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.

Point of Reference

Points of Reference *measured in dBA or decibels:

• 0 The softest sound a person can hear with normal hearing
• 10 normal breathing
• 20 whispering at 5 feet
• 30 soft whisper
• 50 rainfall
• 60 normal conversation
• 110 shouting in ear
• 120 thunder

Good Hearing?

A typical person with good hearing can hear from about 20Hz to 20kHz (the audio bandwidth). A person's voice will usually range from 500Hz to 2kHz.