Critical subwoofer tip

I have a question for people who have phase controls for their subs. How do these work?

see ieLogical SubterraneanHomesickBlues

Most Phase controls are All Pass filters. They don't affect all frequencies equally. see http://www.ielogical.com/assets/SubTerrBlues/PhaseControl.png

To properly integrate a 'generic' sub controls for Level, Phase, Polarity, Crossover Hz & Order are required. Delay is icing on the cake. Bespoke subs mating to a specific set of mains may get by with fewer controls.

MC's response is nonsense. But I repeat myself.

Thanks @golfnutz I get it and their reason to listen for minimum bass makes sense.  I suppose with two subs, the method would be to measure and adjust each sub separately, one at a time.

Miller Carbon and all of you that are "amazed by his knowledge" need to come to my house. My Velodyne subs, like the OP’s, also have four selectable amounts of phase delay. If you can’t hear the differences in 0, 90, 180 and 270 degrees with your ears and see them on an spl meter, then you are deaf and blind.  This is a system with two subs rolling off above 40Hz and the loudspeaker pair running full-range.

While it would seem that getting the phase to match the mains is ideal, theoretically this isn't necessarily going to result in no peak or notch at the crossover point.  Not unless the slope of the cutoffs for both are the same.  For a mains woofer, in a cabinet, this isn't actively controlled and is prob more gradual than a sub.  Perhaps this is why best sound and SPL may be something other than zero.  It mitigates that complex interaction, peak or notch.  One of the advantages to wiring speakers to a (some) sub's speaker output and using its high-pass.   Also, distance from sub to listener vs mains to listener further makes this issue more complex.   Adjustable phase is an aid for both issues.  Good stuff on this (in discussions of tweeter to woofer xo designing) at Linkwitz Lab site.  

Fun little story...  I was helping my brother set up and dial in his 2 Sumiko S9 subwoofers. I played around with them for a few hours and just couldn’t get them to sound right. Turned out that I had one of the subs 180 degrees out of phase and it was pretty much cancelling out all of the bass from the second sub.