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In different industries, loudness may have different meanings and different measurement standards. The study of apparent loudness is included in the topic of psychoacoustics and employs methods of psychophysics. The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. More formally, it is defined as the "attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". In acoustics, loudness is the subjective perception of sound pressure. The horizontal axis shows frequency in Hz For the Japanese band, see Loudness (band). "Vuvuzela – good for your team, bad for your ears" (PDF). ^ Swanepoel, De Wet Hall III, James W.^ a b Realistic Maximum Sound Pressure Levels for Dynamic Microphones – Shure.Archived from the original on 16 March 2014. ^ "LRAD Corporation Product Overview for LRAD 1000Xi".^ a b c d e f g "Did You Know How Loud Balloons Can Be?".: CS1 maint: multiple names: authors list ( link) Īccording to the inverse proportional law, when sound level L p 1 is measured at a distance r 1, the sound level L p 2 at the distance r 2 is Because of the effects of reflected noise within a closed room, the use of an anechoic chamber allows sound to be comparable to measurements made in a free field environment. A distance of one metre (1 m) from the source is a frequently used standard distance. In the case of ambient environmental measurements of "background" noise, distance need not be quoted, as no single source is present, but when measuring the noise level of a specific piece of equipment, the distance should always be stated. The distance of the measuring microphone from a sound source is often omitted when SPL measurements are quoted, making the data useless, due to the inherent effect of the inverse proportional law. Some sound measuring instruments use the letter "Z" as an indication of linear SPL. Unweighted sound pressure level is called "linear sound pressure level" and is often written as dB L or just L. B-weighted sound pressure level is written either as dB B or L B, and C-weighted sound pressure level is written either as dB C or L C. In order to distinguish the different sound measures, a suffix is used: A-weighted sound pressure level is written either as dB A or L A. Because the frequency response of human hearing changes with amplitude, three weightings have been established for measuring sound pressure: A, B and C. Humans do not perceive low- and high-frequency sounds as well as they perceive sounds between 3,000 and 4,000 Hz, as shown in the equal-loudness contour. Human hearing does not have a flat spectral sensitivity ( frequency response) relative to frequency versus amplitude. Equal-loudness contour, showing sound-pressure-vs-frequency at different perceived loudness levelsĮars detect changes in sound pressure. e., if the thermodynamic properties of the air are disregarded in reality, the sound waves become progressively non-linear starting over 150 dB), larger sound waves can be present in other atmospheres or other media, such as underwater or through the Earth. While 1 atm ( 194 dB peak or 191 dB SPL) is the largest pressure variation an undistorted sound wave can have in Earth's atmosphere (i. The lower limit of audibility is defined as SPL of 0 dB, but the upper limit is not as clearly defined. Most sound level meters provide readings in A, C, and Z-weighted decibels and must meet international standards such as IEC 61672-2013. The main instrument for measuring sound levels in the environment is the sound level meter. These references are defined in ANSI S1.1-2013. In other media, such as underwater, a reference level of 1 μPa is used. Most sound-level measurements will be made relative to this reference, meaning 1 Pa will equal an SPL of 94 dB. The proper notations for sound pressure level using this reference are L p/(20 μPa) or L p (re 20 μPa), but the suffix notations dB SPL, dB(SPL), dBSPL, or dB SPL are very common, even if they are not accepted by the SI. Which is often considered as the threshold of human hearing (roughly the sound of a mosquito flying 3 m away).