We took a look at some of the accelerometers that we have in the CEB during the acoustic injection done with white and band-passed shaped noise.
The broadband noise injection (10 to 1990 Hz) from 10:28:00 to 10:34:00 UTC is mainly visible in:
ENV_IB_CT_ACC_X
ENV_SIB2_ACC_Z
ENV_PR_ACC_Z
ENV_PR_LINK_ACC_Z
ENV_SPRBLINK_ACC_Z
ENV_WI_ACC_X
ENV_WI_CT_ACC_Z
ENV_NI_ACC_X
ENV_NI_CT_EXT_ACC_Z
ENV_NI_LINK_ACC_Z
ENV_SR_ACC_Z
ENV_SR_EAST_ACC_Z
ENV_SQZ_PIPE_ACC_Y
ENV_DT_ACC_Z
ENV_DT_CT_ACC_Z
(but the effect of the acoustic noise ismore or less visible in all *ACC* sensors)
It is worth noting that some of these ENV_ACC sensors are dominated by mains harmonics; these are:
ENV_TCS_CO2_NI_ACC_Y
ENV_TCS_CO2_WI_ACC_Y
ENV_SQZ_PIPE_ACC_Y
ENV_SQZ_ACC_Y
We see some Hrec structures growing from 400 to 500Hz, characteristics of DET diffused light, and we also see noise between 160 and 170 Hz and a "volcano" structure around 50Hz
The detail of the band-shaped noise injection (time always UTC) is given below:
Band-limited noise (0-50Hz) 10:41:00 to 10:49:00 level 5e-3
"Volcano" 40-60 Hz growing in Hrec, but no coherence in ACC sensors
Band-limited noise (0-120Hz) 10:35:00 to 10:40:00 level 1e-3
level too low, not really visible in Hrec
Band-limited noise (100-200Hz) 10:51:00 to 10:57:00 level 2e-3
bump 160-170 Hz growing in Hrec, mainly visible in the accelerometers ENV_NI_* and in ENV_SQZ_PIPE_ACC_Y plus ENV_DT_ACC_Z ; some coherence in ACC sensors, but only for some sharp lines within the bump, around 166Hz; not for the whole bump
Band-limited noise (200-300Hz) 10:59:00 to 11:09:00 level 2e-3
some thin lines that grow in Hrec at 273Hz, 282Hz, from 290 to 300Hz, 326Hz, 343Hz (in addition to the usual DET scattered light bumps from 400 to 500Hz, due to the harmonics of the sound generated by the speakers)
Due to the global spread of this noise within the CEB (and also due to the bad sound insulation of the internal walls), it is difficult to find a clear witness; some frequencies seem more prominent in some accelerometers, others in other sensors.
