sound values calculator sound pressure level acoustic intensity level particle velocity energy amplitude acoustics formulas decubel reference dB - sengpielaudio
 
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Sound  Quantities, their Levels and References
Conversions, Calculations, and Formulas

 The reference sound pressure p0 = 20 µPa = 2 × 10-5 Pa is
 equal to the sound pressure level Lp = 0 dB as auditory threshold. 

Readings of a pure 1 kHz tone should be identical, whether weighted or not.

Enter a value in the left or right box, then press the TAB bar or make
a mouse click at an empty space at the side, to get the solution.
The calculator works in both directions of the ↔ sign.

Sound pressure p:
Pa = N/m2		  ↔  Sound pressure level Lp:
dB-SPL
Formula   Formula
Standard reference sound pressure p0 = 20 μPa = 2 × 10−5 Pa ≡ 0 dB

Acoustic intensity I:
W/m2		  ↔  Sound intensity level LI:
dB-SIL
Formula   Formula
Standard reference sound intensity I0 = 1 pW/m2 = 10−12 W/m2 ≡ 0 dB

Acoustic power Pac:
W		  ↔  Sound power level LPac:
dB-PWL
Formula   Formula
Standard reference sound power Pac0 = 1 pW = 10−12 W ≡ 0 dB

There is also the reference power P0 = 1 milliwatt = 0,001 watt ≡ 0 dBm.

Particle velocity v:
m/s		  ↔  Particle velocity level Lv:
dB-SVL
Formula   Formula
Standard reference particle velocity v0 = 5 × 10−8 m/s ≡ 0 dB

Sound energy W:
J = W·s		  ↔  Sound energy level LW:
dB-SWL
Formula   Formula
Standard reference sound energy W0 = 1 pJ = 10−12 J ≡ 0 dB   J = W·s

Sound energy density E:
J/m3 = W·s/m3		  ↔  Sound density level: LE
dB-SEL
Formula   Formula
Ref. Sound energy density E0 = 1 pJ/m3 = 10−12 J/m3 ≡ 0 dB   (W·s/m3)

Sound Field Quantities    AnimatedLaughingSmiley
Sound pressure, sound or particle velocity,
particle displacement or particle ampliude,
(voltage, current, electric resistance).
Inverse Distance Law 1/r		 Sound Energy Quantities
Sound intensity, sound energy density,
sound energy, acoustic  power.
(electrical power).
Inverse Square Law 1/r²

Since sound measuring instruments (meters) respond to sound pressure the "decibel"
is generally associated with sound pressure level. Sound pressure levels quantify in
decibels the strength (not intensity!) of given sound sources. Sound pressure levels
vary substantially with distance from source, and also diminish as a result of intervening
obstacles and barriers, air absorption, wind and other factors.
Sound Pressure Level (SPL): 20×log (p/p0) = 10×log (p/p0)2, where  p0 = 2×10−5 N/m2.
p = root mean square sound pressure  (N/m2 = Pa).
The usual reference level p0 is 20×10−6 Pa. Note that the noise from motors is
documented in sound power level. "Threshold of audibility'' or the minimum pressure
fluctuation detected by the ear is less than 10−9 of atmospheric pressure or about
2×10−5 Pa(pascal) at 2000 Hz. "Threshold of pain'' corresponds to a pressure 106
times greater, but still less than 1/1000 of atmospheric pressure.  The standard
airpressure is 101325 Pa = 101.325 kPa or 1013.25 hectopascal. Because of the
wide range, sound pressure measurements are made on a logarithmic decibel scale.
Sound power levels are connected to the sound source and are independent of
distance. Sound powers are indicated in decibel. Lw = 10×log (P / P0) where:
P0 = reference power (W).
The usual reference level is P0 = 10−12 W, calculated from p0 = 20 micropascals,
which is the lowest sound persons of excellent hearing can discern. Sound power is
measured as the total sound power emitted by a source in all directions in watts
(joules / second). Sound power levels do not vary with distance from source.

Questions:
1. How many decibels is the sound pressure p = 1 Pa?
2. How many decibels is the acoustic intensity I = 1 W/m2?
3. How many decibels is the acoustic power P = 1 W?
4. How many decibels is the particle velocity v = 1 m/s?
5. How many decibels is the sound energy W = 1 J?
6. How many decibels is the sound energy density E = 1 J/m3?
The calculators above can help to give the answers.

Table of Sound Levels, Sound Pressure, and Sound Intensity
Conversion of Sound Units (Levels)
Damping of Sound Level with Distance

Frequently used false statements in the context of sound values
and the distance of the sound source

Wrong expression Correct version
Sound pressure falls inversely proportional
to the square of the distance 1/r2 from the
sound source.		 Sound pressure falls inversely proportional
to the distance 1/r from the sound source.
That is the 1/r law or distance law.
Sound pressure level decreases as the
distance increases per doubling of distance
from the source by (−)3 dB.		 Sound pressure level decreases by (−)6 dB per
doubling of distance from the source to 1/2 (50 %)
of the sound pressure initial value.
Sound intensity (energy) falls inversely
proportional to the distance 1/r from the sound
source.		 Sound intensity (energy) falls inversely proportional
to the square of the distance 1/r2 from the sound
source.
Sound intensity level decreases inversely as the
square of the distance increases per doubling of
sound source with (−)3 dB per doubling.		 Sound intensity level decreases by (−)6 dB per
doubling of distance from the source to 1/4 (25 %)
of the sound intensity initial value.

Neither the sound power nor the sound power level decreases in doubling the
distance. Why is this so?

The psychoacoustic subjective sensations of loudness do not belong to those
predictable and measurable sound quantities; see:

Correlation between volume level in phone and loudness in sone

People feel and judge sound events after:
- exposure duration
- spectral composition
- temporal structure
- sound level
- information content
- subjective mental attitude

"Sound level" is the sound pressure level in decibel (SPL), or sometimes 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: Sound pressure p is a "sound field quantity" and
sound intensity I is a "sound energy quantity". Amateurs often
think wrongly, that sound pressure and intensity mean the same.

Notice, that the calculation I ≈ p2 is effective for progressive plane waves.
It can be seen that "sound intensity" (acoustic intensity) may never be equated with "sound pressure".
The sound pressure is thealternating sound pressure as RMS value. The sound pressure amplitude is the
peak value of the sound pressure.
The sound volume is determined by the sound pressure p and expressed as sound pressure level Lp in dB.

Level formula

Note: The sound intensity is a sound energy quantity. Membranes (diaphragms) of microphones and our
eardrums are moved by alternating sound pressure, that is a sound field quantity.

Sound Level Comparison Chart and the Factor

Table of sound level dependence and the change of the respective factor to subjective
volume (loudness), objective sound pressure (voltage), and sound intensity (acoustic power)
How many decibels (dB) level change is double, half, or four times as loud?
How many dB to appear twice as loud (twofold)? Here are all the different factors.
Factor means "how many times" or "how much" ... Doubling of loudness.

Level
Change		 Volume
Loudness		 Voltage
Sound pressure		 Acoustic Power
Sound Intensity
+40 dB 16 100   10000
+30 dB   8    31.6 1000
+20 dB   4 10 100
+10 dB  2.0 = double   3.16 = √10 10
  +6 dB   1.52 fold  2.0 = double        4.0
  +3 dB   1.23 fold 1.414 fold = √2  2.0 = double  
  - - - - ±0 dB - - - - - - - - 1.0 - - - - - - - - - - - 1.0 - - - - - - -   - - - - - 1.0 - - - - -  
  −3 dB     0.816 fold    0.707 fold         0.5 = half
  −6 dB     0.660 fold    0.5 = half 0.25
−10 dB     0.5 = half 0.316    0.01
−20 dB          0.25 0.100    0.01
−30 dB          0.125 0.0316    0.001
−40 dB          0.0625 0.0100      0.0001
Log. quantity Psycho quantity Field quantity Energy quantity
dB change Loudness multipl. Amplitude multiplier Power multiplier

For a 10 dB increase of the sound level we require ten times more power from the amplifier.
This increase of the sound level means for the sound pressure a lifting of the factor 3.16.
Loudness and volume are highly subjective. That belongs to the domain of psychoacoustics.

The standard atmosphere is 101325 Pa = 101.325 kPa or 1013.25 hectopascal.

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