No. 538 November 2009 

Acoustic Enclosure to Reduce Noise From 

Vibrating Screen Mechanism Housings
 

Objective 

To reduce operator exposure to noise from vibrating screens at coal preparation plants. 

Background 

Hearing loss is one of the most common occupational illnesses in the United States. In the U.S. mining industry, hearing loss is 2.5 to 3 times greater 

than what is expected for the average population that 

is not exposed to occupational noise. Furthermore, 

studies by the National Institute for Occupational 

Safety and Health (NIOSH) showed that by age 50, 

90% of coal miners have a hearing impairment 

versus only 10% of the population that is not exposed 

to occupational noise. A NIOSH cross-sectional survey of coal preparation plants showed that 43.5% of 

employees were overexposed to noise. The study also 

found that vibrating screens were one of the top five 

loudest types of equipment at these plants—as well 

as the most numerous—making them a key noise 

source to address. 

Approach 

A team of NIOSH researchers, in partnership with 

Conn-Weld Industries, Inc., conducted noise source 

identification studies on a Conn-Weld G-Master 1000 

dewatering vibrating screen. They determined that, 

above 1 kHz, the mechanism housings are the main 

noise sources. A common technique to control noise 

from a source to a receiver—in this case, the operator’s ear—is to block the noise from the source with 

an acoustic enclosure. NIOSH has developed such an 

enclosure to surround the mechanism housings, thereby reducing the noise that reaches the operator’s ear. 

The enclosure is a modular design with components that can be hand-carried and installed on any 

Conn-Weld G-Master 1000 vibrating screen, including retrofits. This design can also be modified to 

adapt to other sizes or types of vibrating screens. It 

consists of a steel frame (Figure 1), which provides a 

stiff structure, and panels that enclose the noise 

source.

 Figure 1.—Steel frame for the acoustic enclosure installed on a 

Conn-Weld G-Master 1000 vibrating screen. 

 The panels act as a barrier to block the noise 

from reaching the operator. A layer of acoustic foam 

lining the panels on the inside of the enclosure absorb 

a portion of the noise. In addition, the frame-andpanel design allows easy access to service ports on 

the mechanism housings or removal of a mechanism 

altogether, without disassembling the entire enclosure 

(Figures 2–3). 
 Figure 2.—Panels can be easily removed for mechanism 

housing maintenance. 

Figure 3.—Completed mechanism enclosure. 

Results 

Four different panel materials were tested with the 

steel enclosure frame. The best results were achieved 

with an enclosure made with damped steel panels. 

Laboratory testing in the NIOSH hemi-anechoic 

chamber showed that the enclosure with damped steel 

panels reduces the sound power transmitted by the 

vibrating screen by up to 2 dB(A), per ISO 3744. In 

the frequency range for which the enclosure was designed (1.0–10 kHz), the damped steel panels reduce 

levels by 4 dB (Figure 4) compared to the baseline 

configuration with constrained layer damping (CLD) 

treatments on the mechanism housings. 

55 

60 

65 

70 

75 

80 

85 

90 

95 

100 

105 

A-weighted Sound Power Level (dB)

100

125

160200250

315

4005006308001000125016002000250031504000500063008000

10000

Overall 

1-10 kHz

1/3-Octave-Band Center Frequency (Hz) 

 Figure 4.—Sound power level data show an improvement over 

the CLD configuration of up to 4 dB in the 1- to 10-kHz frequency 

range with a damped steel-paneled enclosure. 

Baseline 93.7 102.1

CLD w/ Enclosure 86.7 99.3

CLD 90.6 100.9

Overall  1 - 10 

kHz Case

For More Information 

For more information on the mechanism housing 

enclosure for vibrating screens to reduce noise exposure at coal preparation plants, contact M. Jenae Lowe 

(412-386-4076, MLowe@cdc.gov), Dave S. Yantek 

(412-386-4498, DYantek@cdc.gov), Lynn A. Alcorn 

(412-386-6732, LAlcorn@cdc.gov), Hugo E. Camargo 

(412-386-6158, HCamargo@cdc.gov), or the Health 

Communications Coordinator (OMSHR@cdc.gov), 

NIOSH Office of Mine Safety and Health Research, 

P.O. Box 18070, Pittsburgh, PA 15236-0070. 

To receive NIOSH documents or for more information 

about occupational safety and health topics, contact: 

1-800-CDC-INFO (1-800-232-4636), 1-888-232-6348 

(TTY), e-mail: cdcinfo@cdc.gov, or visit the NIOSH 

Web site at http://www.cdc.gov/niosh 

Mention of any company name or product does not 

constitute endorsement by the National Institute for 

Occupational Safety and Health. 

DHHS (NIOSH) Publication No. 2010–109