•
The mass requirement can be fulfilled using a support structure with one layer of 16 mm and one layer of 19 mm plywood sandwiched. When the panels are applied to both sides of a stud, 90 mm wide, they may be less massive, typically 13 mm to 16 mm plywood. Virtually any thickness of concrete or concrete masonry unit that is self-supporting will meet the mass requirement.
•
A stucco wall is very effective. Stucco is 22 mm thick
•
Precast concrete panels, treated to look like wood or brick and supported by I beam columns, are commercially available. The panels are held in place at their ends by the flange of the I beam.
•
Corrugated sheet metal panels sometimes are used to construct noise barriers.
•
Commercial barriers with both solid and sound-absorbing perforated skins are available, usually in 18 Ga. steel supported by steel columns.
•
Absorbing materials such as fiberglass can be incorporated behind the perforated panels to reduce barrier reflections. The fiberglass is encased in a plastic bag to protect it from the weather.
•
Noise barriers should be constructed so that there are no openings between the barrier and the ground. Openings allow the sound to pass under the barrier and can reduce its effectiveness. 34
Figure 22: Barrier Acoustics and treatments
