Thanks again guys, all great suggestions. But as I said, I can't afford to do any type of reconstruction, so I guess what I am asking is what's the best material I can use on the existing walls. And I also plan to make the door as airtight as possible, using the material to make a seal between the door and wall.

The only thing you can do on the existing walls is make them thicker or denser... that's why an extra layer of dry rock is useful... it does both things relatively cheaply.

The thing is... doing anything to the walls is useless if the seals at the joints of the basic room shape are letting sound come around the thick wall.


There are lots of convenient things you can use to absorb sound... which is good for managing sound that is in the room. Sound absorption materials do not necessarily help with sound "proofing"... they can absorb some of the sound getting in, but relying on absorption to control extraneous noise is the least efficient way to sound proof. 

Sound absorption can help tailor the tonality of the room... that is where it is most useful... after you have settled with the sound proofing.


That's the gist of what the book I have suggested will explain.

all the best,
mike

Drywall is fairly cheap. An extra layer can be applied to the existing walls and no one is likely to notice the modification. The extra layer can be glued up with a product called Green Glue. This is a special resiliant adhesive that doesn't transmit sound well. Doubling the mass of the wall will give you a 35-50 db increase in transmission loss; using green glue gives about an extra 8-10 db of attenuation. Note that there is little you can do to stop very low frequencies below about 150Hz without taking drastic measures.

bitflipper


Note that there is little you can do to stop very low frequencies below about 150Hz without taking drastic measures.

True dat.  The best I did was to put my bass stack on Aurelex Gramma Pads to reduce the transmission through the floor.
 

 

That really works? I'd assumed they were a scam.

+1  to what bitflipper said about an extra layer of drywall and Green Glue. That's what I used when I built my basement studio, and it's really quiet down here.
 
Mitch I.

is there really that much of a difference in standard glue compared to green glue?
ive typically used liquid nail in my applications.

I will guess that it is the basic physics of differing densities being sandwiched together rather than the particular material.

But this page has all the links to the test data that refutes my guess:

http://www.greengluecompany.com/test-data


best regards,
mike

http://www.greengluecompany.com/sites/default/files/Green_Glue_Vs_Construction_Adhesive.pdf

If you're going to add drywall, you might as well blow in insulation in the existing cavity first. Blown in cellulose - does a pretty good job. It has a higher density than fiberglass and fills voids pretty well.