Noise Engineers recently installed acoustical treatment to a factory in Mexico. The installation was done to reduce worker noise exposure. In this blog we will discuss the noise problem, the treatment options, and the expected noise reduction.
The worker noise levels in this truck assembly plant are between 85 and 95 dBA. The primary noise sources are pneumatic hand tools throughout the plant.
The noise experienced by workers is a combinations of direct noise and reflected noise from the hand tools.
- The direct noise level is related directly to the distance from each tool where there is direct line-of-site to a worker.
- The reflected noise is a function of the size of the space and the acoustical absorption of the exposed surfaces.
We worked with our client to identify possible noise mitigation measures.
Replace the Noise Source
The most effective is to change the tools they use. There are many tool options: quieter pneumatic tools, hydraulic tools, DC (electric) tools. Tests showed that the noise from the tools could be reduced by over 10 dBA by using a very expensive alternative but by more than 5 dBA with a more reasonable replacement.
Reducing the noise levels of the noise source lowers the direct and reflected noise levels.
The second method that was explored was installing various acoustically absorptive barriers. This would block the direct noise from some of the sources to some of the plant and add some acoustical absorption. We proposed using barriers of NE Quilted MLV on metal frames. The frames can be taken apart to provide access throughout the facility.
The acoustical barrier will reduce the noise from the tools by more than 10 dBA when a tool or worker is near the barrier – but only the tools that are on the opposite side of the barrier from the worker. These barriers have little impact on the reverberant noise because they are not that large. Hence, the noise reduction provided by the barriers will be improved with the installation of acoustical treatment on the ceiling. The reflected noise level will be reduced making the barrier more effective.
A barrier with acoustical absorption was used so that the noise was not simply reflected to other parts of the facility.
Install Acoustical Absorption
The third option that was explored was to add acoustical absorption to the ceiling and to the walls. Almost all of the noise produced by a tool will eventually hit the ceiling. Treating the ceiling is out of the way of the operation.
Treating the walls at the level of the noise sources and workers ears was proposed in one area where the walls were exposed, parallel and close to the workers.
The predicted noise reduction varied depending on where tools were being used and for how long. Acoustical absorption on the ceiling and wall no impact on the direct noise for a working actively using a tool. We estimated that the noise exposure for a worker would be reduced by 4-6 dBA with the ceiling and wall treatments.
Noise Engineers provides information and resources to help people address acoustical issues. In these episodes my goal is to provide resources, inexpensive tools, rules of thumb when dealing with acoustical issues. I would like to explain basic acoustic principles and answer any questions. I will describe actual projects to make this as practical as possible.