Will I benefit from a subwoofer with 20Hz speakers?

@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

This is really a side comment and doesn't apply to main speakers vs subwoofer.  I have found that frequency response down to 20 Hz is not necessarily that important, especially for music.  There are definitely recordings which you can get that do go down to 20 Hz, but they are a rare item.  If you really look at how most people respond to bass in music, the most important area is the 40-70 Hz area.  That is where we feel and perceive most of the visceral impact of bass.  The low 20 Hz rumble is nice, but if you have a hole or bass null at 50-60 hz, you will feel a significant lack of bass.

Oh, one more note.  I would be very careful about using Dirac to eq the response of these speakers flat down to 20 Hz.  The Cabass is stated to having response down to 41 Hz, which is definitely possible with the right 6.5" drivers.  However, past a certain point, the driver response is radically reduced the closer it gets to 20 Hz.  While those drivers -could- be reproducing a 20 Hz signal, the actual sound level can be something like -20db or -30db.  This means that Dirac is putting a +20db eq for the 20Hz point and will create a massive over-excursion of the speaker cone if you do actually hit a sound with this frequency.  This will definitely cause the woofers to either peak and clip - and can damage your speakers.

 IMHO don't waste your money. There is very little musical content in that octave 20-40Hz and in my experience having too much bass becomes annoying after a while.