le niveau de pression continu (acoustique) équivalent LA eq
"... rapide, lente et impulse; mesure du niveau continu équivalent Leq, pondérations
A, C et ... SVAN 912 Sonomètre portable multifonction (Sonomètre: SLM Lp, Crête ..."
"... sonomètre» Dispositif de mesure du niveau de pression acoustique qui répond
aux exigences de rendement d'un instrument de type 2 énoncées dans la norme ..."
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... celle d'un son de 50 décibels ... A) indiquent la pression acoustique à ... Equivalente
sur le plan énergétique ... est appelée niveau continu équivalent (L ...
Some info in English, if interested:
sound pressure level
The level, in decibels, of acoustic pressure waves.
Sound pressure is the dynamic variation of the static pressure of air and is measured in force per unit area. Sound pressure is normally represented on a logarithmic amplitude scale, which gives a better relationship to the human perception of hearing. Typical values on this open-ended scale are a sound level of 0 dB, which is the average threshold of human hearing, and 60 to 70 dB for normal conversation, 110 dB at an extremely loud concert, and 150 dB for the noise of a rocket takeoff or a jet engine at close range.
You can measure the sound pressure level with various "weighting filters" whose characteristics approximate the sensitivity of the ear at various frequencies and levels based on the Fletcher-Munson curves. Most commonly used is the "A Weighting," which is most sensitive in the mid-frequencies. Other, less common weightings are B, C, and D.
The Sound Pressure Level (SPL or LP) in dB is defined as:
SPL = 20 log10(p/pref)
Where p = the actual sound pressure
pref = 20 µPa, which roughly corresponds to the threshold of human hearing
Important Note: Because of the many factors potentially influencing a decibel reading, be careful when reporting acoustical data. Without a complete description of all the instrument settings during the measurement, the information could be ambiguous. A complete statement would include the following elements:
The level as a numeric, as NN.N (Note that one decimal place is sufficient precision for almost any test.)
dB for decibels or B for Bels
SPL for sound pressure level, PWL for sound power level, SIL for sound intensity level
The reference quantity used in the level computation, as appropriate (for example, 20 ìPa)
Frequency weighting filter used
Time weighting used
Octave or one-third octave band filter used
For example, a complete description of an acoustics measurement is: "85 dB SPL re 20 ìPa A-weighted, Slow", "47 dB PWL re 1 pW flat-weighted in the 250 Hz one-third octave band, equivalent continuous level."
Pa or dB re 20 µPa
Related NI Products:
LabVIEW Sound and Vibration Toolset
ISO Standard 13.140 Noise with respect to human beings
ISO Standard 13.160 Vibration and shock with respect to human beings
ISO Standard 17.140.01 Acoustic measurements and noise abatement in general
Airborne Noise from Computers ECMA 74
High Frequency Noise from Computers ECMA 108
Declared Noise Emission Values of Comput and Business Equipment ECMA 109
Determination of Sound Power Levels of Comoputer and Business Equipment Using Sound Intensity Measurement ECMA 160
Helpful Web Sites:
Glossary of Terms from Institute of Noise Control
How to Measure Sound Pressure and Sound Pressure Level
The sound pressure level of an imaginary continuous steady sound that, within a given time interval, has the same mean-square sound pressure as the sound being measured. Normally, this measurement is normalized to a 1 second time duration. Therefore, transient events -- such as aircraft flyovers or drive-by noise -- can be compared in terms of the total energy content.
The symbol is L EQ.