Virgo Logbook

Since Friday the central Bd. Clean Room (CR) airco machine serves only clean air to the CleanRooms, as the air ducts branch to and from the LL have been meccanically disconnected and the air flux deviated all into the CleanRoom branch (see elog 30818). Figure one (RED) shows the residual acoustic noise in the LL room from the CleanRoom room machine. The CR was running in "reduced" mode. BLACK corresponds to the CR airco switched off. We noticed audible sound wistles originating from along the perimeter of the separation door between the LL and clean room. After Nicola sealed the door with some tape, the 200-1000Hz noise reduced significantly (Purple to RED in Figure 1). The intermittent high frequency noise 3k-5kHz bump is likely due to frogs (we met one walking around inside LL) or crickets. Figure 2 compares the noise produced inside the LL room by the CR airco before the air duct separation (BLUE, data of May 3rd switch off, only CR machine on) and now (RED). Before saying it is/or not complient with AdV, it is necessary to convert in sound levels and compare with the reduction requirement. However, we might already tentatively say that: (1) the noise reduction is more pronounced above 300Hz; (2) of some concern are some acoustic peaks below 100Hz were immitted noise apparently has not reduced or reduced very little: around 10Hz, at 18.6Hz (fan rotation!), 15Hz, 50Hz, 60-80Hz. Possible break-through paths for the acoustic noise could to be: (1) through the air ducts (still) running in the underfloor or ceiling (these openings can catch and vehicle acoustic noise), through the CR-LL separation wall (Parteco wall) and/or underneath, the 18.6 Hz is a well known vibration of the machine could it be transmitted as wall vibration? There was concern that some noise in the INJ lab could originate from the water flowing in the post-heating system, still connected. The primary hot water pump has been switched off and then on. Figure 3. shows noise increase possibly associated to switching on of the hot pump at about 11:33UTC (to be better checked). This noise looks however negigible with respect to the noise from the CR machine itself, described above.