Controlling Outside Noise

In certain situations, an outside space must be protected from the surrounding outside noise. Encapsulation, barriers, increased distance or masking the noise source are some possible solutions.

General rules of thumb for controlling outside noise:

• By doubling the distance from a noise source, the level is reduced by 6 dB, a clearly noticeable amount. The reduction will not be experienced to this extent with a line source, such as a railroad or freeway (the reduction is around 3 to
  4-1/2 dB).
• A barrier must block the line-of-sight between the source and the receiver in order to be effective.
• You will typically not need a barrier with a surface weight/density greater than four-pounds/square foot, as long as there are no openings in the wall.
• It is difficult to reduce the noise by more than 10 dB with a barrier wall.
• Noise barriers can be solid walls, berms or a combination of the two.
• The noise wall must be continuous with no openings to be effective. If air is going through the wall, so will sound.
• Vegetation, such as trees and bushes, provides very little, if any, noise reduction.
  

Case Study

Location: Cemetery

Area of concern: A column burial area with a meandering path

Additional information: This space needed to facilitate a solemn and contemplative setting while minimizing distractions from a nearby street. Originally, a concrete block wall was used, but the results were not sufficient.

Questions to ask client:

• Describe the problem.
• Describe the ambient noise conditions.
• Are there any existing barriers?
• What is the desired result?

Client feedback:

• The cemetery is next to a relatively busy road. The traffic noise is distracting to visitors who expect a quiet, intimate setting.
• Aside from the traffic noise, there are no other major noise sources in the area.
• A concrete block wall was used, but the results were not sufficient.
• The desired result is a relaxed, meditative atmosphere that is aesthetically consistent with the rest of the space.

Evaluation: Since it was not feasible to increase the barrier wall height, a sound masking system (that is typically used in an office environment) was implemented in this case. To blend in with the atmosphere, rock speakers that generated pink noise were placed along the meandering path. Water features served as additional atmosphere enhancers, and helped to make the masking system sound more natural. These fountains also eliminated hot and cold zones and created a consistent noise through the entire space. Water features alone would only work when a visitor was standing directly next to the water.

Additional comments: In many cases, the best outdoor solution is a barrier wall. Other solutions include encapsulating a noise source (such as an emergency generator) and adding distance between the receiver and the noise source.