The floor, ceiling and wall cavities are 1 1/2" and filled drywall and closed cell foam. This does significantly cut down the noise of the xcarve itself. However at this point it is moot since the Harbor Freight dust collector runs right next to it.
Here are a few pics of the construction:
I have some ideas on what I want to do to isolate the dust collector, mainly placing it outside. However, the shop is in the process of being insulated and fully heated/cooled, so I don’t want to dump my nice conditioned air outside when the xcarve is running. I’ll probably end up pass the vac intake out to the collector, the the exhaust back in then through a filter stack. That’s a lot of work to avoid having to wear hearing PPE.