Today as agreed we performed some acoustic noise injections in CEB. The setup was prepared and tested yesterday during maintenance: two subwoofers and two loudspeakers were positioned on DET terrace (NE corner of CEB).

Injection times:

12:15 UTC to 12:29:20 UTC (ITF unlocked) - white noise 100-1900Hz with  ENV_NOISE_CEB_DetTerrace send to both loudspekers and white noise 0-200Hz from Fede's box to subwoofers.

13:13 UTC to 13:15:40 UTC (stopped as requested) - white noise 10-1990Hz with ENV_NOISE_CEB_DetTerrace send to loudspeakers and subwoofers.

Figure 1 shows trend data. Figure 2 shows spectra. During the first injection acoustic noise in CEB increased largely both in the hall and inside the detection lab, especially the low frequency part (40-200Hz). During the second injection we injected less acoustic noise below 200Hz, yet excess noise was still about a factor 10 in the hall, a factor 2 to 5 roughly  in DET lab.

Some excess noise in Hrec was produced between about 40Hz and 500Hz. as shown in Figure 2.

Some Hrec structures seem to excite during the injection: 86Hz, 255Hz, 267Hz, 408Hz, 440Hz: see Figure 3.