Hearing Protection and NRR (Noise Reduction Rating)

For all hearing protection devices from ear plugs to ear muffs, there is a NRR (Noise Reduction Rating) score that informs consumers how much of a decrease in noise exposure to expect with use. For example, if an ear plug has a NRR score of 30, use of the device would be expected to reduce a 90 decibel sound by 30 decibels resulting in a noise exposure of 60 decibels.

If two hearing protection devices are used, an ear plug inside the ear canal followed by ear muffs over the ear, the ultimate noise exposure would be an additional 5 to 10 decibels greater than the higher rated NRR of the two devices.

How is NRR determined anyways? This single number rating is determined by the Environmental Protection Agency as specified under 40 CFR (Code of Federal Regulations) Part 211, Product Noise Labeling, Subpart B - Hearing Protective Devices. The raw data compiled from test subjects is than plugged into a formula which than produces the NRR:

Given that, there are MANY different types of hearing protection devices on the market. Regardless of style, most devices offer a NRR between 20-30. However, as a general rule, ear plugs typically offer a higher NRR than ear muffs. Among high NRR earplugs, disposables offer higher NRR than reusables. BUT... ear muffs typically block sound more consistently than ear plugs which require some degree of molding and fit for optimal effectiveness. Using both obviously is better than using just one.

Also, keep in mind that unless hearing protection devices are correctly fit and used properly, the attenuation suggested by NRR may not over-estimated. Indeed, lay-use of such devices without training typically result in sound attenuation far below what NRR may suggest.

The highest rated NRR disposable ear plugs are around 33:


The highest rated NRR ear muffs are around 30:

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Cure for Noise-Induced Hearing Loss?

Normally, when mammals (including humans) are exposed to very loud sounds, permanent hearing loss may result due to cochlear hair cell injury. However, an experimental drug code-named LY411575 was found to regenerate new hair cells by suppressing a protein called Notch.

In essence, this drug restored hearing to mice deafened by loud noise.

Listen to an explanation by Harvard researcher Dr. Edge in this video.

However, human trials are a very long way off… so prevention is still the best way to avoid permanent noise-induced hearing loss. Wear hearing protection whenever loud sounds may be present!

Reference:
Notch Inhibition Induces Cochlear Hair Cell Regeneration and Recovery of Hearing after Acoustic Trauma. Neuron Volume 77, Issue 1, 58-69, 9 January 2013

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Opera Music Improves Heart Transplant Survival

Sara Maines of The MaineStudio

Not kidding... This research was actually published in the Journal of Cardiothoracic Surgery in 2012. I should add that the research was done in mice rather than humans and won the 2013 Ig Prize in Medicine.

To quote from the abstract:

"recipients of a B6 cardiac graft that were exposed to opera music and Mozart had significantly prolonged allograft [transplant] survival... whereas those exposed to a single sound frequency (100, 500, 1000, 5000, 10,000, or 20,000 Hz) or Enya did not... Our findings indicate that exposure to opera music, such as La traviata, could affect such aspects of the peripheral immune response as generation of regulatory CD4+CD25+ cells and up-regulation of anti-inflammatory cytokines, resulting in prolonged allograft [transplant] survival. "

Wonder if this research can apply to other surgical healing and survival...

Reference:
Auditory stimulation of opera music induced prolongation of murine cardiac allograft survival and maintained generation of regulatory CD4+CD25+ cells. Journal of Cardiothoracic Surgery 2012, 7:26 doi:10.1186/1749-8090-7-26

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Teens (People) Who Listen to Music Loudly... A Possible Solution

Now parents may not like this, but I do have a possible solution to getting teenagers to turn the music volume down so not to damage their hearing... Get them noise-cancelling headphones.

As an occasional audiophile myself, I understand that when listening to music with headphones, you invariably HAVE to turn the music volume up in order to hear everything clearly, especially when listening to music in noisy environments. Such environments include city sounds while walking, airplane buzz when flying, and car engine/road drone while driving.

Test this out yourself next time you drive a car. First, listen to the car radio with the engine turned off. Note the volume.

Now, see how well you hear the music from the car radio when driving on the highway.

It's the main reason why one may constantly fiddle with the volume knob while driving. It's also why people have to raise their voice in order to be heard in a loud restaurant.

For teens and other people who are audiophiles, the only solution is to turn the music volume up in order to hear the music clearly... which can damage their hearing over time.

So what to do? One can listen to music only when the environment is silent, but that's not going to happen for music-loving individuals who want to hear it all the time.

The other solution is to get a nice pair of noise-cancelling headphones.

A good pair of NC headphones significantly reduces if not eliminates the buzz, drone, white noise of the environment which is a very common cause of requiring a volume increase.

Now, not all NC headphones are created equal. Bose NC headphones are perhaps the best but are pricey at around $300.

However, cheaper brands do not noise-cancel at all or do so poorly even if they are labelled as noise-cancelling.

Generally speaking, Bose is by far the best followed by Panasonic, Sony, and AKG. You can read a Pogue's New York Times review of different noise-cancelling headphones here.

So... perhaps you can make a deal with your teen or adult loved one to turn the music volume down to protect their ears by getting them a Bose NC headphones which come in headphones and earbud models. Available for purchase on Amazon.

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Cicadas Can Cause Permanent Hearing Loss!

Cicadas are pretty darn ugly... But beyond their ugliness and making cars look pretty messed up... the sound they make is not only irritating, but potentially harmful.

Sometime the end of this April 2013, billions of large flying insects called cicadas will make their appearance along with their characteristic stridorous noise. The male cicadas are the ones making this mating noise with "tymbal" soundmakers amplified by large resonance chambers found on body.

Occurring every 17 years, this year's swarm is known as Brood II and has not been seen since 1996. Expected to cover much of the East Coast, the buzz created by these insects can reach 90 decibels... about as loud as a jackhammer. If one is right next to your ear, the sound can reach 120 decibels are equivalent to sandblasting or a loud rock concert. [see noise chart]

At 90 decibels, possible hearing damage may occur if a human ear is exposed to this level noise for more than 8 hours a day. At 120 decibels, less than 15 minutes of exposure can induce possible permanent hearing loss.

So... keep a pair of ear plugs in your purse or pants pocket and use them if the sound starts to get too loud.... or too irritating.

Sources:
17 years in the making, this spring's cicada invasion generates early buzz. NBC News 4/10/13.

Cicada. Wikipedia

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Dr. Chang Quoted in Washington Post Regarding Hearing Damage from Noise

The Washington Post on April 8, 2013, published a story about how loud noises can lead to hearing loss, even in young teenagers.

Dr. Chang was liberally quoted throughout this informative article.

"...That’s according to Christopher Chang, an ear, nose and throat doctor at Fauquier ENT Consultants in Warrenton, who sees patients every day with hearing-related issues. “What he’s hearing is way too loud, because it’s concentrated directly into the ear itself,” he says of my son, adding that the anatomy of the ear magnifies sound as it travels through the ear canal." 

"And when someone turns the music up louder? Well, in short spurts, that’s okay. Loudness is only one part of the equation. How long you’re exposed to loud noises also affects your risk. “The biggest concern is that teens and 20-somethings are using music players so regularly,” Chang says. 

"Cheap earplugs that you can buy at the drugstore offer some protection, Chang says. In addition, there are specialized ear plugs, such as ones for hunters that amplify low-level sounds and block out gunshots. Musicians’ earplugs reduce noise with higher fidelity than the muffling effect that regular plugs have: You want to hear the music that you and your orchestra mates are playing, after all."

Read the entire article here.

Source:
Hearing loss may be caused by cities’ noises and music that’s played too loud. Washington Post 4/8/2013.

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Hearing and Understanding ONE Voice Among Many Sounds

Have you ever wondered how is it that a normal hearing human being can hear and understand one person talking in an environment where there are many other people talking just as loudly be it a restaurant, conference, county fair, etc?

How is it that you can hear and understand one particular person over another, even if they are both talking equally loud?

Researchers are just beginning to understand how a human does it... Before explaining, lets use an analogy.

In the past, I used the analogy of an old antenna based radio to explain how human hearing works... A given antenna radio has a volume knob that one can adjust up or down (as would occur with a hearing aid) as well as antenna reception which allows one to get a clear signal vs one full of static.

The ear is like the volume knob and the brain is the antenna... As such, if the reception is bad and there's a lot of background static, a person will have a hard time understanding what is being said on the radio... regardless of whether the volume knob is turned up all the way or not.

Similarly, if the brain is not filtering out the background noise to isolate the sound or person you want to hear and understand, you will have a hard time understanding what is being said.

While the ear indiscriminately hears everything, I've always just stated "the brain" acts to filter out the background noise you don't want to hear, but nobody really understood how, until recently...

Researchers in New York determined that there are different regions of the brain that perform this sound filtration that is completely separate from the auditory cortex (part of the brain that "hears" sounds transmitted from the ear).

Furthermore, the brain areas responding only to the selected voice constantly fine-tunes the reception to allow further improvement in comprehension over time... just like fiddling with an antenna to get as clear a signal on a radio station.

If the brain is not able to properly focus and filter the sound, the individual will have a hard time understanding conversation in a noisy environment, regardless of whether the person has normal hearing or not (for example, in patients with ADHD).

Of course, if hearing loss is also present along with an unfocused brain, it just makes it that much harder (for example, in the elderly who not only have hearing loss, but also decrease in brain function as well).

On the opposite extreme are people who make their living focusing on a specific sound among many sounds and have much greater ease in understanding people talking in a noisy environment. Take professional musicians in an orchestra who excel at hearing a single instrument during a Beethoven orchestral performance.

Source:
Hear That? In A Din Of Voices, Our Brains Can Tune Into One. NPR 3/6/13

Reference:
Mechanisms Underlying Selective Neuronal Tracking of Attended Speech at a “Cocktail Party”. Neuron, Volume 77, Issue 5, 980-991, 6 March 2013

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Noise Hyper-Sensitivity in Kids

Although we mainly see kids for hearing loss due to fluid in the ears, chronic ear infections, or eustachian tube dysfunction, every so often, a child will show up with the exact opposite problem.

The child hears just fine, but suffers from noise hypersensitivity, also known as auditory hypersensitivity. Such children are overwhelmed from everyday noises whether doorbells, sirens, key clanking, etc; typically high-pitched sounds. The hands will go over the ears in an attempt to dampen the sound and may even become tearful.

This phenomenon is not uncommon in kids with developmental delays, autism, central auditory processing disorders (CAPD), Down's syndrome, etc. But "normal" kids may suffer from this condition as well.

Before going into treatment, one first needs to understand how sound is perceived first.

Human hearing is a complex listening device composed of not just the ability to "hear" the sound, but also to "comprehend" the sound. Disorders like CAPD is analogous to dyslexia where the patient can "hear" sounds perfectly normally, but has trouble understanding what they hear.

As a child develops, the auditory neural pathways in the brain that govern the comprehension of sounds are either reinforced or dampened down with time. For example, auditory neural pathways that allow for speech comprehension are reinforced whereas neural pathways perceiving background noises and other random sounds are dampened with time.

In auditory hypersensitivity, for whatever reason, the auditory neural pathways governing the perception of certain miscellaneous noise like sirens or doorbell are reinforced causing the perception of the sound to be more significant and tremendous than it should be. In a normal child without sensitivity, such pathways are suppressed.

To use an analogy, consider the auditory neural pathway like the road system in the United States. Over time, certain roads like the interstate highway is "reinforced" leading to more drivers using such streets to get from point A to point B far more quickly than if they used local roads. Problems occur if for some reason, cars avoid the highways and local roads are taken preferentially leading to traffic jams and irate drivers.

Auditory hypersensitivity is kind of like that... local roads being "reinforced" when it should be suppressed.

So what can be done to treat this frustrating condition?

In essence, therapy is geared towards reinforcing good auditory neural pathways and suppressing the bad ones that lead to noise hypersensitivity.

Such therapy programs include listening to special music and ear training exercises. One such program is "The Listening Program".

But one thing is clear... keeping someone with noise sensitivity in silence is the worst thing that can be done. It just reinforces the bad pathways!

Of course, there are other causes of noise sensitivity:

1) Migraines (children may not exhibit the classic head pain, but they still can suffer from noise sensitivity)
2) Cochlear hydrops (if associated with hearing loss, tinnitus, sound distortion)

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Katie Couric Gets a Hearing Test

On July 10, 2012, Katie Couric reported on a personal story during which she obtained a hearing test.

In a modern society like the United States, there are many sources for hearing loss with our alarms, lawn-mowers, and loud music.

As the article correctly pointed out, damage due to loud noises is due to two factors: loudness and duration.

The louder something is, the shorter time of exposure before hearing damage can occur. The quieter something is, the longer a person can listen before suffering noise-induced hearing loss.

Otherwise, hearing aids may be in your future... even if you are in your 20s or 30s!

Source:
Am I Going Deaf? Yahoo News 7/10/12

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Noise Charts as It Relates to Hearing Damage

Fun hearing facts collected from a variety of sources...

Environmental Noise
Weakest sound heard	0dB
Whisper Quiet Library at 6'	30dB
Normal conversation at 3'	60-65dB
Telephone dial tone	80dB
City Traffic (inside car)	85dB
Train whistle at 500', Truck Traffic	90dB
Jackhammer at 50'	95dB
Subway train at 200'	95dB
Level at which sustained exposure may result in hearing loss	90 - 95dB
Hand Drill	98dB
Power mower at 3'	107dB
Snowmobile, Motorcycle	100dB
Power saw at 3'	110dB
Sandblasting, Loud Rock Concert	115dB
Pain begins	125dB
Pneumatic riveter at 4'	125dB
Even short term exposure can cause permanent damage - Loudest recommended exposure WITH hearing protection	140dB
Jet engine at 100'	140dB
12 Gauge Shotgun Blast	165dB
Death of hearing tissue	180dB
Loudest sound possible	194dB

OSHA Daily Permissible Noise Level Exposure
Hours per day	Sound level
8	90dB
6	92dB
4	95dB
3	97dB
2	100dB
1.5	102dB
1	105dB
.5	110dB
.25 or less	115dB

Perceptions of Increases in Decibel Level
Imperceptible Change	1dB
Barely Perceptible Change	3dB
Clearly Noticeable Change	5dB
About Twice as Loud	10dB
About Four Times as Loud	20dB

Sound Levels Found in Music
Normal piano practice	60 -70dB
Fortissimo Singer, 3'	70dB
Chamber music, small auditorium	75 - 85dB
Piano Fortissimo	84 - 103dB
Violin	82 - 92dB
Cello	85 -111dB
Oboe	95-112dB
Flute	92 -103dB
Piccolo	90 -106dB
Clarinet	85 - 114dB
French horn	90 - 106dB
Trombone	85 - 114dB
Tympani and bass drum	106dB
Walkman on 5/10	94dB
Symphonic music peak	120 - 137dB
Amplifier, rock, 4-6'	120dB
Rock music peak	150dB

Sources:
The National Institute for Occupational Safety and Health (NIOSH)

Binge Listening: Is exposure to leisure noise causing hearing loss in young Australians? [pdf] – Australian Hearing, National Acoustic Laboratories

Occupational Noise Exposure. OSHA




   

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Human Ear Contains a Built-In "Ear Plug"

According to one Australian researcher, by just chewing a gum or singing/talking loudly, one could be protecting your ears from noise-induced hearing damage. How???

It is not common knowledge that the human ear contains two muscles that attach to the middle ear bones called the stapedius and tensor tympani muscles.

The middle ear bones, composed of the malleus, incus, and stapes, are what transmits sounds from the eardrum to the cochlea which allows a person to hear. The stapedius muscle attaches to the stapes and the tensor tympani to the malleus.

If something prevents the middle ear bones from vibrating, that effectively dampens the sound transmission from the eardrum to the cochlea... just like an ear plug or a bad case or earwax dampens sound transmitted through the ear canal to the eardrum.

SO... if the middle ear muscles tighten which are attached to the middle ear bones preventing them from vibrating, less sound is transmitted to the cochlea... just like an ear plug, except it is built-in.

Just how effectively does this reduce sound?

According to the researcher who has been studying this phenomenon, by about 30 decibels (or 1000x fainter).

That's about the same as foam earplugs!

How does one "activate" the middle ear muscle contraction?

By chewing a gum or singing/talking loudly!

Some individuals can sense this contraction if they close their eyes and try to "pull the muscles around the ears together"... a fluttering sensation inside the ear may be heard/felt which is the contraction of the middle ear muscles. In rare patients, this contraction may occur involuntarily and continuously.

SO... if you happen to have forgotten your ear plugs and are attending a very loud rock concert, chew gum and/or sing along with the band loudly! This may actually protect your hearing!

Of course, it's better to wear hearing protection, or better yet, avoid such circumstances altogether.

Read more about this here.

Reference:
How do middle ear muscles protect the cochlea? Reconsideration of the intralabyrinthine pressure theory. Journal of Hearing Science 2011; 1(2): RA 9 - 23

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