| Deutsche Version |
• 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.
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. |
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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