a) for transduction of an electric signal into an acoustic signal, quotient of the resulting sound pressure in the blocked acoustical system by the excitation voltage in the electrical system;

b) for transduction of an acoustic signal into an electric signal, quotient of the resulting short-circuit current in the electrical system by the excitation volume velocity in the acoustical system

NOTE – These definitions are best applied to a reciprocal electroacoustic transducer with transformer coupling, for example an electrostatic or piezoelectric transducer, in which case the two quotients have equal magnitude.