Characteristic Acoustic Impedance
Characteristic acoustic impedance of air vs temperature at atmospheric pressure
| Temperature | Speed of sound | Density of air | Acoustic impedance |
|---|---|---|---|
| in °C | c in m·s−1 | ρ in kg·m−3 | Z in N·s·m−3 |
| +35 | 351.88 | 1.1455 | 403.2 |
| +30 | 349.02 | 1.1644 | 406.5 |
| +25 | 346.13 | 1.1839 | 409.4 |
| +20 | 343.21 | 1.2041 | 413.3 |
| +15 | 340.27 | 1.2250 | 416.9 |
| +10 | 337.31 | 1.2466 | 420.5 |
| +5 | 334.32 | 1.2690 | 424.3 |
| 0 | 331.30 | 1.2922 | 428.0 |
| −5 | 328.25 | 1.3163 | 432.1 |
| −10 | 325.18 | 1.3413 | 436.1 |
| −15 | 322.07 | 1.3673 | 440.3 |
| −20 | 318.94 | 1.3943 | 444.6 |
| −25 | 315.77 | 1.4224 | 449.1 |
The characteristic impedance of a medium, such as air, rock or water is a material property:
where
- Z0 is the characteristic acoustic impedance (; N·s/m3 or Pa·s/m)
- ρ is the density of the medium (; kg/m3), and
- c is the longitudinal wave speed or sound speed (; m/s)
The characteristic impedance of air at room temperature is about 420 Pa·s/m. By comparison the sound speed and density of water are much higher, resulting in an impedance of 1.5 MPa·s/m, about 3400 times higher. This differences leads to important differences between room acoustics or atmospheric acoustics on the one hand, and underwater acoustics on the other.
Read more about this topic: Acoustic Impedance