The horizontal axis shows frequency in Hz

In acoustics, loudness is the subjective perception of sound pressure. More formally, it is defined as, "That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud."[1] The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. The study of apparent loudness is included in the topic of psychoacoustics and employs methods of psychophysics.

In different industries, loudness may have different meanings and different measurement standards. Some definitions, such as ITU-R BS.1770 refer to relative loudness of different segments of electronically reproduced sounds, such as for broadcasting and cinema. Others, such as ISO 532A (Stevens loudness, measured in sones), ISO 532B (Zwicker loudness), DIN 45631 and ASA/ANSI S3.4, have a more general scope and are often used to characterize loudness of environmental noise.

Loudness, a subjective measure, often confused with physical measures of sound strength such as sound pressure, sound pressure level (in decibels), sound intensity or sound power. Filters such as A-weighting and LKFS attempt to compensate measurements to correspond to loudness as perceived by the typical human.


The perception of loudness is related to sound pressure level (SPL), frequency content and duration of a sound.[2] The relationship between SPL and loudness of a single tone can be approximated by Stevens's power law in which SPL has an exponent of 0.67.[a] More precise measurements, a model known as the Inflected Exponential function,[3] indicate that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels.[4]

The sensitivity of the human ear changes as a function of frequency, as shown in the equal-loudness graph. Each line on this graph shows the SPL required for frequencies to be perceived as equally loud, and different curves pertain to different sound pressure levels. It also shows that humans with normal hearing are most sensitive to sounds around 2–4 kHz, with sensitivity declining to either side of this region. A complete model of the perception of loudness will include the integration of SPL by frequency.[5]

Historically, loudness was measured using an "ear-balance" audiometer in which the amplitude of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated. Contemporary standards for measurement of loudness are based on summation of energy in critical bands.[6]

Other Languages
العربية: جهارة
català: Volum (so)
Deutsch: Lautheit
eesti: Helivaljus
français: Sonie
hrvatski: Glasnoća
magyar: Hangosság
Nederlands: Luidheid
日本語: 音の大きさ
norsk nynorsk: Lydstyrke
polski: Głośność
português: Volume (som)
Simple English: Loudness
українська: Гучність звуку
中文: 響度