Critical subwoofer tip

Worth noting that when choosing source material to tune phase with that is where a sound meter is crucial.  You have to be sure there is bass down in the frequency range the sub is covering.  Many recordings with good bass will not do much below 40 hz or so. So Adjusting phase on a sub with music containing little or nothing in the range the sub is covering will do little or nothing.  Details matter!  🏆

kick drum or many modern pop recordings with synthesized percussion will do nicely. You want to maximize the “kick”.

there I said something positive about modern pop recordings. 👏👏👏

Yes doing anything perfectly is always very hard but with the right sub to fit your system, a sound meter app on a smartphone and streamed white noise, doing it very well is not hard at all.

If you do that versus merely doing it by ear you might be surprised about the difference. 

also the more subs to integrate the harder it will be to get it perfect. That’s basic math. Well enough is always much less difficult.

Agree about the measurements needed to do it right and get full value from a sub. I use a simple sound meter app and white noise for level and crossover but not enough alone for phase. Have to tune that by ear and only after the other two are dialed in. YMMV.

My sub has continuous level crossover and phase adjustments. It is right next to my listening position so very easy to adjust properly. Phase matters the least of the three but still matters and makes a subtle difference on the sound. Granted it is not easy to get tuned in in many cases especially where sub cannot be adjusted from listening position.
The more subs the more randomized the wave patterns are in the room which is a good thing and playing with phase an exercise in diminishing returns.
Funny to me how everything is a black or white issue. Phase either matters always or not at all.   Even fuses:  same deal. Yardda yadda yadda. I know. I know. Thinking is hard. Sometimes I try to think but nothing happens.