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
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  
7-15-21 for late comers.  Another DBA believer here after replacing a single REL Britannia 1 with three SVS subs in main room. Not going back.