Sound pressure level

Sound pressure level expresses a sound’s root-mean-square pressure relative to a reference pressure on a logarithmic scale, in decibels. In air, the standard reference pressure is 20 micropascals.

Sound pressure: Sound pressure is the deviation from ambient pressure caused by a sound wave. Sound pressure level starts with this physical quantity before comparing it with a reference.
Reference sound pressure: Reference sound pressure is the baseline pressure used to express sound pressure level as a ratio. The reference sets the zero point of a sound pressure level scale.
Environmental noise: Environmental noise is unwanted or harmful sound in outdoor and community settings. Regulations often express environmental sound using measured pressure levels and time averages.
Sound power level: Sound power level expresses a source’s acoustic power relative to a reference power on a decibel scale. It describes emitted power, whereas sound pressure level depends on the sound field and measurement position.
Root mean square: The root mean square is the square root of the mean of squared values. Sound pressure level commonly uses RMS pressure to represent fluctuating sound.
Sound wave: A sound wave is a mechanical disturbance that propagates through a medium as pressure and particle motion variations. The pressure fluctuations in a sound wave are the input measured by sound pressure level.
Occupational noise exposure: Occupational noise exposure is a worker’s cumulative exposure to sound during work activities. Workplace assessments use sound levels to estimate hearing risk over a shift.
Sound intensity level: Sound intensity level expresses acoustic intensity relative to a reference intensity on a decibel scale. It quantifies energy flow per area rather than local pressure amplitude.
Decibel: The decibel is a logarithmic unit expressing a ratio relative to a specified reference. Sound pressure level uses decibels to report its pressure ratio.
Acoustic frequency: Acoustic frequency is the number of cycles of a sound vibration per second, measured in hertz. Frequency weighting can change a sound pressure level reported for the same waveform.

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