Originally Posted by OllieS
My question has to do with summing or cancellation of bass. In the Triad thread Paul Scarpelli said that if a speaker response is superimposed on to the subwoofer response you end up losing bass.
I'm just trying to understand why this is. If hypothetically I had a 5 speakers that had a -3dB 40 Hz, set my processor to a 40 Hz low-pass, with a 24dB/octave and the subwoofer itself had a -3db of 30 Hz dialed in to 70hz, what can I expect from this set up? Huge cancellation? I asked this question in the other thread but I would be interested to know as my buddy has his system set up this way and he swears by it.
If you were to set an AVR's crossover to 40Hz, the only overlap between the speakers and sub would be in the octave above and below that crossover setting, and that overlap is supposed to be there in order to provide a smooth transition between the subwoofer and speakers. That is what a crossover does.
And you wouldn't want to set the subwoofer's own low-pass to 70Hz. There is no reason to do this. You'd want to set that as high as possible or completely bypass it if your sub allows that. The AVR provides the proper low-pass to the bass-managed bass that is sent to the subwoofer. The LFE channel can contain info as high as 120Hz. You will truncate this info if you set the sub's low-pass to 70Hz. And you could also create undesirable issues if you "cascade" the AVR's low-pass filter and the subwoofer's low-pass filter like that.
If you wanted to configure a setup in the most "Geddes-like" way, this is how you would do it:
Connect the subwoofer to the AVR's front L/R channels either via the AVR's front channel pre-outs or, if you don't have those, via a speaker-level connection. Configure the AVR (or allow Audyssey or whatever autoCAL/EQ your AVR has to configure it) as having NO SUB (sub OFF or whatever your AVR calls it). Adjust the subwoofer's own low-pass to the front speakers' natural roll-off. You can do this by ear or with measurements, if you have the capability.
With this configuration, the LFE channel and any rerouted bass from any speakers set to SMALL will be mixed in mono and split into the front L/R channels. This mix of bass will then be spread across the sub and speakers at reproduction. The front speakers will reproduce that part of the front L/R channel bass + the LFE channel + the rerouted bass from any speakers set to SMALL, that they are capable of down to their low-end roll-off. Since its low-pass would be adjusted to the speaker's low-end roll-off, the subwoofer would take over and reproduce that part of the front L/R channel bass + the LFE channel + the rerouted bass from any speakers set to SMALL, below the speakers' low-end capability.
Bear in mind that many people here in these forums would strongly disagree with setting up a system this way. It goes against much of the conventional wisdom regarding the benefits of "normal" bass management. The front channel amplifiers would now be burdened with reproducing not only the bass of the full-range L/R channels but the full LFE channel bass and rerouted bass from any speakers set to SMALL, as well. Likewise, the front channel speakers would be asked to reproduce this same mix of bass, too. In relying upon the front speakers for so much of the low-end info's reproduction, you also remove some potential placement flexibility that a subwoofer (or subwoofers) affords.