On the Generalised Impedance Concept, Analogies and Acoustic Applications

TNTRODUCTIONThe term impedance, universally identi ed by capital zetha (Z) was introduced in the electrical eld in 1886 by the famous English Physicist Oliver Heaviside to describe the voltage to current ratio in a circuit comprising a resistor (R) and a inductor (L).( g. 1), R va m) L Z_K "I FigJ It was a step forward to the Ohms law, soon extended to circuits including capacitors (C).The impedance concept has proved to be very useful to relate any voltage to current ratio.It has had a great development in electric network theory, as well as in other elds of physics including acoustics.A particularity of acoustics is that the systems involved in most acoustic problems, do not have physically concentrated parameters as is the case of most electromechanical systems in acoustics we have in general mechanical vibratory sources with concentrated parameters, immersed in continuous media with distn'b'uted parameters in which the vibratory energy is propagated by elastic waves that may re ect, diffracts, absorb or transmit energy in obstacles, or develop sound sensations in living species through the ear mechanism.The electro-mechanical-acoustical analogies is a very useful tool to describe acoustical systems with concentrated parameters as can be the case of the Helmholtz resonators.The ow of Factors V,l F.U p.Q Exl l T.S (entropy) Power(watts) Voltamp.N. m/s N/m2.mz.m/sVolt./m