how to calculate sound level in decibel?

Answer 1

Decibels is a logarithmic scale, like the Richter scale for earthquakes and the luminous magnitude scale for star brightness. Zero is the faintest sound most people can hear, which is assumed to be 10^ -16 watts per square metre of sound . 10 dB is 10x 10 times this level, which is 10^ -14 watts/sq.m. 65 dB, about the level of a conversation in a restaurant, is 10x 10^6.5 times the threshold level of 10^ -16 which works out at 3.16x 10^-10 watts/ square metre. 120 dB is about the level of a pneumatic drill, or 10 metres behind a jet aircraft on its takeoff run, or a couple of metres from the loudspeaker at an outdoor rock concert.It is 10 times 1 000 000 000 000 times the threshold level, or 0.001 watts / sq.m. of sound. So every time you multiply the sound power by 10 you go up 10 dB. 150dB is reckoned to permanently and immediately deafen you. Absolute silence is minus infinity dB because the logarithm of zero is minus infinity.