Yesterday evening Federico and Valerio performed acoustic injections in CEB, both white noise and sweeps. Loudspeakers were positioned at the north terrace (same setup as 39698).

Here the times:
% white injections, three levels, frequency range: 30Hz to 2kHz (used server ENVnoise with channel ENV_NOISE_CEB_DetTerrace)
% quiet 1192981218 (Oct 25 15:40 UTC), 600s
% level LOW (parametro "density" = 0.001): 1192982063 (15:54:05 UTC), 550s
% level HIGH (parametro "density" = 0.005): 1192983043 (16:10:25 UTC), 380s
% level MEDIUM (parametro "density" = 0.002),1192983543 (16:18:45 UTC), 300s
%
% sweep injections, twice, the second with doubled intensity (used commercial signal generator)
% 1192983986 to 1192984538  (from 30Hz to 1kHz)
% 1192984563 to 1192984773  double intensity,

When the second sweep reached about 265Hz the ITF unlocked  and injection was stopped. It seems that  the ITF unlock was caused by NI suspension which got excited.

Figure 1 shows white noise injections: the most excited Hrec region is between 400 and 500Hz.

Figure 2 shows that the excitation is maximum around some Hrec existing peaks: 421 Hz, 439 Hz, 448.2 Hz and 452.2. These are new peaks that appeared after the recovery (see 39867).

Figure 3 shows as acoustic and vibration noise increased all over CEB hall and in DET lab as well (much less in LaserLab)

Figure 4 shows sweep injections, here as well the 400-500Hz region is the most excited.