Room Mode Calculator — Axial Frequencies & Acoustic Resonances
Room dimensions
Your measurements stay in this browser. No room data is uploaded or stored.
Axial mode results
First mode on each axis
Close-frequency overlaps
Potential coincidences across different axes will appear here.
| Mode | Axis | Order | Frequency | Wavelength | Gap above |
|---|
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How to use this room mode calculator
- Measure finished inside dimensions. Use the clear distance between the wall surfaces, and from finished floor to finished ceiling. Do not use exterior building dimensions.
- Choose metres or feet. Switching the selector converts the current values, so the physical room remains the same.
- Enter a representative temperature. Temperature slightly changes the speed of sound and therefore every calculated frequency.
- Choose the number of modes. Eight per axis is a useful starting view; use more to inspect higher harmonics.
- Review close overlaps. Modes from different axes inside the selected tolerance are flagged because they may concentrate resonances in the same bass region.
Tip: measure wall-to-wall in more than one place if the room is not perfectly square. This ideal model assumes each pair of surfaces is parallel.
Axial room mode formula
For one room dimension, the axial resonances are:
fₙ = (n × c) ÷ (2 × d)
- fₙ is the axial frequency in hertz.
- n is the mode order: 1, 2, 3, and so on.
- c is the speed of sound in metres per second.
- d is the length, width, or height in metres.
The calculator estimates dry-air sound speed from absolute temperature with c = √(γRT), using γ = 1.4 and R = 287.05 J/(kg·K). This gives about 343.2 m/s at 20 °C. Humidity and local atmospheric composition are not modelled.
For a 5 m room dimension at 20 °C, the first mode is approximately 343.2 ÷ (2 × 5) = 34.32 Hz. Higher axial modes are whole-number multiples of that fundamental.
Formula references: Penn State Acoustics — resonance frequencies of a one-dimensional room, MIT OpenCourseWare — room acoustics and reverberation, and NASA — speed of sound.
How to interpret axial frequencies and acoustic resonances
Axial modes form between one pair of opposing surfaces. The length series is labelled (n,0,0), the width series (0,n,0), and the height series (0,0,n). Because axial modes involve the most direct two-surface reflection path, they are a practical first check when planning a small studio, listening room, rehearsal space, or home cinema.
A calculated frequency is a location to investigate, not a predicted EQ curve. At a modal frequency, pressure maxima and minima occur at fixed positions. Moving a speaker, subwoofer, microphone, or listening position can therefore change the measured level without changing the room’s underlying modal frequency. Absorption, leakage, wall flex, openings, and furniture affect how strongly and how long a mode rings.
Close frequencies from different axes deserve attention because their effects may combine. A square room often places length and width modes at the same frequencies; simple dimensional ratios can also make one axis harmonic coincide with another. More even spacing is generally easier to manage than repeated clusters separated by large gaps, but this calculator alone cannot grade a room or prescribe treatment.
Use the table to prepare measurement frequencies, then verify the actual response with calibrated measurement software and several microphone positions. Broadband bass trapping, careful placement, multiple subwoofers, and construction changes can all alter practical results, but treatment decisions should be based on measurements rather than calculated frequencies alone.
Model limits
This engineering estimate assumes a rigid, empty, rectangular enclosure with parallel boundaries. It calculates axial frequency locations only and does not calculate sound-pressure level, decay time, damping, tangential modes, oblique modes, or structural resonances. Irregular rooms and lightweight walls can differ materially from the ideal result.
Room mode calculator FAQ
What is an axial room mode?
It is a standing-wave resonance between one pair of opposing surfaces: front to back, side to side, or floor to ceiling.
What formula does the calculator use?
For each dimension, f = n × c ÷ (2 × d). The first order uses n = 1, the second uses n = 2, and so on.
Why do some mode frequencies overlap?
Similar dimensions and simple dimension ratios can put resonances from different axes close together. The overlap tolerance lets you decide how close two calculated frequencies must be before they are flagged.
Does this include tangential and oblique modes?
No. This page focuses on axial modes. Tangential modes use two room dimensions, while oblique modes use all three.
Will every mode cause an audible peak?
No. The formula predicts ideal resonance frequencies, not magnitude. Real response depends on boundaries, damping, leakage, room contents, and source and receiver positions.
Does the calculator upload my dimensions?
No. Calculations and file generation run locally in your browser.