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.
128x128millercarbon
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.  :) 

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, 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. 
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