Sound walls, noise barriers, acoustical walls are an important tool for environmental noise reduction. Here are 9 tips to maximize the effectiveness of these walls.
- A barrier needs to block the line-of-sight between the noise source and the receiver to have any impact. A barrier provides approximately 5 dBA noise reduction if it just blocks the path.
- The higher the barrier is the more noise attenuation is achieved. For every foot that the barrier breaks the line-of-sight between the source and receiver, about 0.5 dBA additional noise reduction is achieved. The actual amount of attenuation depends on the spectrum of the noise source (low vs high frequency, high frequencies are more easily attenuated by barriers) and the distance from the barrier to the noise source and receiver.
- A barrier is more effective close to the noise source or noise receiver. A barrier is least effective half way between the two.
- They should be constructed airtight with no leaks along the bottom or between individual pieces of the barrier.
- In many cases, the barriers should have an acoustically absorptive treatment on the side facing the noise sources. This prevents noise from reflecting off of the barrier, back to the source, and over the wall.
- Barriers should be solid (at least 2 pounds per square foot) and airtight. However, the transmission loss of the barrier does not need reduce the noise by more than 10 dBA below the level attenuated by diffraction effects over and around the barrier. Vegetation alone is not an effective barrier, unless it is dense and more than 50 feet thick.
- To select a material for your barrier consider: cost, durability, wash ability, weight, wind load, and space available.
- An earthen berm alone or in conjunction with a wall can be used.
- Acoustical barrier materials include:
- 4″ thick poured in place or pre-cast concrete panels,
- 6″ thick CMU wall,
- 1-½” thick board and batten,
- tongue and groove wood on one side of post,
- cementitious wood panels.
- prefabricated metal panels consisting of a solid metal barrier on one side and perforated metal on the side of the noise source with fiberglass in the air space. An independent structure is required.
- PVC barriers are similar to metal but lighter weight
- Loaded vinyl can be used as an exterior or interior barrier. It is flexible and can be hung on a cable so that it can easily move.
- Acoustic cement blocks have absorption inside and openings on the noise source side of the wall. Acoustical absorption can be applied to a block wall to prevent noise from reflecting back to the noise source and back over the wall.
Noise Engineers provides information and resources to help people address acoustical issues. In these episodes my goal is to provide resources, inexpensive tools, rules of thumb when dealing with acoustical issues. I would like to explain basic acoustic principles and answer any questions. I will describe actual projects to make this as practical as possible.