Subwoofer recommendation for swarm

One feature you might want to look for is a steep rolloff slope for the variable-frequency lowpass filter. You want to rapidly roll off the top end of any subs that are closer to you than the main speakers are, so that they don’t pass upper bass/lower midrange energy loud enough to give away their presence. (The ear tends to localize by arrival time, which is why this matters for subs closer than the main speakers.) If that’s not possible, then use a lower low-pass frequency setting for subs that are closer to you than the main speakers, and a higher low-pass frequency setting for subs that are equal distance or farther away than the main speakers.

In case you decide to "roll your own", here is the amplifier I use, which has a 24 dB per octave lowpass filter:

https://www.parts-express.com/dayton-audio-sa1000-subwoofer-amplifier-rack-mountable--300-811

Parts Express offers several passive subwoofer kits (you’d have to paint or othewise finish the enclosures after assembly). 

So does SpeakerHardware.com. I designed three high-output 12" subwoofers which are offered as kits by Leland Crooks of Speaker Hardware. (I don’t get any royalties or other kick-backs from the kit sales, just so you know.) Four of these plus the Dayton Audio amp would strain your $2k budget, but I mention them just in case.

Duke
Swarm guy

Would something like a miniDSP with 4 output channels fit the bill?

Duke - Do you recommend trying to feed a stereo signal to the swarm? Summing left and right to mono? Only running the right channel to all four subs? Something else?

My DIY Swarm was built earlier this year. Based on Duke's and using two of the Dayton amps he recommended above, together with four 10" Morel woofers from Parts-Express the total cost excluding Rosewood veneer was not much more than $2k. You could easily build it for less than $2k simply by using one Dayton amp instead of two. Two are not really necessary, the extra amp just adds more flexibility. Based on my experience the first thing I would cut to save money is the extra amp.

Even if you have your own shop and skills and materials its still hard to beat the kits. I have all that, including the MDF just sitting there, yet still went with the kit. Savings in sawdust alone makes it worth it. Although if you have the time and inclination to dig into it you might be able to learn enough to make your own enclosures custom for your particular situation, which might repeat might be worth it. 

I would also seriously consider anything Duke has to say on the subject. He was a huge help to me and always recommending whatever would work best for me, never pushing anything in particular even though it would have been much easier to just try and sell me his Swarm.

There are a lot of options. By far the most significant decision you can make is the one to go with a distributed bass array. The DBA is so inherently better than everything else its hard to believe until you experience it first hand. 

How do you distribute the subs? Can they all be on the same side of the room or on just two walls?

mkgus, a DSP designed for bass management will work fine. The subs can be placed anywhere in the room. I think against a wall or in a corner is best as this placement increases efficiency. I would put the two front subs in the front corners and the others anywhere. Ideally if your crossover is low enough a mono bass channel is optimal. With a swarm system I think it behooves you to use a cross over below 80 Hz and as Duke suggests use a steep curve, 24 db/octave or higher. If you are using a DSP bass management system I have seen crossovers as steep as 80 dB per octave which I actually think is too steep. The speakers do not blend well. 48 dB/oct is the steepest I would use. If you put them all along the front wall they may actually overwhelm your speakers. It is always OK to experiment. Just leave yourself extra wire until you are sure of the placement.