What Are Decibels, and How Are They Measured?

Decibels (dB) are units used to measure the intensity or level of sound. They are commonly used in noise measurement to express sound levels in a more manageable way, especially when dealing with a wide range of noise sources.

The decibel scale is logarithmic, which means it uses a base of 10 rather than a linear scale. This allows for easier representation of large ranges of sound levels. On the decibel scale, the quietest audible sound is typically considered to be 0 dB. Each increase of 10 dB represents a tenfold increase in sound intensity. For example, a sound that is 10 times more powerful than another sound is 10 dB louder.

Some common sounds and their corresponding decibel measurements include:

Near-total silence: 0 dB
A whisper: 15 dB
A library: 45 dB

A normal conversation: 60 dB
A noisy restaurant: 90 dB
A jet engine: 120 dB

A balloon popping: 157 dB

When measuring noise levels with a sound level meter, it’s important to understand how to interpret decibel readings. For example, a 3 dB increase represents a doubling of sound energy, while a 3 dB decrease represents halving the sound energy.

Adding decibel levels together is not as straightforward as simple addition due to the logarithmic nature of the scale. Instead, specific rules are used to determine the combined level of two or more sound sources.

Different frequency weightings, such as A-weighting and C-weighting, are also applied to decibel measurements to account for the sensitivity of the human ear to different frequencies of sound. These weightings adjust the sound pressure readings to reflect how the human ear perceives sound at different frequencies