impedance mismatch

In physics, an impedance mismatch occurs when a wave encounters a boundary between two different mediums with differing acoustic impedances. This difference causes some of the wave's energy to be reflected and some to be transmitted into the second medium.1

Acoustic impedance is a measure of how easily a sound wave propagates through a medium. It is calculated as the ratio of acoustic pressure to volume velocity. When a sound wave hits an interface between two mediums with different acoustic impedances, an impedance mismatch results, leading to reflection and transmission of the wave.1

This principle is analogous to electrical impedance, which measures the total opposition a circuit presents to electric current, including resistance and reactance. For example, the efficiency of a sound source is improved by minimizing the impedance mismatch between the source and the surrounding air.21