The Wall - Warehouse Blog

Series: Noise Control 101

Posted on: May 28th, 2013 by joreilly No Comments

Noise Source Modification Randall Manufacturing Noise Curtain

Part 4:  Noise Controls – Source Modification

A noise problem has three parts:  a source; a path; the receiver (employee). Intervention at any point in the path from the source to the receiver can reduce employee exposure to noise. Noise produced by a source travels outward in all directions. If walls, floors, and ceiling are hard surfaces, they will reflect the noise back into the room. This is called reverberant noise. Direct noise is that which travels by a straight path from the source to the receiver. The total noise in an area is the sum of the direct and reverberant noise.

Source Modification: This consists of a broad range of options that reduce the noise produced by a noise source.

Path Modification: This consists of using barriers or absorptive materials to reduce the amount of noise transmitted from the source to the receiver. Some types of path modification are:

  • Enclosures: The enclosure wall should be of a hard nonpareil material which prevents the direct transmission of sound energy. Lining the enclosure with a sound absorptive material will reduce the buildup of reverberant energy. An enclosure may be constructed around a source, or a noisy area can be partitioned off. Enclosures may also be provided around the work station to isolate the employee from the noise sources.
  • Shields/Barriers: Barriers and shields are placed between the source and the receiver to reduce direct noise. This is an effective control for high frequency noise, but it is ineffective with low frequency noise. Most effective are high barriers that are very close to the source or receiver.
  • Room Absorption: Small reductions in noise can be achieved by adding sound absorptive materials to hard reflective walls, floors, and ceilings. The objective of this type of control is to reduce reverberant noise. The material thickness and composition, method of mounting, and sound frequency all affect the amount of noise absorbed.


Source:  Berger, E.H. Noise and Hearing Conservation Manual. Akron, Ohio: American Industrial Hygiene Association, 1988.

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