Mechanical filters for the gravitational waves detector VIRGO: Performance of a two-stage suspension

Mechanical filters using cantilever springs as elastic elements have been developed for the seismic isolation system of the VIRGO gravitational wave detector. A two-stage suspension has been built in order to study how the attenuation performances of individual filters combine when the filters are cascaded. An attenuation $\text{⩾80\hspace{0.17em}}\mathrm{dB}$ in the vertical direction and $\text{⩾110\hspace{0.17em}}\mathrm{dB}$ in the horizontal direction has been attained for frequencies above 10 Hz.