Noise Curtains

by dB Engineering

Innovative curtain enclosure hushes granulator

Industrial Noise Curtain Enclosure

Curtain enclosure constructed of BBC-13-2" reduced noise levels by 10 to 15 dB(A). Inset Custom feed-flap protects operator during loading.

Like other manufacturers, this plastics producer has a certain amount of waste inherent in the making of a product. But fortunately, they are able to recycle waste. Waste is loaded into a granulator which grinds the plastic into tiny pellets. Eventually these pellets are reused in a finished product.

The problem was that no employee wanted to go near the granulator. It was the loudest machine on the shop floor peaking at 110 dB(A).

Finally, the noisy granulator became too much for management to deal with. Complaints from shop employees became more frequent, waste piled up meaning that potential raw materials were being squandered and the threat of an insurance claim or an OSHA violation grew every day.

Something had to be done quickly.

Company management figured that the best way to overcome the problem was with some type of acoustical enclosure, either metal or one constructed from composite materials.

A metal enclosure would help reduce noise levels once the granulator was up and running, but the proposed design provided no protection for the operator when loading the machine. Another disadvantage of the metal enclosure is that access to the machinery would have been limited.

Applications engineers offered an enclosure design featuring their BBC-13-2" composite material, a combination sound absorber and noise barrier product. The composite is made up of a 1 lb/sq.ft. reinforced loaded vinyl noise barrier and 2" thick quilted fiberglass sound absorber. Typically, a 1" thick absorber is put on the interior of a reinforced barrier. But because of the extreme conditions in this case, the 2" thick material was utilized.

The BBC-13-2" composite gives overall noise protection comparable to the metal enclosure and because of our extensive fabricating capabilities, the enclosure could be customized to meet every specification of the plastics manufacturer.

A critical design feature that our engineers developed was a feed flap that gave the operator a substantial amount of protection when loading the granulator. Prior to the installation of the enclosure, the operator was subjected to 110 dB of noise at close range. Continuous loading of the granulator without hearing protection would have been disastrous. With the new enclosure featuring the feed flap, an operator no longer needs hearing protection.

The double curtain track and hardware design allows access at nearly any point in the enclosure.

Another key design feature is the ventilation system. Too often, the installation of a roof panel means sacrificing ventilation for enhanced acoustical performance. But a   curtain enclosure can incorporate intake and exhaust ventilation baffles without compromising acoustical performance.

v1n2dia1.gif (8596 bytes)The idea of "one-stop shopping" also appealed to the plastics manufacturer. Many noise control companies only sell the materials which comprise the enclosure. These companies leave it to the customer to find someone who can provide the structural framework for the enclosure and handle the installation. We have our own line of free-standing or suspended structural support systems, and an installation team. In fact, this enclosure was installed in just four hours.

Employee response to the enclosure has been tremendous. Loading and running the granulator is no longer the dreaded task it once was. Consequently, waste no longer piles up and materials are quickly recycled. The granulator is finally the productive machine management always hoped it would be.


Octave Band Center Frequencies (hz)

Location A 31 63 125 250 500 1k 2k 4k 8k
Before at Operator 110 80 82 96 99 102 104 109 96 90
After at Operator
(Feed hatch closed)
88 73 81 90 91 89 83 79 73 70


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%