Subwoofer placement itself can be optimized alongside DSP settings

Evidence

The idea seems to have originated with Goertz et al. (2001), who used an arrangement of subwoofers on the front wall, generating an approximation of a plane wave that propagates to the rear of the room where a similar arrangement of subwoofers, appropriately delayed and polarity inverted, cancels the wave when it arrives. Ideally this eliminates standing waves and everyone in the room should hear good bass. It requires a perfectly rectangular room and at least four subwoofers to work well. The scheme was called double bass array (DBA). — Toole, Floyd E, Sound reproduction- the acoustics and…, 1604 (#expands, via linked claim)

Most often they are not identical subwoofers, and they are not located where they need to be, and they may or may not be driven with the same bass-managed signal. Unpredictable results and debates are almost inevitable. — , Toole, Floyd E - Sound reproduction-…, 1044 (#expands, via linked claim)

Categorization

• XREF: connects to: Opposite-polarity subwoofers can null a specific room mode’s coupling; Optimizing any two of room, subwoofer, and seating yields the third; Optimized multi-sub systems can use much smaller subs at some locations (+5 more)

Broader Connections

• Delayed, inverted subwoofer arrays can cancel standing waves in rectangular rooms #expands (0.85) — Toole, Floyd E, Sound reproduction- the acoustics and…, 1604
• Subwoofers must be equalized together, not individually, to sound right #expands (0.80)
• Adding extra subwoofers rarely improves bass without controlled placement #expands (0.78) — , Toole, Floyd E - Sound reproduction-…, 1044
• Equalizing subwoofers individually yields unpredictable combined in-room response #expands (0.75) — , Toole, Floyd E - Sound reproduction-…, 1045
• Sound Field Management extends bass optimization to irregularly shaped rooms. #expands (0.72)