Room & listening
Room gain
Free bass reinforcement from walls, floor, and corners.
Simple
Free bass from your room. Walls, floor, and corners reinforce low frequencies, so a speaker near a boundary plays bass louder than it would in open air — sometimes a lot louder. You can dial this in from 0 (open space) up to ~12 dB (a small, boundary-loaded room).
The theory
Below the frequency where a room's longest dimension equals roughly half a wavelength, the room stops behaving like open space and starts acting like a pressure vessel: the speaker pressurizes the whole volume rather than radiating waves, and SPL rises as you go lower. Each reflecting boundary near the driver adds reinforcement. The engine treats this as a flat dB bonus added to effective sensitivity, easing the amp's power burden.
For experts
The mechanism is twofold. Boundary reinforcement (Roy Allison's work) is the discrete part: each nearby surface restricts radiation into a smaller solid angle, adding theoretically +3 dB per boundary (half-space → quarter → eighth) for wavelengths long enough to "see" the boundary as adjacent. Room/cabin gain is the continuous part: in a sealed-ish small room, below the pressure-zone cutoff (≈ c/2L for the longest dimension L), output rises at ~12 dB/octave as frequency drops — the same effect that makes car subwoofers hit absurdly hard in a tiny sealed cabin. The two stack, which is how you reach double-digit dB. The trade-off the model doesn't show: that same reinforcement excites room modes, so the gain is rarely flat — it's lumpy, and the lumps are why bass measures ±10 dB across a sofa.
Below the pressure-zone corner set by the room's longest dimension L, output rises at ~12 dB per octave.