Opposite-polarity subwoofers can null a specific room mode’s coupling

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)

When measurements are done, it is common for some individuals to try equalizing each subwoofer separately and then to combine them. Again, disappointment is almost guaranteed because when the system is in “play” mode all subwoofers are operating simultaneously, and the result of the acoustical summation is unpredictable. The measurement that matters is the one done with all subwoofers operating simultaneously. For individually measured subwoofer outputs to sum in a predictable manner, the measurements must be of the transfer function—amplitude and phase—not the steady-state amplitude response. — , Toole, Floyd E - Sound reproduction-…, 1045 (#complicates, via linked claim)

Categorization

• XREF: connects to: Room mode coupling depends on source and listener positions, not frequency; Equalizing subwoofers individually yields unpredictable combined in-room response — , Toole, Floyd E - Sound reproduction-…, 1045; Delayed, inverted subwoofer arrays can cancel standing waves in rectangular rooms — Toole, Floyd E, Sound reproduction- the acoustics and…, 1604 (+3 more)

Broader Connections

• Delayed, inverted subwoofer arrays can cancel standing waves in rectangular rooms #expands (0.88) — Toole, Floyd E, Sound reproduction- the acoustics and…, 1604
• Equalizing subwoofers individually yields unpredictable combined in-room response #complicates (0.82) — , Toole, Floyd E - Sound reproduction-…, 1045
• Subwoofer placement itself can be optimized alongside DSP settings #expands (0.72)