Which term describes the fraction of sound transmitted at a boundary and the fraction reflected at a boundary?

• A. Intensity transmission coefficient
• B. Intensity reflection coefficient
• C. Acoustic impedance
• D. Attenuation coefficient

Answer: (A)

When a sound wave hits a boundary between two media, part of the energy crosses into the second medium and part is reflected back. The term that specifically quantifies the portion that makes it through the boundary is the intensity transmission coefficient. It represents the fraction of the incident sound energy that is transmitted, and in the absence of absorption, the remaining energy is reflected, so the transmitted and reflected fractions together account for all the energy.

The transmitted fraction depends on the acoustic impedances of the two media; for normal incidence, a common expression shows how the transmitted energy scales with those impedances. Acoustic impedance itself is the property that governs how much energy is reflected or transmitted, but it is not the fraction by itself. Attenuation describes energy loss as the wave travels through a medium, not how energy partitions at a boundary.