Design of a shock and vibration isolation system for a phonograph turntable

Problems have been recognized for turntable operation in the presence of high sound pressure levels and floor shock disturbances in a listening room with flexible structure. These problems are due to the inadequate isolation of structure-born shock and vibrational disturbances provided by existing turntables and auxiliary isolation devices. A practical turntable isolation system design is presented in this thesis that provides low transmissibilities at frequencies of 10 Hz and above in all 6 degrees of freedom.

Both analytical and experimental results were used to select the best shock and vibration isolator. The method of eigenvalue analysis was used to obtain the natural frequencies and mode shapes for various isolation system configurations. Standing wave transmissibility equations were then derived and evaluated for various isolator configurations, assuming the isolator to be a distributed parameter rod or beam. The transmissibility of some of the more promising isolators was then measured. The shock acceleration ratio (SAR) of four isolators, selected on the basis of their transmissibility performance, was then measured with actual floor shock excitation. An isolator consisting of a 6-inch (free length) extension spring with distributed viscous damping, having a damping factor of .041 in longitudinal vibration, was found to have the lowest transmissibility at most frequencies and a low SAR. This isolator was selected for use in the final design of the turntable isolation system.