Why placement is so sensitive
Low-frequency wavelengths are measured in meters, and every room mode is a fixed pressure map. Your mains are pinned by stereo imaging, but a sub is omnidirectional and free to move — which makes it the one variable you control over which modes get excited. Corners give maximum gain and maximum boom; a quarter-way position along the wall is often far smoother. The mechanism is covered in room modes.
The crossover is a region, not a line
Around the crossover — typically 60–120 Hz — the mains and the sub play the same notes. In phase they add and the bass thickens; out of phase they cancel into a hole. “Weak bass” is often not a small sub — it is the sub fighting the mains across that band.
Alignment adjusts three things
Delay (the time offset from path-length differences), gain (relative level) and polarity. Acouvero measures the mains and the sub separately, predicts their complex sum, computes the settings and shows the summed curve before and after — you see the theoretical result before touching a knob.
Multiple subs, multiple seats
Two or more subs are not about louder bass but smoother bass: staggered placements let one sub’s peaks fill another’s nulls, collapsing the seat-to-seat variance. Acouvero supports 1–4 subs with independent per-seat, per-sub measurements — optimizing for the all-seat average, capping the worst seat, or protecting the main seat only.
Prediction, then verification
Alignment is a prediction, not a finish line: rooms, device latencies and phase responses are all more complex than the model. The correct loop is measure → compute → apply → measure again to verify. And because low frequencies have long wavelengths and long reverb, use the low-band sweep preset (15–300 Hz) and keep the room quiet.