Band Sound Pressure Level • Effective Sound Pressure Level • Equivalent Continuous Sound Pressure Level • Instantaneous Sound Pressure • Peak Frequency Weighted Sound Pressure Level • Peak Sound Pressure • Reference Sound Pressure • Sound Pressure • Sound Pressure Level • Sound Pressure Reflection Coefficient • Weighted Sound Pressure Level

**Sound Pressure** is measured in Pascals, symbol Pa

**Sound Pressure** is a sound field quantity, not a sound energy or sound power quantity.

Because of the immense range of human hearing, *sound pressure* values are not practical for everyday use, see the range of Pascals in the table below and the *sound pressure level* practical solution.

**Sound Pressure Level** in decibels is 20 x the logarithm of the ratio of the sound pressure to the reference sound pressure of 20 micropascals.

**Sound Pressure Level** *(SPL or Lp)* = 20 log (p/po) dB, where : po = 2 x 10^{-5} Pa = 20 µPa ≡ 0 dB in air ≡ to the threshold of hearing at 1KHz

Sources at 1 m | Sound Pressure | SPL re 20 µPa |

Rifle | 200 Pa | 140 dB |

Threshold of pain | 20 Pa | 120 dB |

Pneumatic hammer | 2 Pa | 100 dB |

6 dB = double the Pa | 1 Pa | 94 dB |

Street traffic | 0.2 Pa | 80 dB |

Talking | 0.02 Pa | 60 dB |

Library | 0.002 Pa | 40 dB |

TV Studio | 0.0002 Pa | 20 dB |

Threshold of hearing | 0.00002 Pa | 0 dB |

**Sound Pressure Level** *(SPL or Lp)* is a sound field quantity and uses the 20 log factor so, as a rule of thumb:

6 dB = a factor of 2 in sound pressure

10 dB = a factor of 3 in sound pressure

20 dB = a factor of 10 in sound pressure

10 dB = a factor of 3 in sound pressure

20 dB = a factor of 10 in sound pressure

● Note 1: unless otherwise specified, the reference sound pressure is 20 µP for airborne sound and 1 µPa for sound in media other than air.

● Note 2: unless otherwise specified, the sound pressures are understood to be expressed in root-mean-square values.

● Note: the band may be specified by its lower and upper cut-off frequencies, or by its geometric centre frequency and bandwidth. The width of the band may be indicated by a modifier such as one octave band (sound pressure) level, one-half octave band level, one-third octave band level.

**Effective Sound Pressure** is the RMS (root-mean-square) of the instantaneous sound pressure, measured over a given period of time

● Note: unless otherwise specified, the reference sound pressure for airborne sound is 20 μPa.

Also known as the *Time-average Sound Pressure Level*

NOT to be confused with the Equivalent Continuous Sound Level Definition IEC 801-22-16

Impact Sound Pressure Level under Sound Insulation

● Note: if frequency weighting is not specified, the A-frequency weighting is understood.

Also known as the *Peak Sound Level*

**Peak Sound Pressure (Lpk or Lpeak)**, the maximum instantaneous sound pressure during a measurement period or noise event. Very important in the assessment of sound exposure at work and not to be confused the Lmax. See also peak hold, true peak and other time weightings

See also : Sound Exposure Action Values and Limit Value. and Time Constants and Weightings

**Reference Sound Pressure (po)** was chosen to equal the threshold of hearing = 20 micropascals at 1kHz.

If you divide the measured **sound pressure** by the ** reference sound pressure**, convert to logarithms and multiply the results by 10, then you get the *sound pressure level* in decibels (dB), i.e. more manageable numbers

See also other Standard Reference Levels.

● Note 1: standard frequency weightings A, B and C and standard exponential time weightings fast (F), slow (S) and impulse (I) are given in IEC 651 : Sound level meters.

● Note 2: time and frequency weightings employed should be specified, but if not stated explicitly, Fast (F) exponential time weighting and A-frequency weighting are understood

**Weighted Sound Pressure Level** is also known as Sound Level

See also: Sound Levels • LA • LAF • LAFmax • LAFmin • LCpeak etc. and the IEC Definition of Level

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