Build a muffler? Like a drywall box filled with insulation?
Do the walls need to be attached to the cement floor?
Rrog, I owe you an apology. Called my old drummer (who doubled up as our recording man/sound sound technician!) and he confirmed what you said. The egg boxes were more about the echo/reverb. Apparently they help to some extent with sound-proofing but not a lot. He went right into one about why we recorded one track in a church as is was the reverb that we needed.
A product that is used in commercial sound proofing is rock wool. Roxsul is the brand name and is mfg. by saint gobain. It comes in batts just like other insulation. It is used to dampen the noises made by hvac units traveling through the ducts. It also is used around bathroom walls for the same purpose. I figure that if you are going to frame and drywall, that would definitely be a plus with your build.
A quick google came up with this.
http://www.gowallpaper.co.uk/category/Wallrock_Range/Wallrock_Thermal_Liner,b.html
One thing I did was build a housing for all of my inline fans, which are the loudest. I took 2 x 4's and built a box to fit each one, enclosed the sides with drywall, placed the fan in it, made the connections, then stuffed the entire box around the fans with insulation. I then closed it up, and used expanded foam to seal in the ducting. You can barely hear them run. There is little you can do for the Ac and the standing fans, but this will at least quiet the big loud ones. You can still hear my rooms run, but it isn't as loud as it should be LOL.
Rrog, I owe you an apology. Called my old drummer (who doubled up as our recording man/sound sound technician!) and he confirmed what you said. The egg boxes were more about the echo/reverb. Apparently they help to some extent with sound-proofing but not a lot. He went right into one about why we recorded one track in a church as is was the reverb that we needed.