Concept

# Sound pressure

Summary
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. The SI unit of sound pressure is the pascal (Pa). A sound wave in a transmission medium causes a deviation (sound pressure, a dynamic pressure) in the local ambient pressure, a static pressure. Sound pressure, denoted p, is defined by where ptotal is the total pressure, pstat is the static pressure. Sound intensity In a sound wave, the complementary variable to sound pressure is the particle velocity. Together, they determine the sound intensity of the wave. Sound intensity, denoted I and measured in W·m−2 in SI units, is defined by where p is the sound pressure, v is the particle velocity. Acoustic impedance Acoustic impedance, denoted Z and measured in Pa·m−3·s in SI units, is defined by where is the Laplace transform of sound pressure, is the Laplace transform of sound volume flow rate. Specific acoustic impedance, denoted z and measured in Pa·m−1·s in SI units, is defined by where is the Laplace transform of sound pressure, is the Laplace transform of particle velocity. Particle displacement The particle displacement of a progressive sine wave is given by where is the amplitude of the particle displacement, is the phase shift of the particle displacement, k is the angular wavevector, ω is the angular frequency. It follows that the particle velocity and the sound pressure along the direction of propagation of the sound wave x are given by where vm is the amplitude of the particle velocity, is the phase shift of the particle velocity, pm is the amplitude of the acoustic pressure, is the phase shift of the acoustic pressure.
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Sound
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the reception of such waves and their perception by the brain. Only acoustic waves that have frequencies lying between about 20 Hz and 20 kHz, the audio frequency range, elicit an auditory percept in humans. In air at atmospheric pressure, these represent sound waves with wavelengths of to . Sound waves above 20 kHz are known as ultrasound and are not audible to humans.
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In acoustics, loudness is the subjective perception of sound pressure. More formally, it is defined as the "attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The relation of physical attributes of sound to perceived loudness consists of physical, physiological and psychological components. The study of apparent loudness is included in the topic of psychoacoustics and employs methods of psychophysics.
Sound pressure
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. The SI unit of sound pressure is the pascal (Pa). A sound wave in a transmission medium causes a deviation (sound pressure, a dynamic pressure) in the local ambient pressure, a static pressure. Sound pressure, denoted p, is defined by where ptotal is the total pressure, pstat is the static pressure.
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