Thank you Duke for the explanation. My sole purpose for using subs in a system is frequency extension and foundation for the main the speakers not the strategies you mentioned...
IF subs could help an arguably too-small room sound more like a big room, would that be potentially useful?
...nor do I understand how it works physically when the speaker cone, membrane, etc. can only operate moving front to back or back to front never seen them move sideways, how’s 30/60/90 degree phase inversion physically achieved?
The movement of two cones in "phase quadrature" would be 1/4 of a cycle apart in time. When one cone is halfway through the cycle, the other cone is either 1/4 of the way through that same cycle, or 3/4 of the way through that same cycle. By way of imperfect analogy, they dance the same dance but one is always 1/4 of a step behind the other.
In room low frequency cleanup in this manner is basically bass canceling which usually comes at too high a price sonically when high end speakers with articulate bass are involved and I don’t think that this is what Ron is looking for, at least not at this point.
Bass cancellation to smooth out bass response is a different thing which I find problematic at best and definitely not something I’d go for in a high end system.
Imo you just put your finger on the heart of the matter! But I think you are missing one critical piece of information:
Bass cancellation is inevitable!
You cannot choose between having cancellation and not having it; you can only choose between ignoring it and doing something about it (and most of us ignore it because we don't realize it's happening). Bass cancellation is what dips in the in-room frequency response are caused by. All non-anechoic rooms have them.
In-phase reinforcement is not exactly desirable either. That's what creates in-room peaks. Perceptually, peaks are even more objectionable than dips.
The way to minimize cancellation would be to use one big sub in a corner. This will give you the deepest and loudest bass, but it will also be very far from smooth.
A fairly even distribution of cancellation and reinforcement results in smooth bass, and "smooth" bass = "fast" bass. So what we are trying to do with a distributed multisub system is, deliberately and intelligently manage cancellation and reinforcement, because both are inevitable and too much of either is undesirable.
There is no perceptual price that is paid in "articulation" when you smoothe the in-room frequency response via a distributed multi-sub system. The ear does not hear the "leading edge" of bass energy. The ear responds too slowly to the presence of bass energy to do so. What it DOES hear are the higher harmonics (perceptually that's where the "leading edge" comes from), and it also hears the in-room frequency response. As I previously explained, the ear actually has a heightened sensitivity to frequency response in the bass region relative to the rest of the spectrum, so this is the most important issue from a perceptual standpoint. Decay is directly tied to frequency response in the bass region - if a note is taking too long to decay, it is because there is an in-room peak at that frequency. Solve the one problem and you have solved the other.
I readily admit that the whole idea of a distributed multi-sub system seems highly counter-intuitive at first glance. The question is whether it actually makes a worthwhile sonic improvement, which of course cannot be established with words. But it might be useful to look at this from another angle anyway:
With a single subwoofer, in-room peaks and dips with a spread of plus or minus 8 dB are not uncommon. Let's say your worst peak is 8 dB above the "average". And let's say we can tolerate a bass peak 3 dB above the "broadband average" of our main speakers before that peak "blooms" too much. So we set the level of our subwoofer such that the peak is not objectionable, which puts the "average" level of the subwoofer region (which was 8 dB below that peak) about 5 dB down relative to the rest of the spectrum. So we'd be missing out, but this is usually preferable to turning the sub up louder and cringing whenever that peak is excited.
With a good distributed multi-sub system, our in-room peaks and dips will typically be about plus or minus 3 dB. Now we can turn up the gain on our subwoofer amp and get our 'average" bass region SPL to approximately match the "broadband average" SPL of our main speakers without the remaining small peaks being objectionable, so we are no longer missing out.
One alternative method of getting this kind of in-room smoothness is to use a single sub and rely on equalization, which has this drawback: With only one sub, the more we use EQ to improve the in-room frequency response at one listening location, the worse we are making the frequency response elsewhere in the room. This is because the room-induced peak-and-dip pattern is significantly different at different locations in the room. With a distributed multi-sub system the frequency response is much more uniform throughout the room, so that if we do still have a problem frequency, chances are it's a "global" (throughout-the-room) problem rather than a "local" one... which actually makes it a very good candidate for correction via EQ! In other words, not only does a distributed multisub system reduce the in-room peaks-and-dips, but it also reduces the variation in that peak-and-dip pattern from one location to another throughout the room. And EQ can make a distributed multisub system better for everyone in the room, not just for the sweet spot.
IMHO the "natural" school of thought in WBF will not appreciate this idea [using phase quadrature on laterally-distributed subs to synthesize the impression of being in a larger room]
When we reduce the signature that our small rooms super-impose on top of the recording, we hear more of the recording and less of the room. This is difficult to do in the bass region because the wavelengths are so long, but the phase quadrature technique is one way of making an improvement in this area, by "pushing back" the walls of the room much like professional room treatments can do higher up the spectrum.
So in one sense it's not natural, but maybe it actually
sounds more natural.
...I could not expect [David] would endorse a technique that adds artificial hall ambience and spatiousness from recordings with mono-summed bass.
That's a perfectly reasonable argument, but sometimes the ear does not PERCEIVE the way the mind reasons.
Please click on the link at the bottom of this post, and scroll down to the section entitled "The Spatial Effect." It's only a few paragraphs long. The writer is a mathematics professor at UCLA and a concert violinist. (The last time I spoke with him in person, Robert Greene was developing the nineteen-dimensional mathematics that will constitute the theoretical foundation for the next step beyond string theory.)
Assuming you already have at least two subs, you might even try it and see if it sounds more or less like you are hearing a live performance. If not, it is easily reversible.
Probably not when you put it that way but I’m still curious, might be another tool in the tool bag for a H/T room.
Another tool for the bag is the most I could hope to convey to an industry professional.
If your system is already as close to perfect as you can reasonably imagine, then YOU have no need for anything I have described. But if you have a CUSTOMER who is fighting a losing battle against a small room, having another tool in your bag is not a bad thing! (If you are ever in that situation feel free to contact me, don't worry I won't try to sell any of my stuff to anyone involved.)
Below is the link to Robert Greene's review, read it as a commentary on the distributed multi-sub CONCEPT, rather than as a commentary on a particular product. For the record, TAS went on to give the system a "Product of the Year" ("POTY"??) award, so presumably some of the ideas it embodied had some merit. But those ideas could be even better implemented via state-of-the-art subwoofers. If nothing else, take a look at the section entitled "The Spatial Effect":
http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/
David Griesinger has patented this technique, we can find some detailed explanation in his patents.
