Simple Explanation

The quietest sound a healthy human ear can typically hear.

Concise Technical Definition

A reference sound pressure level equal to 20 micropascals (µPa) RMS, defined as the threshold of human hearing in air.

Layman-Friendly Analogy

Like the faintest whisper you could barely detect in complete silence.

Industry Usage Summary

Used as the baseline reference for measuring sound pressure levels (SPLs). All SPL measurements are made relative to this standard.

Engineering Shortcut

0 dB SPL = 20 µPa RMS; reference point for acoustic measurements.

Full Technical Explanation

0 dB SPL (sound pressure level) is the standard reference for the threshold of human hearing in air. It corresponds to a root-mean-square (RMS) sound pressure of 20 µPa (micropascals), or 0.00002 Pa. This is not “zero sound,” but rather the quietest level that the average human ear can detect under ideal conditions. SPL is logarithmic, so every 20 dB increase represents a tenfold increase in pressure. SPL measurements above 0 dB reflect louder sounds; negative values are possible but indicate quieter-than-threshold levels.