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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's avatar
millercarbon OP
12,531 posts
 
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.


douglas_schroeder
3,281 posts
 
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.    :) 
millercarbon's avatar
millercarbon OP
12,531 posts
 
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!
noble100's avatar
noble100
2,419 posts
 
     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
jbrrp1
423 posts
 
@

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!
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