The type-B SAS, used for seismic is

The type-B SAS, used for seismic isolation of the BS and signal recycling mirrors, has smaller number of attenuation stages and a room temperature payload. The base of the suspension system sits on an external support frame enveloping the attenuation chain. The support frame is supposed to be a rigid structure and transmit the seismic vibration to the suspension system directly. However, in practice, it has inevitable mechanical resonances and thus enhances the vibration entering the suspension system. The type-B SAS also has the IP stage for pre-isolation and static control of the suspension chain, as for the type-A SAS. Three stages of GAS filters provide vertical seismic attenuation in the detection band of gravitational waves. The optic is suspended from the penultimate stage, called the intermediate mass, by two loops of wires. It works as a marionette and the alignment of the optic can be adjusted through rotating the intermediate mass.