The document summarizes the anatomy and physiology of the human ear, how sound is detected and transmitted through the ear, and how we perceive qualities of sound like loudness and pitch. It also discusses different types of hearing loss and methods for testing hearing thresholds.

3. • Pinna or auricle –
external part
• Ear proper is divided
into three parts :
outer, middle and
inner ear

4. •Ear canal and
terminates at the ear
drum (tympanum)

5. •Pressure variations
in sound waves exert
forces on the ear
drum and cause it to
vibrate.

6. •Hammer, Anvil and
Stirrup (malleus, incus
and stapes) – three
small bones.

7. •Cochlea – converts
sound waves into
nerve signals.

9. • Sound waves ENTERS
HAMMER
PRESS
OVAL URE
WINDOW
VIBRATIONS
STIRRUP ANVIL
Fluid Electrical impulse
Hair Cells
BRAIN
Auditory nerve

11. •Awareness through
the senses.

12. •The human ear has a
remarkable sensitivity
and range.
•It can detect sounds
varying in intensity by
a factor of 10^12.

13. •Frequency :
20-20,000 Hz (Hertz)

15. • is the perception of
frequency.

16. •Frequencies usually
must differ by 0.3%
or more to be told
apart.

17. •Example, 1000 and
1003 Hz are
noticeably different
in pitch.

18. •A person with a poor
sense of pitch.

19. • Multiple frequency sounds
are often perceived
subjectively. A number of
terms are used to describe
multiple-frequency sounds
such as:
• *Noise *Rich *Mellow
• *Music *Shrill

20. •Most music utilizes
frequencies whose
ratio are integers/
simple fractions.

21. • Humans are able to
recognize individual
frequencies played
simultaneously even
though the combined
sounds may be
complicated in
appearance.

23. •Is the perception of
intensity, a well-
defined physically
measurable quantity.

24. • At a given frequency the
more intense a sound is,
the louder it seems. The
ear does not respond
linearly to intensity; a
sound ten times as
intense as another does
not sound ten times as
loud.

25. • Are physically measurable
and are fairly
representative of the
comparative numbers that
people would assign to the
loudness of sounds.

26. •The smallest difference
in intensity an average
person can sense is
about 1 dB, and an
intensity difference of 3
dB is easily
discernable.

27. • Loudness depends strongly
on frequency as well as
intensity. Two sounds of
different frequencies but
equal intensities rarely
sound equally loud. This is
because the ear is more
sensitive to some
frequencies than others.

28. • Vey large intensities are
needed for sound audible
near the extremes of the
normal range of hearing-
approximately 100 dB at
20 or 20,000 Hz, for
example.

29. •The threshold for
normal hearing is often
defined as 0 dB at 1000
Hz, corresponding to
10^-12 W/m^2 (Iₒ in
definition of decibels).

30. • One cause of the sensitivity of the
ear to the frequencies in the
2000-5000-Hz range is resonance
of air in the outer ear. The length
of the ear canal is such that
sounds of about 3000 Hz will
cause the air in it to resonate,
amplifying the sound and making
the air more sensitive to
frequencies around 3000 Hz.

31. • Perception of loudness depends on
frequency as well as intensity.
• Loudness is at least as important as
intensity.
• Loud sounds can be very irritating, to the
point of increasing blood pressure. It is
important to keep the sound level low in
hospitals, for example, but it is not
important to reduce the intensity of all
frequencies by the same amount.

32. • Unit for loudness.
• Phons and decibels are
said to be the same at
1000 Hz. A 60-dB 1000 Hz
sound has a loudness of
60 phons, for example.

33. • At high intensities the ear
responds equally well to
most frequencies, although
it remains more sensitive in
the region around 3000 Hz.
For example a 100 dB 60
Hz sound and a 100 dB 800
Hz sound are both of equal
loudness.

35. • Sound-level meters
• Are designed to measure
sound levels as humans
would respond to them; their
output is representative of
loudness rather than
intensity.

36. •The three internationally
accepted weightings
given to sounds in
sound level
measurements are…

38. • The A weighting makes the meter
respond most like the ear at low
intensities since it suppresses the
response to low frequencies.
• The B and C weightings are more
representative of the response of
the ear to moderate and high
intensities, with the C weighting
being nearly equal at all
frequencies.

39. • 3 aspects
1. Distance from a source
2. Attenuation by absorption
3. Reduction of sound output
from the source (most
effective)

40. • The smaller the area of the object,
the less air it can interact with and
the lower level it will create. The
more rigid the materials of which
the vibrating object is made, the
smaller amplitude its surface will
have, producing smaller pressure
waves in the air. The vibrating
object should be cushioned from
contact with other objects it might
cause to resonate.

41. • Perception is traditionally
the domain of disciplines
other than physics.
Knowledge of sound
perception aids greatly in
treating hearing loss,
designing musical
instruments and reducing
noise.

43. • Age (most common)
• Trauma (sudden injury)
• Prolonged exposure to
high sound levels
• Disease
• Congenital birth defects

45. •Caused by defects in
the structures that
conduct sound to the
inner ear

46. • Also called sensorineural, for
sensory and neural
• Results from damage to the
cochlea or neurons that send
sound information to the brain.
• Like any nerve damage, it is
generally difficult to correct.

48. • One step in evaluating
hearing loss is to
administer hearing tests.
These tests not only
determine the severity of
a hearing loss but also
aid in determining its
type and correctability.

49. • The most common testing
procedure is to place the
patient in a soundproof room
and ask him/ her to signal
when a sound becomes
audible. The intensity of sound
is raised and lowered to
determine the threshold of
hearing for that person. Each
ear is tested individually,
usually using a headset.

50. • Using a bone conduction of
sound rather than normal air
conduction. In bone conduction
tests a probe is placed against
the skull behind the ear and
sound vibrations of various
frequencies and intensities are
sent to the inner ear.

51. • Bone conduction tests
bypass the outer and
middle ear structures; if
hearing is significantly
better by bone
conduction, then the
hearing loss is
conductive rather than
neural.

52. • A graph of the results of a hearing
test. The hearing threshold levels
graphed on the vertical axis are the
number of decibels above the
normal threshold needed to be
barely audible to the person tested (
A person with normal hearing will
have a test result of 0 dB at every
frequency)

54. • Attenuation of sound in bone
varies with frequency and differs
with from attenuation in air.
• At high intensities, bone
conduction carries the sound to
both ears, and the testing device
may make significant air noises.

55. • Most of these difficulties
are overcome by careful
and consistent technique
and by putting noise into
the ear that is not being
tested, this is called
masking.

56. • Air conduction tests are more
accurate because air attenuation
is negligible for all frequencies
and the equipment can be
calibrated more easily. Sound
conduction by air into one ear is
attenuated by about 50 dB before
it gets o the other ear, so there is
little confusion as to which ear is
responding.

57. • A 45-year old person
usually has a 10 dB loss
and cannot hear
frequencies over 12,000
Hz at all. A person 65-
years old typically has a
30 dB loss for
frequencies above 3000
Hz.

58. • Conduction failures affect more
than just a narrow range of
frequencies. Bone conduction
tests are considered unnecessary
for such conditions. The loss is not
easily treatable, because sound
amplification at one frequency is
not easy in a device as small as a
hearing aid, and neural damage
cannot be repaired surgically.