Critical subwoofer tip

I assume that everyone already knows the importance of phase matching a sub to the main speakers but it’s a little more complicated than simple 90 degrees or 180. The B&W sub that I have has four choices. In every case there has been a definite correct position that can be non standard. My current setup shined at 270 degrees vs the std positions. It’s completely obvious and the other choices would not have been satisfying. 
From my lengthy experience I would want a subwoofer with several phase choices. I personally don’t see how one could seamlessly integrate the mains and the sub without this flexibility. No one asked but i thought this info might be useful to anyone purchasing a subwoofer. YMMV
An appropriate topic for me!

I just added the Martin Logan 1600X to my Classic 9 eStats. This subwoofer has all the adjustments you can think of via phone and tablets remotely.

I read the manual front to back. ML suggests (when pairing with their electrostats) to (through remote app.) INVERT the signal, and then dial the phase control to 90 degrees. I set all parameters to ’0’ otherwise and crossed it over with the 3rd order filter at 35Hz. I am really impressed so far.

Today, I await for the ’Bass Kit’ software to arrive. This sub connects to the laptop via USB and runs Anthem Room Control software. I will be eager to see what it comes up with. From the features, it can sample up to TEN positions at your LISTENING AREA. ...and then, once that is set, you can adjust the settings to your liking after the fact. (to taste, lol)

Can’t wait. Oh, and for the nay sayers on subs in 2 channel systems, I like the lowest octave of the symphonic bass drum when tuned low in orchestral music, and being a pipeorgan tech for the same company for 32 years, l sure want to experience those frequencies below 25 Hz. Now, how many PASSIVE stand alone speakers can really reach 16 Hz?

Right, therefore, a subwoofer is a great way to ’augment’ your 2 channel system when done properly.

Why else would Parasound put a point one on their P6 2.1 preamp with a built in LPF via balanced line?

Have a productive one my friends, and enjoy the music (O:
The effect of phase adjustment (or delay if you will) is clearly measurable if you do frequency sweeps around the crossover point. Setting the correct phase is much more important with a single sub, and less important to not important at all as you add additional subs.
Here’s some REW measurements I did today showing how changing the phase on the subwoofers effects frequency response.
This isn’t about how good/bad the subs/mains/room are.
No changes for volume or crossovers on the subs, phase only.
Descriptions in the images should be self explanatory.
The first image are the speakers, and basically my best attempt to get the frequency as flat as possible without using and EQ or DSP. The results are a combination of crossover/loudness settings and room position.
I tried adding a third sub yesterday, and couldn’t improve on what I have with two subs. Mind you, it’s only an 8"/150 watt sub, compared to 15" and 900 watts.

Setting the correct phase is much more important with a single sub, and less important to not important at all as you add additional subs.
Does it also become less important the lower you set your sub's roll-off point?  For example, I have two subs set to roll off at a pretty low 40Hz because of the low frequency extension of my main speakers.

If you're subs are hitting any frequency same as the mains, then it matters. It's either in-phase or out-of-phase, that is, the sub drivers are moving in the same direction as your mains. When they are out of phase, you run the risk of having frequencies cancel because the drivers are moving in opposite directions. There's lots of illustrations on the internet showing this.