Acoustic Impedance
- In order to produce a sound wave, molecules must move closer together or further apart.
- There must be a velocity component associated with the sound wave; the molecules will be stationary at both the peak of compression and the trough of rarefaction, and will be at various different stages in between. It will be at its peak in between the compressions and rarefactions.
- The force needed to set the molecules in motion is the pressure component, and it is always in phase with the velocity component.
- If the displacement component is a sine wave, then the velocity and pressure components are a cosine.
- Pressure has no direction. Velocity, however, does. The velocity component gives the sound wave its direction.
- The velocity and pressure components of a sound wave are also related in terms of the density and springiness of the propagating medium. A low density medium will have a higher amplitude in its velocity component for a given pressure amplitude compared to a denser medium, for example.
Pressure component amplitude ÷ Velocity component amplitude = Constant = Zacoustic = ρ ÷ υ
| ρ | = pressure component amplitude |
| υ | = volume velocity component amplitude |
| Zacoustic | = acoustic impedance |
© Matt Bellingham 2003 – 2006
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