Acoustic impedance



Acoustic impedance Z (Characteristic impedance or sound impedance) is the ratio of sound pressure p to sound velocity (particle velocity) v, which is constant at every point of a room.
Also it is the product of the density of air ρ (rho) and the speed of sound c.
The acoustic impedance Z in N·s/m³ is:

The acoustic impedance (characteristic impedance) of air is Z = 410 N·s/m³ at the temperature 25 °C (77 °F) or 413 N·s/m³ at 20 °C (68 °F). °C = degree Celsius and °F = degree Fahrenheit.
p = Sound pressure in N/m² = Pa = pascal
v = Sound velocity (particle velocity) in m/s
J = Sound intensity in W/m²
F = Force in N = newton
ρ (rho) = Density of air in kg/m³
c = Speed of sound in m/s
Z = Acoustic impedance, sound impedance, or characteristic impedance in N·s/m³
Table - Acoustic impedance Z, Speed of sound in air c,
density of air ρ vs. temperature °C
Impact of temperature
°C c in m/s ρ in kg/m³ Z in N·s/m³
- 10 325.4 1.341 436.5
- 5 328.5 1.316 432.4
0 331.5 1.293 428.3
+ 5 334.5 1.269 424.5
+ 10 337.5 1.247 420.7
+ 15 340.5 1.225 417.0
+ 20 343.4 1.204 413.5
+ 25 346.3 1.184 410.0
+ 30 349.2 1.164 406.6

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