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?
In: Physics
It’s easiest to think of dB as a RELATIVE measurement. It tells you how much more or less intense (louder) something is compared to something else. So when people give hearing protection a NRR of “30 dB” its saying it’ll make the noise 30 dB less intense. Less intense relative to *what* you may ask? Relative to the noise youre talking about. So if it’s a jet engine taking off (around 140 dB) it’ll reduce it to 110 dB.
But then you might ask “well, if dB is only a measure of increase or decrease in intensity, then what does it mean when someone says a jet engine is 140 dB at takeoff??? 140 dB relative to WHAT?!?!?”. When people talking about noise volumes in term of dB, that is STILL not an absolute measurement; it uses the dB scale so it must be a RELATIVE merasurement. But relative to what? When we’re discussing hearing/volume, the reference level (i.e. 0 dB) is the baseline hearing perception curve. It’s basically the quietest noise the average human ear can detect. Technically, if anyone is listing the volume of a noise and using dB, it should likely be correctly listed as dBA (somedtime dB-A). This denotes that you’re using the “A-Weighting” reference curve as your baseline (this A-weighted curve is that “quietest noise humans can hear”). More info on A-weighting can be found here: [https://en.wikipedia.org/wiki/A-weighting](https://en.wikipedia.org/wiki/A-weighting)
So put it all together. The dB scale is a way to represent RELATIVE levels of intensity (volume). When so hearing protection with an NRR of 30 dB means it lowers the nosie youre hearing by 30 dB. And when people talka bout the loudness of a thing in terms of dB, they usually mean dB-A, which shows how muhc louder something is than the quietest noise we can detect. So if someone says a jet engine is 140 dB-A loud, and you put on earmuffs with a 30 dB NRR, what that means is a jet engine is 140 dB louder than the quiestest noise you can hear, but the headphones reduce that to only 110 dB louder than the quietest noise you cna hear (140 dB – 130 dB = 110 dB).
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