Room Mode Calculator
Your room's dimensions create standing waves that make some bass notes boom and others disappear. This finds them, flags the problem spots, and rates your room ratio.
Room modes for common room sizes
The lowest axial modes (the strongest standing waves, running between one pair of parallel walls) for five typical rooms, computed by the same engine as the calculator above. These are the frequencies where bass tends to boom or disappear; a good ratio spreads them out, a poor one bunches them. All assume a 2.4 m (8 ft) ceiling — enter your own dimensions above for an exact map.
| Room | Size (L × W) | Lowest axial modes (Hz) | Modes < 200 Hz | Ratio |
|---|---|---|---|---|
| Small bedroom studio | 3 × 2.4 m 10 × 8 ft | 57, 71, 71, 114, 143 | 27 | fair ≈ Sepmeyer A |
| Small home studio | 3.6 × 3 m 12 × 10 ft | 48, 57, 71, 95, 114 | 38 | good ≈ Sepmeyer B |
| Typical project studio | 4 × 3 m 13 × 10 ft | 43, 57, 71, 86, 114 | 41 | good ≈ Sepmeyer B |
| Medium control room | 4.5 × 3.5 m 15 × 11.5 ft | 38, 49, 71, 76, 98 | 50 | good ≈ Louden |
| Large room / home theatre | 5.5 × 4 m 18 × 13 ft | 31, 43, 62, 71, 86 | 62 | fair ≈ Bolt area (mid) |
A room's fundamental axial mode is roughly 172 ÷ the dimension in metres, so longer walls put the first (loudest) mode lower. Smaller rooms push their modes higher and further apart, which is why they often sound boomy in a narrow band. You cannot move these frequencies without changing the room, but corner bass traps tame their peaks.
What is a room mode?
A room mode is a standing wave. When half a wavelength divides evenly into one of the room's dimensions, the reflected wave arrives back in phase with itself and reinforces instead of dying away. At that frequency the room develops loud spots and near-silent spots that do not move — walk two feet and the bass changes.
Modes exist at every frequency, but only in the bass are they far enough apart to be heard as individual problems; higher up they overlap into a dense field that behaves like plain reverberation. That is why room modes are a low-frequency problem and why this calculator stops at a few hundred hertz. They come in three kinds, in descending order of strength:
- Axial — one pair of parallel surfaces, one non-zero index. The strongest, and the ones worth acting on.
- Tangential — four surfaces, two non-zero indices. Roughly half the energy of an axial mode.
- Oblique — all six surfaces, three non-zero indices. Weakest; rarely audible on their own.
Rectangular rooms have a closed-form answer, the Rayleigh equation: f = (c / 2) × √( (p/L)² + (q/W)² + (r/H)² ), with c = 343 m/s and p, q, r whole numbers from zero up. For a single axis that collapses to about 171.5 ÷ the dimension in metres — the shortcut worth memorising. Derivation and sources are on the methodology page.
Preferred room ratios, as real dimensions
Published "good" room ratios are always quoted as bare numbers — height : width : length — which nobody can act on until they are metres. Below, the 4 reference ratios this calculator rates against are worked out for a standard 2.4 m (7.9 ft) ceiling and then run through the same engine as the calculator above. Use them when you can still choose or partition a room; once the walls are up, the ratio is fixed and only treatment is left.
| Ratio | H : W : L | Room size (L × W) | Lowest axial modes (Hz) | Axial modes < 200 Hz | On distinct frequencies | Closest axial pair |
|---|---|---|---|---|---|---|
| Sepmeyer A | 1 : 1.14 : 1.39 | 3.34 × 2.74 m 10.9 × 9.0 ft | 51, 63, 71, 103 | 8 | 8 | 8.8 Hz |
| Sepmeyer B | 1 : 1.28 : 1.54 | 3.70 × 3.07 m 12.1 × 10.1 ft | 46, 56, 71, 93 | 9 | 9 | 3.7 Hz |
| Louden | 1 : 1.4 : 1.9 | 4.56 × 3.36 m 15.0 × 11.0 ft | 38, 51, 71, 75 | 9 | 9 | 2.7 Hz |
| Bolt area (mid) | 1 : 1.5 : 2.1 | 5.04 × 3.60 m 16.5 × 11.8 ft | 34, 48, 68, 71 | 10 | 9 ⚠ | 0.0 Hz |
| Cube (counter-example) | 1 : 1 : 1 | 2.40 × 2.40 m 7.9 × 7.9 ft | 71, 143 | 6 | 2 ⚠ | 0.0 Hz |
The two right-hand columns are the point of the exercise. When two axial modes land on the same frequency they stack into one larger peak instead of spreading the energy out, so "distinct" should equal "axial modes". 3 of the 4 preferred ratios manage that exactly. Bolt area (mid) is the exception: its height : width is exactly 1 : 1.5 — the small whole-number ratio 3 : 2, and a width that is a simple multiple of the height makes the two axes share harmonics. It loses 1 axial frequency to coincidence, and 53 modes below 200 Hz land on 48.
The 2.4 m cube shows what that failure looks like taken to its limit: all three axes produce an identical series, so its 6 axial modes land on just 2 frequencies and its 19 modes overall on 6. Its low mode count looks flattering and is exactly the problem — fewer, much larger peaks with wide gaps between them. The engine rates it poor. Equal or simply-related dimensions are the one geometry mistake worth avoiding.
What to do about room modes
You cannot remove room modes without changing the room's size, but you can tame them: put broadband bass traps in the corners (where modal pressure is highest) and choose a listening position that avoids the strongest peaks. A good dimension ratio spreads the modes out so no single frequency dominates. Formula details are on the methodology page.
Frequently asked questions
What is a room mode?
A room mode is a standing wave: a frequency whose half-wavelength divides evenly into one of the room's dimensions, so the reflected wave reinforces itself instead of dying away. At that frequency the room has loud spots and near-silent spots that do not move. Modes exist at every frequency, but only below roughly 200–300 Hz in a small room are they far enough apart to be heard individually — which is why room modes are a bass problem, not a treble one. Axial modes (between one pair of parallel walls) are the strongest, tangential modes (four surfaces) are weaker, and oblique modes (all six) are weakest.
How do you calculate room modes?
Rectangular rooms use the Rayleigh equation: f = (c / 2) × √( (p/L)² + (q/W)² + (r/H)² ), where c is the speed of sound (343 m/s at 20 °C), L, W and H are the room dimensions in metres, and p, q and r are whole numbers from 0 upward. A mode with one non-zero index is axial, two is tangential, three is oblique. For the strongest case — the first axial mode along one wall — this simplifies to about 171.5 ÷ the dimension in metres, so a 3.34 m wall puts its fundamental at 51 Hz.
Does this calculator work for non-rectangular rooms?
No, and neither does any other closed-form room mode calculator. The Rayleigh equation assumes a rigid rectangular box; an L-shaped, splayed or sloped-ceiling room has modes that can only be found by numerical simulation (finite or boundary element methods). The useful approximation is to run the largest rectangle that fits inside your room, then again with the full bounding box: the real modes mostly fall between those two sets. Treat the result as a range to investigate, not a measurement.
Can you get rid of room modes?
Not without changing the room's dimensions — the frequencies are fixed by geometry. What you can change is how much each mode rings and how evenly they are spread. Corner bass traps absorb modal energy where pressure is highest, and moving the listening position away from the exact centre and away from walls avoids the worst peaks and nulls. Choosing dimensions with a good ratio spreads the modes apart before any treatment is bought, which is what the table of preferred ratios on this page is for.