A Method of Measuring Acoustic Impedance

Abstract

A method of measuring acoustic impedance is described which is independent of the instrument constants. A system of acoustic tubes, a sound generator of measurable vibratory velocity and an acoustic pressure meter of Gerlach's principle are required.
A general tube system considered is shown in Fig. 3 (A), where A, D, ZR are the sound generator, pressure meter and the acoustic load to be measured. The value of ZR is given by equation (29), where xA and FD are respectively the vibratory velocity at A and the acoustic total pressure at D and those with a suffix ∞ correspond to the values when ZR=∞. And xA is proportional to the motional impedance of the sound generator and FD to the balancing current of the pressure meter. Thus these two are measurable and therefore ZR. For actual measurements, however, special cases such as shown in Fig. 4. are sufficient.
Moreover, a method of measuring mechanical impedance of a diaphragm and also those for acoustic constants of cloth or similar materials are added.