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