Sound Levels

Decibels (dB) are most commonly used as a measure of sound level, but they are also used in electronics, signals and communications.

Sound is a variation in pressure detectable by the ear, whereas noise is undesired sound, or any sound which causes disturbance or annoyance to the recipient. The unit used to describe sound wave intensity is the bel, named after the inventor Alexander Graham Bell. The human ear is sensitive enough to detect changes of as little as 1/10 of a bel, and so sound intensity levels are described in decibels.

A sound wave’s intensity is the average amount of energy transmitted per unit time through a unit area in a specified direction. The sound intensity level, I, in decibels is 10 times the logarithm of the ratio of the intensity of a sound wave to a reference intensity.

Reverberation Time

The ‘reverberation time’ of a space changes the way the space ‘sounds’ and can affect the intelligibility acoustic information. A high reverberation time can make a room sound muffled, loud and noisy. Rooms designed for speech typically have a low reverberation time, whereas a higher reverberation time can add depth, richness and warmth to music.

The reverberation time of a room is defined as the time it takes for sound to decay by 60 dB after an abrupt termination. It is linked to the total quantity of soft treatments and the volume of the room.

Sound Intensity

Sound intensity is measured in Decibels (dB). This is a logarithmic scale in which an increase of 10 dB gives an apparent doubling of loudness.

Sound pitch is measured in Hertz (Hz), the standard unit for the measurement for frequency. The audible range of sound for humans is typically from 20 Hz to 20,000 Hz, although, through ageing and exposure to loud sounds the upper limit will generally decrease.