Noise barriers are walls constructed to reduce excessive sounds by absorbing them or reflecting them back toward their source. Such barriers are often used in residential areas to reduce noise from road or train traffic. The height of these barriers can be calculated based on the location of the "audience" and the desired sound level.
Measure the level of sound using the sound-level monitor from the point at which people would hear the noise. In this example, the noise from the highway would be measured from the side of homes along the highway. The sound-level monitor will express the level of noise in decibels with the symbol "dB."
Measure the height of the line of sight from where a person can see the source of the noise. For example, this might be the height of a window on the side of a house that faces a highway. The height of this line of sight could be 1.5 meters (5 feet, 10.5 inches).
Calculate the difference between the noise level you measured in Step 1 and the desired noise level in decibels. For example, if the reading in Step 1 showed the noise level is currently 13 dB and the desired level is 3.5 dB, the difference is 9.5 dB.
Subtract 5 dB from the difference you calculated in Step 3. A wall equal in height to the line of sight you measured in Step 2 blocks 5 dB of sound. In this example, the remaining difference would now be 4.5 dB.
Divide the remaining difference by 1.5. Each additional meter of the sound wall's height blocks 1.5 dB of sound. In this example, the sound wall would have to be 3 meters taller than the line of sight measured in Step 2 to reduce the sound level to 3.5 dB.
The above calculations apply to barriers constructed from materials with a density of 20 kilograms per square meter. Such materials can include wood, stone or brick. To reduce the noise coming around the ends of the barrier, the length of the barrier should be at least 8 times as long as the distance between the homes and the barrier. For example, if a home is 20 feet from the barrier, the barrier should be 160 feet long, with 80 feet on each side of the home.