More on Shop Noise

Q:

David Heim’s article (FWW #189) on shop noise gives figures on noise levels for various tools and noise reduction by several types of earplugs and muffs. How do I determine the noise level of two tools running together? And what is the noise reduction of earplugs and muffs worn together?

John Rennie, Knoxville, TN

A:

According to Les Blomberg, director of the Noise Pollution Clearinghouse, if one machine is at least 10 decibels louder, or twice as loud as another (decibels are on an exponential scale), then the noisier machine sets the resulting level. If the machines are about equally loud, then their combined sound level is a bit greater than the louder one. For example, two machines that each generate roughly 90 db. of sound produce 93 db. together, the equivalent of a 30% increase.

Bear in mind that the louder the sound, the less time you safely can be exposed to it without protection. As for combining hearing protectors, research indicates that the practice would serve little or no purpose for woodworkers. Earplugs with muffs, for instance, are only marginally superior to plugs or muffs alone.

Photo: Steve Scott

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