Fundamental physical quantities

Sound intensity

Sound intensity refers to the average sound energy passing through a unit area normal to the direction of sound wave propagation per unit time. It is a physical quantity that indicates the magnitude and direction of the sound energy flow in the sound field. Sound intensity is usually expressed as I, and its unit is watts per square meter (W/m2). Sound intensity is determined by the magnitude of the vibration amplitude of the articulation body. The larger the amplitude, the stronger the sound intensity, and the weaker the sound intensity. The sound of a bomb explosion is powerful because of its amplitude.

Sound intensity level

Sound intensity level is a logarithmic rating of the ratio to the reference sound intensity. Psychophysical research shows that people’s perception of sound intensity is not proportional to the intensity of the sound, but is proportional to its logarithm. The objective sound intensity increases 10 times, the subjective feeling increases 1 times; The objective sound intensity increases by 100 times, and the subjective feeling of the person increases by 2 times.

Sound pressure

Sound pressure refers to the alternating pressure caused by adding an acoustic disturbance to the atmospheric pressure, which is an important acoustic fundamental quantity. The sound pressure is generally denoted by p, and its unit is Pa.

Sound pressure level

Because the absolute value of the sound pressure between the hearing threshold and the pain threshold is different by a million times, it is not convenient to express the size of the sound pressure, so according to the response characteristics of the human ear to the intensity of the sound, the sound pressure level is derived to express the size of the sound pressure. We often use the relative magnitude of sound pressure (called sound pressure level) to express the strength of sound pressure. Sound pressure level is a quantity that describes how the receiver feels.

Since the maximum sound pressure that the human ear can withstand is about 20Pa, and the usual reference sound pressure in the air is 2×10-5Pa, that is, the maximum sound pressure level that the human ear can withstand is about 120dB. This is what we often call the pain threshold, but this pain threshold is not suitable for all people. Some people can reach 130dB or even 140dB due to the working environment or natural ear structure. Usually, the sound pressure level audible to the human ear ranges from 0 to 120dB

Sound power level

People usually use the sound power level to measure the sound radiation ability of a sound source, and the sound power is defined as the sound energy radiated outward by the sound source in unit time, and the unit is W. Acoustic power is an absolute quantity, which is only related to the sound source and has nothing to do with others, and it is a physical property of the sound source.

Your task

What is the relationship between sound pressure and sound intensity?

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