A DIY Swarm-based Distributed Bass Array for SOTA Bass


State of the art bass turns out to be a lot more affordable - and achievable- than you think. It just requires a new approach.

The physical realities of low bass in small rooms is discussed by Earl Geddes in "Why Multiple Subs?" http://www.gedlee.com/Papers/multiple%20subs.pdf

Basically, a 20Hz wave is 56.5 feet long. So any bass that low is bound to bounce off a wall long before it even becomes a full wave. Then as it bounces back it runs into itself, either canceling or reinforcing itself, and this all happens even before one full wave can be produced. This is just physics, or acoustics if you prefer, and happens in every room and always regardless of speaker design. As Geddes has shown the shape of the room hardly even matters. At residential sizes they are all pretty much the same. So the conventional approach of one or two subs cannot possibly work. It never could. It was doomed by the physical and acoustical constraints of home-sized rooms.

With four however it becomes almost trivially easy. Not in the sense of being perfect. Its not magic. The quality and performance of the four speakers still matters. But its trivially easy in the sense that the improvement inherent in using four is so great as to swamp these details.

Or at least that is the conclusion that led me to build my own distributed bass array.


The Distributed Bass Array

The system I built is based on the Audiokinesis Swarm subwoofer system http://www.theabsolutesound.com/articles/audiokinesis-swarm-subwoofer-system/ with help from Audiokinesis himself, Duke Lejeune.

It uses four 10" Morel drivers https://www.parts-express.com/morel-ultimate-uw-1058-10-subwoofer--297-130

These drivers at the time included sealed 1.25 cf cabinets. These go together easily with minimal woodworking skill and tools, but that would mean four sealed cabinets. Duke suggested building two ported would give the added option of being able to easily tweak the bass response if needed by simply plugging a port or two.

With ported enclosures there is a relationship between volume, port dimensions, and tuning frequency. Basically, a bigger cabinet volume, longer port, and smaller port diameter yield a lower tuning frequency. A smaller diameter port doesn’t need to be as long. But it needs to be big enough to pass the volume of air quietly, without chuffing. Just a few of the many details designers like Duke know in depth. Me, I used one of the on-line port length calculators. Which just happened to give the same answer as Duke gave me. So I know the calculator was right.

As a result, two subs are 16" sealed cubes, and two are 16x16x24 ported cabs, with 3" diameter by 20" long ports. According to Parts Express this results in an f3 of 52 Hz for the sealed subs, while according to the on-line calculator the ported subs are tuned to 20 Hz. I take all this with a big grain of salt or as an estimated starting point at best, as room reinforcement at low frequencies is so big a factor. The goal is simply to get in the ball park, or close enough for a little port plugging, phase adjusting, maybe even a touch of EQ to do the rest.


The Amps

Duke’s Swarm system uses the Dayton subwoofer amp https://www.parts-express.com/dayton-audio-sa1000-subwoofer-amplifier-rack-mountable--300-811
While one amp would do nicely, because almost all bass is mono, still there is an advantage in terms of flexibility in using two. The Dayton amps are adjustable for crossover, level, and phase. A main reason a DBA works so well is the four source locations results in a smoothing of modes. Another factor is the way we perceive the size of the space we are in is related to the mixing or randomness of the lowest frequencies. The idea is that being able to adjust phase can further smooth or blend modes resulting in a greater sensation of being in a larger space.

At this point however I had a bit of a problem. My Melody 880I amp has no pre-out while the Dayton amps have only line-level inputs.

There are plenty of Line Out Converters but they all look cheesy to me. So instead I opted to convert one of my unused RCA inputs to a Line Out.

Converting speaker output to line level is a simple two resistor circuit. One 10k drops the speaker level, one 1k provides a little impedance to the outboard component. http://www.epanorama.net/circuits/speaker_to_line.html With a foot or two of spare silver wire and $2 worth of resistors soldered inside the Melody retains its stock look and is ready to drive the Dayton sub amps.


The Setup

This is the hardest part with the conventional approach, figuring out where exactly to put the sub to get smooth flat bass. Okay, technically not hard- impossible! With four however...

I spread the four around the room- near the left corner of the front wall, a little further than that from the front corner of the right wall, the remaining two on each side a little further back than the sweet spot. Fairly random. They all face the wall.

One run of ordinary 14 ga wire, at least for now. The two 8 ohm subs on each amp wired in series is 16 ohms, or 4 ohms in parallel. I tried both. The bass is a little more taut and defined at 16 compared to 4. Either way the result is leagues beyond a conventional sub.


The Sound

Finally! Setting up the Talon Roc the DBA replaced I knew would be a chore so for that I used a warbled test CD. Having read so much I was so sure the DBA would not be like that this time that I put on Bela Fleck’s Flight of the Cosmic Hippo. This track features some incredible low bass. Bass that trailed off to nothingness with my Talon Roc. Bass so low I had only heard it done even halfways decent one time- in the gigantic basement of a speaker designer (Linaeum) in Beaverton.

The DBA, speakers plopped down with zero effort, no cones, plain old lamp cord, and only the crudest guesstimate levels set, reproduced the Cosmic low bass of the Hippo so perfectly I could hardly believe it. Everyone talks about sub compatibility, matching, phasing, yada yada- forget about it. If my experience is anything to go by just plop four subs down, sit back, and enjoy. Try not to giggle. Seriously. Try.

The bass from these things is just crazy fast, articulate, powerful and smooth. Uncannily so. The Absolute Sound review above describes this so beautifully I have little to add. What I will add, as amazing as the obviously low powerful bass that you’re aware of hearing is, what is even more amazing is the effect of the very unobviously unpowerful low bass that you’re not.

What I mean is, several times now I have been listening to music that seemed to have no low bass content at all. Why then does it sound so much better? What is the DBA doing??? Sometimes, as with piano, it makes sense. The piano is a physically large instrument. The lowest A on a modern piano is about 27.5 Hz. With string bass its 31Hz to 41Hz, four or five string, depending. All likely with a physical presence that extends a bit lower than their fundamental notes. So with a little thought its easy enough to see why these sound better with the DBA. But what about the rest? Why am I getting the sense of the whole recording being bigger, better, more real and present in the room?

Or should I say, not that the recording is in my room but that I am in the recording room? Duke and others have talked about a sense of envelopment. Something I have experienced for a very long time going back to my first concert hall experience as a youth is the unique sonic signature of large spaces. If you’ve been to a concert you know the feeling. You walk in and not only your ears but your whole body feels the sensation of really, really, REALLY, I’m talking subterranean low bass.

Now honestly, the DBA is not that. Maybe with four 15" subs it would be. If its even on the recording to begin with. Not the point. The point is, the DBA is at least getting to the point where this is where you have to go to try and describe it. Its that good.
millercarbon
millercarbon,

     Excellent post.  You not only detailed how to technically construct a custom  4-sub distributed bass array system and how you positioned/distributed the 4 subs in your room, you also did a very good job of describing the extremely high level of bass response performance that users of 4 sub distributed bass array systems should expect to achieve in their own rooms.
     As I know you're aware, I have been using an Audio Kinesis Debra  4 sub distributed bass array system in my room for about 4 years now.  The Debra is priced identically to the AK Swarm at $2,800 but with more rectangular subs than the squarer Swarm subs and both are good choices for those who don't want to build their own custom dba.  They're both complete kits that include 4 subs and a 1,000 watt class AB amp that also controls the crossover frequency, phase, volume and has a limited eq.  
    My main reason for posting is to state that the 4-sub dba concept has provided the best bass performance I've ever achieved in my combo 2-ch music/ht system and 23'x16'x8' room by a wide margin.  The bass is very natural, seems effortless and integrates seamlessly with my large (6'x2') Magnepan dipole panel main speakers. The system has the versatility and capacity to accurately reproduce fast, rhythmic, taut bass just as well as deep, powerful and impactful bass on both 2-ch music and ht content.
     Good bass response is generally considered to be the most difficult portion of the audio spectrum to reproduce in a high fidelity manner in typical homerooms.  As I understand it and you mentioned, this is mainly due to physics and the extremely long sound waves of bass frequencies. The lower the frequency, the longer the sound wave and these waves continue to bounce/reflect off room boundaries until they eventually run out of energy.  The direct and reflected bass sound waves inadvertently meet or collide at specific spots in the room at which points the bass is perceived as a peak, dip or null (bass is heard as exaggerated, attenuated or even absent). 
 Here's how the owner of Audio Kinesis, Duke Lejeune, has described the reasons and benefits of using a distributed bass array system: 
"The problem the Swarm addresses is, audibly lumpy in-room bass response. This is a fundamental acoustic characteristic of small rooms ("small" meaning "smaller than a recital hall" in this context). This room-induced peak-and-dip pattern will ruin the response of any sub no matter how smooth it starts out, and the Swarm is an acoustic solution to this acoustic problem.

The Swarm consists of four small subs that are intended to be distributed around the room. They are all driven by one central shelf-mounted amplifier.  The idea is, each individual sub inevitably generates a room-interaction of a peak-and-dip pattern, just like any other sub does. But these peak and dip patterns change dramatically with sub (or listener) location. So with the Swarm, you have four dissimilar peak-and-dip patterns summing at any given listening location.  

The net result is far smoother than any one of these patterns could have been without EQ, and this smoothness holds up much better at different listening positions around the room than it would with one or two equalized subs. And "smooth bass" = "fast bass", as it is the peaks in the response that make a subwoofer sound slow (the ear has poor time-domain resolution at low frequencies, so group delay is not nearly as bad as it looks "on paper")."

     I think this is a very good summary of the bass forces at work in a typical room and the reasons a 4-sub dba system is such an effective solution.  Based on my experiences with the AK Debra dba system, I can state without any reservations that the dba concept works like a charm in my system and room.

Enjoy,
 Tim
millercarbon, congratulations on being an explorer! Sounds like you are discovering a new world of enjoyment - isn't that what the hobby is all about?  :) 

There is no way to get the same precision with an array of subs, but there also is no replacing the sense of scale possible with an array of subs. These two sit on a spectrum that the audiophile must select their optimum result. 

I have had systems with anywhere from two to one dozen 15" woofers operating. The difference in presence is striking, and the difference in the depth of soundstage and sense of vastness to the recording environment is also striking. You are now hearing some of the detail and effects of adding subwoofers (or sub systems) to a fine stereo. Without subs it is nearly impossible to achieve that level of sound quality. 
douglas_schroeder
There is no way to get the same precision with an array of subs
Well if you've heard more precise than this then color me jealous. Because the bass I'm getting is a whole lot more precise, clean, articulate, whatever you want to call it, than the Talon Roc I was using before. Even what I've heard from monster mega-buck Wilsons comes nowhere near this DBA. My post spent more time talking about the sense of space because that's the most interesting aspect.

But I could just as easily have left that out and focused entirely on speed, smoothness, and surprisingly, detail. Nobody thinks of bass in terms of detail. Listening to Pink Floyd Welcome to the Machine on other systems the machine makes this very low throbbing sound. With the DBA you can hear so much detail in this its crazy! The level doesn't just throb up and down, there's lots of times where it changes really fast, and you hear it and feel it, exactly like what it sounds like, a huge door opening and closing.

noble100 Tim, you put it beautifully.

I probably would have done this anyway but your experience was a big help. Duke's too, but guys like him are just an exceptionally rare breed whereas no offense but when it works for normal guys like you then it makes me sure it will work for a normal guy like me as well. I actually wouldn't recommend DIY for anyone who hasn't already done something like this. You don't really save all that much, certainly not in terms of time! lol! Mine still need veneer, which even then covered in Rosewood I doubt they will have quite the professional finish of Dukes Swarm or your Debra. 

The details you're talking about hearing, oh yeah! There's the classic thing of the bass line where the volume changes as the notes go up and down the scale. Gone. The classic thing where the notes go lower and just sort of fade out. Flight of the Cosmic Hippo, the best part fades to almost nothing. Its just so low, it almost disappears. Not any more! Now you hear every note clear and strong and precise.

Which in a way you kind of expect. What I didn't expect was the tremolo. The kind of speed and precision it takes to hear not just the note, but really tiny fluctuations in pitch and volume (tremolo) within the note. And not only on obvious tracks like the Hippo. I've been surprised how many times this shows up with music I had no idea had any low bass content at all!

Just as a reminder, I still have not hardly even begun to dial these things in. Just plopped em down and started enjoying. Levels set almost certainly too high. Crossovers not dialed in, EQ still flat, no playing with phase. Long way from being dialed in. Even so, wow.
millercarbon, it's all good! I understand your enthusiasm when you say, "Well if you've heard more precise than this then color me jealous. Because the bass I'm getting is a whole lot more precise, clean, articulate, whatever you want to call it, than the Talon Roc I was using before. Even what I've heard from monster mega-buck Wilsons comes nowhere near this DBA. My post spent more time talking about the sense of space because that's the most interesting aspect." 

There is an entire spectrum of performance which is very wide pertaining to the character of the LF alone. It's endlessly fascinating as one tunes that LF, how much derivation can be obtained, and how precisely it can be tuned in terms of coherence, tonality, presence, etc. You will have a lot of fun with it should you choose to explore ongoing.  :) 

You are entering a realm where a LOT of action takes place, and perhaps now when you say, "Which in a way you kind of expect. What I didn't expect was the tremolo. The kind of speed and precision it takes to hear not just the note, but really tiny fluctuations in pitch and volume (tremolo) within the note. And not only on obvious tracks like the Hippo. I've been surprised how many times this shows up with music I had no idea had any low bass content at all," you are realizing how much of upper end performance is left on the table by persons who discount LF.  :) 

It sounds sublime!I'll be interested to read about your further experiences with your swarm.
douglas_schroeder
You are entering a realm where a LOT of action takes place, ... you are realizing how much of upper end performance is left on the table by persons who discount LF.


For sure and amen. This is something I was sure had to be the case as for years I struggled and gave up long ago in frustration when it seemed impossible due to all the physical constraints of room resonance. The problem is being stuck in the outdated, false, counterproductive and doomed to failure paradigm of one sub. Or even two. Or anything where the focus is on treating really low bass the same as really high treble.

Which is what everyone does. Despite the fact it does not work. Despite the fact it flies in the face of human perception. As Duke and others have pointed out many times, high frequency sounds are heard with such precision we can determine location from within a range of a few milliseconds, yet we cannot hear low frequency sounds that brief at all.

At all!

Another really big problem with the sub approach is even if you somehow with EQ or whatever manage to get fairly smooth response at one location, it always results in really big modes at other locations. But of course the energy in those locations takes time to dissipate, and as it does so it reverberates around the room which takes time which because of the way we hear things we interpret as mushy or slow bass. Someone could tell me that's what's going on. I could read about and understand that's what's going on. But to actually experience it, that is a different thing altogether!

We have all had the experience of the person who comes over and is so shocked to hear imaging for the first time they stare in disbelief or even sometimes get up walk over and touch a speaker. I had a guy one time ask me three times how many speakers, finally get up and walk over and lift the blanket off the TV. Convinced there was a speaker hidden behind it. Well recently between the Herron, ECT, PHT, HFT, etc, etc mine had gotten to the point where sometimes even I would open my eyes to check and see.

But that feeling of fidelity, even though I knew it was missing a lot deeper down until now I had no idea all I was hearing was just the thin skin on the onion. Which already seems to me to be a nice big juicy Yakima Sweet. So hell yeah I will be playing and tweaking. And if my eyes water it'll be from tears of joy.


Also, revisit music that you thought was just awful in terms of distortion; you may find humbly that much of what you thought was in the recording was in fact incapacity of the system to reproduce the music faithfully. So much music that is disdained among audiophiles for purportedly being poor sonically is in fact being reproduced poorly by owner's systems.  When a system becomes good enough the realization hits that much of the compressed music is not nearly as bad as reported. I'm not saying this in regard to the genre, but in regard to the sound quality�. 

For instance, Lorde's "Royals" is a good piece to assess one's LF. The low throbbing beat, and the strong bass line, is actually very tight, extremely well defined when one has a system capable of reproducing a note under 15Hz. It sounds like crap to many because their rig is not even close to capable in handling it. So, the recording is inappropriately damned by audiophiles, when in reality it should be the system's LF capacity that should be damned.  

Daft Punk is a gimmicky sound, imo, but the LF is good for assessing systems. Here the LF seems wretchedly loose, ugly - that is, if your rig can't play it well. With a capable system to handle such things the LF is clean, quite interesting. Perhaps 20% or less of audiophiles' rigs can do such music with excellent fidelity.  But everything from symphonic to chamber music is benefitted. Vocals are substantively superior, with more color and warmth. 

Many laugh off suggestions that such changes could cause a sea change in the system's performance. Many are as derisive of the importance of LF as they are the importance of cables. In many respects cables as important as the changes you have made to the LF. I suspect you do not believe that, but perhaps seeing as how your eyes have been opened to LF, perhaps you will also discover some things about cables as well.  (Remember, this comes from a once adamant cable skeptic). For instance, cables to subs, both power and signal, are hugely important in terms of quality of the LF. I completely ignore people who declare this or that about what cables can and cannot do with subs. I build far too many rigs to care what they say; I get incredible results and tune LF continuously in rigs. 

You have much to explore and a lot of fine tuning over time to do. In six months it will sound quite different than now, much better, if you keep at it.    :) 
douglas_schroeder
Many are as derisive of the importance of LF as they are the importance of cables.


lol! The fools! 

I've got Synergistic Research Active Shielding on just about all of mine. Most of my wire has been cryo'd. Including the wire from the breaker box. Which leaves the box at 240v and goes through a pure silver wire step down transformer en route to the Bybee power line conditioner. All the power cables are high end, including the two Electraglide Fat Boys I pulled out of a drawer when I needed them for the two Dayton amps. I been doing this so long back when I bought them there wasn't even an Audiogon on-line because there wasn't even an on-line, so with no market figured why not just keep em? Staggering to think that today, decades after this should have long since been put to rest, that anyone doubts the importance of wire.

But then again once I learned about this I was surprised to discover the idea was not at all new. Not only had Duke been making the Swarm with Audiokinesis for many years, but then I saw a paper by Geddes which was many years before that, and wait it gets better, because in the paper Geddes references work he did THIRTY YEARS before that!

So in reality this is something like fifty year old news, and yet it was news to me, and still would be had I not stumbled across it here by accident. Which is my main motivation in writing, because people need to know. People need to know what a total waste of time it is trying to get good bass any other way. People need to know there is an answer.

Not that I expect it will do much good. People are incredibly good at believing whatever is endlessly repeated regardless of it being true or not. Person? Or parrot? Hard to tell some times.

Oh well. The hardest part, what is always the hardest part for me, is I get to a point where it sounds so doggone good I want to stop messing and just relax and enjoy. That to me is what its all about, relax and enjoy. Little more work but man is it getting close!
     I think Duke has a knack of mentioning things that really illustrates how well a 4-sub distributed bass array system actually performs in a given room compared to 1 or 2 sub systems.  Things like, and I'm paraphrasing this, "Fast bass= Smooth bass.  Two subs are twice as smooth as one, four subs are twice as smooth as two and eight subs are likely good grounds for divorce". 
     Accurate, descriptive and kind of funny=memorable and effective, right?
     I find the most fascinating aspect to dbas for me is the psychacoustic dynamics involved in the how and why these bass systems work so well.  Things such as the fact that a single sub causes a large number of bass peaks and dips in any given room and the solution, counter-intuitively,  is adding 3 more subs at different room positions in order to cause a lot more bass peaks and dips to the room with the knowledge that the time domain is much less important on bass sound waves but the human summing of all the bass peaks and dips and the bass pressure levels in the room are.
     My experiences with the AK Debra dba in my system and room has also convinced me that running the subs all in mono mode, as opposed to stereo mode, has no detrimental effect on system imaging.  My perception is that the sound stage illusion has become, if anything, even more expansive, solid, stable and detailed. 
     I was a bit concerned, with the bass coming from 4 subs spread around my room, about whether the bass would integrate seamlessly within this sound stage illusion, that is that the bass was perceived as coming from the proper bass instruments positions within this sound stage illusion.  I was very pleased to realize that the bass produced by  the Debra dba was seamlessly integrated and I did perceive the bass as  coming from the proper bass instruments positions within this sound stage illusion.
     Since the source of bass sound waves below about 80-100 Hz is generally considered undetectable and my 4 subs were only set to operate below about 50 Hz, however,  I was a bit perplexed how I was able to perceive this low frequency bass as coming from specific spots (the kick drum in the center, an upright bass to the left, etc.) in this sound stage illusion in my room. 
     I've theorized that I'm able to localize the locations of instruments producing deep bass notes only due to the higher frequency harmonics or overtones of these instruments being reproduced by my main speakers and giving clues to the specific spot the related deeper fundamental tones of these instruments are originating from.  I'm assuming my brain is doing the important work of associating the fundamental bass tones with the associated harmonics and deciphering the specific locations of these bass instruments within my sound stage illusion.  All quite a bit of processing but the illusion sure seems very palpable and real.  
     I'm thoroughly enjoying these sound stage illusions on many, but not all, recordings and the added realism provided by the excellent bass response of the dba.  But I'm still uncertain if my theory is correct.  Any thoughts?

Tim
@

Hey, Tim, could you elaborate on the placement of the 4 subs in your room?  Are they spread throughout the room (even behind you), or are they concentrated on one end with the main speakers?

I ask because I am considering the Swarm, and Duke has recommended an "all around the room" placement that just spooks my intuitive sense.  I'm curious what your experience has been.  Thanks!
For sure its coming from the main pair. Has to be. People will probably find this hard to believe, but there have been several times when I wasn't sure if mine were making any sound at all. Couple times I would walk right up to one, sometimes not hear it until my head was so close I could touch it, sometimes not even then, sometimes not be sure until I put my hand right on the cone. 

I've used mine stereo and mono and yes, no difference, at least not that I've been able to hear. Maybe with some material it might matter although it seems there is none. No such thing as stereo when it comes to deep bass. 

Imaging either way is outstanding, at least as good if not better than before. I'm sure you're right and this is because all our imaging perception is higher frequency. But the low bass adding the perception of the true recording venue spaciousness adds to rather than blurs or subtracts from what the stereo up front is telling us.

One thing I know for sure, you guys who have had more time with it have had more time to think things over and it shows. Beautiful explanations. To those who haven't tried it, they know what they've been talking about. This is for real.
Adding this to my threads for later reference.  Congrats on your beautiful creation, and kudos to Duke for helping people recreate his product.
jbrrp1
Duke has recommended an "all around the room" placement that just spooks my intuitive sense.


Tim followed a very well thought out methodical approach he's posted before but would be great to be included here if he doesn't mind writing it up again.

The locations Tim wound up with are almost exactly what Duke recommends and what I did- basically one per wall, asymmetrically spaced, ie different distances from the corners. Also same as what is recommended in all the research you will find if you go looking around for Geddes, Toole, et al.

I wouldn't say its counter-intuitive, but it sure is counter the status quo. But that's why this thread exists- to counter the counter-productive status quo!

Hello jbrrp,

     Below is a link to a thread I started awhile ago that describes the procedure I followed to first find the ideal position for each of the 4 subs in my room and, second, exactly how to wire everything up to the supplied amp.  
https://forum.audiogon.com/discussions/anyone-else-using-an-audio-kinesis-swarm-or-debra-distributed-bass-arra

     My room is a 23 x 16 x 8 ft living room that I also use for both 2-ch music and ht.  I have a 65" hdtv centered on the 16' front wall with a 6' wide and 2' high equipment rack centered below the wall-mounted tv.  I have Magnepan 2.7QR main speakers straddling the tv and a CC3 center channel speaker above it. My listening chair is centered on the 16' rear wall.
     For the subs, 2 are located at opposite ends of my front 16' wall with each about 2' away from the corner.  The other 2 subs are located more toward the rear of the room, with one along each 23' side wall, about 2' away from each rear corner and directly across the room from each other.  My listening chair sits between these 2 subs with each about 7-8' away from my chair. 
     So, I'd describe my setup as an "all around the room" sub placement like the placement Duke suggested for you.  I just followed the sequential sub locating procedure I described in detail on my thread linked above.  I had no preconceived idea where each sub would ultimately be positioned, I was determined to just follow the sequential procedure and trust that, if I did, the subs would be properly positioned in my room so that the 4 subs working in unison would provide the optimum dba system bass response performance in my room. 
      I had already decided I was going to position each sub in the room where it sounded the best and would redo the position of the furniture in the room if necessary rather than compromise the system's bass response performance.  Fortunately, I only had to move a couch a few feet forward along a 23' side wall to position one sub.
   
 I hope this helped,  
       Tim
When running a swarm system, are all four subs handling a summed (left and right channel) signal?
I run two subs in the front so each side gets its own signal but I have considered adding a third and I remember reading that running a third sub with a summed signal (only on the third sub) could also be a significant improvement.
mitch2
When running a swarm system, are all four subs handling a summed (left and right channel) signal?
I run two subs in the front so each side gets its own signal but I have considered adding a third and I remember reading that running a third sub with a summed signal (only on the third sub) could also be a significant improvement.


When 2 or 4 are connected to the same amp and the amp is mono (like the Dayton SA1000) then yes they are summed. Connecting a third will of course be a lot better. Geddes (I think it is, probably) gets all mathy and expresses the improvement in terms of variance as being 1/n with n being the number of sources. In other words, the more subs the bigger n is and the smoother the bass will be. Doesn’t take a lot of math to see going from 1 sub to 2 is twice as smooth, going from 2 to 3 is 50% smoother, from 3 to 4 is 30% better. Notice the gains, big at first, get smaller as you go. Or as Duke says, four is great, eight is grounds for divorce. Or something like that.

Running two amps as I do does allow them to be run in stereo. But there’s virtually no stereo low bass and that’s not the main reason for doing it anyway. Its done to be able to even further smooth the modes by being able to adjust phase. I’ve hardly had time to try this so stand by for now but from what Duke and others have said it can add an even greater sense of space and envelopment.

If you add a third sub one thing you can try even without any phase adjustment is to reverse phase on one or more of the subs. Equivalent to adjusting phase 180 degrees in other words.

So adding a third sub is a good idea- more bass, smoother bass (which equates to faster bass) and more phase tuning options.

Edit: Yeah, it was Geddes after all. https://mehlau.net/audio/multisub_geddes/
And I missed the part about your amp being stereo. You can connect the third to either one of the channels. Won't matter, since low bass is mono anyway. Just wire them whatever combination of series/parallel results in a driveable load to your amp.
At a number of RMAF's, Danny Richie of GR Research placed a pair of his (and Rythmik Audio's) OB/Dipole Subs along side his main speakers at the front of the room, with a pair of sealed box subs (Rythmik F12G) at the rear, for a total of four subs. The OB/Dipoles were run in stereo (they can be used up to 300Hz, used as not just subs but also woofers for bass-shy loudspeakers like 5" minimonitors), the rears I don't know. His room was awarded Best Bass At The Show by attendants several years.
Yeah, its freaking amazing what happens when you get four in a room. Way better than I was expecting. And I was expecting a lot.
Thanks @millercarbon  -  Yes, going from one to two was revelatory - easily twice as good.  I am using Aerials and I have my eye on a third.
If your two are located according to the old customary way then you might notice a further small improvement moving one or both a lot closer to a wall, and more importantly, asymmetrically. The more asymmetry you can get the better. In other words, one on the front left the other on the right front is better than left and right on the front- and better still, each a different distance from the corner.

Placement with subs is super critical with only one, but the more subs there are the less important it becomes.
Thanks for this info, Tim!  Your description is very thorough and makes it all seem quite approachable.

I am going to take the plunge some time in the next couple of months.  I am planning to use two of the Dayton amps for stereo (even though that is apparently futile!) and the greater adjustability. 
jbrrp1,

No problem, it really is very approachable. Funny, I even get excited about dbas if someone else decides to buy or build one.
It’s your choice, of course, but my opinion is that 2 Dayton amps can be beneficial since they’ll provide more reserve power for even better bass dynamics, more system flexibility for setting crossover frequencies, sub phasing and sub volumes and the potential to run the 4 subs in a stereo configuration.
However, I think you’ll be disappointed in configuring them for ’stereo bass’ for a couple reasons:
1. I don’t believe there’s such a thing as directional bass perception or ’stereo bass’ below about 100 Hz. I don’t know the exact bass Hz frequency that I perceive bass as directional, but I know it’s closer to 200 than 100 Hz.
To be fair and objective, though, you may be more sensitive to the direction of deep bass than I am. I’ve also never configured my dba system in stereo mode since I only have a single Dayton amp. But I do think it’s at least possible that higher frequency harmonics and overtones of deep bass notes, reproduced by the main l+r speakers, could provide clues to the location of the sources of deep bass fundamental frequencies.
Overall, therefore, I don’t think it would be wise to dismiss the possibility of perceiving ’stereo bass’ solely because it’s generally understood that bass is not directional below about 100 Hz. I believe this premise deserves further study, or perhaps I just need to further study the research and knowledge that may already exist on this subject. You don’t know what you don’t know, right?

2. Very few recordings, actually I’m aware of absolutely none, contain ’stereo bass’. I believe the bass is summed by recording engineers due to physical limitations on vinyl recordings and more out of convenience or traditional/common practice on cd recordings. However, with the significantly increased capabilities of current and potential future direct to digital recording techniques and technology, this may to lead to more recordings containing ’stereo bass’.

In my over 4 year experience of using the AK Debra distributed bass array system running in mono configuration, I’ve been more than thrilled with the bass response and consider it state of the art bass performance for 2-ch music and ht. It may be due to psycho-acoustic principles, but I perceive the mono bass as very well integrated, emanating from the proper locations and instruments on the sound stage and overall very ’stereo bass....ish’.
If progress does result in more content containing ’stereo bass’ in the future, I or you could always buy a 2nd sub amp and reconfigure the dba to run in stereo.

Your choice,
Tim
I am planning to add 2 more subs to my system. Do to the nature of my room they will need to be in the corners of the back wall. Will this get me close? Can i high pass the mains at 80hz? Will it smooth the bump i have between 50-100hz?
Close, yeah. Remember the goal is more modes so if one is right in the corner then try and get the other a little one way or the other. But if you can't, you can't and in any case more is better. 

Smoothing the hump, I can relate since I have the same thing with my mains. At least with the subs its less noticeable because they drop off less below the hump. Its possible but probably unlikely the added subs can be set up to cancel the hump a bit. More likely though you would move the mains. Unless you high pass the mains, in which case you can EQ. But that to me is kind of a last resort. In addition to the usual EQ shortcomings you will be losing the mains as additional bass sources which is foundational to the whole distributed bass array approach.
Nobody thinks of bass in terms of detail.
Oh yes they do :)  Bass definition (such as bass ambience) seems to me to the first thing that suffers if things aren't right.


Good work and Kudos to Duke!
One key to better bass definition: higher impedance. Check it out:

The Swarm/distributed bass array setup I’m using consists of two amps and four 8 ohm subs. This makes it easy to compare the same speakers being driven at 4 ohms, 8 ohms, or 16 ohms. Simply change a few connections.

With two amps then each pair connected in series gives a 16 ohm load, or 4 ohms connected in parallel. With one amp, each pair is connected in parallel (4 ohms), then both pairs are connected to the amp. Since the amp drives them in series this results in an 8 ohm load.

Duke said all his customers who have compared have preferred the 16 ohm load. Me too. Its pretty obviously better.

At 16 ohms the bass is noticeably more taut, dynamic, and well-defined. This is the way mine were first connected, and its clear now this had a lot to do with my enthusiastic initial impressions. Going to 4 ohms the amps do make a lot more power. But the volume gain from the power isn’t all that much, and is only noticeable at the highest levels anyway. The improvements in transient detail and clarity on the other hand that you hear with 16 ohms are bigger and are there all the time.

8 ohms is somewhere in between. If forced to guess, maybe a little closer to 4 than 16. Theoretically of course, one vs two amps, the comparisons aren’t exactly the same. But its been demonstrated (comments above) there really is no noticeable difference in bass running with one vs two amps. The advantage of two is flexibility, mostly being able to fine-tune with phase. Take phase out of the picture and its a pretty valid comparison.


Before the Swarm there was the one Talon Roc subwoofer. That came out, intending to sell, when the DBA went in. But too busy to sell it was just sitting there in another room. One thing I've definitely learned about bass: the more sources the better!

So curious, the Roc went back in. Stuck right in a corner. Crossover turned as low as it would go. 50 Hz, higher than ideal since we are at this point down to that lowest octave. But whatever. Give er a go.

Which honestly, wasn't expecting much at all. My biggest let down with this sub was always that no matter what or where it went it just wouldn't go real low. Always blamed the sub. So if it was incapable of really low bass then how's it gonna be any different now?

Well part of it may be the way we hear bass. Duke has said many times we perceive bass volume a lot different than higher frequencies. So even a little more (measured) can sound like a lot more (perceived). Part of it may also be a sort of reinforcement effect with the Swarm. Which ultimately that comes back to the first reason. I don't think its location, since I tried one of the DBA subs in the same spot. 

Anyway, whatever the why, the result is clear. The sound with the 5th sub is sublime! 

Tim's room is almost identical to mine. About 1 foot difference each way. His set up and listening position however is completely different. I've checked his in mine and its no wonder he raves the way he does. In my room however, with my locations, the sweet spot is just about the biggest bass null in the whole room. Its sweet because the bass there is super tight and clean, but a bummer because its hard to get enough. 

Until now. The 5th sub has solved that problem! Before, with "just" the 4 DBA subs it wasn't possible to get this much really low bass without sometimes driving the Daytons to clipping. Now though with the Roc filling in that last little bit the Daytons get a break and its awesome.

Again, same as with the others, its impossible to localize the sub. Bass "imaging" is at least as good as ever. Best of all, there is definitely an increased sense of the walls disappearing and being in a much bigger space. 
Hello millercarbon,

     I like your experimental nature, always exploring and pushing the envelope.  You've become the mad scientist of in-room bass exploration.  I'm fairly sure you now wear a white lab coat when you're experimenting.
     I'm in the process of thinking of a good nickname for you, I'll let you know when the light bulb goes on.
     Very interesting how the Roc as a 5th sub helped so much. It makes sense according to Geddes (the more subs the smoother and better the bass) but the gain of going from 4 to 5 subs is expected to be marginal and not significant like you experienced.
     With the DBA concept working so well being based on using more subs to create more peaks and dips in the room, and our brains being relied upon to process all the resulting bass variances and average them out via psycho-acoustic principles to provide a perception of smoother overall bass response, it's a lot like making order out of chaos.  It makes sense to me in a macro sense but I have almost zero understanding of how this works in detail.
     Maybe the scientific explanation is you just got lucky.  My opinion is that we're very fortunate our brains are capable of making a 'bass smoothie out of a bunch of lumpy bass room modes'.  Don't bother trying to patent that phrase, buddy, I already did.  
     We're also fortunate Geddes, Toole, Welti, etc. took advantage of this brain peculiarity in processing deep bass tones and developed it into the black arts creation of the DBA concept.  It really does remind me of alchemy or an awesome magic trick.
     So, I'd suggest not trying to explain it and just enjoy it.  I'd be concerned I might sprain something important trying to make sense of this one.  I'm just going to refer to it as the Talon Roc Fifth Sub Mystery for now.


Later,
 Tim
Its really only a mystery in the sense of not being able to say for certain exactly why. But I have a pretty good idea.

The marginal 4 to 5 improvement I interpret as "all other things being equal." Which would apply if all I did was add one more sub just like the other 4, run off the same amp, at the same power, and volume. 

Which is not what I did at all. Instead what I did was add a completely different sub, a lot bigger (the Roc is two woofers in an isobaric ported enclosure) and with its own amp, and its own volume level. 

Probably if I was to go to the trouble of measuring and calibrating the Roc level to match the other subs, and then measuring and comparing, probably then it would turn out to have only marginal improvement. But that's the difference between serious guys who earn the lab coat and guys like me who really only care about the bottom line. Or bass line. Whatever.

Also in case I forgot to mention the improvement is mostly in the sense of headroom. The original 4 in other words could be set to give about the same amount of really low bass. But at that setting the amp would sometimes clip pretty bad. When the Daytons clip it sounds really bad. The Roc adds enough headroom to fill in the bottom end without running the Daytons too hard. 

Now if I was worth the lab coat then I would measure and probably find the really low bass that impresses me so much is really only 2 to 4 dB louder. But in human perception terms we experience that as more like 10 dB, which is a lot. 

I guess from reading these posts it seems like all I do is experiment. In reality I hate this stuff. I just want my Seal, Warnes, etc and movies to sound real good. Getting there..... getting there....
millercarbon,

     I think perception is reality in a practical sense.  If you consistently perceive the bass as better, then the bass is better.  It'd be nice if a few others perceived it, too, just to validate your sanity but it's not necessary.
     I'm thinking the Roc alone didn't work well previously in your system because there were bass standing waves causing bass modes at your listening seat. Now, with 5 subs, those aren't perceived and the Roc is freed to add its extra and more extended bass to the mix.
     I ordered some new white lab coats for you with 'Duke DBA Disciple' printed on the back.


Later,
 Tim
Alright. But I only wear the Tommy Bahama silk lab coat with subtle palm tree pattern. Goes with the whole Pina colada listening theme. Just so you know. Which reminds me, get that pineapple juice chillin'.

     I was able to change the lab coat order but they were out of the Tommy Bahama silk lab coats.  So I got you 4 sets of their silk pajamas instead.  The pants have footies but I figured that'd be okay just around the lab, right?

     pineapple juice is already chillin'.


Tim
Hey guys love what your doing with the bass! Only those that have heard real bass done right get it... aka how everything just sounds better. So here is my dilemma, I have a really small listening room 14 x 16 feet with one large opening of 8x7 feet to the rest of my "divorced 650 sf" haha. I already own 2 HSU Uls sealed 15's. They sound great in stereo and pressurize the room nicely but I know it can get just get better with a swarm setup. Would it be possible to integrate these ULS 15's with another 2 Morell swarm subs with the Dayton amp? Or should I get one more Hsu Uls 15? Or sell it all and just get four of these with the Dayton amp for 2k? I'm an Audiophile so swarm sound that is acoustically correct is everything to me.    
Guess I should follow up my post... Is it possible to get the swarm effect with three subs and not four given my space restrictions? 
The more, the better. Regardless of room size. My impression is most of the problems people associate with getting good bass in a smaller room is due more to their old-school thinking than anything else. I mean if you think the answer is one big sub then you put that in your little room and sure enough you get one big problem with one big mode. But if instead you put 4 subs in there, well then you get 4 smaller modes and therefore much smoother, which equates to faster more articulate, bass.

There even was a guy on another thread asking how should he try running his 4 full range speakers. I suggested using two of them in corners as make-shift subs. It worked! Which is not to say the quality of the sub doesn't matter, just that having more helps a lot even if they aren't the best subs.

So I would go for 4 but not let that stop me from trying 3. 

My experience has me convinced that another outmoded or unfounded view is this idea of integration. Not saying the subs don't need to be adjusted for smooth frequency response. Not saying that at all. But when people talk about integrating I never get the impression that frequency is all they're talking about. There always seems to be the underlying assumption there is timing to consider, as if the subs need to be equidistant the way the stereo pair do. Or that they need to be voiced the same, or have the same response characteristics (my electrostatic speakers are hella fast, so only hella fast subs yada yada) all of which I think is unfounded, unsupported, indeed in many cases totally disproven by actual research. Let alone practical experience. 

So yeah, no problem getting whatever you want- Morel, more Hsu, more whatever- to work well with whatever you have. Which is better comes down to your personal preference as to what will fit, where it will go, and what it will cost. On that score the main thing to keep in mind is the more you have the less sensitive they become in terms of placement. With one or two you struggle to get smooth response. With 4 it becomes easy, just spread them around asymmetrically. Sure some locations are better than others its just nowhere near as critical as with only one.

As far as which one to do, the advantage of the Dayton setup is the amp has a really nice combination of crossover, level, boost and single band EQ. But at the disadvantage of space for the amp, and limiting your two (or more) subs to the same setup. With individually powered subs you might lose a little EQ control but you gain a lot by being able to set level and everything else individually. That can come in real handy especially in a small room. You may for example find one little spot of low end bass hard to fill when setting levels for two or more subs that you could easily cover with just one sub set to get just that one little band.


Hello haywood310,

     Your 14 x16 ft room is on the small size and it's easy to swamp it with too much bass, especially with two HSU ULS15s. 
     I think the best solution for you is to sell the HSUs and get 4 morrell subs with the Dayton amp for about $2k.
     The 4-sub Swarm type DBA would be a better fit for your room and will be easier to configure and adjust the volume, crossover frequency and phase settings for optimum performance.  
     The 4-sub Swarm setup will actually make a small room like yours seem bigger, AK's Duke Lejeune says the smaller the room the better the DBA concept actually works.  The bass will be detailed, smooth and natural with plenty of reserve power for good dynamics.  
     The quantity of bass in your system/room will be completely adjustable via the Dayton amp's volume and crossover controls.  The trick will be maintaining some restraint to achieve, millercarbon's favorite, seamless integration with your main speakers.

Tim
Actually comparing dimensions, the HSU subs are virtually the same size as my Morel cabinets. The freebie sealed ones I used are only 2.5" smaller each way- 15.5" vs 18". But the ported ones I made have to be higher volume, they are the same footprint but 8" taller. Call it a draw.  But the HSU subs are self-powered. The Morel need an amp. Add in the Dayton amp, hard to see how the whole package is taking up less space. Probably 4 HSU overall total space is less than my Morel/Dayton setup.

Honestly having read the reviews and specs on the HSU if I was doing it again today I would just buy 3 of those to add to my Talon Roc. That would be more and deeper bass, with more headroom (able to play louder), take up less space, be more flexible (control of each individual sub), and cost less! Even paying extra to get the Hsu in Rosewood would merely bring the Hsu up to about the same as my DIY Swarm in Rosewood. Same money but huge time and effort savings!

Another thing I have learned, once you get the bass nice and smooth and deep by having four subs, its really, really hard to have too much bass. I'm talking headroom, not level. Its easy to have too much bass, just set the level too high. Its also easy to have too much bass, just use one sub to have too much bass here and there. But with four subs, set up so the bass is nice and smooth and deep, its just really hard to have too much headroom. In any case its certainly better to have it and not need it than to need it and not have it! 


millercarbon,

     If he's going for maximum bass then he may want to use one or two of the HSUs.  I think four of the Swarm or Morrell subs with the Dayton amp would supply plenty of bass and headroom in his room, it does in my 23 x 16 ft room for music and ht.
     From my perspective, having some amplified subs like the HSUs does add more bass power, extension and flexibility as far as control and fine tuning is concerned but I find the convenience of controlling all 4 subs for volume, xover and phase preferable.  It's probably best haywood just is aware of his options and choose what he prefers.

Later,
 Tim