Sound travels in several ways. Airborne sound travels through openings such as doors, cracks, holes and voids. Structure-borne sound is caused by the vibrations of sound resonating through building materials. Impact sound is caused by whole assembly movement, such as thumping on a floor or wall.
Sound can be controlled to varying degrees. The simplest sound control method is to install insulation and seal the penetrations between rooms, which will lessen airborne sound. Structure-borne sound is more complicated to control. To stop the vibrations of sound through building material, mass needs to be added to the wall. This mass is is generally added in the form of extra layers of drywall. Metal furring strips or RC channel can be used to help break the direct contact of building materials, thus reducing vibrations. Impact sound control at ceiling and floor levels is best accomplished by a surface conditioner, such as a concrete topping, or with layers of sound board.
Sound control is measured in two ways. The first is the Noise Reduction Coefficient, or NRC. This method measures the ability of a specific material to modify sound and echoes. The higher the NRC rating, the more sound absorptive the material is. The second method is the Sound Transmission Class, or STC. This is the most common measurement of sound control. STC measures the overall sound qualities of an assembly. This includes the type of framing, insulation, amount of drywall and RC channel, if applicable. The higher the STC number, the better sound quality the building assembly has.
Installing insulation in the walls is the most cost-effective way of providing some sound control. However, the insulation alone does not make a sound-proof wall. A combination of insulation, drywall, caulking and efficient design are required to produce a truly quiet wall.
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