Noise Reduction of a Consumer Electric Clock

The noise from a consumer electric clock was studied. The clock was placed in an anechoic room for sound pressure level analysis to determine the noise sources, which were found to be impacts at the electric motor rotor bearing and impacts between gear teeth of the rotor pinion and the first reduction gear. Study of the clock case revealed that case resonances were being excited by the impacts within the mechanism with resultant noise radiation. Modifications to the case to increase damping were successful in reducing the noise associated with these resonances, although a different damper must be devised for production feasibility. Noise reductions were also obtained by modifications to the clock motor itself including reduction in magnetization of the rotor; use of softer rotors and first reduction gears; reduction in the inertia of the first reduction gear; and increase in load applied by a friction drag to the gear train. [This work was supported by Westclox Division, General Time Corporation, LaSalle,...