Sound waves are caused by vibrations such as that from a tuning fork, a loudspeaker cone, or the human voice.
These vibrations need air to travel through. They cannot travel through a vacuum.
The air itself doesn't travel.
The sound causes compression and decompression of the air as it moves through it.
There is a regular spacing between one pressure peak and the next.
This distance is called the WAVELENGTH.
Sound travels at about 330 metres a second.
A pure sound tone consists of a single frequency of vibration.
The range of human hearing is about 20 Hertz to 20 KiloHertz.
Most sounds are a mixture of frequencies. See the page on HARMONICS.
Microphones convert sound pressure waves into electrical signals.
Loudspeakers convert electrical signals into sound waves.
Loudspeakers and microphones are TRANSDUCERS.
Frequency, wavelength and the speed of sound are interrelated.
Wavelength x frequency = the speed of sound in metres per second.
