Frequency to wavelength
Wavelength is wave speed divided by frequency. Concert A at 440 Hz has a wavelength of 0.78 metres in air. A 40 Hz bass note is 8.6 metres, and a 10 kHz treble note is just 34 millimetres.
How to find a wavelength
The enormous range of audible wavelengths; from over seventeen metres at 20 Hz down to seventeen millimetres at 20 kHz, a factor of a thousand: explains most of what is difficult about acoustics. High frequencies are directional and easily absorbed because they are small compared with objects in a room. Low frequencies wrap around obstacles and interact with room dimensions because they are not. That single fact is behind why tweeters need aiming, why bass leaks through walls, and why a small speaker cannot produce deep bass efficiently.
Questions
About 0.78 metres in air at 20 °C.
Over seventeen metres. Longer than most rooms, which is why deep bass is so hard to control indoors.
Porous absorbers are most effective at a quarter of the wavelength deep, which sets the panel thickness needed for a given frequency.
Enormously. Sound travels four times faster in water, so wavelengths are four times longer at the same frequency.
A quarter-wave antenna is a quarter of the wavelength. Select the vacuum option for radio frequencies.