The frequency of a sound wave is determined by the source of the sound, specifically by the rate at which the source vibrates or oscillates. In simpler terms, the frequency is the number of oscillations or cycles per second that the source produces.
For example, if you pluck a guitar string, the frequency of the sound produced depends on how fast the string vibrates back and forth. Similarly, in the case of a speaker, the frequency of the sound wave is determined by the rapid back-and-forth movement of the diaphragm.
In general, higher frequencies correspond to faster vibrations or oscillations, resulting in a higher-pitched sound. Conversely, lower frequencies correspond to slower vibrations, resulting in a lower-pitched sound.
The frequency of sound waves is measured in hertz (Hz), which represents the number of cycles per second. The human audible range typically spans from about 20 Hz to 20,000 Hz, although individual hearing capabilities may vary.