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I 0 is the reference sound intensity; 1 Np = 1 is the neper; 1 B = 1 / 2 ln(10) is the bel; 1 dB = 1 / 20 ln(10) is the decibel. The commonly used reference sound intensity in air is [5] = /. being approximately the lowest sound intensity hearable by an undamaged human ear under room conditions.
Historically, loudness was measured using an ear-balancing method with an audiometer in which the amplitude of a sine wave was adjusted by the user to equal the perceived loudness of the sound being evaluated. [6] Contemporary standards for measurement of loudness are based on the summation of energy in critical bands. [7]
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.
If the sound pressure p 1 is measured at a distance r 1 from the centre of the sphere, the sound pressure p 2 at another position r 2 can be calculated: =. The inverse-proportional law for sound pressure comes from the inverse-square law for sound intensity: I ( r ) ∝ 1 r 2 . {\displaystyle I(r)\propto {\frac {1}{r^{2}}}.}
It is well established that human hearing is more sensitive to some frequencies than others, as demonstrated by equal-loudness contours, but it is not well appreciated that these contours vary depending on the type of sound. The measured curves for pure tones, for instance, are different from those for random noise.
Dynamic range is a measure of how small you can measure a signal relative to the maximum input signal the device can measure. Expressed in decibels, the dynamic range is 20 log (Vmax/Vmin). For example, a device with an input range of ±10 V and a dynamic range of 110 dB will be able to measure a signal as small as 10 μV.
The smallest sound that a person can hear, known as the threshold of hearing, is nine orders of magnitude smaller than the ambient pressure. The loudness of these disturbances is related to the sound pressure level (SPL) which is measured on a logarithmic scale in decibels.
Quantity Unit Remarks Name Symbol Definition Name Symbol period, periodic time: T: time of one cycle: second: s: frequency: f, ν: f = 1/T: hertz: Hz: 1 Hz = 1 s −1: loudness level: L N: L N = ln(p eff /p 0) 1 kHz where p eff is the root-mean-square value of the sound pressure of a pure tone of 1 kHz, which is judged by a normal observer under standardized listening conditions as being as ...