Konverzija zvučnih jedinica

Nivo zvuka L 

dB (SPL) 
 | Zvučni pritisak p 

 | Intenzitet zvuka I 

   |    |  
        |         |       
   |    |  
 Zvučni pritisak p 

 | Nivo zvuka Lp 

dB (SPL) 
 | Nivo zvuka LI 

dB (SIL)
Intenzitet zvuka I 

 | Širenje zvuka u vazduhu  |  

Popunite sivi gornji okvir i kliknite na dugme za izračunavanje. 1 Pa = 1 pascal = 1 N/m2.

The atmospheric pressure is not the same as the sound pressure. Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure caused by a sound wave. The sound pressure p are the pressure fluctuations in air that the static air pressure is superimposed.

The standard atmospheric pressure is 101,325 pascals = 1,013.25 hPa = 101.325 kPa
● 1,000,000 µPa = 1 Pa = 1 N/m2 ≡ 94 dBSPL (and 1 bar = 105 Pa)
20,000,000 µPa = 20 Pa = 20 N/m2 ≡ 120 dBSPL
1 µPa = 10−6 Pa = 10−6 N/m2 ≡ −26 dBSPL
1 kPa = 103 Pa = 1,000 Pa = 1,000 N/m2 ≡ 154 dBSPL
SPL = Sound Pressure Level (SIL = Sound Intensity Level)

Sound intensity I as Sound energy quantity:
The auditory threshold is calculated as the reference sound intensity I0 = 10−12 W/m2.
The threshold of hearing corresponds also to the sound intensity level LW = 0 dB at f = 1 kHz.

Sound pressure p = √ (I × Z0) Sound intensity I = p2 / Z0 acoustic impedance Z0 = 400 N·s/m3

Sound pressure p (RMS) as Sound field quantity:
The auditory threshold is used as the reference sound pressure p0 = 20 µPa = 2 × 10−5 Pa.
The threshold of hearing corresponds to the sound pressure level Lp = 0 dB at f = 1 kHz.


What does sound level mean?

A reduction of the sound power level of the sound source by 6 dB is resulting in a reduction of the sound pressure level and the sound intensity level at the location of the receiver by also 6 dB, even if the sound power drops to a factor of 0.25, the sound pressure dropsto a factor of 0.5 and the sound intensity drops to a factor of 0.25. The reference value for the sound level was chosen so that with a characteristic acoustic impedance of Z0 = ρ · c = 400 N·s/m3 the sound intensity level results in the same value as the sound pressure level. We therefore simply speak of the "sound level" and leave it open whether sound pressure level or sound intensity level is meant.

Sound engineers and sound designers ("ear people") think by the short word "sound level" simply of "sound pressure level" (SPL) as sound field quantity. Acousticians and sound protectors ("noise fighters") mean by the short word "sound level" probably "sound intensity level" as sound energy quantity. Equating sound pressure with sound intensity must cause problems. I ~ p2.

Sound pressure and Sound pressure level

Note: The radiated sound power (sound intensity) is the cause and the sound pressure is the effect, where the sound engineer is particularly interested in the effect.
The effect of temperature and sound pressure:
Sound pressure and Sound power – Effect and Cause.

Acousticians and sound protectors (noise fighters) need the sound intensity (acoustic intensity). As a sound designer you don't need that sound energy size. The eardrums (tympanic membranes) of our hearing and the diaphragms of the microphones are effectively moved by the sound pressure or the sound pressure level.
See also: SPL meter.

If you are a technician checking the sound quality by listening with your hearing, think of the sound waves that move your eardrums by the effect of the sound pressure as sound field quantity. That is why there is the advice:
In sound recording try to avoid the use of sound power and sound intensity as sound energy sizes.

How many decibels (dB) is the sound energy W = I×t×A in J = W×s?
This question is asked quite rare. For calculations we use more the following sound energy sizes: Sound energy density w or E = I / c in J/m3, sound intensity I = Pac / A in W/m², and sound power Pac in W = J/s and their corresponding levels. It is wise to use the sound pressure p in Pa or the sound pressure level SPL in dB.

The sound pressure or acoustic pressure (alternating pressure changes) is a dynamic pressure. However, the air pressure (atmospheric equal pressure) is a static pressure. The dynamic sound pressure is superimposed on the static air pressure (atmospheric pressure).

Sound pressure, Sound intensity and their Levels

The following calculator shows the often desired direct conversion of sound pressure to sound intensity and vice versa with the specific acoustic impedance of air Z0 = 400 N·s/m3. Sound level is given in dB (decibel).

To use the calculator, simply enter a value.
The calculator works in both directions of the ↔ sign.

Sound field quantity   Sound energy quantity
Sound pressure p (air)

Pa (pascal) 
 ↔  Sound intensity I (air)

Reference sound pressure p0 = 20 μPa = 2 × 10−5 Pa      Reference intensity I0 = 1 pW/m2 = 10−12 W/m2
Specific acoustic impedance of air Z0 = 400 N·s/m3   Sound pressure p = √ (I × Z0)   Intensity I =
p2 / Z0

While the sound pressure level in the air is matched with the sound intensity level when a reference sound characteristic impedance Z0 = 400 N·s/m³ is chosen, this is not the case with the distance independent sound power level.

Sound pressure and Sound power − Effect and Cause

Note! Since the sound power level is difficult to measure, it is common to use sound pressure level (SPL) measured in decibels instead. Doubling the sound pressure raises the sound pressure level by 6 dB.

Be precise: Double the sound pressure and double the sound power, or double the acoustic intensity

To use the calculator, simply enter a value. The calculator works in both directions of the ↔ sign.

Factor, ratio, and gain
Ratio x for loudness (volume) 

times (sensation)
 ↔  Level change Δ Lloud (psychoacoustics)

Factor loudness   = 33.22·log (x)
Ratio y for sound pressure (voltage)

times (field quantity)
 ↔  Level change Δ Lp (pressure level)

Ratio z for acoustic intensity (power)

times (energy size)
 ↔  Level change Δ LI (intensity level)


Sound pressure level SPL and sound pressure

"Sound level" is the sound pressure level in dB SPL or the sound intensity level in dB SIL. For Pa say, Pascal. This is the size for the pressure p = force F by area A. The reference sound pressure is p0 = 20 µPa = 2×10−5 Pa. The reference sound intensity is I0 = I0 = 10−12 W/m2.

DAGA and also DIN request the indication of the sound level in dB alone. The attached SPL comes from the United States and is frowned by acousticians.

The often used term "intensity of sound pressure" is not correct. Use "magnitude", "strength", "power", "effectiveness", "amplitude" or "level" instead. "Sound intensity" is sound power per unit area, while
"pressure" is a measure of force per unit area. Intensity as sound energy quantity is not the same as pressure as field quantity.

Sound pressure is not intensity

Differentiate: Sound pressure p is a "sound field quantity" and sound intensity I is a "sound energy quantity". In teachings these terms are not often separated sharply enough and sometimes are even set equal.

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 the alternating sound pressure as RMS value. The sound pressure amplitude is the peak value of the sound pressure. The sound volume (loudness) is determined mostly by the sound pressure p and expressed as sound pressure level Lp in dB.

Comparison of sound pressure level SPL and sound intensity level

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

Reference values (hearing threshold): p0 = 20 µPa = 2 × 10−5 Pa or also I0 = 10−12 W/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. The calculator works in both directions of the ↔ sign.

Sound pressure p (in air)  

Pa = N/m2
 ↔  Sound pressure level Lp 

Reference sound pressure p0 = 20 μPa = 2 × 10−5 Pa ≡ 0 dB