Sound intensity

Sound intensity describes how loud a sound is. Sound intensity is expressed in decibel (dB).

Sound is air molecules that vibrate systematically. When a stone is thrown into the water we see surface waves spreading in circles. In the same way, sound waves propagate from their source in spherical waves.

Sound intensity and distance

The further away the sound waves move from the source, the lower the sound intensity. In a completely unobstructed area, for example in an open field, the sound intensity will be halved every time the distance from the sound source is doubled. This means that a person standing 20 metres from a sound source only experiences 50% of the sound intensity experienced by one standing 10 metres from the sound source.

However, this rule does not quite apply if the sound is emitted indoors, where walls, ceilings and furniture absorb or reflect the sound.

Describing a sound

Sound can be characterised in different ways, but primarily in terms of intensity and frequency:

The sound intensity describes how soft or loud the sound is.

Frequency (or pitch) describes how high-pitched or low-pitched the sound is.