Acoustics sound pressure level particle velocity acoustic impedance Z sound units intensity acoustic characteristic impedance dB SPL calculations ohm's law acousticequivalent pascal audio calculations sound units audio engineering

• Formulas and calculation •

• Ohm's law as acoustic equivalent •
for plane progressive waves

Calculation: sound pressure p, particle velocity v,
specific acoustic impedance of air Z, sound intensity I or J

The particle velocity v is not the speed of sound c = velocity of sound.
Unless otherwise stated, the sound pressure is always meant as RMS value.

eff = RMS

Enter any two of the following values and click the calculation button.
The missing values will be calculated. One of these values could be the
specific acoustic impedance (characteristic impedance) of air:
Z₀ = 413 N·s/m³ at 20 °C = 68 °F or Z₀ = 410 N·s/m³ at 25 °C = 77 °F.

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In acoustics sound pressure, particle velocity, and acoustical impedance are linear
sound field strength quantities. The sound intensity is a quadratic sound energy strength quantity.

Intensity J or I is not the same physical quantity as sound pressure p
... and the sound power does not decrease with distance r from
the sound source - neither with 1 / r nor as 1 / r².

The well known law V = I × R means accordingly (equivalent) in the acoustics p = v × Z.

Ohm's Law of the electronics V = I × R

Conversion of acoustic values to sound level L in dBSPL

Conversions and Calculations of Sound Quantities and their Levels

Relationships of acoustic quantities associated with acoustic sound waves

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.

Acoustic impedance of a medium = Sound pressure / Particle velocity
Characteristic acoustic impedance Z₀ = p / v

Please enter two values, the third will be calculated.

Acoustic impedance of air at 20 °C is Z₀ = 413 N·s/m³.

Acoustic impedance = Density of medium × Speed of sound
Z₀ = ρ × c

Please enter two values, the third will be calculated.

Medium	Density ρ in kg/m³	Speed of sound c in m/s at 20 °C	Acoustic impedance Z₀ in N·s/m³
Air	1.204	343	413.5
Water	1 000	1 440	1 440 000
Aluminium	2 700	6 100	16 500 000
Steel	ca. 7 500	ca. 6 000	ca. 45 000 000

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