Appendix: Useful Concepts from Circuit Theory

For understanding the physics of sound and the biophysics of acoustic sensors in animals, the concepts of impedance and admittance, impedance matching, transducer, transformer, passive and active, bidirectional coupling, and resonance are widely used. They all arise from the circuit-theory metamodel, which has been applied extensively in acoustics. As the name suggests, the circuit-theory metamodel provides recipes for constructing models. The example applications of the metamodel in this appendix involve a few elementary concepts from classical physics: the adiabatic gas law, Newton's laws of motion and of viscosity, and the definitions of work and of Gibbs free energy. They also involve a few elements of calculus and of the arithmetJc of complex numbers. All of these should be familiar to modem..biologists t.nd clinicians. For further examples of the application of circuit concepts to acoustical tHeory and acoustical design, see Baranek (1954), Olsen (1957), or Morse (1981).