How to deal with SBIR (Speaker Boundary Interference Response)

Posted by Goran Egić on

SBIR (Speaker Boundary Interference Response) is a term used in audio engineering and it refers to the way in which a speakers performance is affected by its proximity to boundaries such as walls, floors, and ceilings.

When a speaker is placed close to a boundary, the sound waves it produces can interact with the boundary in ways that can cause constructive and destructive interference. This can result in an uneven frequency response, with certain frequencies being boosted or suppressed. SBIR is a problem because it can cause coloration and distortion in the sound, making it less accurate and less pleasant to listen to. At least one big dip and boost in low frequencies is expected in any small home studio. 

There are a number of techniques that can be used to minimize SBIR:

1. Adjusting the position of the speaker:

a) Symmetrical setup: Place your speakers symmetrically along the length and width of the room. This helps to minimize uneven reflections and cancellations caused by SBIR.

b) Avoid corners: Keep the speakers away from corners of the room, as bass buildup tends to be more pronounced in corners.

c) Speaker distance from boundaries: Speaker distance from the back wall is crucial in controlling the SBIR dip/boost.

In bigger studios usually the best approach is to distance the speaker from the back wall and let the treatment do the rest. Just avoid landing the listening positions at 1/4 or 1/2 of the room length. 

In smaller home studios a different approach is usually better (but not as a rule, you should always experiment yourself in your own room) - place the speakers as close to the wall as you can. The logic behind it - it will result the dip/boost being in higher frequencies, but not bass frequencies. The more you move the speakers away from the front wall - dip/boost will happen lower in the frequency range and harder to control or minimize. This works in untreated rooms as well as treated rooms. In treated rooms the dip/boost caused by SBIR will be minimized more likely the higher it is in frequency range (lets say 150Hz or up).

2. Bass traps:

Bass traps or thick acoustic panels (beyond 15cm in depth) can help with minimizing the effects of room modes and SBIR. Placing them in corners and even front/back wall plus ceiling can go a long way. Back wall is an ideal place to treat it fully with bass traps/ acoustic panels for a chance to fully eliminate SBIR.

3. Room correction software:

Although this solution doesn't replace the above 2 methods, it can help in 2 ways:

a) The 2 methods above got you to a point, but the dip/boost from SBIR is still bothering you - room correction software can help with the last bit - it will close the gap and provide a better eq curve at a listening position. It will not solve SBIR, but it will help you hear better the frequencies affected by SBIR.

b) You can't move your speakers around to find the best position nor you can't treat your room - doing something is always better then doing nothing. The software can help a bit, but it will create big phase problems if your try to overcompensate an eq curve by a big margin (over 10db in some frequencies).

4. Soffit mounting speakers:

Soffit mounting speakers is a technique used to minimize SBIR (Speaker Boundary Interference Response) by mounting the speakers flush with the surface of the soffit or a wall. A soffit is the area between the top of a wall and the ceiling.

By mounting the speakers in this manner, they become less affected by nearby boundaries, such as the floor and nearby walls, resulting in reduced SBIR. Soffit mounting is commonly used in professional recording studios and home theaters to achieve a more accurate and controlled low-frequency response.

This approach is beneficial as it reduces the impact of reflections and cancellations that can occur when speakers are mounted away from boundaries or placed on stands within a room. By integrating the speakers into the structure of the room, soffit mounting can result in improved low-frequency performance and a more even bass response. However, it is important to plan and design the soffit mounting properly to achieve the desired acoustic results.

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