Purchase a soundproof bottom for your door. Install the bottom to any door located in the room in order to fill the gaps between the floor and door. The door bottom is designed to seal any sound from any cracks caused by the door and to lift up when the door is opened, to allow for easy access in and out of the room.
Add a layer of plywood that covers the entire door. The plywood will further dampen the sound outside that is generated from within the room.
Apply a layer of a paint---known as "green glue"---over the plywood on the door and surrounding walls. This product dampens sound vibrations caused by sound waves and reduces the sound transferred through objects. It works well on drywall and wood, the two components that are normally used to construct rooms.
Affix carpet to the walls and ceiling. Use nails or heavy-duty glue to secure the carpet firmly on surfaces. If your band room is made of drywall, wood or any smooth surface material, adding carpet to the surfaces will stop sound waves from passing through the wall, as well as preventing vibrations from within the room for a non-resonant timber.
Place several layers of carpet to the floor. If there is another room beneath your band room, it is a good idea to apply extra layers of carpet underneath the drums, amps and anything else that comes in contact with the floor. Soundwaves will transfer more easily if objects are in direct contact with one another.
Insert acoustical caulk around the edges of the windows. If you have windows, this material will seal up any air cracks caused by aging of the surrounding materials. The caulk is chemically bonded to many different types of materials, such as metal, wood, drywall and concrete, to ensure a tight seal.