The Outer Part of the Ear

Outer Ear

The parts of the outer ear include:

• Pinna
  • The pinna is the visible portion that is generally referred to as “the ear.”
  • Its function is to localize sound sources and direct sound into the ear.
  • The dimensions and folds of the pinna cause certain sound frequencies to be amplified and other frequencies to be weakened.
  • Each individual’s pinna puts a distinctive imprint on the acoustic wave traveling into the auditory canal.
• External Auditory Meatus (ear canal)
  • The ear canal extends from the pinna to the eardrum and is about 26 millimeters (mm) in length and 7 mm in diameter. Size and shape vary among individuals. This is an important factor to consider when fitting hearing protectors.
  • The ear canal protects the eardrum and acts as a resonator, providing about 10 decibels (dB) of gain to the eardrum at around 3,300 Hertz (Hz).
  • The net effect of the head, pinna, and ear canal is that sounds in the 2,000 to 4,000 Hz region are amplified by 10 to 15 dB.
    • Sensitivity to sounds is greatest in this frequency region and noises in this range are the most hazardous to hearing.
• Tympanic Membrane (eardrum)
  • The eardrum separates the outer ear from the middle ear, creating a barrier that protects the middle and inner areas from foreign objects. It is somewhat cone-shaped in appearance, and is about 17.5 mm in diameter.
  • The eardrum vibrates in response to sound pressure waves. The actual distance that the membrane moves is incredibly small (as little as one-billionth of a centimeter).