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I keep looking for better ways of protecting my hearing when shooting, and it looks like doubling up (where you wear both plugs and muffs) is recommended for indoor shooting (centerfire gunshots range from 160-170 decibels).

However, if you look at the OSHA recommendations, one will notice that they say that doing so only adds,

Note: 5 dB can be added to the NRR of the most protective device when using both earplugs and muffs.

Given that earplugs often have a NRR of 32 decibels and muffs 22-28 decibels, why is doubling up not more effective?

Wouldn't the noise be reduced by 22 decibels by the muffs and then 32 by the plugs instead of just 5 more decibels?

  • No. See audiologyonline.com/articles/… – topshot Dec 10 '18 at 17:23
  • @topshot Are you going to make that an answer, or would you care if I self answer from that article? – Reinstate Monica Dec 10 '18 at 17:25
  • Feel free to self answer – topshot Dec 10 '18 at 17:37
  • Perhaps you already know, but since decibels work on a logarithmic scale, a 5 dB reduction is still nothing to sneeze at! That’s still a roughly 70% reduction in volume. – Sebastiaan van den Broek Dec 11 '18 at 6:01
  • @SebastiaanvandenBroek depends what you mean by volume :) The sound intensity drops by 70%, but the sound pressure would only drop by less than 50% and the loudness would change by even less. With OSHA, a 5 dB reduction, roughly doubles the time you can be exposed. – StrongBad Dec 11 '18 at 12:51
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As in the article linked by @topshot, it is because of two factors,

  1. Sound is being conducted by your bones around the hearing the protection.

  2. They don't act as two separate devices.

The principal reason is the bone-conduction (BC) limits to attenuation, which are also illustrated in Figure 1. The BC limits represent sound that effectively flanks or bypasses the HPD to directly stimulate the middle and inner ears of the wearer. Another limitation on the performance of dual protection is that the plug and muff interact mechanically with each other, and thus do not behave as two completely independent attenuators.

Extra Protection: Wearing Earmuffs and Earplugs in Combination

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    Note that the article concludes: Thus in critical high-noise instances, where TWAs exceed 100 to 105 dBA, the use of dual hearing protection is warranted. so while you don't get great improvements at low frequencies and at high frequencies you hit the bone conduction limit, you should still wear double protection. This is especially true since researchers are only beginning to understand the causes and effects of hidden hearing loss. – StrongBad Dec 10 '18 at 20:49

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