Bass Traps
Bass traps work through depth and placement; thin foam and small corner blocks barely touch the bottom octaves.
Related
Five centimetres of foam on every surface, and 50 Hz still booms; two shop-bought corner blocks, and the bottom octave hardly moves. Bass traps fail for two reasons: not enough depth, or the wrong position.
Absorption follows wavelength, not area
A 50 Hz wave is nearly seven metres long, so a quarter of it is about 1.7 metres. Porous material only works seriously when its depth approaches that quarter wavelength, and ten centimetres of fibre gives up below roughly 300–400 Hz. Corners stack the pressure of two walls, which is why the same thickness does more there; an air gap acts as extra depth, and 20–30 cm of corner fill reaches the 80–90 Hz region.
Four constructions and the band each covers
| Type | Typical depth | Working range | Floor space | Best for |
|---|---|---|---|---|
| Porous panel | 5–10 cm | Above 300 Hz | Small | Midrange and flutter echo |
| Thick fill with gap | 20–30 cm | 80–150 Hz | Medium | Corners, rear wall |
| Membrane or panel | 10–20 cm | 60–200 Hz | Medium | Front wall, in patches |
| Helmholtz | Tuned | Narrow band | Small | One stubborn peak |
Those ranges are a starting point, not a promise. The same material against the wall and ten centimetres off it absorbs very differently at the bottom, and published coefficients come from reverberation chambers rather than a real corner.
Put them where pressure peaks
At a rigid boundary the low-frequency pressure is highest and air velocity is lowest, so traps belong in corners, at wall-ceiling junctions and behind the speakers. Treating all four corners is more even than only the front pair; with room for two, take the ones behind the speakers and add one behind the listener. A near-square room crowds its modes together and needs thicker corner treatment.
Where a trap cannot help
If one side is a stud wall or glazing, bass leaves through it, and corner absorption cannot fill the resulting dip. A very extreme length-to-width ratio spreads modes so thinly that no practical trap evens them out; change the layout or the room's use instead. Treating a trap as soundproofing is the other common error: absorption shortens the decay inside, it does not stop sound reaching the neighbours.
Listen in the library
All tracks from midicn-lib — inline badge is the license tier (C1 commercial / C2 non-commercial / C3 study only).
Along the same line
Sources
- Everest, F. Alton，Master Handbook of Acoustics（McGraw-Hill）— 多孔吸声材料与低频处理
- Newell, Philip，Recording Studio Design（Focal Press）— 小房间低频处理与角落构造
- Howard, David M. & Angus, Jamie，Acoustics and Psychoacoustics（Focal Press）— 吸声系数与驻波