How Long Is a 21 Hz Wavelength?
A 21 Hz sound wave has a wavelength of 16.34 meters, 1634.36 cm, 53.62 feet (53 feet and 7.45 inches) or 643.45 inches when traveling in air at 20°C (68°F).
The formula for the wavelenght is λ = c/f where:
cis the celerity (speed) of sound = 343.21 m/s or 1126.03 ft/s in air at 20°C (68°F).fis the frequency = 21 Hz
λ of 16.34 meters, or 53.62 feet.
21 Hz Wavelength Depending on Temperature
The speed of sound in air depends on temperature. Here is how the wavelenght of a 21 Hz sound wave will vary according to temperature:
| Temp (°C) | Temp (°F) | 21 Hz wavelength (m) | 21 Hz wavelength (ft) |
|---|---|---|---|
| -40 | -40 | 14.5754 | 47.8194 |
| -35 | -31 | 14.7308 | 48.3295 |
| -30 | -22 | 14.8847 | 48.8342 |
| -25 | -13 | 15.0369 | 49.3337 |
| -20 | -4 | 15.1876 | 49.8282 |
| -15 | 5 | 15.3369 | 50.3179 |
| -10 | 14 | 15.4847 | 50.8029 |
| -5 | 23 | 15.6311 | 51.2832 |
| 0 | 32 | 15.7762 | 51.7592 |
| 5 | 41 | 15.9199 | 52.2307 |
| 10 | 50 | 16.0624 | 52.6981 |
| 15 | 59 | 16.2036 | 53.1613 |
| 20 | 68 | 16.3436 | 53.6206 |
| 25 | 77 | 16.4823 | 54.0759 |
| 30 | 86 | 16.6200 | 54.5275 |
| 35 | 95 | 16.7565 | 54.9753 |
| 40 | 104 | 16.8919 | 55.4195 |
21 Hz Half Wavelength and Standing Waves
The half wavelength of a 21 Hz sound wave is 8.17 meters, 817.18 cm, 26.81 feet (26 feet and 9.72 inches) or 321.72 inches when travelling in air at 20°C (68°F).
Modes (or standing waves) will occur at 21 Hz in rooms where two opposing walls (axial mode), edges (tangential mode) or corners (oblique mode) are spaced by a distance d = nλ/2 where:
nis a natural (positive integer greater than or equal to 1)λis the 21 Hz wavelength = 16.34 meters, or 53.62 feet in air at 20°C (68°F).
21 Hz Standing Waves Distances
| n | Distance (m) | Distance (ft) |
|---|---|---|
| 1 | 8.17 | 26.81 |
| 2 | 16.34 | 53.62 |
| 3 | 24.52 | 80.43 |
| 4 | 32.69 | 107.24 |
| 5 | 40.86 | 134.05 |
Given the relatively large 21 Hz half wavelength, standing waves will occur at that frequency in small listening rooms.
You can try to minimze the room modes at 21 Hz by trying different speaker positions, listening positions or by placing bass traps. These can absorb frequencies as low as 63 Hz.
How To Convert 21 Hz To ms
A Hz (Hertz) is a cycle (or period) per second.
Because a 21 Hz wave will ocillate 21 times per second, we can find the time of a single cycle (or period) with the formula p = 1/f where:
fis the frequency of the wave = 21 Hz
The result will be expressed in seconds, so let's multiply by 1000 to get miliseconds:
1 / 21 Hz * 1000 = 47.62 ms.