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Fill in the top box and click on the calculation button. 1 Pa = 1 Pascal = 1 N/m2.
"Sound level" can be the sound pressure level in dB (SPL), or the sound intensity level in dB (SIL).
The reference sound pressure is p0 = 20 µPa = 2 × 10-5
Pa - the reference sound intensity is I = 10-12 W/m2.
Differentiate between sound pressure p as a "sound field quantity" and sound intensity I as a "sound energy quantity".
Notice, that the calculation I ≈ p2 is effective for progressive plane waves.
The volume (loudness) is determined by the sound pressure p and expressed as sound pressure level Lp in dB.
Reference values: p0 = 20 µPa = 2 × 10-5 Pa and I0 = 10-12 Watt/m2.
The sound pressure is always the sound excess pressure as RMS value.
Sound pressure, Sound intensity and their Levels
To use the calculator, simply enter a value. Then use the TAB key or
click the mouse in an empty area of the page to update the result.
Calculator works in both directions of the ↔ sign.
Note: The often used term "intensity of sound pressure" is not correct.
Use "magnitude", "strength", "amplitude", or "level" instead.
"Sound intensity" is sound power per unit area, while "pressure" is a
measure of force per unit area. Intensity is not equivalent to pressure.
The sound pressure decreases with 1/r from the sound source.
The behavior is not inverse-square, but is inverse-proportional: p ~ 1 / r.
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Change of the sound level Δ L with the distance r
| Note: You cannot convert dBA to dBSPL or vice versa. |
See also: Weighting filter- calculation frequency f to dBA
What is the threshold of pain?
You can find the following rounded values in various articles:
| Sound pressure level Lp | Sound pressure p |
| 120 dB | 20 Pa |
| 130 dB | 63 Pa |
| 134 dB | 100 Pa |
| 137.5 dB | 150 Pa |
| 140 dB | 200 Pa |
Conversion: sound pressure, particle velocity, acoustic impedance, and intensity
Table of sound levels (pressure and also intensity)
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Sound Field Quantities :-) Sound pressure, sound or particle velocity, particle displacement or particle ampltide, voltage, current, electric resistance. Inverse Distance Law 1/r |
Sound Energy Quantities Sound intensity, sound energy density, sound power, electric power. Inverse Square Law 1/r² |
Hearing is directly sensitive to sound pressure (ear drums). In stereo the level differences have
been called "intensity" differences, but sound intensity is a specifically defined quantity and cannot
be sensed by a simple microphone, nor would it be of value in music recordings if it could be.
"Intensity" stereophony is better termed as level difference stereophony.
Important to notice: 1 Pa = 1 N/m2 ≡ 94 dB and 1 bar = 105 Pa.
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ASACOS Rules for Preparation of American National Standards in ACOUSTICS, MECHANICAL VIBRATION AND SHOCK, BIOACOUSTICS, and NOISE states: 3.16 Unit symbols - 3.16.1 When to use unit symbols in the text of the standard, the unit symbol for a quantity shall be used only when the unit is preceded by a numeral. When the unit is not preceded by a numeral, spell out the name of the unit. In text, even when a numerical value is given, it is desirable to spell out the name of the unit. Moreover, the name shall be spelled out when it first appears in the text, and more often if the text is lengthy. Thus, in text write "...a sound pressure level of 73 dB; or "...a sound pressure level of 73 decibels." Do not write "sound pressure level in dB"; the correct form is "sound pressure level in decibels." Do not write "dB levels", "dB readings", or "dB SPL". Levels or readings are not of decibels; they are of sound pressure levels or some other acoustical quantity. Write out the word "decibel" for such applications, and be sure that the word 'decibel' follows, not precedes the description of the relevant acoustical quantity. The guidelines given for the National Standards clearly excludes the use of "dB SPL". The reference added to the decibel article ends up being a document that merely includes "dB SPL" in a list of terms. The glossary within the same document does not even list this supposed term, even though weighted decibel terms are defined. The glossary in the file does have an entry for "sound pressure level", which is Sound pressure level: (1) Ten times the logarithm to the base ten of the ratio of the time-mean-square pressure of a sound, in a stated frequency band, to the square of the reference sound pressure in gases of 20 micropascals (µPa). Unit, dB; symbol, Lp. (2) For sound in media other than gases, unless otherwise specified, reference sound pressure in 1 µPa (ANSI S1.1-1994: sound pressure level). A reference level of 20 µPa is often used. In general, it is necessary to know the reference level when comparing measurements of SPL. The unit dB (SPL) is often abbreviated to just "dB", which gives some the erroneous notion that a dB is an absolute unit by itself. |
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The intensity I is defined as the power per unit area. The surface area of the sphere is A = 4 π r2, so the sound power P passing through each square metre of surface is: I = P / A = P / 4 π r2. So we see that, for a uniformly radiating sound source, intensity is inversely proportional to the square of the distance r away from the source: I2 / r12 = I1 / r22. But intensity is proportional to the square of the sound pressure, so we could equally write: p2 / p1 = r1 / r2. So we see that sound pressure is inversely proportional to the distance r away from the source. If we double the distance, we reduce the sound pressure by a factor of 2 and the sound intensity by a factor of 4. In other words, we reduce the sound level by (−)6 dB. |
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