How are noise levels measured in decibels?

The decibel (dB) is the unit used to measure the intensity (I) of sound or noise level, and it is given in terms of a logarithmic function of a ratio of power intensities. In physics, the formula used for decibels is dB = 10 log₁₀ (I/I1), where I1 is a reference value called the threshold of hearing intensity. In this equation, it is possible to express the intensity I as a multiple of I1.

To find different sound intensities or noise levels, it is a matter of using the formula. For example, find the sound intensity of a noise or a sound that is 1,000 times louder than the threshold intensity I1.

1. Use the formula

Substitute into the formula 1000 x I1 for the intensity I to find that dB = 10 x log₁₀ (1000 x I1)/I1, or 10 log₁₀1000.

2. Express the logarithmic function as a power

Realize that log₁₀1000 is the same as 1000 = 10 ^y, or y =3. Replace 3 into the equation 10 x log₁₀1000 which becomes 10 x 3 and the sound intensity is equal to 30 dB.

On the decibel scale, the lowest sound intensity is 0 dB, which is near complete silence. A normal conversation is equivalent to an intensity of 60 dB, and a very noisy rock concert is about 110 dB. Noises or sounds that are at or above 85 dB can cause hearing problems. If a person listens to noises at this dB level for 8 hours, it can potentially cause hearing loss, as noted by the Centers for Disease Control and Prevention.