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Acoustic impedance

From Academic Kids

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:

<math>

Z = \frac{p}{v} = \frac{J}{v^2} = \frac{p^2}{J} = \rho \cdot c <math>

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/m 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

Template:Sound measurements

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