Originally Posted by Ex-Calif
Sounds like you've attached a small vibration to a large sub-woofer cum amplifier.
This unless you can stop the transmission
of the vibration through the mounting bolts you have to stop the bulkhead from vibrating.
Amplitude & frequency. You can't change the frequency (easily) so you have to deaden the amplitude.
You have to change the resonant characteristics of what I am guessing is a thin bulkhead - plywood
double - bigger than you think. You need to stop the bulkhead from vibrating.
Hi Ex Calif, my thinking too, "changing the resonant characteristics" of the sounding board. The bulkhead is actually thick but as this boat is from 1975, I'm thinking it is nice and seasoned, like a Stradivarius violin. I will try a doubler first and as I'm converting the locker into a workshop will be building a stroage cupboard against it, bisecting the flat area with an epoxy
glued cupboard front. All will be well but I really do appreciate everyones help with this curious problem.
Before I do that I have to fit a new electric
toilet over the next two weekends. This could set up a new combination of natural and unnatural acoustic challenges