Transcript PHY238Y Lecture 9

PHY238Y
Lecture 10


The human ear (outer and middle)
Physics of hearing (II)
References:
Haliday, Resnick, Walker: Fundamentals of Physics, 6th ed. 2003, Ch. 18 (18.5, 18.6)
Hallett et al.: Physics for the life sciences, 4th ed., Ch.2 (2.6)
K. Bogdanov: Biology in Physics: is Life Matter, Acad. Press 2000, Ch. 6
Hyper Physics: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/ear.html#c1
Thanks to dr. Rod Nave for the permission to use the above resource
PHY238Y
Lecture 10

Structure of the human ear
PHY238Y
Lecture 10



The outer ear, or
pinna acts like a
funnel to collect
sound;
For a given sound
intensity, a larger
ear captures more
of the sound wave
and its energy;
The outer ear
structures enhance
the sensitivity of
hearing.
PHY238Y
Lecture 10

The outer ear

Sound perception: The
Fletcher- Munson curves

The hearing curves show a
significant minimum in the
range 2000-5000 Hz with a peak
sensitivity around 3500- 4000
Hz.
There is another enhanced
sensitivity region at about
13,500 Hz.
The high sensitivity region at 25kHz is very important for the
understanding of speech.


PHY238Y
Lecture 10

The outer ear

The maximum sensitivity
regions of human hearing
can be modeled as closed
tube resonances of the
auditory canal. The
observed peak at about 3700
Hz at body temperature
corresponds to a tube
length of 2.4 cm. The higher
frequency sensitivity peak is
at about 13 kHz which is
somewhat above the
calculated 3rd harmonic of a
closed cylinder.
PHY238Y
Lecture 10

FletcherMunson
(equal
loudness)
curves
PHY238Y
Lecture 10


The middle ear
The tympanic
membrane
or eardrum receives
vibrations traveling up the
auditory canal and
transfers them through the
tiny ossicles to the oval
window, the port into the
inner ear. The eardrum is ~
fifteen times larger than the
oval window, giving an
amplification of about
fifteen compared to the
oval window alone.
PHY238Y
Lecture 10

The middle ear:
ossicles

The three tiniest bones in the
body couple the vibration of the
eardrum and the forces exerted
on the oval window of the inner
ear
The ossicles form a compound
lever which achieves a
multiplication of force.

PHY238Y
Lecture 10

The middle ear: Ossicle
vibration

Ossicles achieve an
amplification by lever action.
The lever is adjustable under
muscle action and may actually
attenuate loud sounds for
protection of the ear.
PHY238Y
Lecture 10
ODE TO THE OSSICLES
(by Allison and Susan Sekuler)
Every creature, live or fossicles,
Cannot hear without their ossicles.
Except, as hard as they may wish,
There are no ossicles in fish.
You might think this quite unfair,
but fish do not live in air,
so they simply do not care….