A soundproof door is a door which has been designed or retrofitted to cut out as much external noise as possible. However, a soundproof door is also very dependent on a well-designed frame, or sound can leak around the edges of the frame. Unwanted noise can also filter through walls and windows, which is an important consideration for people who are attempting to soundproof a room or building.
There are a variety of situations in which a soundproof door can be useful. Musicians and recording studios rely on such doors to keep sounds from getting out, both for the comfort of the neighbors and for the benefit of other musicians and recording facilities which could be compromised by sound leakage. Soundproof doors are also used to seal noisy rooms like boiler rooms and entrances to factory floors. People can also utilize soundproof doors to keep unwanted sound out of their homes.
Several companies specifically manufacture soundproof doors, along with frames. Together, the door and frame cut out much of the noise. A number of techniques can be used to filter sound, including using a snug padded frame which creates a tight seal, mounting a door sweep seal to prevent leakage under the door with a flap of rubber which closes the gap at the base of the door, and covering or filling the door with something which works as an acoustic baffle. For people who cannot afford commercially produced soundproofed doors, sometimes just replacing a hollow core door with a solid door can do the trick.
It is also possible to retrofit an existing door and frame to radically improve its soundproofing qualities. Peel and stick acoustic baffles or panels can be attached to the inside of the door, or a door can be lined with foam or even egg crates to cut down on sound pollution. Adding weatherstripping around the door frame can help to create a seal, as can the installation of a door sweep seal. Creative soundproofers sometimes hang two doors, with the air pocket between them acting as a very effective acoustic baffle.
A good soundproof door can make a significant impact in the ambient noise level, and if an entire room or structure is treated with soundproofing measures, noise deadening may be achieved. In addition to preventing noise pollution, soundproofing often improves heating and cooling efficiency along the way, since it increases insulation, keeping a space warmer or cooler as desired.