[jtwrace]

As a follow-up to an earlier post, Earl Geddes wrote his doctoral thesis on small room acoustics primarily in the modal region back in 1980.  I don't know at what point Earl came up with the idea of multiple subs asymmetrically distributed, but he's on record as saying that all of his thinking on low frequency reproduction in small rooms ("small" meaning "any sized room that you'd find in a home") goes back to that study.

Yep.  There is no doubt this by far the best way to do it. 

[jriggy]

Took a while to get noticed but finally you are getting the accolades you deserve.   

Seems like I have had the Swarm V2 for years.  Great with Soundlabs in an untreated room.

I had the same thought!
I have been interested in The Swarm for years. My personal audio evolutions moves slowly, like many others must, I presume. But it does seem like this should of gotten some praise from the professional review world years ago.

[Larkston Zinaspic]

It's funny that when I mentioned The Swarm a number of years ago on another audio-centric discussion board, i thought people would be just as interested as I was, but those guys just stamped all over the idea...and a certain audio engineer who frequents this forum, responded with: "I'm sorry but this sounds like an audio salesman or an audio reviewer speaking. I read it as saying if we create enough problems, the ear won't be able to just focus on one or two. (With several randomly placed subs -vs. one deliberately placed badly - I can see why one would think this way.)"

It didn't quite have the snob appeal they were looking for, because then they might have to challenge their own firmly held beliefs if it actually worked.

I wonder how often Duke had to deal with the obstinate response, "I can localize every one of those subs blindfolded" whenever he tried to demonstrate the theory. If at first the idea is not absurd.....

Either way, good to see Duke getting props and hopefully the trend will continue.

[atmasphere]

Congratulations Duke!

Folks, Duke is one of the best reasons for high end audio. 

[Duke]

Thank you very much, Russell and woodsyi and jtwrace and jriggy!   I really appreciate your votes of confidence, coming from your experienced backgrounds.

And thank you too Ralph, top in your field!

It's funny that when I mentioned The Swarm a number of years ago on another audio-centric discussion board, i thought people would be just as interested as I was, but those guys just stamped all over the idea...and a certain audio engineer who frequents this forum, responded with: "I'm sorry but this sounds like an audio salesman or an audio reviewer speaking. I read it as saying if we create enough problems, the ear won't be able to just focus on one or two. (With several randomly placed subs -vs. one deliberately placed badly - I can see why one would think this way.)"

Thank you for your kind words and for sticking up for the Swarm on another forum!   Can you tell me where that was?  Unfortunately I missed out on the discussion you refer to, but would welcome the chance to reply to analysis and critique from an engineer or anyone else interested enough to discuss the subject. 

Actually the observation bolded in your post, presumably made by the engineer. is the beginning of thinking in the right direction.  He doesn't come to the right conclusion because he stops too soon, but the acoustic effect of using multiple distributed subwoofers is a much denser peak-and-dip pattern in the modal region.  This is analogous to what happens in a large room vs a smaller room... and it sounds better for the same reasons.   Those reasons are:  1) The more dense the peak-and-dip patterns the smoother their sum becomes; and 2) the closer together the peaks and dips (another way of saying the same thing), the better the ear/brain system's a 1/3 octave "critical band" averaging mechanism can average out those peaks and dips.

The engineer's intuition leads him to make an understandable mistake:  he assumes that a few peaks and dips are less audible than many peaks and dips, when in fact the opposite is true.  The reason we don't hear major coloration from room-induced peaks and dips over the upper majority of the spectrum is, those room-induced peaks and dips are bunched up so close together that they effectively form a continuum and the net room contribution is essentially the speaker's power response. 

As far as being able to localize every one of those subs blindfolded, that's a setup issue, and isn't a problem if the lowpass filter on the subs is steep enough.  It might still be possible to localize them with a carefully chosen test tone, but not with normal program material. 

[Duke]

I found the forum that Larkston Zinaspic mentioned, it's Steve Hoffman's forum.  I joined up and attempted to post a response, which will hopefully make it past the moderator(s).

Anyway, here's the guts of what I wrote:

"Unfortunately I was unaware that my Swarm multisub system was being discussed here several years ago, as I would have liked to participate.

"If the topic is still open for discussion, I would like to propose a thought experiment.  There will be some simplifying assumptions made, as reality is always more complex than its models, but the idea is to illustrate some of the principles involved.

"Imagine you have a single subwoofer, covering the roughly 1.5 octaves from 60 Hz down to 20 Hz.  And let's say that within this passband you have one big (+6 dB) peak and one big (-6 dB) dip at a given listening position.

"Now let's add a second subwoofer to the room, in a significantly different location.   Let's assume that it also has one big +6 dB peak and one big -6 dB dip, but because this second sub is in a different location, its peak and dip occur at different frequencies at our listening position.

"The sum of these two dissimilar peak-and-dip patterns will have smaller peaks and dips than either one alone, and more of them (four instead of two).  The ONLY WAY that the +/- 6 dB response of the first subwoofer by itself could be preserved would be if the second subwoofer had identical peaks and dips at the exact same frequencies.  So with the addition of our second sub in a different location, we now have improved on the +/- 6 dB situation.   I think that the most improvement we could ideally hope for in our hypothetical would be to +/- 3 dB, and realistically we'd probably end up somewhere in between.

"Now let's add two more subwoofers.   The same smoothing effect would apply, and we'd now have possibly as many as eight smaller-still peaks and dips, though in practice it may not be that many as there would probably be some overlap.

"Anyway the general trend as we add more independent bass sources is a smoothing of the frequency response at any given listening position.  In addition, the spatial variation (variation from one location to another within the room) is also reduced.

"I have multiple Swarm customers reporting in-room response of +/- 3 dB across the bass region without EQ, and they are reporting that this improvement holds up over a wide listening area.

"That is the general acoustic theory; there is also a psychoacoustic aspect that we can look at."

[tesseract]

So many are stuck on the Welti / Devantier approach and still having issues. I've been pointing to you, James, Earl and the Swarm for years. I don't think it generated any sales for you guys, but I mostly wanted people to soak up some of that knowledge and apply it to what they already have.

Speaking of which, I am going to be in the market for a sub upgrade later this year, and the Swarm is at the top of my want list. I already have the amp and the system will fit unobtrusively (unlike my 250 lbs. worth of dual 18's  ) into my space.

Congrats on the recognition, Duke!

[JoshK]

Congrats Duke!   I am glad some are taking notice of good ways to address room acoustics rather than just the sorry old audiophile way of ???

I am planning to do something very similar with my HT room downstairs.   

[CometCKO]

Duke, congratulations on the much-overdue appreciation for this thinking.  I've been extremely happy with the early version Swarm system you sold me to work with my Maggies.  It also is a nice complement to the Prisma's! (as if they need all that much help).

It does seem like a crap-shoot when journalists get hold of you.  Hopefully this one works in your favor.  Here's one of the scattered boxes pretty close to a Maggie in my office.

[Duke]

Thank you, tesseract and Josh and Comet!

That early Swarm did have a nice narrow footprint, and I can see that it comes in handy, Comet.   Thanks for posting that image.   If the day ever comes that I figure out how to do a "mini-Swarm" and make money on it, I may try to replicate that narrow footprint for its versatility. 

Jim Romeyn's "Debra" subwoofer system uses a rectangular footprint, not quite as narrow as the first-generation Swarm, but still more versatile than my square footprint.

[Doublej]

Duke,

Thanks for the explanation. It makes sense to me. My question is, how close can one get using signal processing on a single sub to smooth out the peak and null?

[Duke]

Duke,

Thanks for the explanation. It makes sense to me. My question is, how close can one get using signal processing on a single sub to smooth out the peak and null?

A single sub can be equalized to be quite smooth at one microphone location, and it can be equalized to offer a compromise improvement over a listening area.  The larger the area, the less effective EQ will be a getting a good compromise over that area.

The problem with trying to equalize a single sub is, the peak and dip pattern changes significantly as the listener (or microphone) location changes.  And unless you are addressing a problem that is global (throughout the room), it is pretty much inevitable that EQ which significantly improves the response in one location will make it worse somewhere else.

Whether the more limited listening area of an equalized single sub works for you is a matter of personal taste.  There are quite a few good room EQ systems out there, and some have algorithms that can give improvements over a listening area, but I do not think they would be as effective with a single sub over a decent-sized listening area as a good multisub system.   The multisub configuration is an acoustic solution to what is fundamentally an acoustic problem. 

[James Romeyn]

Congratulations Duke, for this well-earned honor!  It must feel great to have now won two awards from respected magazine.

Regarding the issue of proximity effect: even standing directly over a sub in a distributed array, bent down, with my head only a foot or so above the sub, I can not detect whether or not the sub works.  I have to reach my hand around and physically contact the woofer. 

Normal setup for one sub specifies maximum distance between sub and main speaker at one half wavelength of the crossover frequency.  For distributed array I have one sub at the back of a 25.5 foot long room, with seamless blending and no proximity effect even with xo pole set around 70 Hz.

In my last room I spent the equivalent of about $7k on acoustic treatment with mixed results at best.  The distributed array works infinitely better.   

[James Romeyn]

Thank you Russell and JLM!  Robert Greene is indeed quite thorough.  Although TAS doesn't publish measurements, Robert runs them and runs them well.  He's an amazing person aside from audio... he turned down a job as head of the mathematics department at Tulane University (arguably an "Ivy League of the South" school) in order to take a position at UCLA, where (as of a few years ago) he was working on developing the multidimensional mathematics and theories for what comes after String Theory.   And he participates very actively in a Doberman Pinscher rescue organization... at any given time there are several Dobies living with him and Paige, just getting used to gentle interactions with humans....

It's nice that Robert has so much free time to be a violin virtuoso recording with world class orchestra (he brought his CD into our Newport room).  Oh, and still more time to be a linguistic expert such that he tutored Russell Crowe for the movie "A Beautiful Mind."  He's also one of the nicest and most caring people you'll ever meet.  Duke was not with us at 2014 Newport (thanks to Tony Chipelo for allowing us to share his Electra-Fidelity room).  Robert asked how Duke is doing and it was obvious he really cared, it was not just a casual question. 

Robert tutored Russell in violin technique for the great movie Master And Commander (realistic early 19th C Navy battleship reenactments).  Robert said Russell was one of the hardest working and most dedicated persons he ever met.  Russell learned to play violin moderately well (unknown if he had prior music training). 

BTW, the sound engineers recorded real live vintage canon for the sound track in the above movie, and when you hear it on SWARM you'll know it's not synthesized.  Ironic that even with today's technology no synthesizer could recreate the realism of those canon shots, which are startling. 

Canon shots at moderately high level revealed no indication of stress (have the remote handy because canon shots are recorded at proper level relative to dialog and the rest of the sound track).   

After my friend retires, he plans to move and build a house with a big sound room.  SWARM minimizes anxiety concerning ideal room dimensions related to modal effects.  He is a Marine Aviator, and prefers extreme over adequate.  I long wondered, and hope to eventually find out, whether eights subs (or even a mere six) might result in +/- 1 dB FR window, minus any EQ of course. 

IIRC my room with one sub ideally placed = 13 dB FR window, current distributed array = 6 dB FR window.   

[borism]

Duke,

Congratulations on the great review of the Swarm System in the April issue of TAS by Robert Greene. He definitely liked it.

Boris

[Duke]

Thank you very much, James and Boris!

I think I'll start a new thread, as the review goes into a lot more depth than the text that accompanied the Editor's Choice award.