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Decibel scale
Intermediate
Logarithmic unit of sound level.
β = 10 log(I/I₀)Sound level β = 10 log₁₀(I/I₀) with I₀ = 10⁻¹² W/m². Each 10 dB is a tenfold intensity increase; 3 dB roughly doubles it.
A conversation of 60 dB is 10⁶ I₀.
Two 60 dB sources give 63 dB, not 120.
In more detail
The decibel scale is logarithmic, with a sound level of L = 10 log(I/I0) dB, where I0 is the threshold of hearing. A 10 dB increase means ten times the intensity.
Real-world uses
- Noise regulations use decibels to limit workplace and environmental noise.
- Audio equipment specifications are given in decibels.
- Noise regulations and hearing-safety guidelines quote levels in decibels, which compress a huge range of intensities into a simple scale.
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Frequently asked questions
What is 0 dB?
The reference intensity of 10⁻¹² W/m², near the threshold of hearing.
What is a safe long-term level?
Prolonged exposure above about 85 dB can damage hearing.
What is 0 dB?
A reference intensity set at the threshold of human hearing, equal to 10⁻¹² watts per square metre.
Related topics in Waves & Sound
Sound as pressure waves · Pitch and frequency · Loudness and intensity · Intensity and distance · Timbre · Range of hearing