Eli5: Why do earplugs max out at 33db of noise cancelling?

39 views
0

Eli5: Why do earplugs max out at 33db of noise cancelling?

In: 3288

It’s mostly because the decibel scale is logarithmic meaning each step is larger than the one before. For that specific scale 20db is 10 times louder than 10db. 30db is 10 times louder than 20, etc. So earplugs that cancel out 33db are over ten times more effective than the standard rated ones, and going up one more dB is even harder than 32-33.

Also the goal with earplugs is to take dangerous levels of sound down to safe levels (under 100 usually). 120db is using a jackhammer. 130 is standing right next to a jet engine on takeoff and will burst your eardrum.

There’s also the fact that you can only fit so much into your ear. Due to this, extremely loud workplaces/environments like gun ranges or aircraft carriers call for double-protection (plugs and over-ear

If you block 100% of noise going into the ear, you’ll still hear at about -40db (to -60db depending on frequency) from conduction through your skull/bones instead, so that sets the absolute lower limit for blocking noise.

Also db is log not linear, and -30db is already about 1000:1 (99.9%) blocking so that is already pretty amazing.

Material limitations

Your ear canal is only a certain length and width, and the material that fits in there is all that’s doing the work of stopping the sound. So soon enough the material used in such a small quantity is no longer able to dampen or block the sound energy

Ear plugs + ear defenders combo work because the ear canal is blocked, and then around that sealed quite well to the side of your head is essentially a small room of extra sound deadening material. You could keep stacking it just building more and more thickness of sound insulation around your head but eventually it’s going to get too heavy to carry or block your view. You can also build dampening around the thing making the noise in some scenarios, or put yourself in a sealed sound booth to observe it

I asked an Audioligist recently and he said anything more that that is useless because at a certain point the vibrations of your skull will still activate the bones in your ear. We were discussing highway wind noise on a motorcycle and I am heavily paraphrasing.

33dB of noise reduction is reducing the sound pressure by a factor of 1000. Any more requires you do more then block the ear, you’d need to surround your whole head in dampening foam.