Distributed Bass Array configuration

Another novice arguing that it can matter and it's not all mono. SOME benefits of running subs as STEREO. Paul McGowan. 
https://youtu.be/Pp-0vvqERAs?t=254
But what would he know?

Brian Ding includes a continuously-variable 0-180 degree (0-16ms delay) Phase Control on his top-level Rythmik subs for a reason. If a loudspeaker is mated with a subwoofer or two---the speaker and sub(s) used with an electronic cross-over set to, say, 80Hz, the loudspeakers receiving a high pass-filtered signal, the sub(s) a low pass-one---if the loudspeaker and sub are reproducing an 80Hz signal in opposing polarities---creating a null at that frequency, the two will produce a combined frequency response with a deep notch centered at 80Hz. The Phase Control is provided to make possible getting the loudspeaker and sub in phase at 80Hz, thus avoiding the deep hole in frequency response centered at that frequency. This is loudspeaker design theory 101.

As for stereo bass in recordings: some music contains two---or even three---different basses being played simultaneously. Brian Wilson has an electric 4-string, an acoustic (upright) 4-string (both producing a bottom note---E---41 Hz in frequency), and a baritone 6-string all playing at the same time on some of The Beach Boys recordings. But Brian mixed to mono, one reason being he wanted to determine the balance between all instruments and voices, not leave it to the mercy of the hi-fi speakers and their placement.

But some recordings made in large churches, cathedrals, and music halls (Classical, mostly) are well-known to contain out-of phase low-frequency information between the two channels in a true stereo recording, caused by the long wavelengths created in large rooms. Left and right channel mics may received sound from the same sources at different times---the very definition of phase. The bottom note played on an organ fitted with a 32 ft. pipe produces a 16Hz tone! Recording engineers work hard to keep the sound of the room intact, which requires maintaining that out-of-phase information at low frequencies (you can read about it---it’s in the literature.). If your music collection contains such recordings, please respect the engineer’s work, and use your front subs in stereo pairs. Additional subs may be in mono.

     Millercarbon has it right:

1.  There is no such thing as stereo bass below 80 Hz since it's a fact that humans cannot determine the originating location of any sound deeper than approximately 80 Hz.  This is the reason I also configure my Audio Kinesis Debra 4-sub distributed bass array in mono mode.  If anyone thinks they're able to distinguish the specific originating location of bass below 80 Hz, I'd suggest testing this for themselves with test tones.  These test tones are available on-line via a Google search.

2.  I also found the Phase setting is not very important in attaining excellent bass performance in a 4-sub DBA system.  Timing and arrival time of deep bass sound waves at an individuals ears are, therefore, also not anything to be overly concerned with since a 20 Hz bass tone sound wave is about 56 feet long, which likely exceeds the dimensions of at least the length or width of most domestic rooms.  See the linked sound wave lengths in inches as a reference below:

https://www.jdbsound.com/art/frequency%20wave%20length%20chart%202013.pdf

     Bass sound waves under 80 Hz also emanate outward from the sub driver and are dispersed into the room in an omnidirectional direction, which means these multiple sound waves have likely bounced off at least one room boundary (floor, ceiling and wall) before they reach an individual's ears at the listening position and they perceive a bass tone.  
     The truth is our brains are capable of summing and averaging these bass sound waves by frequency/tone, that arrive within about 10 milliseconds of each other, but we're still not able to determine specifically where these bass sound originated from if they're below about 80 Hz.
     Finally, even if our brain could locate where these multiple and bouncing sound waves/tones were coming from, there are apparently no examples of commercially available prerecorded music, in any format, that bother to record discrete left and right bass under about 80 Hz.  Recording engineers have been routinely summing left and right bass under about 80 Hz as mono, and sometimes even higher, as a standard practice for over 4 decades. 
     Why?  Because these recording engineers have known the truth about the myth of stereo deep bass for about the last 100 years, ever since scientists first discovered and formally established this fact through the scientific method.  Don't believe me?  Try and find any recording, in any format and any date, that has deep bass below 80 Hz recorded in stereo. 
     Perhaps some near future recording engineers will utilize the full capabilities of the latest and greatest hi-resolution direct to digital recording method and introduce the first commercially available music with stereo deep bass.  But I wouldn't hold your breath.

Later,
 Tim 
 
     

My Mezzo Utopia's go down to 35Hz.

Sometimes I turn my sub off the Mezzo's are so good at bass.


However, is the consensus to set a single Subwoofer's(Sub Utopia)crossover to 80Hz?

Hello vinylshadow,

      I believe most set their cutoff frequency according to their main speakers bass extension capabilities and personal preference discovered via trial and error experimentation. 
      My opinion is that 80 Hz is too high since that's the generally accepted borderline between bass being directional or nondirectional.  You can't tell where the bass is coming from below about 80 Hz but can begin to tell above this frequency.  
     The goal is to integrate the bass from 1 or more subs as seamlessly as possible with one's main speakers.  The subs should remain completely silent until the source recording contains bass content at or below the low pass crossover frequency setting.  The first step, which you've already done, is to find out the rated bass extension of your main speakers, which you stated is 35 Hz.
     By coincidence, my main speakers (Magnepan 3.7i)also have a rated bass extension of 35 Hz but I utilize an Audio Kinesis Debra 4-sub distributed bass array (DBA) system to supplement the bass performance.  My point is that your optimum crossover frequency is probably going to be a bit different than my setting (currently set at between 40 and 50 Hz) for seamless integration.  But I'll describe the procedure I used in the hope that it'll work similarly as well for your single sub as it has for my 4 subs:

1.  Optimally locate your sub in the room using the "sub crawl" method (you can google it).
2.  Play some music with good and repetitive bass content.
3.  Sit at your listening position, set the crossover frequency control on your sub to 60 Hz, set the phase control to"0".  Then have an assistant slowly turn up the volume control on the sub until the volume of the bass from the sub matches and blends with the volume of your main speakers as closely as possible.
4.  Still seated at your LP, have an assistant slowly lower the sub's crossover frequency as low as possible with the bass still sounding very good to you ( "very good" meaning the bass remains solid, powerful, detailed, dynamic, seamlessly blended with the main speakers and natural sounding). Remember, the goal is to not even hear the bass from the sub until the source material calls for it. 
5.  Still seated at your LP, have an assistant slowly increase the sub's phase control upward from the "0" position to the "180" position until the bass sounds best to you ("best" meaning loudest, most detailed. best blended with the main speakers and most natural).  Note that these changes in phase settings will be subtle and you may need to closely listen through several slow "0" to "180" cycles to discover the optimum setting.  Just do your best since this setting isn't usually critical.

Hope this helped,
      Tim