Calculate wavelength – with quarter wave and temperature

How it is calculated

c = 20.058 \frac{m}{s} \cdot \sqrt{\frac{T}{K}} λ = \frac{c}{f}

$c$ – speed of sound in dry air in m/s
$T$ – absolute temperature in kelvin ( $T = ϑ + 273.15$ , with $ϑ$ in °C)
$λ$ – wavelength in m
$f$ – frequency in Hz

At 20 °C, this gives approx. 343.4 m/s. Humidity increases the speed of sound slightly; the calculator works with dry air.

Example

100 Hz at 20 °C: $λ = 343.4 / 100 \approx 3.43 m$ . The quarter wave is therefore approx. 86 cm.

What you need the quarter wave for

The quarter wavelength comes up constantly in PA practice: with cancellations caused by wall and floor reflections, with spacings in subwoofer arrays and with delay corrections. If you know it for a frequency, you can classify placement problems more quickly.

Calculate wavelength – with quarter wave and temperature

How it is calculated

Example

What you need the quarter wave for

Further reading

Sources