Will I benefit from a subwoofer with 20Hz speakers?

@dmilev73  Yes you will definitely benefit from a sub or 2 or 3  When this is suggested people think of being overpowered by thunderous bass which if properly implemented is not that at all. Think of the subs as tuning devices. An enlightened poster mentioned a SWARM and I encourage you to read up on this. (aka DBA)

But the thing is that rooms and speakers are random.

This comment displays a lack of understanding. If nodes developed randomly it would be impossible to treat them because you have a moving target. Any given speaker in room will set up a consistent pattern if nothing is added or removed and the doors, windows and drapes are left as they were when first measured. Come back in a week or a month and the room will measure exactly the same.  Nothing random about it.

@lanx0003, Who told you to toe-in your speakers to cross in front of you? This relies on the proximity method and works with speakers that use constant directivity waveguides and a power response that is even.  A 180 degree waveguide, like the ubiquitous dome tweeter will not work which is probably what you have. A CD waveguide toed-in like you tried provides great imaging and a nice w-i-d-e  listening area.

@lemonhaze Erik (@erik_squires) has advised so.  So let me get this right since it is kind of interesting.  You mean if you had CD waveguides tweeter like horn, you will benifit from toe-in to cross in front of you as it will provide great imaging and wide soundstage AS COMPARED TO straight or slight toe-in, right?  I wonder what is the "theory" behind it but will definitely give it a try when I get or audition speakers with CD waveguide tweeter someday.  It may be my biased preconception but I never had an interest for horn speakers as it are a bit too bright for my taste.  But maybe some other less "agressive" (not sure if this is a right description) CD waveguide tweeter speakers will serve me better.

It’s good you’re using Dirac in that room otherwise your system would be unlistenable because of the bass amplitude.

But I’m not sure there is a need for using Dirac above 500hz.

And, don’t trust the Dirac curve too much. If you measure your system as @djones says you will almost certainly get something else. And what you measure right now may also be distortion to a great extent. The freq. curve is just the beginning.

I use some Dirac for the bass yes, but then apply Roon eq according to my hearing.

I’m not of the opinion that Dirac and similar dsp tools gives a too lean bass. Quite the opposite. Don’t trust the smooth calibration curve.

I also use a phenomenal sub to my true 20hz speakers. For the possibility to show off when someone wants more bass :-) but also for HT use and for the fact that some recordings really need a push down low.

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.

@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!

This comment displays a lack of understanding. If nodes developed randomly it would be impossible to treat them because you have a moving target. Any given speaker in room will set up a consistent pattern if nothing is added or removed and the doors,

Thanks for taking my comment out of context, @lemonhaze

My meaning was that most audiophiles should not take the -3 dB point of a speaker and think that it means much once it is in a room. While the physics of room modes is understood, the final -3 dB point of a speaker in a room is not something anyone can gauge well by back of the envelope calculations. That is what I meant by "random" and why I encourage measurement as a much better place to start than speaker specs.

Room mode simulators like the great one from AM Acoustics are fantastic tools which should be leveraged when considering room treatment, and I encourage it’s use as well.

https://amcoustics.com/tools/amroc