Why does one bass note boom and another vanish in your room? Its dimensions decide which low frequencies resonate. Enter them to see every room mode up to 300 Hz and where they pile up.
| Hz | nx, ny, nz | Type |
|---|
A rectangular room resonates at f = c/2 · √((nx/L)² + (ny/W)² + (nz/H)²), for whole numbers n — the Rayleigh formula. Axial modes bounce between one pair of opposite surfaces and are the strongest; tangential modes involve two pairs, oblique modes all three. The speed of sound c follows the air temperature: 343 m/s at 20 °C.
When axial modes from two dimensions land on the same frequency — a room 5 m long and 2.5 m high, for example — that note is reinforced twice over; the warning line lists those within 1 Hz of each other. Above the Schroeder frequency, 2000 · √(RT60 ÷ volume), modes overlap so densely that the room behaves smoothly; below it, individual modes rule, which is why bass trapping matters more than absorption there.
My room is not a rectangle. Does this still help?
The formula is exact only for a rectangular box. For an L-shaped room or a sloped ceiling,
use the main rectangle or average the height; treat the result as a guide to the problem
frequencies.
What RT60 should I enter?
The time sound takes to fade by 60 dB. If you have not measured it, try a few values — the
Schroeder frequency moves with the square root, so it changes slowly.
Can I fix room modes with EQ?
Partly. Cutting a peak with EQ helps at the listening spot; a dip caused by a mode cannot be
filled with boost. Moving the speakers and the listening position, and bass traps, work on
both.