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Acoustics

How does the decibel scale work?

Short answer

Decibels are a logarithmic scale. Two equally loud sources together give +3 dB, and +10 dB sounds about twice as loud.

Decibel staircase: Steps of sound: conversation 60, WHO-safe 80 (40 h/week) and 90 (4 h/week), hair dryer 100, pain threshold 140 dB.
Decibel staircase — Steps of sound: conversation 60, WHO-safe 80 (40 h/week) and 90 (4 h/week), hair dryer 100, pain threshold 140 dB. (The text inside the figure is in Dutch.)

Explanation

Sound is a pressure wave. The decibel scale expresses its strength logarithmically. A-weighting (dB(A)) takes into account how the ear hears different pitches. The human ear hears roughly from 20 to 20 000 Hz.

Rules of thumb

  • Two equal sources: +3 dB. [SW-S11]
  • +10 dB: sounds about twice as loud. [SW-S11]
  • Examples according to WHO: conversation about 60 dB, hair dryer about 100 dB. [SW-S10]
  • Pain threshold: about 140 dB(A). [SW-S11]

Pitfalls

  • You cannot simply add decibels: 60 dB + 60 dB is 63 dB, not 120 dB. [SW-S11]

Search terms

These search terms are in Dutch; only terms that also find a topic in English are links.

decibel dB(A) geluidsniveau

Read also

General information, not personal advice. Check the source and reference date.

Sources

  1. SW-S10 Deafness and hearing loss: Safe listening (Q&A) — WHO (Reference date 2026-09-27)
  2. SW-S11 Grondbeginselen van geluid (GGD-richtlijn medische milieukunde omgevingsgeluid) — RIVM (Reference date 2026-09-27)

Reference date: 2026-09-27 · Translated with AI from the Dutch original.