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.

Environmental Noise Levels

According to the National Institute for Occupational Safety and Health, the maximum exposure time at 85 dBA is eight hours.

At 110 dBA, the maximum exposure time is one minute and 29 seconds. If you must be exposed to noise, it is recommended that you limit the exposure time and/or wear hearing protection.

A three dBA increase doubles the amount of noise, and halves the recommended amount of exposure time.

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.