Will I benefit from a subwoofer with 20Hz speakers?

Sorry being so stubborn, but "eliminate" - no, "reduce" - yes. If you start from +/- 15 db shifts or more in the bass region, which most of us do (look at the measurement the op did), then I’d say there is no way a swarm setup will flatten that out so you won’t hear any peaks/dips .

@gosta 

No worries- I can't say I'm not being stubborn either. I can turn the subwoofer amp on an off in my system and the difference is dramatic. I was missing the range somewhere around 40Hz, which the Swarms sort out nicely. 

While the vendor's promotion online has been fair and honest the fan boys of this system are out of control.  From reading their posts and their attacks of the ideas posted above it is clear to me the fan boys have never heard a well integrated single sub so their opinion of any other ideas is at least misinformed if not down right deceptive. 

@erik_squires I've read this before (and the rest of it). I certainly don't agree with it either in tenor or theory. For one thing, I'm not a 'fan boy' (I think there was someone posting here who was, who is either deservedly banned or moved on). I've known Duke Lejuene of Audiokinesis (the primary manufacturer of subs specifically meant for use in a DBA, the Swarm) for 25 years. He is one of the more honest people you can deal with in high end audio, and is well educated in speaker theory and design. I've seen Duke pushing the DBA concept now for nearly 20 years. He's garnered 4 Golden Ear Awards for the Swarm simply because it works.

I don't find the application of a DBA in my installation to be particularly cumbersome or complex. Since I prefer the idea of running the subs off the preamp rather than speaker level (to avoid colorations) the use of a subwoofer amp in my equipment stand was easy to execute. I do run long speaker cables, but they are inexpensive- the kind that has one 'silver' conductor and one copper, like you get cheap at a hardware store. I think one run is about 22 feet. I just did this to see how well it would work temporarily, and it worked so well that I see no reason to change it.

Is it possible that since you've not tried it, you might have some mistaken impression about the complexity? The whole thing took me 15 minutes to set up and about 2 minutes (by following Duke's instructions) to dial in. Pretty simple IME.

Now I have several systems in my home. The main system, the home theater, my bedroom system and the basement system. Of those a DBA is only used in the main system. There are single subs in two of the others. To be clear, I'm acquainted with the idea that you can make a single sub work. In one system, I lucked out and the only place the sub could go works fine. In the bedroom system, I had to move the sub around until I found a spot that it could be heard when in the listening position- the most convenient spot rendered it inaudible due to cancellation (standing waves).

My point is you swarm guys always make it sound so easy. It’s not. Theory is fine. You might very well be able to break up a significant dip or “null”. But peaks and dips will still be there in a normal room and will need eq to get fully satisfactory bass.

@gosta 

You are partially correct here- Duke of Audiokinesis says the same thing you do: that the big peaks and valleys are eliminated and in their place are much smaller peaks and valleys which because of their small size become hard or impossible to detect by ear. Duke also says that after than has been done then use room correction and possibly bass traps to really get the room right. So you and he are nearly on the same page.

The formula here is that a DBA does about 95% of the bass correction needed in most rooms (by eliminating standing waves), and room correction and bass traps do the other 5%. The question of this thread though is there benefit to subs if your speakers already go to 20Hz and the answer to that is certainly 'yes' (if used correctly).

I mentioned above it took me about 15 minutes to set up my Swarm setup (keeping in mind I have two Swarm subs, not four, since my main speakers go to 20Hz already). Once I placed the subs (against the wall, out of the room traffic and mostly out of sight) I've not had to move them and I've not had to mess with phase. Pretty easy (so you can blame me for saying that), easier than my bedroom system where I had to crawl around and move the sub bit by bit to get it right.

Each to his own of course, I don't begrudge anyone who doesn't want to do it this way, but FWIW as I explained I have subs installed several ways. IME regarding this topic, those who denigrate this approach really haven't tried it.

 What you say is true, however if you were use a low cutoff filter at 40Hz. With most music I doubt if you could hear the difference. A subsonic filter cuts in about 40 Hz and I could never tell the difference apart from stopping the excess movement of the bass speaker.

@bishop148 

A filter has a cutoff frequency that is defined as the -3dB point. You will get phase shift above that frequency; up to 10X the frequency if a 6dB/octave filter is used, less if a 12dB filter is used but you get more of a 'bump' just above the cutoff. The ear perceives the former as a loss of impact.

I played bass in the orchestra for decades and now play keyboards in a band; I like electronia and there are plenty of ambient recordings that have significant material below 40Hz (roughly low E on a bass). Having a number of speakers laying around, I've two sets where the cutoff is about that frequency and I most definitely miss the bottom end using them without subs.

Yuo tell us acoustics is simple. Put two small swarm subs in the room and your ears won’t hear any peaks or dips. Well, to me it isn’t.

@gosta 

I didn't say acoustics is simple. What I did say is that setting up a set of Swarms is quite easy. I experienced immediate improvement. Also, I only use 2 Swarm subs because my main speakers are flat to 20Hz. I got away with 2 subs but most people would need 4. I can cycle the subwoofer amp on and off and the difference is obvious. 

@erik_squires The data sure seems to suggest a standing wave. There is a dip of about 8dB and then a peak. If this is at the listening chair as described it should be outside the room boundary effect. A bit depends on the room of course. But since we have that dip, no amount of power will correct it since its cause by cancellation. That's why you break up the standing wave with a distributed bass array. Then if the room still has issues they won't be hard to correct.

why I keep saying measurement is important, and we may be adding subs for the wrong reasons. Let the OP clean up his bass first, and then decide, based on his own needs and values if a sub is worth the trouble.

There is very little musical content in that octave 20-40Hz and in my experience having too much bass becomes annoying after a while. 

@bishop148 The point is not more bass! The point is to get the bass right. If the bass is deficient, the ear will perceive the system as being tilted to the highs; if there is too much bass the ear will perceive the system as being muffled in the highs.

@dmilev73 My main speakers are flat to 20Hz. But at the listening chair I have a cancellation, so no bass at that location, while nearly everywhere else in the room the bass is fine.

So I added a pair of Swarm subs. One is to my left, immediately against the wall (I actually have its driver facing the wall about 2" away and the other is behind me and to my right, set up the same way (the Swarm subs are designed to take advantage of the room boundary effect and so are meant to be directly against the wall; most subs are not). Because of the asymmetrical placement, the subs are able to break up the standing waves caused by the room itself. You can turn the subwoofer amp on and off; the difference is dramatic. Off- no bass, on- bass, off- no bass, on- bass. Obviously I leave the sub amplifier on.

So yes, additional subs can help out speakers that go to 20Hz all on their own.

Here are some facts to understand how this works:

1) the ear can’t know the bass note is there until the entire waveform has passed by it.

2) at 80Hz the waveform is 14 feet long; so by the time your ear knows its there, the waveform might already be bouncing off the wall behind you.

3) the ear can’t tell the frequency until a few iterations have passed. By this time the bass in the room is 100% reverberant.

4) because of 3), a mono bass signal can be used for the subs.

5) if you keep the subs from having any output above about 80Hz, they won’t attract attention to themselves.

6) the asymmetrical placement is important for breaking up standing waves.

More subs will also give you a better distributed bass in your room, some says. I’m not so sure that will help a lot. You’ll still have peaks and dips.

Yes, you still have peaks and dips but they are much smaller and are all over the room. Because there are so many more and they are less than 1/3rd octave apart the ear won’t acknowledge them. So it helps a lot!