## Sound Pressure • definitions • terms • units • measurements ...

**Sound Pressure (p)** is the difference between the pressure caused by a sound wave and the ambient pressure of the media the sound wave is passing through.

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

**Sound Pressure Definition IEC 801-21-20,** root mean square of the instantaneous sound pressures over a given time interval, unless specified otherwise

**Sound pressure**is measured in pascals, symbol Pa. However the immense range of human hearing, 0.00002 pascals up to 200 pascals, means the pascal is not practical for everyday use. Fortunately the

*sound pressure level*in decibels, detailed below, neatly solves this problem.

**Sound Pressure Level (Lp)**= 20 log (p/po) dB, where p is the

*sound pressure*in pascals and po is the reference sound pressure of 0.00002 pascals = 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 = twice or half the pressure | 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 |

Reference Sound Pressure | 0.00002 Pa | 0 dB |

*Sound Pressure Level* 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 (double or half the sound pressure)

10 dB = a factor of 3 in sound pressure

20 dB = a factor of 10 in sound pressure

**Sound Pressure Level Definition IEC 801-22-07,** logarithm of the ratio of a given sound pressure to the reference sound pressure in decibels is 20 times the logarithm to the base ten of the ratio.

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

See also our sound pressure level calculations article

Related Terms - listed alphabetically

*Average Sound Pressure*see effective sound pressure

**Band Sound Pressure Level Definition IEC 801-22-12,** level of the sound pressure produced within a specified frequency band.

**Effective Sound Pressure**is the root-mean-square of the instantaneous sound pressure.

*Effective Sound Pressure* is also known as the *average sound pressure*.

See also • the Effective Value Definition IEC 103-02-03

**Equivalent Continuous Sound Pressure Level Definition IEC 801-22-11,** logarithm of the ratio of a given root-mean-square sound pressure, during a stated time interval, to the reference sound pressure. Average sound pressure level in decibels is 20 times the logarithm to the base ten of that ratio.

*Equivalent continuous sound pressure level* should not be confused with

*Equivalent continuous sound level*. To compare these definitions directly click here

*Impact Sound Pressure Level*under sound insulation

**Instantaneous Sound Pressures**fluctuate over time, so a single sample tells us very little. However monitoring the levels over a period of time, accumulates very useful information. For example the effective sound pressure • equivalent sound pressure level • Leq • Lmax • peak sound pressure etc.

**Instantaneous Sound Pressure Definition IEC 801-21-19,** at a point in a medium, is the difference between the pressure existing at the instant considered and the static pressure

**Peak Frequency-weighted Sound Pressure Level Definition IEC 801-22-15,** greatest instantaneous value of a standard-frequency-weighted sound pressure level, within a stated time interval. Also known as the peak sound level.

**Peak Sound Pressure (Lpk or Lpeak)**is the maximum instantaneous sound pressure during a measurement period or noise event. Provides essential information in the assessment of noise induced hearing loss, but should not be confused with the Lmax.

**Peak Sound Pressure Definition IEC 801-21-21,** greatest absolute instantaneous sound pressure during a given time interval.

See also • peak hold, true peak and peak-to-peak • sound exposure action and limit values.

**Reference Sound Pressure po**= 20 μPa ≡ 0 dB, the threshold of hearing at 1 kHz, see our sound pressure table above

**Reference Sound Pressure Definition IEC 801-21-22,** the sound pressure conventionally chosen, equal to 20 μPa for gases and to 1 μPa for liquids and solids.

See also • other standard reference levels.

**Sound Pressure Reflection Coefficient Definition IEC 801-31-05,** at a given frequency and for a given angle of incidence, in plane waves, ratio between the sound pressure amplitude of the reflected sound wave and that of the incident sound wave.

**Time Average Sound Pressure Level Definition IEC 801-22-11,**logarithm of the ratio of a given root-mean-square sound pressure, during a stated time interval, to the reference sound pressure. Average sound pressure level in decibels is 20 times the logarithm to the base ten of that ratio.

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

Also known as the equivalent continuous sound pressure level, Neither should be confused with the equivalent continuous sound level. To compare these definitions directly click here

**Weighted Sound Pressure Level Definition IEC 801-22-14,** logarithm of the ratio of a given sound pressure to the reference sound pressure of 20 μPa, the sound pressure being obtained with a standard frequency weighting and with a standard exponential time weighting. Sound level in decibels is twenty times the logarithm to the base ten of that ratio. *Weighted sound pressure level* is also known as the sound level

● 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