Noise Curtains

by dB Engineering

Noise from punch press area reduced by over 10 dBA with curtain system.

This manufacturer met OSHA noise standards by enclosing its punch presses with an L-shaped system of acoustical curtains hung from overhead tracks.

Noise is a fact of life in plants where industrial machinery is operated.  In most cases, there is no way to quiet the machinery itself.  The best solution is usually to isolate the machinery so that its noise does not disturb workers in other areas of the plant.

Five punch presses, ranging in size from 75 tons to 250 tons, operate in this area, punching out metal parts for motorcycle caliper brakes.  The company wanted to find a way to shield its assembly workers from the noise generated by the punch presses.  A task force was formed to study the noise problem and develop a solution.  They measured the noise near the press area and found that it averaged 108 dB and reached as high as 112 dB with the noisiest combination of equipment running.

The acoustical curtains block and absorb noise from the presses, reducing noise levels in the plant from 108 dB to about 90 dB.

At first they tried enclosing the individual presses.  The barriers that they chose reduced the noise by about 5 dB but created problems for the press operators.  Within the enclosures, there was very little room to move around and not enough access to get stock in and out.   They concluded that individual enclosures were not practical because of the size of the press area.

At this point, the task force decided to enclose the entire press area.  Because of the close quarters and need for easy access, they decided against installing a permanent barrier wall.

Several of the curtain panels have built in windows to allow visual contact between workers inside and outside the enclosures.

By making use of the two existing building walls, the manufacturer was able to enclose the 83-foot by 43-foot press area with an L-shaped curtain system.  Seventeen curtains that measure 16 feet, 4 inches high are hung from each of two parallel tracks suspended from the ceiling.   The tracks are close enough together that the curtains can be attached to one another with Velcro® to form a solid noise barrier.  The Velcro® runs along the edges of the curtains in solid strips on the lower half and intermittent strips on the upper half.  This arrangement makes it easy to pull the curtains apart so that they can be moved out of the way.

The BBC-13-2 curtains are a heavy-duty construction designed for industrial environments.  They contain a 2-inch-thick layer of fiberglass sewn to a reinforced vinyl barrier.  The fiberglass absorbs noise, reducing the noise levels both inside and outside the enclosed area.  The vinyl barrier blocks noise to contain it within the press area.

When closed, the curtains do not form a completely solid barrier.  There is a small open area at the top where the tracks are suspended from the ceiling and at the bottom to make it easier to sweep the floor.

Even with the gaps, the curtain system has improved the noise situation considerably.   The noise has been reduced from 108 dB to 90 dB.

 

Table showing how the human ear perceives noise reduction.

Decibel Reduction Reduction Experienced by Ear
2 15%
4 23%
6 38%
8 48%
10 56%
12 63%
14 68%
16 75%
18 77%
20 81%