The standard symbol used to denote acoustic impedance is which of the following?

• A. Z
• B. R
• C. X
• D. Y

Answer: (A)

Acoustic impedance is the ratio of acoustic pressure to particle velocity, and it’s treated as a single quantity that can have resistance and reactance components. The standard symbol for this complex quantity is Z, writing Z = p/v or Z = R + jX, where R is the resistance (real part) and X is the reactance (imaginary part). Using Z aligns with the general physics and engineering convention for impedance, including electrical impedance, making it the conventional label across disciplines. The other symbols have different meanings: R denotes resistance, X denotes reactance, and Y denotes admittance (the reciprocal of impedance). In acoustics, Z is measured in Rayls (Pa·s/m), reflecting its role as the overall impedance between pressure and velocity.