Tympanometry Tutorial I.  Principles

1)    If something has "high impedance" it has which of the following?
    a)  Low admittance
    b)  High admittance
    c)  Relatively good ability to accept energy
    d)  Relatively poor ability to accept energy

2)    Why does sound energy not transmit through a water very readily?
Why does someone under water not hear as well as when above water?

3)  Suppose that a large cylinder of air had a flexible plastic membrane in the middle of it
A speaker is sealed inside the part on the left, and a microphone is sealed inside on the right-
hand side of the tube, as shown below.

If the left side of the tube were pressurized, so the membrane bulged towards the microphone,
would more or less sound go through the membrane, and why?

4)  What if some of the air were sucked out of the left side, so that a partial vacuum
were in the left side? What would happen to the sound transmission across the flexible

5)  What if the microphone were on the side with the speaker (on the left)?  What would
happen to the amount of sound on the left when the membrane was sucked to the left by
a partial vacuum?  Would it be more or less than when there was equal pressure on each
side of the membrane?

6)  Imagine that the pressure on the left side of this tube starts out very high (lots of
extra air pushing the membrane towards the right), then gradually decreases.
What would the microphone on the left side record as the change in sound level
as the pressure decreases?

7)  And if the pressure went from ambient pressure to becoming more negative,
what would happen to the reading of the microphone on the left side?

8)  If you had a boombox, set to a given volume setting, and took the radio
first into a closet, then out into the middle of the room, where would the
sound be louder?  Why?

9)  Let's say that a scientist produces a given amount of sound in a closed tube that is,
for all practical purposes, a large hypodermic syringe.  The size of the tube can change.
When the space inside tube is made larger,  is the sound louder or quieter in the tube?


The tympanometer is a device used to assess the middle ear system.
The tympanometer measures the sound level in the ear canal.
If the sound source output stays the same, what would happen to the
sound level in the ear canal as the pressure changes from +200 daPa,
to ambient pressure, to -400 daPa?

In questions 8 and 9 you noted that sound levels can be thought of
as being equivalent to the source being in a large or small space.

Relate the change in sound level as pressure is varied (assume the sound
source stays the same, but the energy in the ear canal changes because
of the change in the amount that is reflected off the eardrum due to the
outer ear pressure changes).

11) If the eardrum did not move very well - if it was stiff, what would
the tympanogram look like?  How would it differ from the normal

12) If the eardrum was inordinately flaccid (floppy) and transmitted the
sound through the eardrum more readily than the normal ear, what would
the tympanogram look like?  How would it differ from the normal

13) What if the pressure in the middle ear space is not normal, but is "negative"?
Negative middle ear pressure happens when the mucousa of the middle ear absorb
air, and the eustachian tube is not opening to permit fresh air to enter the middle ear
space.  A partial vacuum occurs within the middle ear space.  What would this do
to the appearance of the tympanogram?

14) What if there were fluid filling the middle ear space?  What would the
tympanogram look like in this case?  Would you see a peak?

15)  The equivalent volume measurement made before the tympanogram is conducted,
while the ear is pressurized at +200 daPa, is often called the "ear canal volume".
Other names are "physical volume" and "base compliance."  If the ear canal is blocked
by wax (totally occluding the ear canal), what would happen to the ear canal volume,
and what would the tympanogram look like?

16)  If there is a hole in the tympanic membrane, what would the "ear canal" volume
be?  What would the tympanogram look like?

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