What is the equation for acoustic impedance?

What is the equation for acoustic impedance?

• A. Rayls = Density / Speed of Sound
• B. Rayls = Density x Speed of Sound
• C. Rayls = Density + Speed of Sound
• D. Rayls = Speed of Sound / Density

Answer: (B)

Acoustic impedance is the ratio of pressure to particle velocity for a sound wave, and for a plane wave in a fluid the pressure and velocity are related by p = ρ c u, where ρ is density and c is the speed of sound. Solving for impedance gives Z = p/u = ρ c. Because ρ has units of kg/m^3 and c has units of m/s, their product is kg/(m^2 s), which is the Rayl unit. So the right expression is Rayls = Density × Speed of Sound. The other forms don’t match the dimensional units or the p = Z u relationship.

Acoustic impedance is the ratio of pressure to particle velocity for a sound wave, and for a plane wave in a fluid the pressure and velocity are related by p = ρ c u, where ρ is density and c is the speed of sound. Solving for impedance gives Z = p/u = ρ c. Because ρ has units of kg/m^3 and c has units of m/s, their product is kg/(m^2 s), which is the Rayl unit. So the right expression is Rayls = Density × Speed of Sound. The other forms don’t match the dimensional units or the p = Z u relationship.