Wavelength

The physical size of a sound wave, drawn against things you know.

Wavelength780mm2.56 ft

Half wave390mm

Quarter wave195mm

Period2.27ms

Speed of sound343.2m/s

One wave, to scale

The wave is slowed down enormously so you can see it travel.

Input

Frequency

f

Air temperature

T

°C

Sound travels at a fixed speed in air, so a tone that repeats more often must pack its cycles closer together. The distance one cycle occupies is

\lambda = \frac{c}{f}

Audible sound spans an extraordinary range of sizes: about 17 m at 20 Hz down to 17 mm at 20 kHz, a ratio of a thousand to one.

The speed of sound depends on air temperature and hardly at all on pressure:

c = 331.3\sqrt{1 + \frac{T}{273.15}}\ \ \mathrm{m/s}

with $T$ in degrees Celsius. At 20 °C that gives 343.2 m/s, rising roughly 0.6 m/s per degree.

Absorbers need a depth near a quarter wavelength to work well. That is 86 cm at 100 Hz, which is why bass is hard to tame with thin panels.
Drivers beam when the wavelength shrinks to about their diameter. A 16 cm woofer narrows above roughly 2 kHz.
Rooms resonate when half a wavelength fits between two walls.
Baffles stop supporting bass when the wavelength exceeds their width, causing the baffle step.

How it works

Sound travels at a fixed speed in air, so a tone that repeats more often must pack its cycles closer together. The distance one cycle occupies is

\lambda = \frac{c}{f}

Audible sound spans an extraordinary range of sizes: about 17 m at 20 Hz down to 17 mm at 20 kHz, a ratio of a thousand to one.

The speed of sound depends on air temperature and hardly at all on pressure:

c = 331.3\sqrt{1 + \frac{T}{273.15}}\ \ \mathrm{m/s}

with $T$ in degrees Celsius. At 20 °C that gives 343.2 m/s, rising roughly 0.6 m/s per degree.

Absorbers need a depth near a quarter wavelength to work well. That is 86 cm at 100 Hz, which is why bass is hard to tame with thin panels.
Drivers beam when the wavelength shrinks to about their diameter. A 16 cm woofer narrows above roughly 2 kHz.
Rooms resonate when half a wavelength fits between two walls.
Baffles stop supporting bass when the wavelength exceeds their width, causing the baffle step.