Decibella

Meet Decibella, who knows that ten more decibels means ten times the sound.

Our ears handle an enormous range of sound intensities, from a whisper to a jet engine. A linear scale would be awkward, so we use a logarithmic one, the decibel. The sound level is L = 10 log₁₀(I/I₀), where I₀ = 10⁻¹² W/m² is about the quietest sound a healthy young ear can detect. The bel is named after Alexander Graham Bell; the decibel is a tenth of a bel.

Every +10 dB multiplies the intensity by 10. A 60 dB conversation has I = 10⁻¹² × 10⁶ = 10⁻⁶ W/m². At 80 dB it is 10⁻⁴ W/m², which is 100 times more intense.

Decibels are used in hearing protection rules, noise limits, audio engineering and acoustics. The same logarithmic idea appears in electronics and radio for signal strength.

Intensity and perceived loudness are not the same. As a rough rule, +10 dB sounds about twice as loud, not ten times. Our sensitivity also depends on pitch, which is why weighted scales such as dBA exist.