Room mode calculator
Enter the room's inside dimensions to see where the low end will pile up, and where it will disappear.
| Hz | Type | Order (L, W, H) | Note |
|---|
*The Schroeder estimate needs the room's reverb time, so it's only shown as a rough guide using a typical small-room RT60 of 0.4 s.
How it works
Sound bouncing between parallel walls reinforces itself at frequencies where a whole number of half-wavelengths fit across the room. The first length mode of an 18 ft room is about 31 Hz: half a wavelength fits exactly between the front and back walls.
Axial modes (one pair of surfaces) are the strongest. Tangential modes (two pairs) are weaker, and oblique modes (all three) weaker still.
Above roughly the Schroeder frequency, modes overlap so densely that the room stops behaving like a set of separate resonances. Below it, individual modes rule the bass.
Field notes
- Clusters and gaps are the problem, not modes themselves. Several axial modes landing within a few hertz of each other make one note boom. A big gap between modes makes another note vanish. Rooms with two equal dimensions, or one double another, stack modes on top of each other.
- Where you sit matters as much as the room. The middle of the room is a null for the odd-order length modes. Mix position and speaker placement can dodge the worst peaks and dips.
- Bass traps work on modes, foam doesn't. Thin foam does little below a few hundred hertz. Thick porous traps in the corners, where every mode has a pressure peak, do the heavy lifting.
- EQ can cut a peak but can't fill a null. A cancellation dip won't come up with boost; you just burn amplifier power. Move the speaker or listener instead.
- Use the inside dimensions, finished wall to finished wall. Real rooms aren't perfect boxes, so treat the results as a map of where to listen, then confirm with a measurement.