We measure the acoustic coupling at WEB before the interventions which will occurr during the commissioning break.

Note: during this measurement the hrec calibration is wrong about -20%

Setup: two amplified loudspeakers on North side, one in front of racks, one in front of cryotrap. Figure 1.

Injected noise: 8-2000Hz, level to dac is 0.004, used ENV_NOISE_MAG_WEB connected to DAC ch7

Times are in the attached log file.

Figures 2 and 3 show the observed effect in environmental sensors, B8 and Hrec. The rised noise structure look similar to those observed in January (elog 66031).

Figure 6 An extra noise in hrec is produced at at low frequency  not coherent with the injected noise.

As noticed before the shape of the structures depend on the level of microseism. Figures 4 and 5 record the wind and seismic noise at the time of this measurement.