Scientists Say: Decibel

This is a scale that describes a sound’s volume

Decibels are a unit for describing how loud sounds are. A typical conversation is around 60 decibels, but whispering keeps noise levels well below.

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Decibel (noun, “DESS-ih-bul”)

This is a measurement that describes the loudness of sounds. It’s used to describe sounds that are in the range of human hearing. The human ear can pick up noises ranging in intensity from the sound of a breath to ones louder than a raucous rock concert. The decibel scale starts at zero decibels (0 dB). Someone with very good hearing would just barely be able to hear a sound at that level.

To capture the wide range of sounds that people can hear, the decibel scale is logarithmic. On such a scale, values that represent a measurement or quantity aren’t evenly spaced. Instead, they increase by multiples of a specific number. For the decibel scale, that number is 10. A 20 dB sound is 10 times louder than a 10 dB sound. The level of noise in a quiet bedroom, 30 dB, is 100 times louder than 10 dB. And 40 dB is 1,000 times louder than 10 dB. A typical conversation clocks in at around 60 dB. But a rock concert would be closer to 120 dB. In terms of intensity, the rock concert is 1,000,000 times louder than the conversation. That level of racket can put people at risk of hearing loss.

The “bel” in decibel comes from Alexander Graham Bell, the inventor of the telephone. “Deci” is a metric prefix that means “tenth.” Put the terms together and you get decibel.

In a sentence

This drone for spying on birds whirrs by relatively quietly, making only around 60 decibels of noise.

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Carolyn Wilke is a staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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