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Acoustics, Ultrasound and Vibration: Units
The quantity to be measured depends on the application.

  • Sound pressure level, Lp, is expressed in decibels (dB). The decibel1 is a non-coherent unit accepted for use with the SI when employing logarithms to the base ten. For airborne sound, Lp indicates the ratio of a physical quantity of sound pressure p (Pa) relative to a specified reference pressure pref which is defined as 20 µPa:
    Lp = 10 log10
    p2
    dB

    p2ref

    When expressing a quantity in decibels, it is important to state the magnitude of this reference value

  • Ultrasonic power is expressed in the SI unit watt (W).

  • Vibrations is the generic term for a time dependent rectilinear or rotational displacement:

    • rectilinear vibration is measured in terms of the respective acceleration in the unit m/s2 or the velocity in m/s
    • rotational vibration is measured in terms of the respective angular acceleration in rad/s2 or angular velocity (sometimes called angular rate) in rad/s.

    1 Logarithmic ratio

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Acoustics, Ultrasound and Vibration
Overview
Committee structure
Units
Strategic plan
International equivalence
Calibration and measurement capabilities (CMCs)
International comparisons
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