Their shared walls, in fact, actually assist sound travel, and the best way to prevent unwanted noise from passing from room to room in your home is to treat the common walls so that they no longer conduct it.
How is that done? Adding Density If you want to keep sound from being transmitted through the walls of your rooms (a process also known as noise bleed) you will have to isolate the rooms from one another by first adding to the density of the existing walls with MLV, or mass loaded vinyl sound blocking material which you will nail or tape over the surfaces of the walls you wand soundproofed.
This MLV will help prevent your walls from vibrating and conducting sound waves.
Disconnecting Shared Walls Once their existing walls have been covered with the MLV, you can proceed to isolate each of the rooms you want soundproofed by disconnecting the walls they share.
These shared walls are the primary conduits by which the sound waves to pass from room to room.
You will actually be building new walls in front of the shared walls in each room, and the space between he new and existingv will collapse the sound waves which enter it.
The sound which actually makes it through will be significantly less than it was when it left its source.
You will create your new walls by adding horizontally positioned furring strips at even intervals from the floor to the ceiling of your room, and covering them with sections of drywall.
Doubling Your Results You can further prevent noise bleed between your rooms by using more soundproofing materials.
Sealing the joints of your ceilings, floors, and walls with a high-grade acoustical caulk, and adding extra layers of both MLV and new drywall will further reduce your noise bleed.
If, for example, you use two layers of MLV (which are not in contact) over your existing soundproof walls, and overlap the seams of each layer by at least 1/2", sealing the overlaps and the perimeters of each layer with the acoustical caulk and PVC seam sealing tape, your make the existing wall much more soundproof.
If you then add a third layer of drywall separated form the second layer, you'll create a second dead space to collapse whatever sound vibrations make it through the first one! While no soundproofing techniques can completely stop noise bleed through common walls, adding density and disconnecting your shared wall surfaces will come as close to doing so as you can reasonably expect!