as a sudden pressure drop toward, but not necessarily reaching, atmospheric pressure (0 daPa). This is repeated until the
pressure is equalised or until the test time has elapsed. The pressures at which the tube opens and closes are reported as
test results.
Typically, an initial build-up of positive pressure will cause the Eustachian tube to open spontaneously. In order to avoid
premature spontaneous pressure equalisation related to positive pressure build-up, the pump speed should be kept at a
maximum of 50 daPa/s.
The pressure range available for positive and negative pressures (including 400 daPa and -600 daPa) is commonly used in
ETF-P testing.
App. 1.5
Susceptance and Conductance, B/G
The
admittance (Y)
of the ear consists of the con-
tribution of the two components
Susceptance (B)
and
Conductance (G)
. The admittance magnitude is the vec-
tor length derived from the Cartesian graph as shown.
App. 1.5.1
Susceptance, B
Susceptance
is determined by the ease with which energy flows through the
Compliant elements
of the ear and the ease
of energy flow through the
Mass elements
of the ear.
•
Compliant elements
are the tympanic and round window membranes, the ossicular ligaments, the middle ear
muscles, and the air in the ear canal and middle ear.
•
Mass elements
are the ossicles and the slugs of air in the middle ear mastoid air cells (moving as units without com-
pression or expansion).
The
compliance
and
mass
contribution to the total
Susceptance
is frequency dependent.
•
Compliant Susceptance
is greater with low frequencies and gradually decreases with higher frequencies.
•
Mass Susceptance
is greater with high frequencies and gradually decreases with lower frequencies.
The total
Susceptance
is the algebraic sum of the positive
Compliance
and the negative
Mass
contributions, jB + (-jB).
Otometrics - MADSEN OTOflex 100
187
App. 1 MADSEN OTOflex 100 Immittance methodology and features
