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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 ] A more precise model known as the Inflected Exponential function , [ 3 ] indicates that loudness increases with a higher exponent at low and high levels and with a lower exponent at moderate levels.
While 1 atm (194 dB peak or 191 dB SPL) [11] [12] is the largest pressure variation an undistorted sound wave can have in Earth's atmosphere (i. 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 ...
An equal-loudness contour is a measure of sound pressure level, over the frequency spectrum, for which a listener perceives a constant loudness when presented with pure steady tones. [1] The unit of measurement for loudness levels is the phon and is arrived at by reference to equal-loudness contours.
A graph of the A-, B-, C- and D-weightings across the frequency range 10 Hz – 20 kHz Video illustrating A-weighting by analyzing a sine sweep (contains audio). A-weighting is a form of frequency weighting and the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. [1]
A sound level meter (also called sound pressure level meter (SPL)) is used for acoustic measurements. It is commonly a hand-held instrument with a microphone . The best type of microphone for sound level meters is the condenser microphone, which combines precision with stability and reliability. [ 1 ]
Equal-loudness contours. The phon is a logarithmic unit of loudness level for tones and complex sounds. Loudness is measured in sones, a linear unit.Human sensitivity to sound is variable across different frequencies; therefore, although two different tones may present an identical sound pressure to a human ear, they may be psychoacoustically perceived as differing in loudness.
The threshold of hearing is generally reported in reference to the RMS sound pressure of 20 micropascals, i.e. 0 dB SPL, corresponding to a sound intensity of 0.98 pW/m 2 at 1 atmosphere and 25 °C. [3]
The reference sound intensity I 0 is defined such that a progressive plane wave has the same value of sound intensity level (SIL) and sound pressure level (SPL), since . The equality of SIL and SPL requires that I I 0 = p 2 p 0 2 , {\displaystyle {\frac {I}{I_{0}}}={\frac {p^{2}}{p_{0}^{2}}},} where p 0 = 20 μPa is the reference sound pressure.