Noise: The Rock Concert Effect
Posted by Liz Ernst on Tue, May 01, 2012 @ 03:37 AM
Sound, or more specifically, noise, is an invisible pollutant that can harm our ears, our hearing, and our health.
Think back to the last time you went to a rock concert or a particularly high volume club; when you left, did you pay much attention to the peculiar ringing in your ears as you headed back to your car, maybe even after you returned home? The sound around you were muffled for a short while, replaced with a buzzing inside your head, almost as if your ears were screaming.
In a way, they were.
IISo, what do we need to know about protecting out ears from IIloud noise, and what do we do when the ringing never stops?
IINoise pollution is encroaching on the everyday lives of all of IIus, and the more we understand about how noise effects our ears, our hearing, and our health and well being, the more IIlikely we are to take action to make changes.
II
Hair cells within the inner ear.
Noise levels louder than a shouting match can damage the hair cells of the inner ear. These delicate hair cells Hair cells within the inner ear contain act as the "gatekeepers of our hearing. When sound waves hit them, they convert those vibrations into electrical currents that the auditory nerves carry to the brain. Without hair cells, there is nothing for the sound to bounce off - compare it to trying to make your voice echo in the desert.
Hair cells reside in the inner ear inside the shell-shaped cochlea. Bundles of hair-like extensions, called stereocilia, rest on top of them. When sound waves travel through the ears and reach the hair cells, the vibrations deflect off the stereocilia, causing them to move according to the force and pitch of the vibration. For instance a soft piano sonata would produce gentle movement in the stereocilia, while heavy metal would generate faster, sharper motion. This motion triggers an electrochemical current that sends the information from the sound waves through the auditory nerves to the brain.
When you hear exceptionally loud noises, your stereocilia actually become damaged and mistakenly keep sending sound information to the auditory nerve cells. After spending time at a rock concert, a loud club, an active race track, an air show, an industrial plant with unmitigated chillers or machinery, or even in heavy traffic, the ringing happens because the tips of some of your stereocilia actually have broken off. You hear the false currents in the ringing in your head, called tinnitus. However, since you can grow these small tips back in about 24 hours, the ringing improves and goes away over time.
There are two ways hearing can be damaged by loud noises, according to Manfred Auer of Berkeley Lab's Life Sciences Division. Noise can stress the stereocilia bundle so much that the tip links break, which Auer refers to as the rock-concert effect, where hearing loss is temporary and the stereocilia tips grow back.
However, loud noises can also shear off whole bundles of stereocilia. In mammals these can't regenerate - the loss is permanent.
Repeated exposure to loud noises can kill the hair cells entirely. So what? We have 16,000 of them in each cochlea, but that number pales in comparison to the eye's 100 million photoreceptors, which do to light what hair cells do to sound. In addition, once those hair cells die, we cannot growth them back. This is why protecting your ears is essential.
How loud is too loud? Sound is measured in units called decibels. Decibels measure the power of sound, rather than the amount. Safe sound levels are considered below 85 decibels. Here's another rule of thumb: If you have to shout to hear someone an arm's length away, the sound is probably above that safety threshold.
Repeatedly crossing that 85-decibel threshold can have unpleasant consequences. While the ringing in your ears from a loud noise is usually brief, for more than 12 million Americans, it never stops, according to the American Tinnitus Association. Chronic tinnitus can be a symptom of infections, high blood pressure, even compacted earwax, but it is commonly associated with noise-related hearing loss.
There are a few simple ways to safeguard your hearing. First, be aware of the noise levels around you. If you know you're going to be in a loud environment, wear earplugs to protect your ears. Also, notice how close you are to the source of loud noises and how long you're exposed to them. And pay attention to the ringing in your ears. Our bodies are sometimes more fragile than we think.