Sound Pressure


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Sound pressure

The incremental variation in the static pressure of a medium when a sound wave is propagated through it. Sound refers to small-amplitude, propagating pressure perturbations in a compressible medium. These pressure disturbances are related to the corresponding density perturbation via the material equation of state, and the manner in which these disturbances propagate is governed by a wave equation. Since a pressure variation with time is easily observed, the science of sound is concerned with small fluctuating pressures and their spectral characteristics. The unit of pressure commonly used in acoustics is the micropascal (1 μPa = 1 μN/m2 = 10-5 dyne/cm2 = 10-5 μbar). One micropascal is approximately 10-11 times the normal atmospheric pressure. See Pressure, Pressure measurement, Wave motion

The instantaneous sound pressure at a point can be harmonic, transient, or a random collection of waves. This pressure is usually measured with an instrument that is sensitive to a particular band of frequencies. A concept widely used in acoustics is “level,” which refers to the logarithm of the ratio of any two field quantities. When the ratio is proportional to a power ratio, the unit for measuring the logarithm of the ratio is called a bel, and the unit for measuring this logarithm multiplied by 10 is called a decibel (dB). The sound intensity, which describes the rate of flow of acoustic energy (acoustic power flow) per unit area, is given by the mean square pressure divided by the acoustic impedance, defined as the product of the medium density and compressional wave speed. See Decibel, Sound, Sound intensity

Sound Pressure

 

the additional pressure developed during the passage of a sound wave through a fluid or gaseous medium. In propagating through a medium, the sound wave creates condensations and rarefactions that produce additional variations in the pressure with respect to the average pressure in the medium. Thus, sound pressure is the variable part of the pressure—that is, the fluctuations of pressure relative to the average value at a frequency corresponding to the frequency of the sound wave.

Sound pressure is a fundamental quantitative characteristic of sound. The unit of measurement for it in the SI system of units is the newton per sq m (N/m2); the unit previously used was the bar (1 bar = 10−1 N/m2). The sound level, which is the ratio, expressed in decibels, of the given sound pressure p to the threshold value p0 = 2 × 10−5 N/m2, is sometimes used to characterize sound. The number of decibels is N = 20 log (p/P0).

The sound pressure in air varies over a wide range—from 10−5 N/m2 close to the threshold of audibility to 103 N/m2 for very loud sounds, such as the noise of jet airplanes. Sound pressures up to 107 N/m2 are produced in water at ultrasonic frequencies of the order of several megahertz by means of focusing radiators. The phenomenon of fluid discontinuity, or cavitation, is observed at high sound pressures. Sound pressure should be distinguished from acoustic radiation pressure.

sound pressure

[′sau̇nd ‚presh·ər]

sound pressure

The minute fluctuations in atmospheric pressure which accompany the passage of a sound wave and give rise to the sensation of hearing; usually expressed in dynes per square centimeter or newtons per square meter.
References in periodicals archive ?
This is defined as a thermal saturation in the thin film by Brungart et al [17], where increasing the input power, does not result in the high sound pressure level at high frequencies.
The results obtained showed that the average sound pressure level in the Lagos metropolis was greater than WHO standard guidelines by 43.
In Figure 6, sound pressure near middle part of transmission housing is of obvious broadband characteristics.
Most studies that have measured sound levels to assess the potential effects of sounds on marine life have considered only sound pressure levels and associated metrics (such as sound exposure levels), while ignoring other components of underwater sound, including particle motion (i.
This is demonstrated using a polymeric particle or floating paper boat on water: using the sound pressure hologram, the team generated a ring-shaped crest on the water's surface which looked as if it had frozen the rippie caused by a stone that was thrown into the water.
Meanwhile, the sound intensity E is expressed by measured sound pressure as shown as:
The general procedure for sound pressure level reduction can be explained by below presented scheme (Fig.
The results of acoustic parameters including maximum, minimum and the mean sound pressure level at each station are as the following Tabale 1.
Once the attenuation of the reverberant chamber is known, sound pressure levels can be measured for the product under test.
The Machinery Directive 2006/42/EC requires measurement and declaration of corrected sound pressure at workstations and, if this exceeds 80db(A), sound power as well; also a value for peak sound pressure is required where that exceeds 130dB(C) at workstations.