Acoustic transmission

The degree to which sound is transferred between two materials depends on how well their acoustical impedances match.

Musical instruments are generally designed to radiate sound effectively.

Without bridge and soundboard, the instrument does not transmit enough sound to the air, and is too quiet to be performed with.

An electric guitar has no soundboard; it uses a microphone pick-up and artificial amplification.

Stethoscopes roughly match the acoustical impedance of the human body, so they transmit sounds from a patient's chest to the doctor's ear much more effectively than the air does.

Example of airborne and structure-borne transmission of sound, where Lp is sound pressure level, A is attenuation, P is acoustical pressure, S is the area of the wall [m²], and τ is the transmission coefficient