If two media have the same acoustic impedance at their boundary, what will occur to the sound?

• A. All of the sound will be transmitted.
• B. All of the sound will be reflected.
• C. Some of the sound will be refracted.
• D. Some of the sound will be reflected and some of the sound will be transmitted.

Answer: (A)

When acoustic impedance is matched at a boundary, there is no impedance jump for the wave to “see.” That means no part of the incident energy is reflected back; all of it crosses into the second medium. The sound energy is fully transmitted, though the wave may change its direction if the two media have different propagation speeds (refraction). The boundary would only reflect energy if the impedances differed, so statements about reflection or partial transmission aren’t correct in this matched case.