The Human Ear
Binaural Hearing
Hearing with both ears helps you to determine the distance of the source
of a sound. It allows you to focus on one sound or conversation when you
are in the middle of a crowded area.
Binaural hearing is a term used to describe the comparing of the sounds
received by one ear with the sounds received by the other ear (the word
"binaural" means "two ears"). The process of binaural
hearing allows you to detect differences in intensity and arrival time
of the sound.
Direct sound reaches your ears before reflected sound. The ability to
perceive where the direct sound is coming from even if the reflected sound
is just as loud is known as the Precedence or Haas effect.
Parts of the Ear
When sound reaches your ear it first encounters the pinna, which is part
of the outer ear. The pinna helps in determining where sound is coming
from.
Next sound travels into the middle ear and reaches the eardrum (or tympanum).
The eardrum is attached to three bones called the malleus, stapes, and
incus. These three bones form the ossicles. The ossicles increase the
small sound pressure of outside vibrations by about 25 decibels.
The cochlea is part of the inner ear and it works to convert the acoustic
energy of the changes in pressure from the vibrations in the ear drum
into information that your brain interprets as sound. The cochlea is filled
with tiny hairs called cilia which respond differently to high and low
frequencies. They will fall off when exposed to very loud sounds and this
results in permanent hearing loss.
The Equal Loudness Principle
White Noise
White noise is created when all frequencies are played equally loud. In
this case, the middle frequencies sound loudest because you can not hear
the low and high frequencies as well. The white noise generator plays
all frequencies on the same loudness level but you hear the middle frequencies
as being louder.
Pink Noise
Pink noise is created when all frequencies are being played so that your
brain interprets them as being equally as loud. In this case, the low,
middle, and high frequencies all sound equal.
A "phon" is a way to measure perceived loudness. Pink noise
is perceived at equal phon level. The low and high frequencies are are
actually boosted so that all the frequencies sound equally as loud, but
are actually of unequal loudness.
Hearing Loss and Prevention
Temporary threshold shift or TTS is the phenomenon occurring when the
ears shut down to protect themselves. You may have experienced this after
attending a loud concert. TTS causes loud sounds to seem quieter. It is
a warning sign of permenant haring damage.
Earplugs should be worn around all loud sounds to prevent hearing damage.
Avoiding loud sounds at all times is the best way protect yourself from
hearing loss.
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