if dB is logarithmic, how do 33 NRR ear plugs subtract 33dB from both 140dB and 85dB, and why are quiet sounds still audible?

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If the decibel scale is logarithmic, isn’t 33dB between 100 and 133 a much different amount in reality than 33dB is between 30dB & 63dB? So how can NRR 33 ear plugs reduce 60dB down to 30 while also reducing 140dB down to 110? Wouldn’t it only, say, reduce a 60dB noise by 33dB, but reduce a 140dB noise by a lesser amount? Does the ear plugs’ ability to reduce the sound increase with the volume?

If they really do subtract 33dB across the spectrum of dB ranges, then why are sub-33dB sounds still audible? Shouldn’t sounds around that range be effectively 0dB and inaudible?
If 60dB sounds are, say, 45dB with NRR33 earplugs, then are 100dB sounds actually 85 instead of 67? Or is there some mechanism enabling sounds that should be lowered to sub-40dB to be above 40, while also lowering 130dB to 100?

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11 Answers

Anonymous 0 Comments

Because as you say it’s logarithmic, and substraction in logarithm equals to linear division.

Most people can hear a little bit below 0dB. But, 33dB is rather quiet, whisper level. Your hearing is limited by the noise, rather than the ear sensitivity.

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