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SBIR Calculator

See which frequencies are cancelled by reflections from nearby walls, floor, and ceiling. Identify speaker placement problems before they happen.

Distance from speaker to each boundary

ft
ft
ft
ft
ft
ft

Cancellation frequencies

Rear wall

8.0 ft

35 Hz

−2.5 dB · minor

also: 105, 176, 246 Hz

Ceiling

5.5 ft

51 Hz

−4.0 dB · moderate

also: 153, 256, 358 Hz

Right wall

5.0 ft

56 Hz

−4.4 dB · moderate

also: 169, 281, 394 Hz

Left wall

3.0 ft

94 Hz

−6.7 dB · moderate

also: 281, 469 Hz

Floor

2.5 ft

113 Hz

−9.1 dB · severe

also: 338 Hz

Front wall

2.0 ft

141 Hz

−8.6 dB · severe

also: 422 Hz

What is SBIR?

Speaker Boundary Interference Response occurs when sound from a speaker reflects off a nearby wall, floor, or ceiling. At the frequency where the reflected path is half a wavelength longer than the direct path, the two signals cancel. The reflection travels out to the boundary and back, so the extra path is 2d and the formula is f = c / (4d), where d is the distance to the boundary. Closer boundaries cause cancellation at higher frequencies.

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What is SBIR?

Speaker Boundary Interference Response (SBIR) occurs when sound from a speaker reflects off a nearby surface. The reflected sound travels a longer path than the direct sound. At the frequency where this extra distance equals half a wavelength, the direct and reflected signals cancel, creating a notch in the frequency response. The reflection travels to the boundary and back, so the extra distance is 2d and the formula is f = c/(4d), where d is the distance to the boundary.

SBIR vs. room modes

Room modes and SBIR are related but different phenomena. Room modes are resonances of the entire room — standing waves between parallel surfaces. SBIR is a local effect between a speaker and its nearest boundary. Both affect bass response, and optimal speaker placement minimizes both. SBIR notches are typically broader and affect a wider frequency range than individual modes.

Frequently Asked Questions

How far should speakers be from the wall to avoid SBIR?

There's no single "safe" distance. The cancellation frequency is f = c/(4d), so at 2 feet from a wall, you get a notch around 141 Hz. At 4 feet, it drops to 70 Hz. The goal isn't to eliminate SBIR (it's always present), but to position speakers so the notches fall at less critical frequencies or where room modes help compensate.

Can EQ fix SBIR cancellations?

Partially. EQ can reduce peaks but cannot fill a true cancellation null — the physics prevents it. If the direct and reflected sound cancel perfectly at a frequency, no amount of EQ boost will restore it at that position. Moving the speaker is the only real fix for deep SBIR nulls.

Related Tools

Speaker Placement CalculatorRoom Mode CalculatorWavelength Calculator

Atuund uses finite element method (FEM) modal analysis to model room acoustics. Built for hi-fi enthusiasts, home theater builders, and anyone who wants better sound from their speakers.