Acoustics

Acoustics is a branch of physics and is the study of sound, mechanical waves in gases, liquids, and solids. A scientist who works in the field of acoustics is an acoustician. The application of acoustics in technology is called acoustical engineering. There is often much overlap and interaction between the interests of acousticians and acoustical engineers.

Sound pressure level (SPL)

The amplitude of a sound wave is most commonly characterized by its sound pressure. In a normal working environment, a very wide range of pressures can occur and it is therefore a convention that sound pressure is measured on a logarithmic scale using the decibel. If p is the rms sound pressure amplitude then the sound pressure level (SPL) is defined as 20 times the logarithm of the ratio of the pressure to some reference pressure.

Related Topics:
Amplitude - Sound pressure - Pressure - Logarithmic scale - Decibel - Rms - Sound pressure level

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Sound pressure level SPL is calculated in decibels as

Related Topics:
Sound pressure level - Decibel

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:

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L_p =20, log_{10}left(rac{p_1}{p_0} ight)=10, log_{10}left(rac{p_1^2}{p_0^2} ight)mbox{ dB} SPL

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The reference sound pressure in air is by convention the threshold of hearing:

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:p_0 = 2 cdot 10^{-5} mbox{ Pa}

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:= 20 µPa in air and 1 µPa in water. (Pa = pascal = N / m²; N = newton)

Related Topics:
Pascal - Newton

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When speaking of sound levels, one must be sure to differentiate between sound pressure levels and sound power levels. Sound pressure levels are recorded by microphones and other devices. This is a measurement of the amount of pressure in the air being sensed at a given location. It follows that its value can be determined through direct experimentation. In comparison, sound power levels are a measurement of the actual energy being put into use by a given device to create noise. Because of environmental factors, and other influences, the amount of energy a device devotes to creating sound may not be equal to the actual level of the sound as it's perceived. It can be useful to express sound pressure in this way when dealing with hearing, as the perceived loudness of a sound correlates roughly logarithmically to its sound pressure. Both microphones and eardrums respond to the sound pressure level. They cannot convert the sound intensity. Sound power measurements cannot be directly measured, and must be inferred through other data.

Related Topics:
Sound pressure level - Microphone - Power - Energy - Noise - Hearing - Sound intensity

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