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Acoustic impedance

From Biocrawler, the free encyclopedia.

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:

$Z = \frac{p}{v} = \frac{J}{v^2} = \frac{p^2}{J} = \rho \cdot c$

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