Acoustic impedance is defined as the product of which quantities?

Acoustic impedance is defined as the product of which quantities?

• A. Density and Propagation Speed
• B. The product of Density and Propagation Speed
• C. The ratio of Density to Speed
• D. Pressure and Volume

Answer: (B)

Acoustic impedance expresses how much pressure a sound wave must generate to drive a unit motion in a medium. For a plane wave in a fluid, this impedance is the product of the density and the speed of sound in that medium: Z = ρ c. This means both heavier (more massive) media and media where sound travels faster contribute to a higher impedance. The relationship also makes sense dimensionally: density is kg/m^3 and speed is m/s, giving the units of impedance (Pa·s/m). The ratio ρ/c would give the inverse of impedance, and pressure paired with volume isn’t how impedance is defined in this context.

Acoustic impedance expresses how much pressure a sound wave must generate to drive a unit motion in a medium. For a plane wave in a fluid, this impedance is the product of the density and the speed of sound in that medium: Z = ρ c. This means both heavier (more massive) media and media where sound travels faster contribute to a higher impedance. The relationship also makes sense dimensionally: density is kg/m^3 and speed is m/s, giving the units of impedance (Pa·s/m). The ratio ρ/c would give the inverse of impedance, and pressure paired with volume isn’t how impedance is defined in this context.