Whether you need to keep noise in a room (your son is a drummer in a band) or keep noise out of a room (you need peace and quiet from your kids in your home office while you work), sound proofing can help.
There are 4 main types of sound proofing.
The most basic is adding mass, which is putting more things in the way of the noise.
You can also absorb the sound with fluffy insulation.
Another option is to disconnect the items in your home that will vibrate (your walls) so they don't touch and transmit the noise vibration.
The last option is to select building materials that do not vibrate.
Here are some basic and more advanced ways to sound proof a room.
If there are any gaps between the noisy room and the quiet room, then seal them first.
Seal any gaps between the door and the floor, any gaps around electrical outlets, and any cracks in the wall.
Insulating foam sealant is easy and inexpensive to seal gaps.
You can also change out your hollow core door with a solid wood door that has more mass to keep the noise from coming through.
If the sound you are trying to keep out is coming from outside, it is most likely coming through your windows.
Caulk all windows with acoustical caulk and use heavy curtains to keep the sound out.
You can even use special sound absorbing curtains if you wish.
Consider changing out your windows to dual paned or more to keep the noise out.
Add insulation to your walls in order to reduce the sound coming through. You can use spray insulation or batt insulation.
You can add acoustic panels to the inside of the noisy room to absorb sound.
There is special adhesive that helps with sound proofing. You can use that adhesive to glue another layer of drywall to your ceiling to greatly reduce the sound transmission.
If the noise is coming from above you, such as an upstairs neighbor, you can add a dropped ceiling in your home to sound proof it.
Make sure to use sound reducing clips to keep the sound transmission to a minimum.
You can modify your flooring to sound proof a room.
The easiest way is to add a rug or carpet to the room (you can even add it to the walls).
You can also use a thicker carpet pad, use a sound proof mat under your floor, add insulation between the framing, and add additional sub floor.
You can add another layer of regular drywall to the inside of your noisy room to help in soundproofing. Make sure to use noiseproofing adhesive to reduce the transfer of noise to other rooms.
Sound Resistant Drywall
There is special sound resistant drywall available for your home.
It costs quite a bit more than regular drywall, but it will greatly reduce the amount of sound coming through your walls.
You can add a layer of sound resistant drywall on top of your existing walls using sound reducing adhesive, or you can remove your existing drywall and replace it with sound resistant drywall after putting insulation between your walls.