What determines acoustic impedance?

• A. Frequency and Propagation Speed
• B. Frequency and Interface Size
• C. Density and Propagation Speed of the Medium
• D. Angle of Incidence and Media Propagation Speed

Answer: (C)

Acoustic impedance is an intrinsic property of a medium that describes how much acoustic pressure is produced for a given particle velocity. For plane waves in a simple medium, impedance is the product of the medium’s density and the speed of sound in that medium (Z ≈ ρ c). That means the factors that determine impedance are density and propagation speed. If either density or the speed of sound changes, the impedance changes accordingly.

Frequency doesn’t set impedance; changing frequency doesn’t alter ρ c. The angle of incidence or the size of the interface affect how much of the wave reflects or transmits at a boundary, but they don’t determine the medium’s inherent impedance.