[Staff note: The original poster asked the Maker Forums community for advice on materials to add to earmuffs to increase their noise attenuation. He has now requested that all his content be deleted from Maker Forums.]
This is one reason why aviation ear protection is different. It is tuned for lower frequencies. Passive attenuation of low frequencies requires mass. ANR tuned for lower frequencies and/or mass are what you need.
I’ve seen very thick noise damping rubbery sheets of something used in the walls of a friend’s home theater, but I don’t know what it’s called, where you would find it, or whether it would work.
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All I know is I really wish I took it More seriously in my youth. years of loud punk rock music when I was young, followed by 20 years in factories and manufacturing plants have done my hearing in. Nothing like the constant ringing of tinnitus to remind you that you were stupid when you were younger.
When I worked at the foundry we had to have yearly hearing checks, and after the fourth straight year of appreciable hearing loss I decided I wasn’t long for that world. The back room was a double hearing protection area, you had to have earplugs in with high quality earmuffs over the top. One of those areas that’s so loud that your pants vibrate against your legs.
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I’m now wondering about an elastomer between the outer cup and an inner layer. It would be interesting to compare attenuation over a frequency sweep with two layers of plastic separated by an elastomer with an outer plastic layer separated from an inner tin (soft and not dangerous like lead) layer by an elastomer.
Elastomeric foam is often used in aviation headsets; a solid elastomer might have stronger low-frequency attenuation. You could experiment with elastomeric caulk for this purpose; in the US this includes products like 3M marine adhesive sealant 5200 and I expect similar products are available worldwide. I believe that the best headsets for low-frequency attenuation use gel ear seals.
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Normal engine RPM in a piston plane is 2200-2800RPM, and the more powerful planes with louder engines are in the low end of that range because they swing a longer propeller, and the speed of the propeller is limited by the speed of sound at the tip of the propeller. Most planes don’t have any gear reduction because of the weight of the gear reduction. 2200RPM is 36Hz.
General aviation headsets are tuned to reduce engine and propeller noise with active noise cancellation.
Sure, that has nothing to do with bone conduction; can’t help you there. But they really are tuned for low frequencies.
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