Architects and engineers use various methods when attempting to control sound in the environments they are designing. The basic theory behind most products used to control sound is to absorb or control vibration. Sound waves striking a solid object like a door, wall or ceiling cause vibration. Vibration is transmitted from one face of the object through it to the opposite face, thus causing noise. If the vibration can be absorbed or dissipated, then the amount of noise will be reduced.

The unit of measure for sound is the decibel. A decibel, or dB, is used to measure how loud a sound is. Zero decibels are the lowest noticeable sound that can be discerned by a healthy human ear. On the other end of the scale, pain can be felt anywhere from 120 to 130 decibels.

STC or Sound Transmission Class is a measure of the amount of sound lost when passing through a wall. Standard testing criteria can be found in ASTM International Classification E413 and E90. The generally accepted STC for walls is 34.

Common methods of controlling sound are:

• Staggering structural supports. A typical interior partition consists of wood or metal studs with gypsum wallboard fastened to opposite faces of the stud. Sound transmission through this type of partition is not interrupted because there is no break in the path the sound must travel. By building the partition with the studs on one face of the wall offset from the studs on the opposite face, the path is interrupted. The result is a wall with a higher STC rating. A 10’ high wall with wood studs placed 16” on center will cost approximately $1.31 per square foot. A 10’ high wall with staggered studs will cost approximately $1.37 per square foot.
• Using materials that soften vibration. Resilient channels are strips of metal fastened to wood, masonry or metal components. Gypsum wallboard is then fastened to the resilient channel. The shape of the channel is such that only one leg is in contact with the supporting component. Thus, because the other side of the channel is “floating,” vibration is softened by the flexibility of the metal. Depending on spacing, the resilient channels can add from $4.00 to over $6.00 per square foot of wall area.
• Using materials that absorb vibration. Acoustical ceiling tiles are used to absorb sound waves instead of reflecting them. The tiles are very porous. They convert acoustic energy into heat energy. Ceiling tiles are usually installed into a grid of supports that are shaped like an upside down T. The supports are hung from the structure by wires, and the tiles are simply laid into the supports. The entire ceiling system can cost anywhere from $2.00 per square foot to over $10.00 per square foot depending on the installation and materials selected.
• Using materials that attenuate sound. Attenuation is the opposite of amplification. These materials reduce the intensity of the sound while it is passing through them. Sound attenuation blankets are used as acoustic insulation in many locations throughout a structure. Fiberglass sound attenuation blanket can cost anywhere from $.76 per square foot to over $1.50 per square foot depending on thickness.

Architects and engineers have a number of ways to solve noise related problems. Understanding the physical nature of sound allows them to make the correct choices.

(All prices are from the 2008 version of RSMeans Building Construction Cost Data.)