Multiple Small Subs - Geddes Approach

After reading about the AudioKinesis "Swarm" sub system and the Geddes paper on loudspeakers, I am fairly convinced that 3-4 randomly placed small subs are well worth trying in both 2-channel and HT rooms. Geddes specifically recommends multiple and different (not matching) subs to force more randomness (and I assume averaging) of room modes. The Swarms are matched drivers/cabinets.

My question is which small commercial subs would be appropriate for this theory? There are hundreds of small 8, 10, and 12 inch subs that are sealed, ported, etc. Has anyone tried this approach and can anyone recommend a combination of subs? I would like to use the smallest possible subs given the need for 3 or 4 or them in my room.
 
I am currently trying the different/multiple sub idea.
I am using (1) 12" Adire Shiva in a Ported Sonotube tuned to 20Hz, and a Aperion Bravus sealed sub with dual 8" drivers - the manufactures measured -3dB point is 35Hz.

Current setup:
Shiva from 20-40Hz, and the Bravus from 35-100Hz.
At the momement the Shiva is in the back corner of the room, about 5 ft from my listining position. The Bravus is up front, withing 1ft of the main RT speaker.

So far I enjoy the bass, sounds to my ear to me more balanced and even. Not had any chance to measure yet.
 
Horizons said:
My question is which small commercial subs would be appropriate for this theory? There are hundreds of small 8, 10, and 12 inch subs that are sealed, ported, etc. Has anyone tried this approach and can anyone recommend a combination of subs? I would like to use the smallest possible subs given the need for 3 or 4 or them in my room. [/B]

You might consider a Linkwitz Transform with a couple of output buffers each having an adjustable level.

The Linkwitz Pluto+ sub woofers (Peerless SLS10 with a Linkwitz Transform) are about half a cubic foot (external dimensions 14 inches square x 7.5" high with 3" feet in a down-firing confiuration)
 
JRace said:
Current setup:
Shiva from 20-40Hz, and the Bravus from 35-100Hz.
At the momement the Shiva is in the back corner of the room, about 5 ft from my listining position. The Bravus is up front, withing 1ft of the main RT speaker.

Multiple subs should cover a wider range of frequencies together, otherwise there is only one LF source at a given frequency. I suggest raising the 40 Hz lowpass of Shiva.
 
What I use, and I'll leave it to Dr. Geddes or someone else to say whether it's the most theoretically sound approach given the equipment I have on hand, is the following:

Corner ultra-low-frequency sub: Exodus Audio Maelstrom-X in an either a ~100L or ~120L (don't remember, and it doesn't really matter) sealed box, equalized ("Linkwitz Transform" of sorts) and powered by a Crown XTi2000. This subwoofer is near the front-left corner of my room. I believe it plays up to 125Hz or so.

Broadband subs: I use two commercial subwoofers, both M-Design Audio's Eleganza Bella. I chose these for two reasons: aesthetics and their use of Aura's underhung NS12-794-4A drive-unit. The ports are closed off. One is at the right "end" of the front wall (it folds into a hallway), and the other is used as a couch end-table, about 42" from the back wall. They are "tuned" differently simply because of their different relationships to nearby boundaries. The highpass of one of them is maxed out, and the other is set to ~90Hz or so, but I don't remember which is which. Points were chosen by iterative measurement-listening-fiddling-measurement loops.

The ULF sub is considerably more capable than the BB subs, with all that power driving an 18" driver with over 30mm of rated xmax compared to 12" drivers with 15mm of xmax, but I have not noticed any signs of overload from the smaller subs at any volume level. Perhaps the main sub is simply overkill, but better overdone than underspec'd.

Here are some pics, for a general idea of how I did it.
An externally hosted image should be here but it was not working when we last tested it.

ULF sub. The Auralex Gramma was completely useless when used under the sub as intended, but the cat likes to play on it so I put it on top of the sub for her to lie down on. Mains are Tannoy 12 DMT II's in bespoke sealed cabinets, designed with baffles the same size as the originals (considerably less depth, and rounded rather than square) but modified with much larger roundovers in light of some of Dr. Geddes' points about diffraction. The Church's house slippers in front of the sub serve no sonic function. :)

An externally hosted image should be here but it was not working when we last tested it.

BB sub 1.

An externally hosted image should be here but it was not working when we last tested it.

BB sub 2.

My current setup (unlike my previous one) violates Geddes' dictum that one subwoofer be above the centerline of the room. However, the mains as you can see are well above the room's centerline, so there are three 12" sources playing in the bass.

As for commercial subs, I would look for anything that's relatively small and sealed or 4th order bandpass. (Sealed/4th-order bandpass simply because I think the beginner would be well advised to avoid the possible problems that might come from the steeper LF rolloff of vented subs.) Maybe a 15" for the "ULF" sub, and 10's or 12's for the "Broadband" subs.

But don't forget the other keys of the Geddes approach, which are to run your mains full-range (LFE+Main and DoubleBass are common names for this mode on modern receivers) and set them up along the lines of Markus's excellent page. That includes both the ideas about placement and use of crossover frequencies that seem awfully high by the misguided standards of conventional wisdom.
 
Hi Pallas,

I'm interested in your subwoofer setup. I have been thinking about the Maelstom-X sealed and powered by a Crown K2 for ULF duty. It would be in combination with two Rythmik DS15 servo subwoofer kits currently in use. More output isn't needed, but more uniform response throughout the room would be a desirable goal. The Rythmik's are quite capable at the extremes, but may benefit from a little roll-off to limit excursion/distortion with the Maelstrom doing its thing. What's your thoughts on the Maelstrom's sound quality, frequency response, etc. Would you make the same driver selection if you were to do the ULF setup again?
Thanks for your insights!

Jerrod
 
I also take the multi sub approach, but not really small so therefor i don't know if this is a healthy comparison to what Mr. Geddes suggests. Front and center below the screen is a single ported 15" crossed at 80hz. Directly in front of the listening position is an LLT console table with dual downfiring 10"s and on either side is sealed 18"s crossed lower and eQ'd for a flatter response. In room response is very smooth and i'm pretty happy with it but for HT you can never have to much.

I believe a properly placed IB or mutiple IB manifolds is probobly the best way to go but until i convince my better half that it's OK to cut holes in the walls and ceilings, i'll leave well enough alone.
 
Three is what I'm proposing. All disguised as unassuming end tables and blended into the decor. Seems downright unobtrusive compared to the twin 23 ft3 folded bass horns that used to occupy my listening space! I'm getting pretty great results with the two cabinets, so I'm needing a push to add the third......will probably happen, but I'm not in a big hurry and weighing options....

Jerrod
 
jlharden said:
What's your thoughts on the Maelstrom's sound quality, frequency response, etc. Would you make the same driver selection if you were to do the ULF setup again?

I would recommend an XTi instead of a K2, though, because it should be cheaper and the built-in EQ is very useful.

Let me put it this way. I doubt I could reliably tell a difference between the Aura NS12, the Maelstrom-X, and the JBL W15GTi in my nearfield system if I didn't know what was playing and they were SPL-limited to the limits of the smallest piston (the Aura). It is simply exceptional, doing everything I could ask.

If I were starting from scratch and knew what I've learned through experimentation and reading since I started down the path that led me to the Maelstrom-X...I don't honestly know. I originally went with the Maelstrom-X because it addressed the shortcomings (in my system) of the Ascendant Avalanche 18 and was a drop-in replacement. And that I bought because my previous super-sub (three Peerless XLS12's with PR's) looked kind of funny when mains having drivers the same size as the sub drivers.

So, I'd probably want the main sub to be an 18" or maybe 15" driver regardless. (The other two would be exactly what they are, because they're beautifully built and I like the looks.) No science behind that thought, just because. A little bit smaller cab would be nice, but not necessary, though I'd spend more money to commission a cab that was finished like the other two subs. In the end, I imagine my choice would probably still come down to the Maelstrom-X, JBL W15GTi, the Aura NS15, with the winner chosen based on cost and availability. Unless I found a great deal on the 21" B&C driver, which looks great for a small closed box with EQ.

markus76 said:
Why do you people spend that much money on subs for a home listening application

Looks, mostly. Like I wrote earlier, with 12" mains, a 12" main sub looked kind of odd. In my head, at least. Also, to some degree a perception of effortlessness. If one knows in his head that he's never going to breach the performance limits of his system, then one stops worrying about such things.

In terms of price-performance, you're probably on the right track. Though I might have built one XLS12 or XXLS12-based main sub and two SLS10 or SLS12 subs if I had Nathan10's.
 
Thanks Pallas for your thoughts. I already have the K2 and a Driverack 260 for nearly infinite crossover and eq options. The Rythmik's are exceptionally articulate and I don't wish to lose that with the third sub. That gives some weight to adding a third identical sub, but I do have the necessary amplifier/DSP to explore other options. I will have to look into that *really* big B&C! Thanks again for your thoughts.

Jerrod
 
Oh, that's a different story. An XTi won't be cheaper for you!

The B&C I was talking about is the 21SW150. 6" voicecoil, 21" diameter, 15mm xmax I think. Ironically, it has almost exactly the same volume displacement as the Maelstrom-X. But with the bigger VC I would expect power compression to be even less of an issue.

I probably would not get a third identical subwoofer. If you want to stick with a known quantity, you might want to get the smaller Rhythmik instead for your third sub. (Or, if you want monster SPL, stack your current two 15's and add two 12" ones as "broadband" subs.) It is easier to place a smaller sub than a bigger one, after all, and placement is more important than unit quality IMO. And like I wrote earlier, I have not noticed any problems stemming from having much more volume displacement in the big sub than in the secondary ones.
 
To whom are you talking, Marcus?

The whole point of employing multiple subwoofers is to smooth out in-room bass frequency response, over as wide a listening area as possible. Nothing more, and nothing less.

And yes, I read the Welti paper (along with Dr. Geddes' postings on several fora) long ago.
 
Cal, take a trip and never leave the farm....

Cal, take a drive and come on down (er ...over, er... you know what I mean)
I'll treat you to the "Spirits". Stereo subs with lots o' juice and Dave's old Jordans. Methinks yer jaw might hit the ground , so wear a helmet with a chin strap ta keep it up where it should be ;)

Dave, I think the concept of multiple subs was effectively demonstrated at your place in the summer, the SD7/ fullrange types (if I remember correctly), and hey, your room is asymmetrical, multiple woofers/subs could be used to great effect (for bass reinforcement and "smoothness")

However...I can thank none other than Moray for demonstrating some subs to me years ago (15? 20? has it been that long?), in a place far, far away, in a land before time...

So many look at only the frequency response of sub systems. There are spatial cues in the nether regions, and of course it all depends where one might cross over the sub(s).

Peace

stew