Eleonora, Irene, Yuhang, Federico

We made the same excercise as yesterday, but now with squeezing ON

fig.1 is a whole spectrum from 10Hz to 100kHz, comparing the squeezing ON with the squeezing OFF conditions

fig.2 is a zoom from 10Hz to 200Hz

fig.3 is a zoom from 100Hz to 2kHz

(note that an offset has been added to the data with no squeezing in order to have the level of noise 4dB above the squeezing curve)

We see and recognize many peaks with seismic origin, and we know for sure that there is also a large noise associated with acoustics.

13.5Hz is associated with a bench resonance; 24.62Hz is a "scroll" vacuum pump; 33.88Hz is a "moving line" that jumps from 34 to 37 Hz with a cycle of about 20 seconds; perhaps it is connected to an air conditioning machine that "modulates" an air flow to maintain the controlled temperature; 603Hz comes from all Turbo Molecular vacuum pumps in operation at that time. The large noise from 400 Hz to 1200 Hz could be of acoustic origin and could be associated with air flows. This is the region where are the resonances of the various mounts, it is not surprising that they are excited by ambient seismic and acoustic noise.

The possible solutions are the suspension of the bench (seismic isolation) and its complete seal with aluminum and rubber panels 1 cm thick; you should get a reduction from these actions.