It can be said that vibration isolation system is the most useful method reducing vibration and structure-borne noise generated by various kinds of machinery and equipments etc. if proper design and execution were carried out. However, the isolation performances of isolation systems are insufficient and so it is difficult to predict and control these effects according to the theory. Then in this study, the way of presence of isolation effects was examined. From this examination, we have extracted the insertion loss as a practical vibr-ation isolation effect, and experimental investigations were carried out. From these investigations the followings were concluded. Insertion loss was influenced of mainly excitation by air-borne sound and vibration characteristics of source and the measured insertion loss was lower than the theoretical value at high frequency range. Also, Isolation effect at the frequency range lower than the resonance frequency of isolated base can be calculated by the formula of vibration transmission loss at two-mass model considering vibration characteristics of isolated base.
To improve effective vibration damper, we have developed a new type damper, Magnetic-Vibration-Damper (MVD). By applying magnetism, MVD doesn't have only good workability but also enhanced damping abilities. As the result of examinations of thickness of constraining layer (TC) and thickness of damping layer (TD) dependencies, the following properties of MVD have been revealed. (1) The damping performance of MVD has a peak value againstTC, and the suitable value of TCincreases in proportion to thickness of vibrating body (TB). (2) The damping performance of MVD increases with the increase of TD in small range of TD, and gradually converges to a value. The values of TD where the damping performance of MVD converges are almost constant against TB. (3) Sample mass effect on constraining type vibration damper has been revealed to be very small. (4) It is found out that only in small range of TD less than 3mm sample mass effect becomes effective. Other than sample mass, flexural rigidity of constraining layer is as influential in frictional loss as in internal loss.