Room mode calculator
Standing-wave frequencies for a rectangular room — axial, tangential and oblique — with flags on clusters that cause boomy or uneven bass.
Speed of sound fixed at 343 m/s (20 °C). Assumes a sealed rectangular room with rigid walls — real rooms shift and damp these values, but the pattern holds.
| Hz | Mode (L·W·H) | Type | Along |
|---|
What room modes are
Below roughly 300 Hz, a room stops behaving like open air and starts behaving like a resonator. Sound reflecting between parallel surfaces reinforces itself at frequencies whose half-wavelengths fit exactly between the walls — these resonances are room modes. At a mode frequency, the room adds its own loud and quiet spots: bass that booms in one chair and disappears in another.
Axial, tangential, oblique
Axial modes involve one pair of surfaces and carry the most energy — they dominate what you hear. Tangential modes involve two pairs (about half the energy), and oblique modes involve all six surfaces (about a quarter). Treat axial modes first.
The formula
f = (c / 2) · √( (p/L)² + (q/W)² + (r/H)² )
where c = 343 m/s and p, q, r are whole numbers counting half-wavelengths along length, width and height. This tool evaluates all combinations up to 4·4·4 and reports everything below 320 Hz.
What to do about problem modes
- Clustered modes (flagged above) pile energy at nearly the same frequency — the classic one-note boom. Position the listening seat and speakers away from pressure peaks: about 38% of the room length from the front wall is a well-tested starting point.
- Bass traps in corners damp modal ringing broadly; thicker is better below 100 Hz.
- Check your decay next: the RT60 calculator estimates how live the room is above the modal region.
FAQ
Why do the numbers change slightly with temperature?
The speed of sound rises about 0.6 m/s per °C, moving every mode with it. This tool uses 343 m/s (20 °C); at 30 °C everything sits ~1.7% higher.
My room isn't a perfect rectangle. Is this useless?
No — angled walls and openings shift and smear the exact frequencies, but the mode density and the problem regions this tool reveals remain a reliable guide for placement and treatment decisions.
Is there an ideal room ratio?
Ratios that spread modes evenly (avoiding shared multiples) behave best — 1 : 1.4 : 1.9 and 1 : 1.6 : 2.3 are classic references. Cubes and rooms with matching dimensions are the worst case because several modes land on the same frequency.