There's a lot more bass in a 6.5" driver than most of you think

     I'm a big fan of the 3-4 sub distributed bass array (DBA) concept. Although I've only personally used the 4-sub Audio Kinesis Debra DBA system in my system/room, it functions so incredibly well that it's not hard for me to imagine that a 3-sub DBA could function nearly as well.
     I agree with Erik that a single sub properly positioned, with PEQ and DSP correction can provide good bass response at a single designated listening position but will likely result in poor bass performance at numerous other positions in the room.  
     There are a few other downsides with this approach. One is that PEQ/DSP is very good at attenuating bass peaks identified at specific bass frequencies at the listening seat, since it simply decreases output power demand on the amp(s)at these peak frequencies. However, PEQ/DSP is limited in its ability to correct all bass dips and nulls identified at various specific bass frequencies at the listening seat, since these require increasing and not decreasing power at these bass dips and nulls. This takes a lot of power especially at deep bass frequencies to correct and the amp(s) need to be powerful enough to supply power for both the normal deep bass notes and the very sudden and high power demands for bass dynamics at varying deep bass frequencies and amplitudes. So, it's really not a limitation of the PEQ/DSP circuitry itself, but a limitation of the amp(s) that must meet this circuitry's power demands.  
    Further, powerful high quality class AB sub amps, possessing more moderate damping factors, reproduce more accurate and natural deep bass frequency note's decay times than high quality class D amps, possessing extremely high damping factors, are capable of. The use of class D amps to power subs often tends to result in the truncation of deep bass frequency note's decay times which sounds inaccurate and unnatural.
    In my experience, I've also found that 2 subs perform and sound about twice as good as a single sub at a designated listening seat. I believe this is due to two factors:

 1. 2 subs reproduce deep bass that is more powerful, dynamic and seems more effortless than a single sub because the bass output of both subs is cumulative and each individual sub is operating nowhere near its limits.
AND
 2. The use of 2 subs, each optimally positioned sequentially and independently in relation to the designated listening position, begins to provide the benefits of having multiple subs launching bass soundwaves into the room and these benefits increase in degree as more subs continue to be added to the room (with diminishing improvements resulting beyond about 4 subs); these additional benefits are bass that is perceived as being smoother, faster, more accurate, more detailed and better integrated with the main speakers.  
    Continuing on the bass upgrade path,I've found that the use of 4 subs independently positioned in a distributed bass array sound and perform about twice as good as 2 subs, maximizing both categories of bass quality improvements listed above.
    My claim is not that the 4-sub DBA concept is absolutely the best bass system in , it's just definitely the best I've heard and used to date. I believe a linear bass array(LBA?), with multiple subs lined up horizontally along the front wall at precise separation distances between them, could outperform a 4-sub DBA. But the LBA concept has serious downsides like the need for no rear wall for soundwave reflections to reflect off of and its dreaded and awful WAF.

Tim

@noble100

I agree with Erik that a single sub properly positioned, with PEQ and DSP correction can provide good bass response at a single designated listening position but will likely result in poor bass performance at numerous other positions in the room.

What you are missing from my argument is bass traps. I never said EQ alone solves all issues, but rather that EQ and room acoustics are complementary.

In theory, you could fix all room modes with proper bass traps, but few of us are able to afford something akin to the Magico listening room.

The magic sauce is the use of both. The traps stop the ringing, the EQ corrects what’s left and you can get something damn good that works for multiple listening locations.

Of course, a true pro will measure several different listening locations and attempt to use an average to decide what to adjust.

Still, Toole’s argument of "how do we know what is right" holds true. Even after this, the use of a discriminating ear is very valuable.

Also, to reiterate, I have nothing against the swarm besides cost, complexity and space. :) I mean, as far as I can tell from reading it should sound great. It’s the cultishness of the idea it is the ONLY possible way to have good bass. It isn’t.  If you have the money and space for 4 subs, by all means, have at it, but don't compare it to a poorly integrated single sub as proof it is the only way to go.

Best,

E

For those interested in "room EQ", including bass, this is an interesting discussion that Floyd Toole joined and argued for multiple subs. It's fairly long, so for those with limited time I quote below relevant excerpts from dr. Toole's contribution. 
https://audiosciencereview.com/forum/index.php?threads/an-enticing-marketing-story-theory-without-measurement.7127/

..." Below this [transition] frequency judicious equalization can be used to address individual prominent room resonances, but it is only functional at the point of measurement - the prime listening location. All other seats will be different. This is the reason why multiple subwoofers are advantageous, along with the greatly increased efficiency.

The one area where EQ is unquestionably needed is in the bass, below about 400-500 Hz - room modes and adjacent boundary effects. It is necessary to attenuate resonant peaks, avoiding filling narrow acoustical interference dips. With multiple subwoofers it is possible to attenuate room modes and for the EQ to benefit more than a single listener. It is not difficult, but not everybody does it. Other mistakes result from trying to "fix" non-minimum-phase ripples in steady-state room curves. EQ at mid and high frequencies should be broadband "tone control" kinds of spectral balance adjustments, but too many systems think they know better.

With bass performance accounting for about 30% of our overall factor weighting in sound quality assessments there is work for EQ at low frequencies - at least for the prime listening location. The fundamental problem is that all bass sounds are propagated through a three-dimensional acoustically resonant chamber - the room. There is no dominant "direct" sound in the normal sense because at all resonance frequencies the energy builds at a rate determined by the Q, and correspondingly decays. This behavior is different at every location in the room, meaning that multiple listeners do not share the same bass experience. To address the needs of multiple listeners multiple subs are powerful assets in attenuating room resonances and thereby reducing seat-to-seat variations. With signal processing in the signal paths to each of the multiple subs room modes can be made to almost disappear, certainly pushed well below thresholds of detection (e.g. Harman's Sound Field Management). Section 8.3 describes elaborate research on this topic, one finding of which was that active multiple sub solutions were better than necessary at attenuating room resonances - a nice result. Because humans tend to ignore ringing - now there was a surprise - even relatively crude frequency response smoothing at bass frequencies can be greatly beneficial.

Any woofer or subwoofer I have ever encountered does not change its power response "vigorously" - they are minimum-phase systems that are quite well behaved. However, room modes/standing waves do change dramatically with location of the ears or mic. That is the problem to be addressed. Mode cancelling/attenuation using multiple subs greatly simplifies the situation, but only when the budget allows. Good news is that with multiple subs the total system efficiency rises, so they can be smaller subs.

My present system uses four subs in a sound-field-managed configuration. There are no "booms". Bass is exceptionally "tight", and there is no audible evidence of being in a small room in what is heard at low frequencies - no measurable or audible resonances.

In my room with four small SFM processed subs fhere are no audible modes in the sub range - the room is "gone", leaving only deep tight bass  No bass traps required. Not everyone realizes that multiple subs are highly efficient - more small subs are vastly preferable to a single monster sub.

...There are passive multi-sub solutions for rectangular rooms:

Welti, T.S. (2012). “Optimal Configurations for Subwoofers in Rooms Considering Seat-to-Seat variation and Low-Frequency Efficiency”, Audio Eng. Soc. 133rd Convention, Preprint 8748.

The core of the problem is resonances in small rooms. Bands don't play in small rooms. A real drum energizes a certain set of small-room modes, giving it a room-modified sound. The same thing happens with a single woofer in the same location. Different small rooms would yield quite different real and reproduced drum sounds. 

The notion of multiple subs and EQ is to neutralize the contribution of the room to what we hear, so that we have a better chance of hearing what the mic picked up and the recording engineer heard.

Seemingly endless promotion of "room EQ" algorithms - a for-profit exercise - is partially responsible, aided by human nature which is inclined to believe a good story. It is an ingredient in "faith based" audio - if you believe it, you just might hear it. Even though some EQ exercises "sound similar" does not mean that any are as good as they could be - perhaps the important similarity is at low frequencies."...

I have Active Linn Tukans, and they sound excellent, no need of any subwoofer. After more than 40 years I founded that the room is the most important aspect.

The one area where EQ is unquestionably needed is in the bass, below about 400-500 Hz - room modes and adjacent boundary effects. It is necessary to attenuate resonant peaks, avoiding filling narrow acoustical interference dips. With multiple subwoofers it is possible to attenuate room modes and for the EQ to benefit more than a single listener. It is not difficult, but not everybody does it. Other mistakes result from trying to "fix" non-minimum-phase ripples in steady-state room curves. EQ at mid and high frequencies should be broadband "tone control" kinds of spectral balance adjustments, but too many systems think they know better.

Well, finally we have enough nuance here to pull apart all the different discussions you’ve been conflating, @pirad. Honestly Pirad, being so well read I have to wonder what your motives are. Did you deliberately misread the Toole article you shared?

This paragraph is pretty much what I’ve been recommending, with the caveat that again, he’s not considering the use of bass traps fully. Bass traps will make those narrow sharp dips less deep, and therefore correctable. He’s talking about the exclusive use of EQ, alone. I have never suggested that as a panacea. I’ve always said that the room acoustics enable the EQ to work. And in fact, his statement here is one you’ve argued against:

The one area where EQ is unquestionably needed is in the bass, below about 400-500 Hz - room modes and adjacent boundary effects.

Yes, this is exactly my point. He’s also recommending a light hand, again, agreed to. Didn’t you try to tell us all EQ was all bad? It’s pretty interesting how you can pull out so many great articles and conveniently omit what doesn’t suit your promotion of swarms. In fact, he never says "if you use multiple subs you don’t need EQ."

Now again, in detail:

With multiple subwoofers it is possible to attenuate room modes and for the EQ to benefit more than a single listener.

Correct. He doesn’t say "you can’t do this with an EQ and bass traps" which is what you keep reading into his words. In fact that’s the whole problem. You keep reading entire phrases into his articles in a very self-serving manner. In fact, like bass traps, he’s saying that multiple subs make the EQ work better. This shoots your entire agenda of not using EQ at all completely out of the water. Wow, @pirad, you’ve basically destroyed your own arguments with Toole. Again.

My original statements, are and continue to be, one sub with bass traps and proper EQ is amazing. I know because I’ve measured and heard it. Further, good room acoustics make small speakers sound larger. They do this by controlling the resonant modes which make the bass sound flabby and boomy. So, again, the vector for the frugal audiophile who wants to limit his hardware purchases to me is clear:

Room acoustics --> Subwoofer --> DSP for EQ and integration


What you may be missing also is that DSP isn’t just about EQ. DSP also plays an important role in setting the proper crossover settings and delay, which JL Audio also points to. And, like Toole, I’ve seen and heard horrible, absolutely horrible sounding ARC. It’s gotten much better, and JL is one of the better brands. It is also FAR TOO EXPENSIVE. Really, besides the woofers, the main selling point of JL is how good they sound and how easy they are to install and have sound good.

So, given that the average audiophile is not a speaker builder, if they don’t have room for a swarm, a single sub, well placed, properly integrated to the room and speakers is really a great solution. Two is better.

The only area of contention really is how good automated systems are, and that as other acousticians have found, you can even fix unfixable dips with the right room acoustics.

And what if you don't want a sub? Again, room acoustics are where you start.