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Sound Pressure Level (SPL)

The Music Telegraph | Text 2019/02/15 [15:56]
Recording

Sound Pressure Level (SPL)

The Music Telegraph| 입력 : 2019/02/15 [15:56]

Sound Pressure Level (SPL)

 

Sound Pressure Level, SPL, is commonly written as Lp and refers to the root mean squared sound pressure of a sound relative to a reference value.

Sound pressure level is the logarithmic measure of the Root Mean Squared (RMS) sound pressure of a sound relative to a reference value.

A simple sound wave may be represented by a sine wave. A diagram of a sine wave which would be the typical output signal of a single tone noise level (i.e. a calibrator tone), if shown on an oscilloscope. The fundamental parameters associated with a sound wave are Peak, Peak-Peak, Periodic Time, RMS (Root-Mean-Square).

 

 

 



Sound level meters measure acoustic pressure and by international agreement they are calibrated in decibels (dB). The sound pressure level (Lp) in decibels is defined as:

 

 

 

Where:

P is the measured root mean squared (RMS) sound pressure

P0 is the reference RMS sound pressure (20µPa)

 

 

Note that the decibel is a ratio of two quantities which have dimensions of power and is not a unit.

 

The reference sound pressure (P0) is by agreement as 20µPa, which is the minimum audible pressure to a person with ‘normal’ hearing. The use of a logarithmic scale, such as the decibel, permits the wide range of audible sound pressures (approximately 1,000,000 to 1) to be compressed into a scale of 120 units. Hence a faint whisper may be measured as 20dBA where as a chipping hammer of a road workman may produce 105dBA. **Excerpts from Castle Group Ltd (https://www.castlegroup.co.uk/guidance/noise-at-work-assessments/sound-pressure-level/)

  

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