The inferred determination of the phase speed of a bubbly liquid of less than 2 m/s by using a transfer function technique.

The phase speed of a bubbly liquid has been inferred at the single bubble resonance. The difficulty in this measurement is the fact that acoustic absorption is very strong at the single bubble resonance making it impossible to measure with standard techniques, e.g., time-of-flight or the use of standing waves. Instead, the strong absorption was exploited by first measuring the change in the reflection coefficient and relating it to the acoustic impedance and the sound speed. A sound speed of less than 2 m/s was determined possibly making it one of the slowest sound speeds ever recorded.