Wave Effects in Vibration Mounts

Abstract

Theoretical and experimental studies of wave effects in vibration mounts have been made. From the standpoint of noise isolation, wave effects are important in the sense that the noise isolating properties of a mount are impaired by the presence of wave effects. The well-known lumped parameter treatment of vibration mounts predicts that the vibration isolation of a mount increases at 12 db per octave for frequencies well above the resonant frequency of the spring-mass system. This is true only when the wavelength of the elastic wave in the mount is large compared to the dimensions of the mount. Standing waves occur as would be expected and often impair the vibration isolation properties of the mount by as much as 20 db. For practical mounts, wave effects are often most deleterious in the audible frequency range 500 to 2000 cps. The theoretical and experimental treatments give good agreement and indicate various means for improving the vibration isolating properties of the mount.