(Corey, Eric, Hugo, Jim)
Investigations continue for the big mechanical resonance peak around 120Hz. Hugo has given us a rough location of where to look (Somewhere around the H3 GS-13). On Monday, we pulled out H3 (replaced with mass), but there was no change. Also on Mon we pulled some walls in hopes of finding anything obvious. One issue noticed were a pair of 90degree Wall Brackets which were loose (at V3); see attached "photo(3)". These were torqued down, but the 120Hz peak was still there---Hugo did notice broadband noise reduction in the high frequencies by torquing these brackets down.
On Tuesday, Jim started banging on things to see if he could hear any rattling/ringing. He noticed a ping when hitting the big Leg Element weight on the Optics Table. We decided to put some Viton pads underneath it. Hugo went with a checkerboard pattern ([48] 0.5"x0.5" 0.0625" thick pads); see attached photos....grrrr, the last photo should be flipped, looks fine on my computer before I uploaded. Waiting to hear how the measurements turned out on these guys.
UPDATE!
Jim just informed me that his banging-on-things technique totally vanquished the ugly 120Hz peak! (I'm sure Hugo will post something in the alog)