HOW loud is too loud? Sounds thought to cause only temporary hearing loss have destroyed nerve cells in the ears of mice. If the finding translates to humans, the laws that determine the noises workers can be exposed to may need to change.
Such regulations focus on preventing the destruction of hair cells in the inner ear, which causes a jump in someone's hearing threshold. This threshold is "the lowest level of sound you can detect", says Sharon Kujawa of the Massachusetts Eye and Ear Infirmary in Boston. Now she and her colleagues have discovered that noises that aren't loud enough to affect hearing thresholds can still cause permanent damage to ear cells.
Noises that aren't loud enough to affect hearing thresholds can still cause permanent ear damage
For 2 hours, Kujawa's team exposed mice to a 100-decibel blare, roughly equivalent to a motorcycle engine or approaching subway train. Several tests indicated that this ruckus caused no long-lasting changes in hearing threshold. Under the gaze of a microscope, however, damage was seen to the part of hair cells that transmits sound via chemical interactions with nearby nerves. A year later, the damage had seemingly spread to nerves that transmit sound to the brain (Journal of Neuroscience, DOI: 10.1523/jneurosci.2845-09.2009).
In people, these changes wouldn't show up in hearing tests that measure thresholds, Kujawa says, as other nerves take up the slack. But such damage could explain more common hearing problems. "The primary complaints that we hear from people is not 'I can't hear soft things', it's 'I can't understand speech amid noise, I have great difficulty understanding unless the speaker is standing right in front of me'."
Neuroscientist Jean-Luc Puel at the University of Montpellier, France, says the implication is that "if you are exposed during infancy or teenage years, you will lose hearing sooner when you are old".
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Have your say
Are Mice Ears Comparable?
Wed Nov 11 22:06:02 GMT 2009 by Mike Davis
http://ps4-zone.com/
Are mice ears similar to human? Is there an animal that has comparable ear structure?
In a word, yes.
Mice are a well-established model for human hearing and hearing loss. Their range is different than ours; they detect higher pitched sounds than we do. But I believe that the strain of mice that the researchers used experiences hearing loss at similar levels of sound as humans (which varies from person to person).
Thanks for reading and for your question.
Ewen Callaway
Reporter
New Scientist
My girlfriend grew up on a farm and from a young age (around age 2 I think) she would accompany her parents on equipment such as tractors. They were not irresponsible and always made sure she was wearing ear protection. Now, in her 20s she struggles with understanding speech when there is other noise around. She recently had her ears tested which showed she has lower threshold in the 2000Hz to 8000Hz range than normal in one of her ears. We are not sure if it was because of her exposure at a young age to farm noise, however, this study would suggest that it very well may be.
A major part of speech intelligibility is the signal to noise ratio in the 2000Hz to 4000Hz range as this is the frequency range of consonant sounds. Vowel sounds are much lower in the 250Hz to 500Hz range.
Your ability to identify consonant sounds is key to speech intelligibility because there are many more consonants than there are vowels. Consider the words 'bad' 'dad' 'sad' 'mad' 'glad'; all those words would sound the same without the consonants.
Loud background noise masks those consonant sounds making speech intelligibility difficult; all you hear is mumble. Try watching TV with the fan on. You hear the speaking but you don't understand. You have turn up the TV (often until it sounds very loud) so that the sound level from the TV in the 2kHz to 4kHz range is sufficiently above the sound level from the fan in the same frequency range. For clear speech intelligibility the signal to noise ratio should be at least 16dB
I have issues making out people talking in a room - If im in a shop or somewhere where it echos my ears seem to become hypersensitive and instantly I can hear everything, but its all at the same volume (in my head...) - Its really weird and made me feel sick at first, these days im used to it.... wonder if its anything like that...
With this new information isn't the redesign of MP3 players essential? They should have a maximum limit and a automatic volume reduction if they have played too long too loud. A simple chip could be designed to moderate noise on MP3 players and be included by law. Until then a warning sign like for cigerrettes should be incleded in the design concerning the poetential impact. Some people have got rich by deafening the next generation and they should be held to account now data is becoming available.
You can't impose a mandatory volume control. That's ridiculous.
You can have warnings but that's as far as anyone can go before they trample on basic human rights of choice.
Yes, this points out the urgent need to increase taxation in order to insure that enough government inspectors are available to enforce mandatory volume control at rock concerts. Too many people have gotten rich by destroying the auditory health of the nation. This is a basic concern for the proper operation of the universal health care system.
We definitely need to.
People (generally) should be assumed to be idiots.
Is it not the role of the people who are better informed to help those who wouldn't know the implications?
The choice will come down to limiting Mp3 players, or educating the nation on the cilia embedded in the organ of corti.
And the prior is easier
Targeting MP3 players is alot sillier (or at least more difficult) that it first appears.
Say for example that the headphones that come with a particular mp3 player may produce 90db at a given output level. Aftermarket headphones will probably produce a range of responses from 80db or so up to 100db+.
Which means either you need to have an option to adjust said volume limiter (rendering it largely pointless) or destroy the market for many types of premium headphones.
Neither is a great outcome.
Many premium headphones can also be listened to at a much lower volume, due to the great clarity and/or noise cancelling abilities. Talk about a double-edged sword.
P.S. For anyone wondering why "premium" headphones are quieter, they generally have a much higher impedance (which requires more voltage to reach a given volume). In fact, many headphones already have trouble reaching good volumes on portable players, and require a "headphone amp" as well.
Why do you want to target MP3 players in particular? We've had close fitting headphones for decades now connected to home stereos which are just as capable of reaching similar sound levels, even through regular speaker systems. Since the goal there is to get realistic sound levels, by your reckoning we should also have "laws" for sound levels at concert halls, including symphonic orchestral works. I suppose we could make more "laws" to limit the maximum number of musicians in an orchestra and even force the redesign of some the instruments which produce "excessive" noise.
I could go on but really your suggestion of warning labels and new laws is absurd. In fact I think you'll find that most audio equipment already has some kind of warning about not exceeding certain sound levels. Would you have sound police lurking outside peoples' homes to arrest them when they turn up the volume control too high? The last thing we need is more govt. meddling in peoples' lives.
MP3 Players are often listened to by young people who will have little or no concept of the long term harm these will cause. In effect this is the evidence the 'health' lobby on hearing has needed to stamp down on this runaway industry of deafness. Headphones are metaphorically cigerettes for the hears and it is time to stub them out. This is crystal! They should be taxed and the tax be directed directly to further investigations into what damage these items are causing.
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