Decibel

The decibel (dB) is a logarithmic unit used to express the ratio of two values of a physical quantity, most commonly sound pressure or sound power. It is not an absolute unit but a ratio; specific reference values are used for sound pressure (20 µPa) and sound power (1 pW). The logarithmic scale is used because the human ear perceives loudness approximately logarithmically and because the range of audible pressures spans six orders of magnitude. A 3 dB increase represents a doubling of acoustic energy, while a 10 dB increase is perceived as approximately twice as loud. In building acoustics, decibels are used for sound levels, transmission loss, noise ratings, and insulation performance. Understanding decibel arithmetic (logarithmic addition, averaging) is essential for acoustic calculations.