It is very distressing to experience a sudden onset of ringing in the ears. This condition is known as tinnitus. The noise of tinnitus may include ringing, screeching, buzzing, chirping, a hissing sound like steam escaping, or similar to the humming sound from high tension power lines.
While the sounds of tinnitus appear to be in the ears, they actually originate in the brain.
Tinnitus can result from a variety of causes. The most common cause is damage to the delicate sound-receiving hair cells within the inner ear. Exposure to a loud noise often damages these cells, resulting in a partial loss of hearing and the subsequent development of tinnitus. This condition is diagnosed as acoustic trauma. It is quite common in hunters, target shooters, police and military personnel, and anyone exposed without sufficient ear protection to loud gunfire or other loud noises.
How loud are various noises, and what levels are safe? What we typically think of as the loudness of sound is actually a reflection of sound pressure, and is measured in decibels (dB.).
A few examples of sound pressures are:
• A whisper or a quiet library: 30 dB
• Normal conversation: 45 to 60 dB
• Home Vacuum Cleaner or Alarm Clock: 75 dB
• Home Blender: 85 dB
• Home Garbage Disposal: 90 dB
• Tractor or Truck without a muffler: 90 dB
• Shouted conversation: 90 dB
• Power saw at 3 Ft away: 110 dB
• Noisy nightclub with live music or DJ, Rock concert: 115 dB
• Gunfire-pistol, shotgun, or rifle: approximately 150 dB
• Jet aircraft, 50 meters away: 140 dB
• Canon fire, 50t ft away: >200 dB
A “normal level” of sound (below 80 dB) will not damage your hearing. Prolonged or repeated exposure to sound levels above 85 dB will damage anyone’s hearing. A single exposure to sound above 135 to 140 dB may cause permanent damage to anyone’s hearing.
The hair cells lie inside a snail shaped structure in the inner ear called the cochlea. When exposed to a loud blast of sound, the sound vibrations enter the ear canal and strike the eardrum. Vibrations are then transmitted via three tiny bones of hearing to the cochlea, where the hair cells pick up the vibration. When the sound pressure is severe enough, it literally vibrates the delicate cells so severely as to cause permanent damage or cell destruction. Most commonly, the resulting hearing loss occurs in the higher frequencies of 4000 cycles per second and up.
Sound vibrations are received in the ear, but transmitted along the auditory nerve to the brain, where they are interpreted and perceived as sound. “Auditory, or hearing cells in the brain function best when receiving sound. For instance, when people with normal hearing are placed inside a soundproof chamber, 95% develop tinnitus within 5 minutes.
Perhaps to oversimplify, when hearing cells in the cochlea and along the auditory nerve no longer transmit outside sounds, associated brain cells search so diligently for sound that they detect the energy flow from one brain cell to another. This is thought to be the primary mechanism whereby acoustic trauma results in the sound of tinnitus.
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