This post is about what amount of noise blocking you can expect from the best earplugs and earmuffs, and what you can do to push the boundaries.
Are you trying to sleep while the folks next door are having a party or concentrate while your coworkers are raving about their weekend?
Feeling tortured by the daily onslaught of chatter, rumbling, stomping, snoring, and screeching you might have asked yourself:
What earplugs or earmuffs block all sound?
If I only found these I would finally be relieved of that noise onslaught.
Unfortunately, earplugs or earmuffs that block out all noise don’t exist.
They cannot exist because of bone conduction: noise doesn’t only reach our cochlea via the ear, but also through the skull.
If you managed to shield your ears from all sound using the perfect earplugs, your hearing threshold would be significantly raised, but noise would still travel through your skull, your nostrils, and your mouth.
What if you shielded your complete head, using a “sound proof” helmet?
Indeed, such an experimental helmet has been tried in studies to block the obnoxiously loud noise that is created in MRI machines.
And for the middle frequencies the helmet exceeded anything ever achieved with earplugs or muffs by a margin. So yes, shielding your whole head could make a heck of a difference.
You still have some sound conducted through the rest of the body, so even the box around your head isn’t going to stop all noise, but we are getting closer.
Wearing such a helmet in a café or in bed would be ridiculous though.
Taking it a step further, just imagine everyone sitting in an open office in their “noise cancelling space suit,” having coffee infused via a tube?
What is bone conduction?
Normal hearing versus bone conduction
Sound reaches our inner ear via two main pathways:
The first one is air conduction, i.e., our normal hearing where sound waves are conducted through the ear canal to the ear drum and then via the three small bones (ossicles) in the middle ear into the cochlea in the inner ear.
The ear drum vibrates in response to sound and excites the ossicle chain (malleus, incus, and stapes are connected together to form a lever) in the middle ear. The stapes, the last of the three ossicles sends these vibrations into the liquid-filled cochlea where they are converted into nerve impulses.
Here is a great 3D-animation that shows how normal hearing actually works.
But sound doesn’t only reach the cochlea via air conduction. It also vibrates the skull. These skull vibrations reach the cochlea via various pathways.
This transmission of sound via the skull is called bone conduction. Bone conduction is much less sensitive (50-60 dB less for most frequencies) than air conduction.
But if we were to perfectly plug our ear canal and cover it with earmuffs, bone conduction would become the dominant pathway by which we hear.
Mind you, most of us never get to experience the maximum noise reduction that would be possible. This article includes background info and tips to get close.
To optimize the fitting of earplugs and understand what is beyond reach, let’s look a bit closer at the pathways of bone conduction.
Bone conduction via the ear canal wall is important for low frequency noise
Vibrations propagated through the skull also excite the ear canal wall. When our ear is unplugged, air conduction of sound is much stronger, so we can ignore this conduction via the ear canal wall.
But when the ear canal is occluded with earplugs, sound entering the ear canal via its wall becomes dominant for lower frequencies (below 1000 Hz). Because they cannot escape, low frequency sounds become amplified. This is called the occlusion effect.
To experience this, just plug your ears with your fingers while uttering the sounds “bee” or “boo.” Alternate between plugging your ears and keeping them open.
You can minimize and perhaps even eliminate the occlusion effect by inserting earplugs very deeply into the ear canal, almost to the point where they touch the ear drum. In hearing protector studies this is called “deep insertion.”
Studies indicate that most conduction into the ear canal is via the cartilaginous parts of the canal, so to optimize low-frequency noise reduction, earplugs should be inserted deep enough to reach into the bony part of the ear canal (shown in grey in the image above).
Bone conduction via the middle ear
A second path for bone conduction is into the middle ear. The ossicles have a resonance frequency of around 1700 Hz. Bone conducted sound also excites these little bones. It is assumed that for sound around the resonance frequency the middle ear pathway becomes dominant and limits how much noise reduction earplugs and earmuffs can provide. From hearing protector studies we can estimate the limit to be around 40 decibels at 2000 Hz. Compared to the 50 – 60 decibels possible reduction at other frequencies, this is a substantial dent.
Bone conduction directly into the cochlea
The third and most important pathway is direct stimulation of the cochlea via bone conducted sound. This is the dominant path for a large frequency range.
Unfortunately, both the middle ear and the cochlea are beyond the reach of earplugs and earmuffs. To reduce these pathways we would have to reduce vibrations to the skull by wearing a helmet or develop noise cancelling technology that could somehow cancel these vibrations.
What are the limits on earplugs and earmuffs imposed by bone conduction?
As mentioned earlier, with open ears the dominant hearing pathway is via the ear canal to the ear drum and then via the ossicles into the cochlea.
By how much can hearing protectors reduce the noise before bone conduction takes over?
Over the years, several studies have been done. In 2003, Elliott Berger and colleagues did an extensive review and conducted new experiments on the limits to sound attenuation; they used a combination of NRR-33 foam earplugs and an experimental earmuff that featured conventional noise isolation and additionally active noise cancelling for low frequencies.
The green line in the chart below shows the noise attenuation for this combination with noise cancelling (NC) switched on. Compared to the off condition, NC only improved the result at 125 Hz (by 3.3 dB).
Between 50 and 60 decibels were achieved, with a dent at 2000 Hz.
What I find remarkable is how much low-frequency noise reduction Berger’s combination actually achieved.
What’s more, except for the 125 Hz frequency band, it did not matter whether the earmuff’s noise cancelling was switched on or off.
The results of the above-mentioned study and other experiments indicate that bone conduction limits the attenuation of earplugs and earmuffs to between 50 and 60 decibels depending on the frequency.
The notch that appears at 2000 Hz indicates that for that frequency band the limit is about 40 decibels, the weakest attenuation across the whole frequency range. The experimental noise isolation helmet surpasses this limit, as can be seen in the chart.
You can find the 2000-Hz notch in laboratory test data for all high-performance earplugs and earmuffs. To illustrate this, I have included the lab attenuation data as published by manufacturers for a few earplugs and muffs in the chart above.
Current belief is that this notch is related to the resonance frequency of the ossicles (1600 – 1700 Hz). Bone conduction into the middle ear becomes dominant, limiting the maximum reduction to 40 dB at 2000 Hz.
In terms of hearing protection, this limits what amount of hearing protection earplugs and muffs can provide in the middle frequencies when extreme protection is required, such as when shooting firearms.
In addition, 2000 Hz is among the most important frequencies for speech intelligibility.
When you consider that normal speech overheard from a distance of 1.5 to 3 meters is between 50 and 55 dB, with peaks reaching 70 to 75 dB, it becomes clear that even the strongest earplugs and earmuffs cannot completely silence this noise.
The same applies to many everyday noise sources. Here is the noise spectrum in my favorite coffee shop just a few minutes ago:
What can you do for maximum noise reduction?
The earplug fit and in particular how deep you (can) insert your earplugs determines how close you can get to bone conduction limits for lower frequencies.
An earplug study by Berger from 2013 distinguished between partial insertion (15 – 20% in the ear canal), standard insertion (50 – 60%), and deep insertion (80 – 100%). Deep insertion was the maximum insertion a participant could tolerate before it became painful.
The attenuation from 125 to 500 Hz ranged from 38 to 45 dB for deep insertion with the 3M EAR Classic foam earplugs.
For standard insertion it was about 6 dB less and for partial insertion it was 18 – 20 dB less. (own estimate from the charts)
Note that these were cylindrical foam earplugs. When they used a tapered foam earplug, a partially inserted plug performed even worse.
When subjects fitted the earplugs themselves, they achieved a noise reduction that was comparable to partial insertion by an experienced experimenter.
This is not good: most people don’t get to experience the good low-frequency noise reduction that can be achieved with foam earplugs and often falsely assume that’s all there is.
For the low frequency range, the average earplug user is losing about 20 dB of protection with cylindrical earplugs (and even more with tapered ones). If you were listening to music this would be like a quadrupling of the volume.
On the other hand, in my own experience, too deeply inserted earplugs are not very comfortable for long-term use, but with good training and repetition, standard insertion should be achievable and comfortable.
Please check this post for how to insert foam earplugs.
Note: If you are getting a large occlusion effect when using foam earplugs, i.e., your voice or jaw movements seem to evoke a boomy bass, or you can hear your heart beat, this could be an indication that you have only partially inserted your earplugs.
What can you do to go beyond the limits of bone conduction for every day noise reduction?
Note: The following doesn’t apply to hearing protection, but rather to eliminating disturbing everyday noise.
During the day, I get distracted by chatter when I want to concentrate. At night, sudden noises startle me when I am about to fall asleep.
Unfortunately, office and coffee shop chatter, children crying on an airplane, loud snoring, and nightly party lovers all tend to be too loud for even the best earplugs or earmuffs to completely silence.
They do help a lot, but can we do more?
Current active noise cancelling is only superior for very low frequencies and only works for frequencies up to 1000 Hz. So that’s not going to work for chatter and crying either.
This leaves us with one fine tool: noise masking.
Speech is distracting, but a waterfall, even one that is twice as loud, not so much. This is because the waterfall produces fairly constant broadband noise. We tend to get used to it and have no problems concentrating.
The same applies when falling asleep. It is mostly the sudden noises (door slamming) or varying noises (snoring) that keep us from falling asleep or wake us up.
How to remove disturbing noise while studying or working in an office?
You first want to reduce the noise by as much as possible. For office noise and while studying, you could use noise blocking earmuffs with built-in headphones. Good noise cancelling headphones also work and are more comfortable, but also a lot more expensive.
Then you add a noise app and play white noise that has been adjusted to emphasize the frequency range you are trying to block. For human speech, this would mostly be from 1000 to 4000 Hz. Waterfall or heavy rain noise are also good.
With the combination of noise blocking earmuffs and noise masking, I can almost completely eliminate distracting everyday noise. For example, in the above post, I succeeded doing this in a busy shopping mall while they were holding a tombola.
How to cancel noise during sleep?
For eliminating noise during sleep, earmuffs are likely not going to be comfortable enough.
To take the sting out of moderate noise, a white noise machine on your nightstand might be all you need.
If you are facing loud noise when trying to fall asleep, you again need to block as much as possible first.
If you sleep mostly on the side, you need earplugs that are comfortable enough for sleeping. These will substantially reduce the noise.
But because they generally don’t reduce all frequencies by the same amount, you might find that suddenly certain noises stand out. It appears as if your hearing has been sensitized for certain noises.
Yes, these noises have also been reduced but less so than the general noise level.
To compensate for this, you can again use the white noise machine on your nightstand and adjust it so that it creates a pleasant, fairly constant noise background. With earplugs that provide a good fit, you can play the white noise machine quite loud actually before it becomes disturbing.
If this is not enough or you are driving away your bed partner, you could also wear sleep headphones on top of the earplugs (or even noise cancelling headphones if you are a back sleeper) and play white noise through the headphones.
That’s it for today. I very much enjoyed writing this post.
I hope it’ll help you to make your life a little quieter.
See the Notes Page for references.
- The Anatomy of the Ear, modified Blausen_0328_EarAnatomy.png, Blausen.com staff (2014), “Medical gallery of Blausen Medical 2014,” WikiJournal of Medicine 1 (2), DOI:10.15347/wjm/2014.010, used under Creative Commons Attribution 3.0 Unported.