How Long Is a 138 Hz Wavelength?
A 138 Hz sound wave has a wavelength of 2.49 meters, 248.71 cm, 8.16 feet (8 feet and 1.92 inches) or 97.92 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 = 138 Hz
λ of 2.49 meters, or 8.16 feet.
138 Hz Wavelength Depending on Temperature
The speed of sound in air depends on temperature. Here is how the wavelenght of a 138 Hz sound wave will vary according to temperature:
| Temp (°C) | Temp (°F) | 138 Hz wavelength (m) | 138 Hz wavelength (ft) |
|---|---|---|---|
| -40 | -40 | 2.2180 | 7.2769 |
| -35 | -31 | 2.2416 | 7.3545 |
| -30 | -22 | 2.2651 | 7.4313 |
| -25 | -13 | 2.2882 | 7.5073 |
| -20 | -4 | 2.3112 | 7.5826 |
| -15 | 5 | 2.3339 | 7.6571 |
| -10 | 14 | 2.3564 | 7.7309 |
| -5 | 23 | 2.3787 | 7.8040 |
| 0 | 32 | 2.4007 | 7.8764 |
| 5 | 41 | 2.4226 | 7.9482 |
| 10 | 50 | 2.4443 | 8.0193 |
| 15 | 59 | 2.4658 | 8.0898 |
| 20 | 68 | 2.4871 | 8.1597 |
| 25 | 77 | 2.5082 | 8.2289 |
| 30 | 86 | 2.5291 | 8.2977 |
| 35 | 95 | 2.5499 | 8.3658 |
| 40 | 104 | 2.5705 | 8.4334 |
138 Hz Half Wavelength and Standing Waves
The half wavelength of a 138 Hz sound wave is 1.24 meters, 124.35 cm, 4.08 feet (4 feet and 0.96 inches) or 48.96 inches when travelling in air at 20°C (68°F).
Modes (or standing waves) will occur at 138 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 138 Hz wavelength = 2.49 meters, or 8.16 feet in air at 20°C (68°F).
138 Hz Standing Waves Distances
| n | Distance (m) | Distance (ft) |
|---|---|---|
| 1 | 1.24 | 4.08 |
| 2 | 2.49 | 8.16 |
| 3 | 3.73 | 12.24 |
| 4 | 4.97 | 16.32 |
| 5 | 6.22 | 20.40 |
| 6 | 7.46 | 24.48 |
| 7 | 8.70 | 28.56 |
| 8 | 9.95 | 32.64 |
| 9 | 11.19 | 36.72 |
| 10 | 12.44 | 40.80 |
| 11 | 13.68 | 44.88 |
| 12 | 14.92 | 48.96 |
| 13 | 16.17 | 53.04 |
Given the relatively large 138 Hz half wavelength, standing waves will occur at that frequency in small listening rooms.
You can try to minimze the room modes at 138 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 138 Hz To ms
A Hz (Hertz) is a cycle (or period) per second.
Because a 138 Hz wave will ocillate 138 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 = 138 Hz
The result will be expressed in seconds, so let's multiply by 1000 to get miliseconds:
1 / 138 Hz * 1000 = 7.25 ms.