Friday, July 19, 2013

How loud is too loud?

Please see the updated post July 2017

Mammals are born with lots of very tiny and delicate hair cells in their inner ears. These cells help to amplify sound.
Exposure to loud noises over our life time damages these cells. ( the high frequencies are the first to go) 
Your baby's ears are more sensitive than those of an adult. Not only do they have thinner skulls, but they also have a full complement of these little hair cells, so sounds will have full amplification. 

Your baby's hearing actually starts to develop between 24-28 weeks of gestational age. It is thought that the noises they hear are slightly muffled (imagine what it feels like when you are under an inch or so of water)
They can certainly hear well enough that they seem to recognize the voices of those who have been talking to them while they were in utero

So yes, we need to make sure that we protect our baby's hearing, but the fact is that all of us need to pay attention to loud noises that can lead to hearing loss.

We pay attention to two different factors

The frequency is measured on the Hertz scale.
The lower tones are the lowest numbers
People with the sharpest hearing may be able to hear frequencies ranging from sounds with tones as low as 20 hertz and as high as 20,000 Hertz
A sound higher that 20,000 is known as ultrasonic
Some animals, dogs for instance, can hear much higher frequencies than humans
Human speech tends to fall between 1000-5000

Because as we get older many of us lose the ability to hear the higher frequencies, some brilliant marketers have taken advantage of this. 
There are now actually ring tones out there for teens only.  Most adults over the age of 20 have no idea when they ring. 

The second aspect of sound that is relevant is the loudness
Sounds are measured in units called decibels.

To give you an idea of how loud various sounds are, take a look at the following list
30    Whisper
            60 normal conversation
      80 Telephone dial tone
      85 traffic noises from inside a car
      90 Bart train ( average...actual sounds range from 73-99) 
      107 power mower
     110 stereo headset
     125 sand blasting or rock concert
     140 gun shot

The longer the exposure to loud noises the more damage that can be done
OSHA has guidelines set for safe exposure on the job.
 85    for 8 hours
       88 for 4 hours
       91 for 2 hours
       94  for 1 hour
       97  for  30 minutes
      100  for 15 minutes
      103  for 7.5 minutes

For those of you who recognize a pattern, good for you
for every 3 decibels over 85, the safe exposure time gets cut in half


Okay, so what do we do with the above information?  
Make sensible choices.
Make sure that all headphones that your kids use are turned down to a reasonable level.
Avoid environments where your child will be subjected to PROLONGED long noises.
That BART platform is probably not going to cause any trouble unless you spend a lot of time down there.
If you know in advance that you will be in a super noisy place, consider some of the new baby friendly headphones that will cut about 20 decibels.
( Ear plugs are a little problematic, because they are a choking hazard and it may be hard to see if your baby pulls them out)

I have actually had parents call me to ask if it is okay to take their baby to a rock concert.

My "NO" possibly reached 100 decibels.


Have your child's hearing tested on a regular basis once they are over the age of  3 or 4 (sooner if you have concern)
You may not know this but most babies in this country are given a hearing test before they leave the hospital after birth.  

When we do a routine hearing test in our office a child who can hear a 25 decibel sound  in frequencies from 500-4000 will pass.

Any in-office hearing test has the risk of being inaccurate, especially for patients under the age of 4.
I will often have a patient who flagrantly failed the test but when I tell them I have a secret question, stand behind them and whisper, " would you like a sticker?" They answer, "yes please".
If you are concerned about your kids' hearing (and remember there is a great big difference between hearing and listening),
play a whispering game with them and see how they do.  
If there is a concern about your child's ability to hear the next step will be a visit to an audiologist for a much more accurate exam as well as a visit to the ENT specialist.

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