If I recall correctly the maximum Noise Reduction Rating (NRR) for earplugs and earmuffs is around 30db. You can combine the two for a slight increase in hearing protection but you still hit a limit because of bone vibration.
Is there PPE out there to go even further beyond this? Where would it be commonly used?
I think we need to define “hearing protection”, and how far your willing to go
For example this is probably less than practical.
It should be noted that active noise canceling doesn’t actually protect your ears. It’s just pumping more noise into them (noise that happened to be exactly opposite in phase, but the pressure is still there.)
Wouldn’t out of phase noise also cancel the pressure? The amplitudes combine to zero.
Yes.
Nope.
So what you hear as frequency is the variation of pressure- hi-low-hi-low-hi-low, right?
We tend to visualize it as a line going up and down, etc, but that’s just a conceptual aid.
To “cancel” noise, it plays a tone whose high and low pressure is out of phase but otherwise identical. So instead of hi-low-hi-low, it plays low-hi-low-hi noise, and you don’t “hear” it.
Great for tuning out the noise of a jet engine, and the loser who keeps trying to talk to you while you’re stuck in a tin can with a bunch of other sardines for 10+hours.
But that pressure is still there pushing against your eardrum, and no matter how good the pick up and driver is for the ANC, it’s never going to perfectly match noise anyhow.
There’s a reason most ANC ear cans are closed back- the passive noise isolation reduces the amount of work they have to do.
I believe, you’ve got some big misunderstanding in that. The wave is the variation in pressure. It doesn’t exert pressure beyond that. There is general air pressure, but that is always there, whether you’ve got a wave going or not.
Maybe it helps you understand it logically to think of how a speaker membrane moves. It does this motion:
| ) | ( | ) ...So, when it bulges to the right, it pushes air molecules closer together, which locally increases pressure on the right and continues to travel to the right, because the molecules push each other.
Then the membrane bulges to the left, which locally reduces pressure on the right and continues to travel to the right, because the molecules make room for each other, so the general air pressure causes air molecules to fill that room back in.
Both of those travel at the same speed, so they reach your eardrum, which is just another membrane and therefore does the same motion that the speaker membrane did.
So, a speaker is like a Newton’s Cradle, it doesn’t actually cause the molecules on the way to traverse across the room, like a fan would.
This may only be within the range of human hearing, and you can and do still suffer damage from excessive amplitude by frequencies above and below what is human detectable. ANC is not a protective technology for this reason, it is a quality of life technology.
So what you’re telling me is, i should really be wearing hearing protection when i go underwater? All that pressure must be wreaking havoc on my hearing.
Active noise cancelling does reduce the actual sound pressure (that’s the only way volume can be reduced). See for example: https://en.wikipedia.org/wiki/Hearing_protection_device#Electronic_hearing_protection_devices.
You understand that all of those devices have passive noise isolation, right?
What the electronics are doing is actually playing back noises that don’t cross certain thresholds. (Like people talking.) so you can “hear” them, but really it’s the speaker drivers you hear. The best will also filter out background noise, but the protection comes from the passive protection.
(Which is again different from acoustic filters, which basically create a chamber that alters the noise wave forms to passively attenuate things that are too loud.)
Hmm, I was under the understanding that it actually cancels out the pressure by creating a wave exactly 90 degrees off from the initial wave, creating reverse pressure and canceling the sound….
Not sure?
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Oops yep. You’re right
It pumps noise at other noise. All that noise literally cancels out. There’s literally no sound.
I doubt that, mate.
The thing is that it needs to be literally perfect polarization flipping to protect you. ANC as we know isn’t perfect; it doesn’t perfectly cancel sound and create absolute silence. You’re still potentially vulnerable to high SPL
Show me electronic ear pro that doesn’t have passive noise reduction.
I’ll wait.
The vast majority are adding ambient low-level noise back in rather than removing loud noises with active noise cancellation.
The electronics are similar if not identical, mind, but there’s a reason active noise cancellation in things like the Bose headphones don’t get an NRR or SNR test done. Because they’re not ear pro
It’s because active noise cancelling is bad at cancelling sudden sounds, so many types of noise people want to protect against (gunshots, metal clanging at a construction site) would be poorly attenuated by current active noise cancellation technology. This is a not really a physics issue, just an active noise cancellation technology issue. Fundamentally active noise cancellation can and does reduce sound pressure, because the speaker basically “pushes against” the incoming pressure waves to flatten them out.
Your example made me wonder how effective coating yourself in sound padding tiles to the point you resemble a lychee fruit would be.