In order to see the acoustic coupling on arm signals, I set 6 microphones and the speaker on the AP table. The microphones are not seismically isolated for now.
I have a signal generator under the AP table.

When I played the 43 Hz triangular wave sound, I could see some coherence between POY error signal and microphones even though there is no peak in POY.

To Do:

• Try to subtract the acoustic signal and see with which microphone the acoustic signal can be subtracted best. But how can I find whether the signal is subtracted or not? Is coherence information enough?
• Make circuits for microphones to come to 40m.
• Make suspension systems for microphones. One idea is that the microphones should be suspended from bridges which is to be put around at the top of the tables since there is no space for stacks for each microphones.
• Prepare a new ADC.
• Perform the same measurements at the other tables, such as POX and POY.