Source-Path-Receiver Concept

A straightforward approach to solve a noise problem is to examine the problem in terms of its three basic elements: the source, the conveying medium and the receiver (see Figure C1). Unless a free field is present, both direct and reflected (reverberent) sound waves that reach the receiver must be carefully looked into. The most appropriate solution to a given noise problem requires alternation or modification of any, if or all of the three basic elements. For instance:

(a) to modify the source to reduce its noise output,

(b) to alter or control the transmission path and the environment so as to reduce noise level reaching the recipient,

(c) to provide the receiver with personal protective device.

The most appropriate solution is the one that can achieve the desired amount of noise reduction by using the lowest expenses and causing least inconvenience to the occupant activities.

Figure C1 Noise Control Procedures are Applied to Source, Path and Receiver

 

2.1 Control of Noise Source by Design

The source may be a single or multiple of mechanical devices that emit acoustical energy. Due consideration on acoustic matter during the design stage of the mechanical equipment will definitely minimize the noise problem. The improvement techniques include the following:

(a) reduction of impact forces,

(b) reduction of speed and pressure,

(c) reduction of frictional resistance,

(d) reduction of noise leakage, and,

(e) isolation of vibrating elements.

2.2 Noise Control in Transmission Path

The next line of defense is to set up devices in the transmission path to block or reduce the flow of sound energy before it reaches the receiver. This can be done in several ways:

(a) to absorb the sound along the path,

(b) to deflect the sound in some other directions by placing a reflecting barrier in its path,

(c) to contain the sound by placing the source inside a sound-insulating box or enclosure.

2.3 Protecting the Receiver

When physical exposure to intense noise fields is unavoidable and none of the measures mentioned above is practical, then measures must be taken to protect the receiver as a final resort. The following two techniques are commonly employed.

(a) Alter work schedule

In order to limit the amount of continuous exposure to high noise levels, it is preferable to schedule an intensive noisy operation for a short'. interval of time each day over a period of several days rather than a continuous 8-hour run for a day or two.

Inherently noisy operations, such as street repair, factory operation and aircraft traffic should be curtailed at night or early in morning.

 

(b) Ear Protection

Ear plugs and other ear protectors are commercially available. They may provide noise reductions ranging from 15 to 35 dB. It should be aware that protective ear devices do interfere with speech communication and can be hazardous when warning calls from a routine part of the operation.