Acoustic impedance is determined by which two properties of the medium?

• A. Density and Propagation Speed
• B. Temperature and Density
• C. Frequency and Viscosity
• D. Pressure and Density

Answer: (A)

Acoustic impedance describes how much pressure a medium develops for a given particle velocity, for a plane wave in a lossless medium the relationship is p = Z u, where Z equals density times the speed of sound. This means the two properties that determine impedance are the medium’s density and its propagation speed (the speed of sound). Temperature can alter the speed of sound, but it’s not the defining pair itself; frequency is a wave property, not a fixed medium property; viscosity affects attenuation rather than the basic impedance; pressure is a dynamic quantity, not one of the intrinsic medium properties that set impedance.