Eh hem!...Subwoofers... What do ya know?

Does anyone technically know what happens when you aim two subs at each other?  Say a foot or 2 feet apart .

What do you mean? In phase? Or out of phase?

Is there an ideal distance apart to do with frequency?

What do you mean? Are we still talking about pointed at each other? Why would you even want to do that?

Does it have an affect on the opposing woofer itself such as improving the rearward movement of each other? Would have to be a specific distance i assume . A possible equation ?

Only thing I can think you might possibly be trying to get at is what's been covered a zillion times, that waves propagate and bounce and reinforce and cancel, everywhere and all the time, and at all frequencies. And regardless of which direction they were pointed first.

Duke LeJeune is Da Man. Aka Audiokinesis, he has done more for this than anyone, which this will probably instigate a reaction owing to the fact his one fault is being blessed with an overabundance of modesty. 

Seriously though the research goes back to Dr Earl Geddes, and another whose name eludes me just now. Anyway, point being what Newton said, if we seem to see far it is because we stand on the shoulders of giants. These guys did the heavy lifting, the down and dirty grunt work of painstakingly measuring actual room modes in actual rooms with different numbers of actual subs in different locations. And then as if that was not enough they applied the brain power to first work out and then ultimately demonstrate- prove!- just how well lots of subs really does work.

Duke however is so much a part of the whole thing that not only did I learn about this from him here, but when I went looking for Swarm type subs and was able to find only two systems on the market, it turned out the other one was designed by Duke as well!

Anyway, congratulations! You did the research, asked the questions, learned what needed to be learned, and then had the courage to buck the trend and the trolls and do what's right. Good for you. Enjoy!

@davekayc I'm fighting a bass null at the sitting position so I wondered about, having the mains spread further apart but toed in at a steeper angle to limit low frequency waves going straight at the wall and being reflected back. Basically having the very toed on speakers sending low frequency waves at the rear wall at a steep angle vs nearly head on to negate the null.

Unless I move at least 38% of the way into the room (better at 50%) I sit in a mid bass null. I always thought the speakers were bass shy but the sub I've been messing with has the same issue so its clearly the room and not speakers. If I mive 3ft to the right of the couch/sitting position which puts me in front of the hallway entrance the sub is delivering THUNDER. Move back to the sitting position and its a little warmer at best.

Right. Same here. Same everywhere. Exact same situation in my room. 

The solution is, first move the main pair and seating position around listening for smooth but not necessarily deep bass. Just try and avoid the worst spot, basically. The bass we will fix later. Then at this point get very precise in tweaking placement for imaging. It is essential at this step to get the speakers exactly equidistant and toed in perfectly symmetrically. Finally, add four subs, one on each wall, wherever they can go but preferably no two the same distance from a corner.

What you will find, any single sub or speaker does exactly what you heard- lumpy uneven bass. Moving around only moves the lumps around. Adding more however creates lots of lumps that all together average out to really smooth. The wavelengths are so long and we hear bass so much differently that it hardly matters where they are, but it does matter a lot how many there are. So use more and the problem solves itself.

Do you have any experience using the Crawl Test for anybody locating less than four subwoofers?

This is the one where you put a sub in the listening spot and walk or crawl around looking for where the bass is best, and that's where you put the first sub. So there's your answer. Because the first step is simply repeated again and again until you run out of subs. 

I did try this and unsurprisingly all the best bass was in the corners. Which anything else would have been a surprise. Bass is always stronger near the walls than out in the middle of the room. No wonder when Tim did this he wound up with speakers in the corners. But that's not hardly even the point. The real point is Tim has great, awesome, impressive, bass that continues to please after many years, and with both movies and music. He does move his chair for music but that only goes further to emphasize the point that having a DBA means having great smooth bass that is not fussy when it comes to speaker or listening locations.

Thanks for sharing your knowledge. How would you determine crossover frequency and gain with less than four subwoofers?

Same as always- by listening! 

Oh, you can use meters too. But there's a problem with that. A really big problem. One that far as I'm concerned kills the whole idea of EQ. That being, meters measure sound all nice and flat and without regard to volume. But people don't hear like that. Really low frequencies we don't even hear at all until they get fairly loud. That's why they made the Loudness switch! Don't believe me? Look up Fletcher Munson Loudness Curves.

Got it? All those lines on the left pointed up and converging? What this says is, if you set your bass to measure flat, you will indeed be able to get it to measure flat, but you will NOT be able to get it to SOUND flat except at one volume level. Then even if you get it to sound flat, it will only ever sound really flat at that one volume level. Turn it up, it will sound like more bass. Turn it down it will sound like less. 

The only real solution is to listen. Listen a long time, and to a lot of music. Listen at or close to whatever volume level you use when you really want it to sound good. Tweak tiny amounts until you're happy. You'll wind up with a little more bass at higher volume, a little less at lower, but there's quite a range recording to recording anyway. 

Doing it this way takes a little longer and if you're one of those needs validation types sorry, but its the best we got.

gochurchgo-

I guess I’d have to see what “placed ideally” equates to. Some light reading have the impression that one on each wall was the answer. How true that is I do not know.

if 2 $500 subs are better overall than 2 $200 subs then so be it. I’m just genuinely curious  as the “4 is better than 1” motto never mentions “good ones“ versus “ones that should work ok”.

Highly recommend searching and reading just about everything posted by Audiokinesis. Awesomely succinct, won't take long, just don't read fast there's a lot to absorb.

The quality/quantity thing is admittedly a hard one and doesn't sort out nice and clean. There's overlap, where one kilowatt 18" REL might be better than four 8 inch Hsu tubes. But not if total cost is the same for both.

Better quality is always gonna sound better. When I told Duke which 10" Morel drivers I bought he had no problem saying mine will kill his. By and large though my sense of it is for the vast majority of choices out there four of just about any of them will beat any one you can buy for the same amount of money.

Put another way the typical Swarm type DBA runs around $2-4k and I just don't think there's any one or even two subs anywhere near that much that can come even close. Just look at the comments. Pretty much everyone who's done this says its the best bass they ever heard. Not the best for $3k. The best, period.

Duke even had a customer choose his Swarm, and he had I think a $20k budget. Not for the system, just for the sub. Coulda bought a $20k sub. Listened to subs in that price range. Thought the Swarm was better.

That's why this is such an uphill battle. As if the physics, psycho-acoustics, mono, and "integrating" aren't hard enough, you got to try and convince people the concept is so powerful it overrides the need for great big expensive drivers. Oh, and lamp cord will do just fine. Its just too much to swallow. Even though its all true. 

uberwaltz:
I use just one ML Dynamo 700w sub right now to compliment my Maggie's.
Strongly considering adding another though.
Room can really only handle two as far as placement goes.
Would a pair work diagonally opposite each other?
So say one front left, the other rear right or?

Say, does that Dynamo hum? Frank Zappa's did.

Placement is all about figuring out where to put one speaker to get the smoothest response at the sweet spot. With more subs it matters less and less where they go. You actually want them different places, particularly asymmetrically different places, because the more different sources the more different modes and they all average out to much, much smoother bass.

With my 5, one is front wall left, two on each side wall, and they are each a little bit different distance from the corners. Tim on the other hand (noble_100) took a more systematic approach and wound up with one in each corner. His room is almost exactly same as mine, like within about a foot each way. His listening is closer to the back wall, but as I recall its dual use, he sits more to the wall for movies, further out for music. Loves it either way.

Stories like his, plus my experience, and Duke's, all agrees with the early papers (Geddes, et al) conclusion of random or at least asymmetrically located is best. 

With 2 I'd put the second one diagonally opposite and spaced a little closer or further from the corner than the first one. With just two you might hear a difference moving them around. The more there are, the less it matters where they are.

1) From what I read here, it seems like multiple in-wall subwoofers would be a good swarm solution...yes/no?

Yuck! The beauty of DBA is quantity matters more than quality. But, come on! A man's got to know his limitations.

2) Millercarbon: what subwoofers do you use for 16ohms?

Morel 10", which are a nominal 8 ohms each. With four subs and two amps you can get a total 4, 8 or 16 ohms simply by changing the way they are connected to the amp(s). 

@millercarbon - do you run your array in mono? Just curious.

The smart-alecky answer would be yeah, because all low bass is mono. Seriously. It is.

Which I know from Duke reporting on what's his name Floyd O-Toole? Or the other one? Whatever, the car audio engineer who analyzed a couple hundred recordings and they were all mono so he called it good and designed for mono bass.

Me, having 2 Dayton amps allowed trying stereo, 2 on each side, and two per amp. Also tried mono. Tried mono connecting all 4 to one amp, mono 2/2. These were all different. But not because of stereo/mono. Because, all low bass is mono. Oh there may be an exception out there somewhere. He only tested a couple hundred, after all. So if anyone reading this finds one send it along, as nobody who's looked into it has found any, they will think its cool. 

What does make a difference though is impedance. Wired 4 ohms the bass is just a bit tubby to my ears. Wired 8 ohms the bass is not so tubby. Wired 16 ohms the bass is tight, taut, articulate, like way better than anything I ever heard anywhere else. Not lean. Plenty full. But fast. Clean. Maybe even a tad more dynamic.

Technically you do trade off some peak power, so if those last few dB of volume really matter and you like really full round bass then wire for 4 ohms. 16 to me is so much more articulate and tuneful, and I like that enough to put up with the occasional clipping when the movie effects go boom.

In terms of stereo/mono though one of the more amazing parts of the whole DBA thing is the way such low bass, which we really cannot localize, nevertheless somehow manages to image so well. I can only guess that what happens is when the low bass is this good then when we get the location from the midrange it blends seamlessly into one whole and so it seems the bass is as much grounded in a real place as everything else in the sound stage.

This is a whole different thing from the way midrange on up works. Anything much above 120, 200, somewhere in there, if its mono its gonna be between the speakers. Where exactly, not my thing. Duke would know. Duke knows everything! (Seriously.)

For those who haven't heard this (DBA) I don't want to give the wrong impression. Its not like the bass is always imaged the way everything else is. Sometimes the bass is completely enveloping in a diffuse, this is just the size of the room kind of way. This I think is one way really good bass improves imaging, by extending it to the point you are enveloped in it. But its also something that is very recording dependent. If its not on the recording you aren't going to hear it no matter how many subs or what kind. Sometimes when listening its like man are my subs even on? When it is there on the recording though, wow!

If subs aren't the most misunderstood thing in audio, I sure don't want to know what is!

Take me. Been into audio since the early 70's. Built my first amp in high school. My first speaker was a transmission line in 1978. Thought I knew all about sound and even so never could get really good bass. Thought it was physically impossible.

Until about this time last year, when quite by accident came across some posts about the Audiokinesis Swarm and started reading articles on the physics and psycho-acoustics of low bass and something called a distributed bass array.

This sounded promising and so after reading a ton of both technical theory type articles as well as feedback from experienced users I decided to take the plunge and built my own distributed bass array.

Based on the same Dayton amp and 10" drivers and cabs similar to the Audiokinesis Swarm this has turned out to be probably the most revelatory improvement ever. 

Combining reading and theory with a lot of hands-on experience this is why I say its so misunderstood. Almost don't know where to begin.

The problem of integrating bass isn't in which sub is used. Its in how many. Every sub no matter how good or how crap has the problem of room modes: some areas too loud, some too quiet. Most try to solve this with more power, or EQ, neither of which does anything but make the fundamental problem- which is physics- even worse.

With lots of subs (I run five) no one individual sub has to put out much power. So they all produce modes, but different modes in different areas because the subs are all over the place. All these small modes average out and the result is impressively smooth, fast, articulate and deep bass.

Integrating or matching with speakers is a non-issue. Read the reviews, the bass is so fast its a match for electrostatic speakers.

Low bass is non-localizable. But read that carefully. That means only you cannot tell where the subs are located. It is as if they don't even exist. It does not mean the bass they produce is unfocused. Quite the contrary, the sense of 3D location of bass is even more focused than anything else I've ever heard.

Location with one sub is everything. You can spend a lifetime moving here and there trying in vain to find the magic location with smooth bass. Placement with a DBA is trivial. You can go the Full Monty if you want. You might even notice an improvement. Or you could just plop them down one near each wall, bothering only to not have them be symmetrical, and congratulate yourself on your expert placement. Either way, state of the art bass.

Almost everything people "know" about bass is wrong. Take timing. Experiments show we cannot even hear low bass at anything other than a full wavelength. That means a 20 Hz wave has to last 0.05 seconds or you won't hear it- at all! Midrange though you can hear in a tiny fraction of that. The same timing that is crucial to imaging and midrange on up simply does not apply at all to sub frequencies.

I could go on and on. Which I tend to do, both because this is so important as well as its really hard to understand. Took me a few weeks of research to really be sure myself. Sure enough to invest $2k anyway. Which is a stone bargain. Nowhere else in audio can you blow away so much expensive gear so easily for so little. Provided only that you actually understand what it is that you're doing.