Question for experienced distributed bass array users


I run an active multichannel stereo system where everything below 70Hz is handled by one channel that sums R + L and sends to two subs. The subs are sealed DIY enclosures for Rythmik DS1200 kits and I want to add one or two additional subs to create a DBA. Ideally I would build additional units based on the same Rythmik kits which provide good flexibility through their PEQ plate amps. But I live overseas and importing these becomes expensive. Plus I recall Earl Geddes saying the third & fourth sub didn’t need to be powerful or as good as they do less work, and commercially available DBAs I understand aren’t necessarily 12” or include PEQ options.

So I’m considering to build sealed DIY boxes with suitable 10” pro drivers and locally available, non-audiophile grade class D amps, and use together with the Rythmiks. All the subs would get the summed mono signal with digital room correction applied to the channel.

What do you guys think? Better to get one Rythmik kit or two plain Jane smaller sealed boxes?

Thank you in advance!

PS: Please let’s not go into merit/demerit of DBAs. I’m convinced it’s the way I want to go; just asking for opinions from experienced users about alternative paths to it.
I'd go with two.

Mine started out with one Talon Khorus sub. Then I built 2 sealed and 2 ported cabs all using the same 10" Morel drivers and powered by 2 Dayton amps. Awesome results and I was initially going to sell the Talon. Until for kicks decided to put it back in. Hate to diss a pioneer like Geddes but the improvement from adding that 5th sub was pretty big. Especially in terms of apparent extension. For whatever reason I do not understand the same sub that never did make really deep bass when used all by itself suddenly now when added to the other 3 makes awesome subterranean bass. So now my DBA is five and I say when it comes to subs more is better.

I'm all about thinking and being creative in getting the most for the money. Even though I have two Dayton amps the main benefit of two was being able to try different things and learn that connecting for 16 ohms sounds a lot better than 4 or 8. There's four times the power and 6 dB more volume at 4 vs 16 so it doesn't seem like that would be the case. What happens though is the extra power and volume only makes a difference on the brief few peaks where you would otherwise be clipping, while all the rest of the time it gives bass that is not nearly as taut and tuneful and well controlled as at 16. Whereas with 16 it sounds better all the time, you just have to be careful not to over drive it because these Dayton amps sound just awful when they clip.

So since you are hands-on capable I would suggest looking at your amps and speakers and considering wiring them in whatever combination will get you to higher impedance with fewer amps. In other words run them all off one plate amp, or two, whatever works with what you have. Because I just don't think you will get much if any benefit from buying more amps.

The other nice thing about having four vs three is it seems to me from everything I've read and done that the more you have the less it matters where they go. I mean technically yes of course it is hard to see how it would not matter. With one sub it certainly does. With four or five though I have moved them around one or two at a time and not noticed any difference. Maybe with the right music? Dunno. Tim I'm sure will chime in. He has even more experience than me, except when it comes to DIY.

Lewinskih, you risk being unhappy with the results. If you like the subs you have hang on for a little while longer and save up for identical units. 
It is absolutely not true that the additional subs can be of a lower quality. They should all be identical. 
I can see how the quality of the additional would not be as important. With more than two you are just smoothing out the room modes. 
Wait- what thread is this? What was the question again? Oh yeah:
Question for experienced distributed bass array users
Really? Sure that's all you want?
just asking for opinions from experienced users about alternative paths to it

Sounds pretty sure to me.

I think you should build one more identical to what you have. That would be easier to set up. You can always add the fourth later. I have four myself and sometimes I turn off the last one and notice very little difference. I could easily have lived with three. Setting them up properly is very important. Pay attention to the time domain as well as the frequency domain. If done right, three should get you 95% there. Hope that helps. 
Thank you guys.

@millercabon: indeed, the more the better as it smooths out frequency response better. I believe Geddes was saying that in the context of minimizing the number of subs, saying optimally placing 3 subs got you almost there (FWIW, like @spenav says above), with a 4th getting you to "100%". That is 4 subs optimally placed get you to his 100%. If the "optimally placed" part gets relaxed, then you need more subs to get you to "100%" (whatever that is). With clear diminishing returns.

This has made me think my listening area is the living room and as such the location of the subs is constrained by living space, so no optimal. Therefore 4 subs should be significantly better than 3.

BTW, millercarbon your experience with mixing 3 different types of subs and getting great results gives me a lot more confidence in the path. Thank you!
Right. I have one Talon Roc, two sealed 10" and two ported 10". Main speakers are Talon Khorus. In the beginning with just the one Talon Roc I tried many different locations none of them working until I finally gave up and lived with the least bad location. Didn't know at the time this is what always happens every time no exceptions when using only one sub.

Then when I built the 4 DBA subs I just put one near the wall different distances from each corner and immediately without any effort at all had bass that was better than I ever heard anywhere ever before.

This bass by the way, without any attempt at integration was not only seamlessly integrated but tight and fast and articulate and powerful and smooth and extended. The bass in other words was darn near perfect and all I needed to do was adjust the levels. My Dayton amps allow both level and EQ and phase adjustments. Rather limited EQ, it really only allows one peak or trough to be tweaked, but with DBA that is more than enough. Phase theoretically must make a difference, although in practice I have never been able to hear it. Duke and Tim seem to, so maybe this is one of those things where there is a difference its just hard to notice until you learn to recognize it. Not having ever heard bass like this before maybe I will in time. What this does however is put it in perspective. The bass is so good most people, even really diligent picky listeners like me, will consider it more than good enough. 

Now having read Geddes as part of my due diligence before building my DBA it seemed adding a 5th sub would bring marginally less improvement. Instead it was a pretty significant improvement. Just my opinion, but I don't think this has much if anything to do with optimal placement. When the Roc went back in it did not go where it was, it just went where I had room. Even so, as I said before, suddenly with that 5th sub I was feeling crazy low bass, much lower than I ever heard from the Roc back when it was used solo. 

In hindsight there's actually a pretty good reason why this would be the case. The Fletcher-Munson curves are a graphic representation of how we perceive sound levels at different frequencies. What they show is when it comes to very low frequencies, below a certain level we just don't hear them at all until they get loud enough. But then when they do get loud enough to cross that threshold all of a sudden we hear them really well. This makes bass especially hard to do. Because until the bass gets loud enough to hear you can change the level 2, 3, 4 or more dB and hardly make a difference. But then suddenly when it reaches the threshold even a 1 dB change matters.

So in a way Geddes is right. Adding that one sub probably only improved things a very small amount. But that amount was enough to get me to the threshold where it is perceived as being a lot.

This is a good example of one of the many ways really low bass is so very different from, and requires different approaches than, the higher frequencies from the mid-bass on up.