Today we performed some measurements for the purpose of IME (new-born ADV+II SS dedicated to Infrastructure Modifications for Environmental noise mitigation) 

Study acoustic modes of the Laser Lab

With the purpose to excite acoustic modes of the room to be seen in the microphones on LB and EIB, we generated low frequency sound waves by acting on the door of the rooms, just moving back and forth repeatedly. Infact we generated sound pressure waves, whose low frequency component was detected by LB and EIB mics mainly below approx 2 Hz. But not enough energy was produced to overcome the noise produced by the air conditioning aboze that frequency. Some effect was visible around 100Hz (Figure 1). We think that it would be useful to repeat this test with the AHU switched off.

With the purpose of possibly modify the sound modes of the laser room, we opened and kept opened for 15 minutes the large door between LaserLab room and Atrium room. We infact produced a slight shift of a few acoustic peaks (roughly, from 7 Hz to 10 Hz, and from  19 Hz to 21 Hz) as shown in the attached spectrograms (Figures 2, 3, and 4). In principle, a shift down of the frequency of the modes would be expected by enlarging the volume. The result seems to go in the opposite direction, it needs to be interpreted. Figure 5 shows the impact of the temperature and overpressure.

Study acoustic noise from WEB racks

In the WEB we moved the temporary microphone named ENV_WEB_MAEL_MIC in front of the racks, as shown in the Picture.

We also performed a set of measurements with the same microphone to understand if noise is produced by the outlet at the end of the hall (see Picture). We moved it in steps closer and closer to the outlet. We did not observe a significant increase of the sound at any specific frequency (apart from a change in amplitude of the 7 Hz bump that we know is the first sound mode of the WEB hall). Overall the low frequency spectrum below 100 Hz seems stable. We shall conclude that there is no low frequency extra sound noise from this outlet.

Study of noise from Vac tunnel UPS 

Federico positioned a magnetic probe (Bartington 3 axial magnetometer with Centaur datalogger) at 390m along the N arm tunnel. The magnetic probe is placed behind the vacuum pipe on top of the IPS cables ducts (Picture). This magnetometer has been in place between 8:45 and 12:00 UTC. Data are to be analyzed.