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Lazerdog
4th Mar 2019, 01:37
Just spent over 30 hours riding on a Dreamliner and I was shocked by the 850 hertz whine on take off and landing. Did Boeing attach that unit to the floor to make sure it had a good sounding board? Curious as to how Boeing could mount it in such a fashion to cause that much acoustic coupling. Quite irritating. Anyone know how that unit is mounted and why it is so loud in the cabin?

lochias
24th Mar 2019, 16:15
most likely the center hudraulic pump or the 4 CAC for air condition depending where you were seating
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/1296x959/787_hyd_e383e21bbc71be05e0657edceae69c8c9dd291dd.jpg