otometrics Madsen ZODIAC 901, Руководство пользователя

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Hysteresis Hysteresis is a common feature of practical compliant materials. It is
characterized by a difference in the deflection resulting from the applica-
tion of a given pressure, depending upon whether the pressure is in-
creasing or decreasing.
Although resistive loss results in a reduction of the amplitude of a
wanted vibration, it can also be beneficial in systems such as the human
ear. It can dampen the effects of resonances and standing waves. It can
also play its part in achieving matching of mechanical impedance.
Hysteresis in the eardrum may be observable in tympanometry if two
different tympanograms are produced from the same ear measured un-
der conditions which are identical except for the sweep direction. How-
ever, this effect could also be caused by too great a pump speed.
8.5 THE STRUCTURE OF THE EAR
Structure of the Ear The ear comprises the parts of the body which convert sound waves into
impulses in the human body’s central nervous system.
The ear is a highly developed organ, capable not only of detecting, but
also of analyzing, weak sounds containing very small amounts of en-
ergy. These capabilities are possible because the construction of the ear
is such as to minimize the loss of energy incurred by a sound wave in its
passage through the ear.
Losses can occur as a result of reflection and absorption of the energy in
the sound wave, as discussed above.
Both of these kinds of losses can be pathologically increased by defects
of the inner ear. Much of the construction of the healthy ear owes its
form to the need to provide an impedance transformation from the low
impedance of free space to the relatively high impedance of the inner
ear.
Each ear consists of three main constituents—an outer ear, a middle ear,
and an inner ear (Fig.8.1).
Outer Ear The outer ear comprises the visible external ear ( pinna ), plus the audi-
tory canal (ear canal, meatus ), which is terminated by a delicate mem-
brane, the eardrum ( tympanum ). The outer ear serves to protect the
eardrum from damage and provide a continuous impedance transfor-
mation from free space to the middle ear. The air in the outer ear is con-
nected to the atmosphere. The bone behind the ear is called the mastoid.
Operation Manual 73
GN Otometrics
PRINCIPLES OF MIDDLE-EAR ANALYSIS
Chap. 8
ZODIAC 901 Middle-Ear Analyzer
THE STRUCTURE OF THE EAR
8.5