Yet another post on "soundproofing" a workshop. But this one is multiple choice.

[Mel Fulks]

Glad to hear of the Safe n Sound product. A while back I installed an attic fan, the install directions said to put it at least 3 inches back from the louvers. Decided to drop back all the way to the next rafter and make a very sturdy box for it. Made the fan sound like an airplane! To quiet it I used a lot of chicken wire and fiberglass insulation.Did not help much,I was surprised at how ineffective it was. After reading thick rubber would block sound I bought some 18 inch carpet tiles from the Restore. Took out the fan and lined the box (and covered the outside)with 2 or 3 layers. That worked pretty well,but what a lot of extra trouble.I am sure I won't be doing any more sound proofing by trial and error.

[Stephen Cherry]

One of the best sound things that I did was move my air compressor to the basement.

[Ole Anderson]

Personally, I think you are overthinking this issue. If you have hardiboard over OSB on 6" studs with R30 rockwool and you plan on drywalling the interior, I say you have done plenty. If you are still concerned, just add another layer of drywall in the interior to match your electrical box standout amount. Any more will give you a virtual unmesurable difference in sound attenuation to the neighbors.

With regard to soundproofing your DC system, you will need to exhaust it to the interior if noise to your neighbors is your concern. If you build a closet in your interior, just add a layer of 3 1/2" safe n-sound to the interior of the closet and add a glued layer of drywall to your door interior and watch your path of exhausting air back to your shop, make it circuitous and line it with rock wool to absorb reflected sound. That is basically what I did and here is the results in sound attenuation: http://www.youtube.com/watch?v=8X8qwMqm3Ek

To directly answer your original multiple choice question, I go with numbr 2: 1/2" rock over 5/8" rock, both screwed and then taped.

My DC door is constructed of a sandwich of 1/2" drywall between 1/2" OSB with a fairly narrow perimeter of 1/2" solid wood at the edges of the drywall. Good and heavy.

[Ruel Smith]

As someone who's in construction, typically, most sound deadening in commercial buildings is done with simply applying bats of insulation between the walls. Sometimes, they use normal insulation, but sometimes they'll use bats that are specifically engineered for acoustical sound deadening, such as this: http://insulation.owenscorning.com/h...cts/quietzone/

Low frequency sounds are subdued best by hard material such as concrete. Higher frequency sounds are subdued by soft materials such as foam or insulation. Hence, as a drummer, it makes the most sense to put my drums in the basement with some sound deadening to boot. The same goes for your workshop. Typically, you're sounds are higher frequency sounds coming from table saws and planers and such. Soft material such as an acoustical foam or bats of insulation should take care of that issue for you.

[Harry Hagan]

Article posted on FineHomebuilding website:
http://www.finehomebuilding.com/item...t-sound-studio

[Alan Lightstone]

When we built our home theater, the walls consisted of 2 sheets of drywall, R30 insulation, air space, insulation, then 2 sheets of drywall. I've measured 130db inside, and ambient noise levels outside it.

Overkill for a workshop? Probably, but it sure is soundproof.