Sound in rooms

Room modes

Some low notes build up between parallel walls.

The notes your room likes

Set the room's size and watch where the modes bunch.

Try it

  • Make a cube room and see the modes stack
  • Find a size that spreads them out
More on this

Between two parallel walls, some low notes fit exactly and build up. Those are the room's modes, and they are why small rooms have uneven bass.

Set the room's size. Each line is an axial mode, a note that fits a whole number of half-wavelengths between two walls. Where lines bunch, the bass booms; where there are gaps, it thins.

An axial mode between two walls L metres apart sits at n × 343 ÷ (2 × L) hertz, for n = 1, 2, 3 and so on. A 4 m wall gap gives about 43 Hz, 86 Hz, 129 Hz...

A cube puts all three dimensions' modes on the same notes, the worst case. Ratios that avoid simple multiples spread them. Tangential and oblique modes exist too; they are weaker and are left out here.