Absorptive vs. Reflective

Noise barriers may be either classed as absorptive or reflective.  Reflective barriers are made of materials such as concrete, wood, or vinyl.  In certain situations such as single sided barriers and parallel barriers, reflective barriers can cause unwanted side affects or degration of barrier effectiveness.  See explanation and diagrams below.

Noise absorptive barriers such as Durisol can greatly reduce or eliminate the impact of noise reflection.

Noise absorption can be scientifically tested through an accredited test lab facility.  The accepted measure of noise absorption is the noise absorption coefficient (NRC).  A typical NRC for an absorptive barrier ranges from 0.6 to 0.9.

The diagrams below show problems that can be created by reflective barriers.

A reflective barrier on one side of the roadway can be result in some sound energy being reflected back across the roadway to unprotected residents on the opposite side.  See diagram below.

Sound refelctions between reflective parallel barriers may also significantly reduce barrier effectiveness due to multiple reflections which defract over individual barriers.  See diagram below.

Use of noise barriers with absorptive surfaces can cure problems with reflected noise such as those shown above.

The diagrams depicted above have been taken from the FHWA Highway Noise Barrier Design Handbook.