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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

Showing 3 responses by douglas_schroeder

douglas_schroeder
3,281 posts
 
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
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.    :) 
douglas_schroeder
3,281 posts
 
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.  :) 

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