Zak Smith
Member
He said "for the" not "to the"
Best Hearing Protection
- Thread starter tegemu
- Start date
- Status
32dB plugs + 20 db muff = 32 (higher of the two) + 5(for the lower of the two) = 37.
It's not intuitivly obvious until you see the freqency profiles for what plugs and muffs filter out. One filters low frequencies better and the other blocks highs. When you combine their curves it's about an additonal 5 dB across the board reduction in noise.
Sure startled me and a bunch of other safety geeks sitting in the room when we saw the graphs and heard the explanation.
It's not intuitivly obvious until you see the freqency profiles for what plugs and muffs filter out. One filters low frequencies better and the other blocks highs. When you combine their curves it's about an additonal 5 dB across the board reduction in noise.
Sure startled me and a bunch of other safety geeks sitting in the room when we saw the graphs and heard the explanation.
Last edited:
Steve 48
Member
When I was in the Army, we often lost our plugs in a firefight or just did not even bother putting them on.We were more interested in getting our butts as low as possible. I got used to just putting in my filters from my cigarretes when I smoked then. Worked better than nothing. I use foam ear plugs and muffs when I can now. I still have a "ring" in my ears even from 38 years ago. Steve 48
Zen21Tao
Member
There's always the ATF's form hearing protection. 
kirby
Member
That's better, but still a bit confusing.
32dB plugs + 21 dB muffs = 37dB.
32dBplugs + 30dB muffs = 37dB.
My intuition (yes, that's been wrong before) tells me that a 9dB different (30 muffs vs. 21 muffs) should make some difference. By themselves, they would be 8 times more protection.
Am I wrong? Is it just, above some level, the lower protection always adds approx 5dB?
Zak Smith
Member
Yep, you're wrong, and most Health and Safety professionals were too for a long time, or so it appears.
We were adding all the combined NRRs, 32+30 = 62. Then we were adding everything and subtracting 5, 32+30-5=57. Thanks to octive band analysis of hearing protection devices we're adding 5 dB to the higher of the two as a rule of thumb, 32+5=37.
It's all because muffs absorb some frequencies better than plugs and plugs absorb some different frequencies better than muffs. Therefore the two don't add up across all frequencies to amount to more than about 5 dB additional protection.
Of course you have to keep in mind that that 5 dB amounts to somewhat better than halving the power of the noise getting through the single set of protection (logrithmic) so it's nothing to sneeze at.
Thanks Zak. Those are 2 of my favorite sites.
kirby
Member
Thanks to both hso and Zak.
- Status
