SBIR Calculator — Speaker-Boundary Interference

SBIR (Speaker-Boundary Interference Response) calculates the interference between the direct sound from a studio monitor and its reflections off nearby surfaces: rear wall, side walls, floor, and ceiling. Each reflection travels a longer path than the direct sound, and at certain frequencies arrives in anti-phase, causing deep dips of up to 15 – 20 dB. The tool computes the frequencies of these dips based on the distances from the speaker to each of the nearest room boundaries. Why it matters: SBIR is one of the most common yet poorly understood problems in home and professional studios. A dip at 80 – 120 Hz is often blamed on the monitors or room modes, when the real cause is the speaker's proximity to a wall. Understanding SBIR lets you avoid placements that inevitably create non-compensable nulls in the critical frequency range. How to read results: the calculator shows the frequency and depth of each dip for all nearby boundaries. Dips below 300 Hz are most critical because they are virtually impossible to treat with absorption. When multiple dips coincide in frequency, the problem compounds significantly. Common mistakes: placing monitors exactly halfway between floor and ceiling, which creates one deep null instead of two less noticeable ones; ignoring the distance to the rear wall; attempting to compensate SBIR exclusively with EQ — equalization cannot recover energy lost to destructive interference. Next steps: adjust your monitor positions using the Speaker Placement calculator and verify how the dip frequencies change after repositioning.