The purpose of this shift was to test a set of values sent to the DAC channel ENV_Noise_CEB_EE_room.
Only two values were tested due to some issues with the lock stability.

Each injection lasted 180 seconds and was performed via the METATRON node.

Some comments are reported below:

• The ITF unlock was not caused by the acoustic injections (see Figure 1).

• Figure 2 shows several monitoring signals from the BPC (BsX_*), the microphones, and their coherence with Hrec, while Figure 3 displays the same signals with a zoom around 800 Hz. At this frequency, Hrec exhibits a coherent structure with some of the BPC signals, suggesting a possible coupling path.

• Figure 4 shows the DAC noise levels.

• Figures 5 and 6 show the acoustic spectra during the injections.

• Figures 7 and 8 show the vibration of the benches during the injections.

• Figure 9 shows the structures excited in Hrec in the frequency range 100–1000 Hz.