A Method of Measuring Mechanical Impedance

The device the mechanical impedance of which at a given frequency is to be measured is driven by one prong of an electrically-driven tuning fork, and the other prong is loaded to restore balance, the load required being the mechanical impedance to be determined. The balance condition is indicated by the absence of vibration of the fork support. An improvement depends upon the experimentally determined fact that mechanical resistance out-of-balance does not appreciably affect the support vibration. If the prongs are balanced for mass, the total resistance can be found from a decay-factor determination or by a single measurement of amplitude with a known current, and the resistance of the device estimated. A measurement is made of the mechanical impedance at 100 cycles per sec. of a certain gramophone pick-up.