish what commsysman is recommending. And there are issues involved with both methods.
#1.) If the subwoofer is to be connected conventionally to an AVR's sub pre-out, in order to send a full-range (LARGE) signal to the front channels as well as route front channel bass to the subwoofer, then a 'double-bass' setting (LFE+Main, LFE+, Plus, Double Bass, etc.) must
be used. Some AVRs allow one to still select a low-pass cutoff frequency for the front channel info which is duplicated at the subwoofer when this setting is used. With other AVRs it is a bit of a mystery as to what front channel frequencies are routed in duplicate to the subwoofer. At any rate, this is the only way to do what commsysman recommends while still using the AVR's sub pre-out.
And, yes, when using this setting ('double bass'), and adjusting the subwoofer's own low-pass filter to the front speakers' roll-off, you risk truncating and completely dropping the rerouted bass from any channels to which a crossover is being applied, somewhere between the subwoofer's low-pass setting and the crossover that is being applied to those other channels. But, more importantly, you will also truncate the LFE channel, which contains info up to 120Hz, at the subwoofer's low-pass setting. So, for example, suppose you were applying an 80Hz crossover to the center and surround channels while leaving the front channels running full-range with a 'double bass' setting. And suppose the low-pass value that was required at the subwoofer was 60Hz. In this case, all the rerouted bass between the sub's 60Hz low-pass setting and the 80Hz crossover setting from those channels to which an 80Hz crossover is being applied would be completely dropped and lost. And, everything in the LFE channel between the sub's 60Hz low-pass setting and 120Hz would also be completely dropped and lost. This is an entire octave of LFE info.
#2.) The other, and probably better, way to accomplish the setup commsysman describes would be to connect the sub to the AVR's front channels, not to the AVR's sub pre-out, and configuring the AVR as having NO SUB connected. This could be accomplished by either connecting the AVR's front channel pre-outs (if present) to the sub's L/R pre-ins or via a speaker-level connection from the AVR's front channel speaker outputs to the sub's speaker-level inputs (provided the sub has them). Then the AVR would be configured as having NO SUB connected. The subwoofer's low-pass filter would still be adjusted to the front speakers' roll-off. This NO SUB setting would reroute the LFE channel and any bass from those channels to which a crossover was being applied into the front channels. The mix of front channel bass, the LFE channel info, and the rerouted bass from those channels to which a crossover was being applied would then be spread across the front speakers and subwoofer according to the front speaker's low-end capability and the sub's low-pass setting. None of the LFE channel and none of the bass from those channels to which a crossover was being applied would be truncated and lost with this sort of setup. What this sort of NO SUB configuration does do, however, is that in addition to the front channel bass that is already being sent there, it routes the full brunt of the LFE channel into the front channels along with any bass from those channels to which a crossover is being applied. Depending upon the front speakers' capabilities and fortitude, this can be problematic.
Ultimately, though, there is really no reason not to use the bass management capabilities provided by an AVR. In doing so, there are multiple benefits to be had at the speakers, at the AVR's amplifiers, and at the subwoofer itself.