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Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone , and in water with a hydrophone .
Sound power or acoustic power is the rate at which sound energy is emitted, reflected, transmitted or received, per unit time. [1] It is defined [2] as "through a surface, the product of the sound pressure, and the component of the particle velocity, at a point on the surface in the direction normal to the surface, integrated over that surface."
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]
As sound pressure is a root-power quantity, the appropriate version of the unit definition is used: = (), where p rms is the root mean square of the measured sound pressure and p ref is the standard reference sound pressure of 20 micropascals in air or 1 micropascal in water. [34] Use of the decibel in underwater acoustics leads to confusion ...
Pressure due to direct impact of a strong breeze (~28 mph or 45 km/h) [27] [28] [31] 120 Pa Pressure from the weight of a U.S. quarter lying flat [32] [33] 133 Pa 1 torr ≈ 1 mmHg [34] ±200 Pa ~140 dB: Threshold of pain pressure level for sound where prolonged exposure may lead to hearing loss [citation needed] ±300 Pa ±0.043 psi
The commonly used reference sound exposure in air is [2] E 0 = 400 μ P a 2 ⋅ s . {\displaystyle E_{0}=400~\mathrm {\mu Pa^{2}\cdot s} .} The proper notations for sound exposure level using this reference are L W /(400 μPa 2 ⋅s) or L W (re 400 μPa 2 ⋅s) , but the notations dB SEL , dB(SEL) , dBSEL, or dB SEL are very common, even if ...
These values are the interval for the sound pressure level to the lower of 30 or 60 dBSPL. It can be obtained by measuring the sound pressure decrease after a sound impulse or by using approximate formulas such as Sabine's or Eyring's. In the case of a diffuse field (low absorption on the walls, and big volumes) Sabine's formula is used.
The speed of sound in seawater depends on pressure (hence depth), temperature (a change of 1 °C ~ 4 m/s), and salinity (a change of 1‰ ~ 1 m/s), and empirical equations have been derived to accurately calculate the speed of sound from these variables. [25] [26] Other factors affecting the speed of sound are minor. Since in most ocean regions ...