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How Hearing Works
Hearing loss is not
just an age-related disability; it is affecting people at younger and younger
ages. A study for WorkSafe BC
found that 25% of young people entering the workforce had the early warning
signs of hearing loss, with a further 4.6% showing “abnormal” results on
hearing tests (WorkSafe BC, 2005). The Anatomy of the Ear
The outer ear consists of the pinna and the auditory canal.
The auditory canal amplifies frequencies in the range 3 to 12 kHz.
The middle ear includes:
o the eardrum (tympanic membrane)
o ossicles - the three smallest bones in the human body
o two muscle tendons
o two nerve bundles: the vestibular (for balance)
the auditory (for hearing)
The inner ear is filled with fluid and includes:
o The cochlea (for hearing), which each have 15,000 hair cells
o The vestibular apparatus
The auditory cortex is the area of the brain that interprets sounds.
The eustachian tubes regulate pressure in the middle ear.
How We Hear
The
ear (known as the outer pinna) directs sound waves down the auditory
canal to the eardrum (known as the tympanic membrane), causing it to
vibrate very slightly. The ossicles include: the hammer (malleus),
anvil (incus) and stirrup (stapes). They work together as a lever system to
amplify the vibrations, which are then passed along to a smaller
vibrating membrane on the surface of
the cochlea of the inner ear (called the elliptical window).
The
mechanical energy of the sound, now translated to a physical vibration,
creates compression waves within the fluid-filled spiral tube of the
cochlea, which in turn move the tiny hair cells lining the inside of the
cochlea. As the hairs move, nerve cells at their base change this
motion into electrical signals that are passed along the auditory nerve
to the central auditory processing centres of the brain, where the
signals are interpreted as recognizable sound. To learn more about how hearing works, watch this video produced by Rockefeller University.
Decibels – How We Measure Sound:
| dB (SPL) |
Source (with distance) |
| 250 |
Inside of tornado; conventional or nuclear bomb
explosion at 5 m (meters) |
| 180 |
Rocket engine at 30 m; Krakatoa explosion at 160 km in air |
| 150 |
Jet engine at 30 m |
| 140 |
Rifle being fired at 1 m |
| 130 |
Threshold of pain; train horn at 10 m |
| 120 |
Rock concert; jet aircraft taking off at 100 m |
| 110 |
Accelerating motorcycle at 5 m; chainsaw at 1 m |
| 100 |
Jackhammer at 2 m |
| 90 |
Loud factory; heavy truck at 1 m |
| 80 |
Vacuum cleaner at 1m; curbside of busy street |
| 70 |
Busy traffic at 5 m |
| 60 |
Office or restaurant inside |
| 50 |
Quiet restaurant inside |
| 40 |
Residential area at night |
| 30 |
Theatre, no talking |
| 10 |
Human breathing at 3 m |
| 0 |
Threshold of human hearing (with healthy ears) | |
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