What process did you use to integrate multiple subwoofers for 2 channel listening?

@hilde45 did I read correctly that your subs go down to 35hz and your mains also not much different in terms of low end extension?

If so, unless the 3 sub array is smoothing out the response at your listening position, there may not be much if any benefit with using any subs at least for those seeking flat response.

Your subs have a lot of controls though which should help tune in however many subs you throw at it to improve whatever might be possible, so that is a good thing.

Your sound meter is your friend. I used white noise as a source to get my sub tuned in optimally with minimal effort.

Some might seek more bass, not necessarily flat response. No problem. To each their own.

Generally, from a pure technical perspective though, you primarily use subs to extend the low end to pick up the lowest octave down to 20hz or so that is missing otherwise. If both subs and mains have same extension to lower 30s hz, they are merely adding more of what you already have, nothing new. Your bass down to the low 30s hz is a combo of mains + subs and you are still not picking up the full lowest octave most can hear (if even in the recording to start with which is typically not a given except with some better recordings involving instruments that produce music down there). See chart:

https://i.pinimg.com/originals/8b/4a/6f/8b4a6fd7b8d65711eed41850a194284e.jpg

I would think it could be very difficult to get a sub array to smooth out response ideally when the mains are also contributing.

If using a turntable, you may pick up power draining rumble or feedback down there which is a bad thing and should be eliminated or filtered if present and not done so already in the phono section of the amp, so need to be careful there. Are the woofers noticeably moving with a record playing and no music? That’s the sign if so. Not an issue with digital sources.

If your mains are truly somewhat responsive into the 30s hz, benefits of using a sub at all is marginal to start with. The control flexibility of even one in your case (rhythmik) would help.

Now if you are crossing over the mains at a higher frequency and offloading the low end below to the subs, then we are talking. That would have benefit of offloading work from you main amps which should be a good thing if done right.

Duke is the bass array man. See what he thinks.

@mapman

@hilde45 did I read correctly that your subs go down to 35hz and your mains also not much different in terms of low end extension?

Subs go lower than 35 hz. The mains are listed at 35 hz. I do not know their roll off slope. In the past, the addition of a single REL to these speakers always helped noticeably. Not dramatically, but noticeably.

You may be right that there’s not much to get from a 3 sub array. I’m definitely trying to test this out in the 30 day trial period for the subs.

To volume match, I need to see how I can get just the subs to play without turning off the tube amps.

No turntable.

If your mains are truly somewhat responsive into the 30s hz, benefits of using a sub at all is marginal to start with. The control flexibility of even one in your case (rhythmik) would help.

This is what Jim Salk said. BUT, I did notice a difference with the RELs. Let me add a report of the latest scan I did (I'm doing them right now):
I increased the bass about +5-6 db from 20-60hz, from nulls to small peaks (up to +3.5db) or so. This is just the latest scan and as you can imagine, pulling all those dips to the flat line or a little above is very hear-able.

Now if you are crossing over the mains at a higher frequency and offloading the low end below to the subs, then we are talking. That would have benefit of offloading work from you main amps which should be a good thing if done right.

I do not have the technology right now to do that.

All good. It’s also possible the speakers are not flat down to their lowest rating. Not uncommon. You would have to measure with a test signal alone to know as a baseline then add the subs. Room size, acoustics and amp are factors for that. Bigger rooms always need a lot more muscle for flat extended bass. Power needs increase exponentially with lower frequency and many  main amps alone are not up to the task of doing it alone at the lowest frequencies.

Hilde45, you absolutely can use a MiniDSP with powered subs you just bypass the crossover section. Many subs have a switch to do this.
powemi, the vast majority of sources now are digital, analog is the outlier except for a few very stubborn individuals. You just stay in the digital domain until you get to the DACs then amplifiers. If you have a turntable you use a high quality ADC to convert to 24/192 which is entirely invisible. Digital crossovers are far superior to analog ones in every way. The advantages of using digital signal processing and digital crossovers far out weighs and disadvantages. 

The instructions most sub manufacturers invent for integrating subwoofers are laughable. Using a one way crossover and trying to avoid matching speakers in time is...pathetic but otherwise there is no way they can be cost competitive. 

@hilde45 , thanks for your answers. You’ve obviously worked very hard on this and your results really are quite good, which makes that 88 Hz peak stick out like a sore thumb all the moreso!

Might it be a floor-to-ceiling mode? Do you have a lower than normal ceiling?

At any rate, here are a few ideas:

- I agree with @erik_squires that THIS is the sort of thing EQ is good at fixing (bass traps too, but I think EQ would be more cost-effective).

- You might try placing the Salks (very nice speakers, by the way) about six feet out from the wall behind them, which will result in the low frequency reflection off that wall arriving ½ wavelength behind the front wave at 88 Hz, hopefully providing some useful cancellation.

- Place one of your subs near the Salks. Run it up high enough that its output overlaps with the Salks in that 88 Hz region, and then adjust the phase control until the sub is CANCELLING the Salks enough in that region to make the peak live-with-able. If you can’t get the cancellation you need going from 0 to 180 degrees, then use the speaker-level inputs on that sub (if you aren’t already) and reverse the polarity of the signal going to them, such than now your phase control is effectively doing 180-360 degrees. You may need to do this overlap/cancellation trick with more than one of your subs, and/or you may need to use the parametric EQ in one or more of your subs to enhance the cancellation effect.

- The contribution from the Salks across the bass region may result in too much net bass energy before you can fully take advantage of what the subs can do. If so, stuff some open-cell foam in the slot ports of the Salks to disrupt the airflow, turning the box into an aperiodic enclosure. If this is a net benefit, you can look forward to further hours of audiophile fun as you fine-tune the foam-in-the-slots. 

- Another way to reduce the contribution of the Salks in the bass region is to wire a small capacitor in series with the amplifier’s input, perhaps by performing amateur surgery on an inexpensive interconnect. You can use an online first order highpass filter calculator, substituting the amplifier’s input impedance where the tweeter’s impedance would normally go. You will probably have some trial-and-error chasing down the best capacitor value.  (Maybe your system already has an easier way to roll off the bottom end of the Salks, but if so I overlooked it.)

- As a ballpark rule of thumb for a distributed multi-sub system (I avoid using the otherwise-convenient term “DBA” because it can also mean “Double Bass Array”, which is something very different), you want to get the subs spaced as widely apart as you reasonably can while distrbuted in as many dimensions as you reasonably can. My mentor Earl Geddes finds two subs are much better than one, and three subs are much better than two, and four subs are an improvement over three but not by as much. So imo you are definitely playing the distrubuted multisub game already! If you can elevate one of the subs so that it is closer to the ceiling than to the floor, you get bonus points. This is one of the things that @hleeid did to get good results in his 11 x 13 foot room; I think he actually elevated three of the four Swarm subs, as that was more practical than the other way around in his room. In your case though, I would still keep at least one of the subs near the Salks if you try that overlap/cancellation thing. For any of the subs which are not near the Salks, and especially if they are physically closer to you than the Salks, you want to roll off their top ends lower and steeper, so they don’t betray their locations by passing upper-bass energy loud enough for you to hear. If that’s not possible, then imo ideally you’d want those other subs to be farther away from you than the Salks so that their output is not the first-arrival sound.

- In my experience it is usually beneficial for there to be some deliberate phase variation between the subs, so don’t be afraid to twiddle those phase controls. The effects of the phase controls are more subtle than the effects of the subs’ volume and low-pass frequency controls.

Hope there’s something useful in this.

Duke