Room mode calculator
Predict which bass notes will boom or vanish in your room from its three dimensions, then play those exact frequencies to hear the effect.
Why one bass note booms: room modes
Between two parallel walls, sound bounces back and forth. When exactly half a wavelength fits between them, the reflections line up into a standing wave: loud in some spots, almost silent in others. These axial room modes happen at frequency = 343 ÷ (2 × distance), and at whole-number multiples. Enter your room size to predict which bass notes will boom.
■ length ■ width ■ height · taller line = stronger (lower-order) mode
| Frequency | Between | Order |
|---|---|---|
| 34.3 Hz | length walls | 1 |
| 42.9 Hz | width walls | 1 |
| 68.6 Hz | length walls | 2 |
| 68.6 Hz | height walls | 1 |
| 85.8 Hz | width walls | 2 |
| 102.9 Hz | length walls | 3 |
| 128.6 Hz | width walls | 3 |
| 137.2 Hz | length walls | 4 |
| 137.2 Hz | height walls | 2 |
| 171.5 Hz | width walls | 4 |
Highlighted rows are modes within 4 Hz of each other; they stack up and cause the worst boom. Play those frequencies with a tone generator and walk around the room: you will find loud and dead spots. Moving the subwoofer or your seat, rather than turning up EQ, is usually the fix.
Hear your room modes
Play the frequencies the calculator flags, then walk slowly around the room. Peaks and nulls of a strong mode can differ by 20 dB or more within a metre or two.
Volume first. Turn your device volume down before pressing play, then raise it slowly. Tones start quiet on purpose. Very low tones can damage small speakers and woofers if pushed hard. Stop if you hear rattling, distortion or cone slap.
Using the results
- Clusters are the problem: two or three modes within a few hertz reinforce each other into a single dominant boom.
- Big gaps are a problem too: a wide spacing between modes leaves a frequency band thin and uneven.
- Seat position: the first length mode has a pressure null exactly halfway along the room, which is why sitting in the centre often sounds bass-light. Around 38% of the room length from the front or back wall is a common starting point.
- Confirm by ear: run the low sweep on the subwoofer test and note where it swells. If it matches a calculated mode, it is the room, not the speaker.
The calculator assumes a rectangular room with rigid walls and shows axial modes only. Real rooms with openings, soft walls or sloped ceilings will differ somewhat.
Questions people ask
What is a room mode?
A standing wave between room surfaces. At certain bass frequencies reflections line up so that some spots in the room get much louder and others nearly cancel. Axial modes (between two parallel walls) are the strongest; tangential (four surfaces) and oblique (all six) modes are weaker.
What is the formula for axial room modes?
f = n × c ÷ (2 × L), where c is the speed of sound (about 343 m/s at 20 °C), L is the distance between the two surfaces and n = 1, 2, 3… For a 5 m long room the first length mode is 343 ÷ 10 = 34.3 Hz, then 68.6 Hz, 102.9 Hz and so on.
What room dimensions are best for bass?
Rooms whose length, width and height are not simple multiples of each other spread modes out more evenly. Cubes and rooms like 3 × 6 × 9 m stack modes on the same frequencies. Published "good" ratios include Sepmeyer's 1 : 1.14 : 1.39 and Louden's 1 : 1.4 : 1.9, but placement and treatment matter as much as ratios.
How do I fix a booming room mode?
Try moving the subwoofer and the listening seat first (avoid the exact middle and the walls), then add bass traps in corners, or use two subwoofers to even out the response. A parametric EQ can cut a peak but cannot fill a null.
Above what frequency do room modes stop mattering?
Roughly above the Schroeder frequency, about 2000 × √(RT60 ÷ volume), modes overlap so densely that the room behaves statistically. In typical living rooms this is somewhere around 100 to 300 Hz.
Keep testing
- Subwoofer testBass tones from 10 Hz, a low sweep and a room-mode calculator.
- Frequency sweepLogarithmic or linear sweeps over any range and duration.
- Spectrum analyzerReal-time FFT of your microphone with peak hold and note readout.