Which is better for a DBA (Swarm); powered subs or unpowered?

Ha!, Very nice spinaker01. I hope advice from a fellow member of the 4-sub DBA Club (AK Debra system) will suffice for cheeg, instead.
My opinion is that 2 subs will sound and perform about twice as well as 1 sub and 4 subs in a DBA configuration will perform about twice as well as 2.subs. I first heard this opinion from the owner of Audio Kinesis, Duke Lejeune, but I’ve verified it’s accuracy via my own experiences in my own system and 21’x14’ room.
You’ll clearly notice the advantages of using multiple subs beginning with the use of 2 properly positioned subs and these advantages have been proven to be optimized in virtually any room and with any pair of main speakers with the use of 4 properly positioned subs. The advantages you’ll clearly notice are the bass being faster, smoother, more powerful and dynamic, more detailed and better integrated with your main speakers. The main difference between using 4 subs rather than 2 subs is that 4 subs will provide improved bass performance throughout the entire room while 2 subs will restrict this improved bass performance to a single designated listening position or seat. You’ll also notice the bass improves in its speed, smoothness, power and dynamics, detail, sense of effortlessness and integration with your main speakers as you move from using 2 subs to using 4.
No matter how many subs you choose to initially or eventually use, it’s very important you have controls to adjust the following: a regular Volume control for level, a Crossover Frequency for adjusting the frequency below which the subs become active and a Continuously Variable Phase control for fine tuning the sub‘s phase from completely in-phase to inverted phase and all points inbetween. If you use self-amplified subs, all 3 of these controls are required and need to be set on each sub individually. If you use a Dayton SA1000 sub amp/control unit with 2-4 passive (not self-amplified) subs, all 3 controls are set once on the Dayton SA1000 sub amp/control unit for all connected subs as a group.
If budget is a concern, I suggest you start by buying the DaytonSA1000 sub amp/control unit and 2 either used passive subs or 2 new passive subs from Parts Express or Monoprice. If you’re handy, you could save even more $ by building your own subs with kits or individual parts from Parts Express, Monoprice or any other source.
I just recommend you choose subs of reasonable size and weight, with a minimum of 10” drivers, rated bass extension down to at least 20 Hz and 4 ohm impedance if you can. Remember, 2 properly positioned subs will provide very good bass at your designated listening position only, but not throughout your entire room. However, it’s also possible, in some rooms, that 3 properly positioned subs will perform as well as 4 With very good bass throughout your entire room.
There’s also a unique wiring method you need to use for best results called series/parallel which I can detail later if you decide to go with this option.
Another option is to use wireless self-amplified subs such as Syzygy or another brand. I also know the SVS SB-1000 self-amplified subs are very good subs at a great price of $500/each which could work very well for you as either a pair or a swarm.

Tim

Is it possible to run 4 passive subs off of one amplifier, say like a Crown XLS series? Run in series or parallel? 

cheeg- sorry, my pager battery died-

Starting with $1000, am I better off buying two used powered subs, three less expensive used powered subs, or a subwoofer amp (eg Dayton SA1000) and two (less expensive) used unpowered subs? What is the advantage of having a discrete subwoofer amp?

Either way will work and depending on your situation and deals you might come across which is better could go either way. Either one will allow you to start small and build. So good question.

That said, the Dayton approach has several advantages:

Reliability- powered subs typically use plate amps that are not all that reliable. Dayton and Parts Express are more reliable.

Quality- having the amp separate from the speakers makes it easier for you to select higher quality subs. With powered subs a little bit of each purchase goes into the amp. You’re buying amps over and over again. So you can get a little more speaker for your money this way. Also if you DIY you can get a lot more speaker this way.

Flexibility- The Dayton has just the EQ, level, filter, boost, and phase control that you need. Most powered subs will have these too. But buying on a budget maybe not all or quite as good. With the Dayton no worries. Also with the Dayton when you get more subs you’ll be able to experiment with connecting subs in series or parallel to change the impedance which changes the sound, which turns out to be a pretty good advantage.

Convenience- With the Dayton you set levels all at once. One interconnect. One power cord.

Main thing to keep in mind when going this route is the unbelievable benefits of a DBA really have more to do with the number of subs than anything else. So you will probably get better results faster with 4 cheap subs than a Dayton and one or two better subs. In the long run though as long as you are sure to complete this with 4 (or more- I have 5 and the 5th really did make it better) then I think the Dayton is the way to go.

Maybe even bigger thing to keep in mind is you just can’t imagine how good the bass will be. Its something you have to experience to believe. Maybe not even then. Had mine a year now and it still amazes me.

Oh, and doing one does not rule out the other. You can do both. Have you seen my system?
https://systems.audiogon.com/systems/8367

Great responses -- thank you!
@spenav what is REW?
@spenav and @noble 100 How would you send the wireless signal to the sub? Wouldn't that eliminate the benefit of reducing the main amp's need to drive the lows?
@noble100 I may hit you up for that series/parallel wiring info; is the benefit related to controlling the impedance of the swarm, or something else?
@millercarbon thanks for the details -- you have a beautiful system, but I couldn't tell from the photos if you were using both powered and unpowered. Do you run your powered subs through the sub amp, too? If so, what is the advantage?
@mofojo I'm pretty sure you can run 4 passives off of a Dayton, but I'm not sure about the Crown. Maybe someone else who knows can respond.

Some subs (I think REL is one) allow you to wire them in a way that reduces the burden on the main amp to cover frequencies below a set cutoff, like 80Hz. Does anyone know if that is possible with the Dayton? Finally (thanks for your patience), is it advisable to use all the same brand/model of subs in the swarm, or does it not matter?

@millercarbon thanks for the details -- you have a beautiful system, but I couldn't tell from the photos if you were using both powered and unpowered. Do you run your powered subs through the sub amp, too? If so, what is the advantage?

Look real close at image #9 you will see a dirt cheap POC IC going from the Melody to the Dayton amps. Its fake gold with a spring and white and red o-rings. A real POC. Immediately to the left of it on the Dayton is a clear plastic IC with a silver RCA with 3 black rings, and just below it you can just barely make out the other one with 3 red rings. The signal from the Melody comes into both Dayton amps, then uses the Daytons built-in bypass to connect to the additional Talon Roc powered sub.

So its "through" the Dayton but Daisy-chained not actually running through any amplification, EQ or level circuits. 

Some subs (I think REL is one) allow you to wire them in a way that reduces the burden on the main amp to cover frequencies below a set cutoff, like 80Hz. Does anyone know if that is possible with the Dayton?

This is another one where you'll hear guys who love tech more than music tell you all the wonderful tech reasons to do this. There are wonderful tech sounding reasons for doing all sorts of things that don't really work out well in practice and this is one of them.

The idea is supposed to be that by relieving the amp and speakers of the majority of energy which is bass that you will get improved detail and a greater sense of ease, and on and on, probably cure cancer, almost certainly cure cancer if a REL is in there somewhere. Amazing sub, REL. Don't even need a DBA all you need is a REL. Yeah I am being super sarcastic.

Because, always left out of the equation is the detail you lose running that signal through the crossover circuit, and extra interconnects, and how its all affected by the quality of the power and on and on and on. They conveniently leave all that out.

What they also leave out and this one is even bigger, is the whole reason we're doing DBA is to take advantage of the superiority of having a lot of different bass sources. Of which your two main speakers are two additional sources. So you shoot yourself in the foot with the bass, add extra stuff in the signal path, don't get the improvement they promised, and actually make the bass worse in the process.