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Sound pressure level (SPL) or acoustic pressure level (APL) is a logarithmic measure of the effective pressure of a sound relative to a reference value.
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 ]
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]
Sound exposure, denoted E, is defined by = (), where the exposure is being calculated for the time interval between times t 0 and t 1; p(t) is the sound pressure at time t, usually A-weighted for sound in air.
[2] [14] The sound level is then measured at the position of the subject's head with the subject not in the sound field. [2] Minimal audible pressure involves presenting stimuli via headphones [2] or earphones [1] [14] and measuring sound pressure in the subject's ear canal using a very small probe microphone. [2]
Ambient noise level is measured with a sound level meter. [4] It is usually measured in dB relative to a reference pressure of 0.00002 Pa, i.e., 20 μPa (micropascals) in SI units. [5] This is because 20 μPa is the faintest sound the human ear can detect. [5] A pascal is a newton per square meter.
where p is the root-mean-square sound pressure and is a reference sound pressure. Commonly used reference sound pressures, defined in the standard ANSI S1.1-1994, are 20 μPa in air and 1 μPa in water. Without a specified reference sound pressure, a value expressed in decibels cannot represent a sound pressure level.
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 loud as the sound under investigation, and where p 0 = 20 μPa: phon
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