HesapHanem

Room Mode Calculator

Enter the room length, width and height to find its axial room modes.

How it is calculated

For each room dimension D in metres (length, width, height) the tool lists the first three axial modes, fn = (c / 2) × (n / D) for n = 1, 2, 3, with the speed of sound fixed at c = 343 m/s. The result is in hertz, rounded to two decimals. The lowest mode is the smallest of the three fundamentals, which always belongs to the longest dimension. Only axial modes are calculated, which involve a single pair of parallel surfaces; the tangential and oblique modes that involve four or six surfaces are not listed. All three dimensions must be above zero. Real rooms with furniture, open doorways or non-rectangular shapes will deviate from these numbers.

Worked example

A room 5 m long, 4 m wide and 2.7 m high. Half the speed of sound is 343 / 2 = 171.5. Length: 171.5 / 5 = 34.30 Hz, then 68.60 and 102.90 Hz. Width: 171.5 / 4 = 42.875, shown as 42.88 Hz, then 85.75 and 128.63 Hz. Height: 171.5 / 2.7 = 63.52 Hz, then 127.04 and 190.56 Hz. The full result reads: Length: 34.30 Hz, 68.60 Hz, 102.90 Hz | Width: 42.88 Hz, 85.75 Hz, 128.63 Hz | Height: 63.52 Hz, 127.04 Hz, 190.56 Hz. The lowest mode is 34.30 Hz.

Try this example →

Common mistakes

  • Entering dimensions in feet or centimetres. The fields are metres, so a 16 ft room must be typed as about 4.9, not 16.
  • Swapping the length, width and height fields. Each family of modes is labelled by dimension, so a swapped entry puts a peak on the wrong wall pair when you plan bass traps.
  • Treating the list as every resonance in the room. Only the first three axial modes per dimension are shown; tangential and oblique modes also exist and add more peaks.
  • Expecting good results from near-equal dimensions. If two numbers in the list almost coincide (as with a 3 m by 3 m floor), the modes stack and the bass boost is stronger.
  • Using the numbers for a room much warmer or colder than normal. The speed of sound is fixed at 343 m/s, so every frequency scales with the real value.

About this calculator

An axial room mode is a standing wave that forms between two parallel, opposite surfaces — say the front and back walls — when a sound wave’s reflection reinforces itself at specific frequencies. The first axial mode along any dimension is f = c / (2 × L), with higher modes at 2f, 3f and so on, where c is the speed of sound (343 m/s) and L is the room length, width, or height in metres.

Because a rectangular room has three axial dimensions, it produces three families of resonances that boost bass at some frequencies and cancel it at others, creating the uneven low-end response and “boomy corners” familiar in small rooms. Acousticians, recording-studio designers and home-theater installers calculate these modes to place speakers and listening positions away from nulls, choose bass-trap locations, and judge whether a room’s proportions will cause modal clustering.

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  • Editorial team

    Compare the three lists side by side. If two room dimensions are equal, their modes land on identical frequencies and the bass piles up there, while moving one wall by even 0.3 m separates them by a few hertz. Peaks from different dimensions that fall close together do the same. What are your room's length, width and height, and which mode ended up lowest?

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