The Loud

To measure the loudness of sound, a unit of measurement called a decibel (dB) is used. A decibel is one tenth of a bel (B), or the unit of measurement devised by engineers of the Bell Telephone Laboratory to quantify the level of sound reduction when a tone is transmitted over one mile (1.6 km) of standard telephone cable. Since the bel proved to be too large for most common sound measurements, the use of the smaller decibel became more popular.The decibel is used in a wide variety of scientific measurements related to acoustics and and electronics. This unit of measurement places a physical value – usually of noise or light intensity – in which a doubling of actual intensity causes perceived intensity to always increase by roughly the same amount. Specifically, a 3 dB increase is about equal to an approximate doubling of sound. This is important to understand because when you look at the dB values given in the following charts and text, you will understand a relatively small numerical increase of 10 dB between the sound of rainfall and a sewing machine accounts for the significantly greater noise level. It also shows that the 110dB sound of a screaming child is only several times less intense than a thunderclap or a rock concert.