Room Mode Frequency Calculator
Rectangular rooms resonate at predictable frequencies where standing waves fit between parallel surfaces. These axial room modes are the dominant cause of uneven bass: certain notes boom while others nearly vanish, depending on where you sit. This calculator computes the first several axial modes for the length, width, and height of a room from its dimensions and the speed of sound. Use it to anticipate problem frequencies, to compare candidate room dimensions, and to plan speaker and listener placement or bass treatment. The speed of sound is editable so you can match your room temperature.
Axial room mode formula
f(n) = n * c / (2 * L)
c = speed of sound (m/s)
L = room dimension (m)
n = mode order (1, 2, 3, ...)
Each dimension produces its own series of axial modes. The fundamental is c divided by twice the dimension; higher orders are integer multiples. This calculator lists the first four orders for each dimension.
Worked example
For a 5 m length at c = 343 m/s, the first axial mode is 343 / (2 * 5) = 34.30 Hz, then 68.60, 102.90, and 137.20 Hz. A 4 m width gives 42.88 Hz fundamental; a 2.7 m height gives 63.52 Hz fundamental.
Room modes: frequently asked questions
What is a room mode?
A room mode is a resonant standing wave that forms between parallel surfaces of a room at frequencies where half-wavelength multiples fit exactly between the walls. Modes cause some bass notes to sound boomy and others to sound weak, depending on listening position. Axial modes, between one pair of parallel surfaces, are the strongest.
What is the axial room mode formula?
Frequency = n times c divided by (2 times L), where c is the speed of sound, L is the room dimension, and n is the mode order (1, 2, 3, and so on). The first axial mode of each dimension is c divided by twice that dimension. This calculator lists the first several orders for length, width, and height.
What speed of sound should I use?
The speed of sound in air is about 343 metres per second at 20 degrees Celsius at sea level, the value adopted as a reference in ISO 9613. It rises with temperature, so the speed is a user-editable input. Enter the value for your room temperature for the most accurate modes.
Why do room modes matter for acoustics?
Modes determine the low-frequency response of a room. Closely spaced or overlapping modes give smoother bass; widely spaced modes leave audible peaks and nulls. Knowing the modal frequencies helps you place speakers and listeners, choose room dimensions, and target bass trapping.
Official sources
- U.S. National Institute of Standards and Technology: nist.gov (speed of sound reference values).
- International Organization for Standardization: ISO 9613-1 sound attenuation.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.