Subwoofers and Phase Question For You Sub Experts

Ideally the sub should be crossing over from the mains at a frequency where localization isn’t possible rendering time alignment not critical. If you force time alignment, then you force maximum wave reinforcement in the listening position which negates the point of a distributed bass array to even out frequency response by negating room modes.

Ideally the sound from the sub should reach the listening position at exactly the same time and at exactly the same phase angle as the woofers in the satellite speakers.

Duke, why dont you tell that to mijostyn? I was quoting him 

Audiozenology wrote: " If you force time alignment, then you force maximum wave reinforcement in the listening position which negates the point of a distributed bass array to even out frequency response by negating room modes."

My understanding is that the in-room frequency response (and therefore our perception) will still be dominated by the steady-state response, to which those initial arrivals obviously contribute, but their synchronization would not negate the benefits of modal smoothing. So I think that as long as we get good modal smoothing there’s nothing wrong with arrival time synchronization, but personally I wouldn’t trade off anything that mattered (including aesthetics) to achieve it. 

Duke

I go back to one thing.

I recommend the OP turn to GIK acoustics first. Ask them for advice on room and then see where he's at.

Best,
E

These three different approaches (bass trapping, EQ, distributed multisubs) each do something different. The goal is "smooth bass", because "smooth bass" = "fast bass"; it is the peaks in the in-room frequency response which decay more slowly and make the bass sound boomy or muddy or whatever, and each of these techniques contributes to "smooth bass" and therefore to "fast bass".

Bass trapping absorbs in-room bass energy which shortens the decay times and thereby reduces the magnitude of both the peaks and the dips everywhere in the room. (The in-room frequency response tracks the time domain response, and vice-versa, in the bass region.)

EQ is very good at reducing peaks but not so good at filling in dips, which are caused by modal cancellation, and driving that cancellation harder can eat up a lot of power and excursion (a 6 dB boost to fill in a dip would call for a doubling of excursion and a quadrupling of power). EQ of a single subwoofer is most effective at a single location, because the room-interaction peaks-and-dips will be at different frequencies for different locations within the room. So EQ can be great in the sweet spot, but it usually make things worse elsewhere in the room. In general the larger the listening area we try to fix with EQ, the less improvement we are able to make at any specific location within that area.

A distributed multisub system results in a significantly improved peak-and-dip pattern. Each sub contributes its own unique peak-and-dip pattern, but each sub is only contributing maybe 1/4 of the total bass energy, so the net result is many small peaks and dips instead of a few large ones. This can have a non-obvious psychoacoustic benefit: When a peak and a dip are fairly close to one another (within about 1/3 octave), the ear/brain system averages them out. So the perceptual improvement tends to be greater than what we would infer from eyeballing before-and-after curves. And this improvement is not limited to a given location, but extends throughout the room.

Obviously there are differences of opinion about how much subjective improvement each of these approaches offers, and the devils are probably in the details.

But as you can see, these three different techniques are almost asking to be used in combination, as each does something different that is beneficial. The reduced spatial variation of a distributed multisub system makes EQ much more effective over a large listening area, and bass trapping provides smoothing regardless of what else you are doing.

Duke