Why is doubling up with plugs and muffs when shooting not more effective?
I keep looking for better ways of protecting my hearing when shooting, and it looks like wearing 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?
1 answer
As in the article linked by @topshot, it is because of two factors,
Sound is being conducted by your bones around the hearing the protection.
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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