i know a fair amount about sound... a lot more about sound than i do cnc which is why i sold off my cnc router and outsourced my cutting to someone else!
the sound you're getting is mostly high-end noise from the cutter. the router motor (while noisy) is pretty much overwhelmed by the cutter noise. there is a LOT of energy in that noise! the structure you'd need to build to really get rid of the noise would be crazy-heavy. and even having small sections like windows or doors that are not isolated like the walls will let a surprising amount of noise leak out. you will have very little success with acoustic foam. i am telling you this from actual measurements and knowledge. you'll burn a lot of money and it won't work for this application. acoustic foam is great stuff but not for this spectrum of noise.
essentially you can choose one of two routes - you either try to stop the noise from travelling out or you try to just dampen/muffle it down to an acceptable level. the good news is that for this kind of noise, you can probably dampen it pretty effectively. while many people here are correct that nothing beats mass in defeating sound, the density and mass becomes more important the lower the frequencies - and this noise is not too low frequency.
my advice in terms of cost effective, and manageable, would be to use a cavity-filling polyurethane foam like handi-foam or similar and fill the wall cavities. use 3/4" drywall on both sides of the wall. use a solid cavity fire-rated door into the room and avoid any windows. this will give you a very reasonable amount of acoustic blocking without expensive materials or extremely heavy structures. will it be soundproof? no but it will significantly reduce the noise. will it be better than x, y or z? hard to quantify because there are so many ways to attack this kind of problem. but it will be a very cost-effective approach and almost always gives excellent results for this kind of sound.
good luck!  |