Acoustic impedance Z (characteristic impedance or sound impedance) is the ratio of sound pressure p to particle velocity v. Also it is the product of the density of air ρ (rho) and the speed of sound c. See table: acoustic impedance vs. temperature.
The acoustic impedance Z in Pa·s/m (or, in the equivalent units common before the pascal was added to SI, N·s/m3) is:
The acoustic impedance (characteristic impedance) of air is Z = 410 Pa·s/m at the temperature 25 °C (77 °F) or 413 Pa·s/m at 20 °C (68 °F). °C = degree Celsius and °F = degree Fahrenheit.
p = sound pressure in N/m2 = Pa = pascal
v = 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 (acoustic wave velocity ) in m/s
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 Pa·s/m
|
| - 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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