Room mode calculator: find the bass resonances of your room
Every rectangular room rings at a set of low frequencies where sound bouncing between the walls reinforces itself. These room modes (standing waves) make some bass notes boom and others vanish depending on where you sit. This room mode calculator lists the axial, tangential and oblique modes of your room, draws them on a chart, checks the spread with the Bonello criterion and the ITU-R BS.1116 proportions, and suggests a better ratio of dimensions.
It also shows where the strongest modes have their quiet spots, which helps with speaker and seat placement. Enter metres or feet; everything runs in your browser.
How to use the Room Mode Calculator
- Enter the room’s inside length, width and height and choose metres or feet.
- Optionally set the air temperature, the highest frequency to list and the room’s reverberation time.
- Read the lowest mode, the counts and the checks, then look for clusters and gaps on the mode spectrum.
- Use the axial-mode table to avoid putting a seat or subwoofer exactly on a strong peak or null.
Room Mode Calculator features
All three mode types
Axial (two walls), tangential (four) and oblique (all six) modes, with their indices.
Spectrum chart
Every mode on one frequency axis, with coincident modes in red and the Schroeder frequency marked.
Bonello check
Modes per one-third-octave band for the first 48 modes.
Room ratio advice
ITU-R BS.1116 proportions and the closest Sepmeyer or Louden ratio for your ceiling height.
Placement help
Null positions for the first three axial modes of each dimension, and a CSV export.
The formula
For a rectangular room with rigid walls, f = (c ÷ 2) × √((nx ÷ L)² + (ny ÷ W)² + (nz ÷ H)²), where nx, ny and nz are whole numbers and c is the speed of sound (343 m/s at 20 °C). A mode with one non-zero index is axial, two is tangential, three is oblique. Tangential modes carry roughly half the energy of axial ones (−3 dB) and oblique a quarter (−6 dB).
Example: a 5.5 × 4.2 × 2.6 m living room has its first axial modes at 31.2 Hz (length), 40.9 Hz (width) and 66.0 Hz (height). The first tangential mode, 1-1-0, sits at 51.4 Hz.
Checking the spread
- Bonello criterion (Oscar Bonello, JAES 1981): count the modes in each one-third-octave band over the first 48 modes. The count should rise (or at least not fall) from band to band, and no band should contain coincident modes. Published summaries differ on how close two modes must be to count as coincident, so the window is adjustable here; coincidences are flagged only in bands holding fewer than 5 modes, where a doubled mode stands out.
- ITU-R BS.1116-3 asks listening rooms to satisfy 1.1 w/h ≤ l/h ≤ 4.5 w/h − 4, with l/h and w/h below 3.
- Recommended ratios (height : width : length) include Sepmeyer’s 1 : 1.14 : 1.39, 1 : 1.28 : 1.54 and 1 : 1.60 : 2.33, and Louden’s 1 : 1.4 : 1.9. There is no single perfect ratio, only ones that avoid stacking modes.
- The Schroeder frequency, about 2000 √(RT60 ÷ V), marks where individual modes stop mattering and the room behaves statistically.
What to do about modes
Axial modes have pressure peaks at the walls and nulls at fractions of the room: the first length mode is quiet in the middle of the room, the second at a quarter and three quarters. Avoid seating exactly at the centre or against the back wall, try the speaker placement calculator for a starting layout, and use two subwoofers on opposite walls to even out the bass. Bass traps in corners and a measured EQ help further. To estimate how long sound lingers above the Schroeder frequency, use the RT60 calculator.
Room Mode Calculator FAQ
How do I calculate room modes?
Use f = (c/2)√((nx/L)² + (ny/W)² + (nz/H)²) for every combination of whole numbers. This room mode calculator does it for every mode up to the frequency you choose.
What are axial, tangential and oblique modes?
Axial modes bounce between one pair of walls, tangential modes between two pairs, and oblique modes involve all six surfaces. Axial modes are the strongest.
What is a good room ratio for acoustics?
Ratios that keep the modes evenly spread, such as 1 : 1.4 : 1.9 or 1 : 1.6 : 2.33 (height : width : length). Avoid rooms where one dimension is a whole multiple of another, and avoid cubes.
What is the Bonello criterion?
A test of how evenly modes are spread: the number of modes in each third-octave band should not decrease as frequency rises, and bands should not contain coincident modes.
Where should I put my speakers to reduce room modes?
Keep the seat and speakers away from the exact centre and from the room’s walls and corners when you want less bass build-up, and away from the null positions in the table for even bass.
Why do my measured peaks not match exactly?
Real walls are not perfectly rigid, rooms are not perfect boxes, and furniture absorbs bass, so peaks shift and broaden a little.