Impedance is the product of ________and ________.

• A. Density and attenuation
• B. Propagation speed and wavelength
• C. Density and propagation speed
• D. Frequency and density

Answer: (C)

Acoustic impedance is defined by the medium’s density and the speed of sound in that medium, Z = ρ c. This product captures how much pressure is generated for a given particle velocity as the wave propagates. When a wave encounters a boundary between two media with different impedances, part of the wave reflects and part transmits, with the amount of reflection depending on the impedance difference. Attenuation, wavelength, and frequency relate to other aspects of wave behavior but do not set impedance themselves. Therefore, density and propagation speed best describe impedance.