Calculate room modes - how it works

If you calculate the room modes of your room, you know the natural frequencies that resonate particularly strongly. You can then do something specifically against the deepest room modes in order to achieve greater sound homogeneity. We explain to you what exactly room modes are and how you can calculate them for a cuboid room.

What are room fashions?

You would particularly like to suppress room fashions in the recording studio or in a room for listening to music. They are frequencies that are particularly loud at regular intervals and stand out from the sound spectrum.

1. Room modes are "standing waves". That sounds paradoxical, because the essence of a sound wave is the spread of a pressure fluctuation.
2. However, if two waves of the same frequency, which come from different directions, overlap, areas are formed in the room in which they cancel each other out.
3. These areas of destructive interference are called "nodes".
4. In other places, the waves overlap constructively. Here they add up and show "bellies" or "antinodes".
5. As long as they overlap, they act like a constant vibration.
6. A YouTube clip shows an example of a standing wave in a one-dimensional case.
7. In the two-dimensional case, the "nodes" become "node lines", as you can see in this YouTube clip of a eigenmode.
8. In a three-dimensional space, these node lines become node levels.
9. If you play a sweep in your listening room, the room modes will be particularly booming.
10. In addition to the room modes, the resonance frequencies of your speaker may also be booming, provided that it does not have a flat frequency response.
11. However, the resonance frequencies of your loudspeaker roar throughout the room, while room modes always have pressure bellies where the frequency is very loud, while they can only be heard very quietly at pressure nodes.

How to calculate room modes

Calculating room modes is all the more complicated the more complex the geometry is. With a simple formula you can calculate the room modes of a cuboid room:

1. Make a note of the length l, width b and height h of your room.
2. Make sure that your room has a temperature of around 20 ° C so that it has a reasonable operating temperature and the speed of sound c is around 343 m / s.
3. The resonance frequencies f_res are calculated using the following formula - for example in Excel:
4. f_res = c / 2 sqrt [(x / l) ² + (y / b) ² + (z / h) ²]
5. "Sqrt" stands for the root of the entire expression in the square brackets.
6. "x", "y" and "z" are the "ordinal numbers". They are integers where you use 0 to 6 to calculate the first 216 natural frequencies in your room.
7. If a frequency occurs several times - such as 133 and 418 Hz in the example shown - or if many frequencies are very close together - such as 69 and 70 Hz and 118 to 120 Hz - this frequency range will particularly boom.

Due to complicated scattering effects, the calculation of room modes above a few hundred Hertz is usually not useful. If you set your equalizer correctly and regulate the phase of your subwoofer, you can counteract extreme room modes somewhat. Otherwise, Helmholtz absorbers help for the lowest frequencies that you have calculated.