Apology in advance if this has been discussed - I honestly have not read all 57 replies … With that said, I admit I am a “double up” hearing protection guy at the range, but realize there is maybe not as much additional attenuation added as might appear on the surface.
I started writing a whole dissertation about this, but found this summary that says it a lot easier to understand:
"How does wearing dual hearing protectors change NRR?
When hearing protectors are worn in combination (i.e. earplugs AND earmuffs), rather than adding the two NRR numbers together, you simply add five more decibels of protection to the device with the higher NRR. For example, using 3M™ E-A-R™ Classic Earplugs (NRR 29) with 3M™ Peltor™ H7 Deluxe Earmuffs (NRR 27) would provide a Noise Reduction Rating of approximately 34 decibels.
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