1.  Central to the success of any hearing aid
fitting is the process of controlling
occlusion effects, acoustic or non-acoustic.
 The most basic method of reducing or
eliminating occlusion effects is by Venting.
 However, opening an air channel through
an acoustic coupling is not the only way of
mitigating occlusion.

2.  Occlusion is created when either supra-
aural or insert earphones are placed on the
patient during standard audiometry.
 It is also present when ear impressions are
in place.
 Since these two conditions are nearly
universal in hearing instrument fitting, the
opportunity for evaluating occlusion effect
is readily available.

3.  Assessment of the degree of occlusion
effect is a fundamental step in the fitting of
any hearing instrument.
 Occlusion is the perception of changes in
auditory processing as a result of some
type of blockage of sound transmission.

4.  Such loss of transmission efficiency is
already in place with a conductive or mixed
hearing loss.
 The presence of a significant (roughly 15 dB
or greater) air-bone gap yields enough
occlusion that further plugging by an
acoustic coupler will generally have little
effect.

5.  Traditional venting charts have attempted
to prescribe different size vents based on
degrees of hearing loss.
 General comments such as "persons with
more than 60 dB of loss will not experience
occlusion", should be disregarded in that
experience has shown occlusion effects to
be present even in the most profound
losses.

6.  Incidents of central auditory processing
disorders, such as those found in post-
stroke, dementia, head trauma, and the
growing variety of survivable pathologies,
produce cases which require special care.

7.  The general process of utilizing larger vents
with milder losses is of considerable value.
 Any rules of venting can be expected to be
modified by changes in the way in which
the brain handles sound.

8.  The degree of bone conduction (BC) sound
enhancement in the presence of occlusion
varies considerably with different occluding
object types.
 The degree of (BC) threshold improvement
under occlusion should also be expected to
vary considerably from individual to
individual.

9. Testing BC while the patient is occluded
addresses the "hollow voice" aspects of
occlusion.
Three tests may be used in this process.
They are:
1. Weber testing, to include lateralization
measurements from 25OHz- 4000Hz.
2. (BC) thresholds at 1 kHz, 750 Hz, 500 Hz, and 250
Hz; measured at each ear’s mastoid process.
3. (BC) SRTs may also be measured for each ear.

10.  Comparison of occluded (absolute) BC with
non-occluded (relative) BC results indicates
the amount of BC sound enhancement
caused by occlusion.
 True comparison requires each of these
tests be administered while the patient is
both occluded and non-occluded.

11.  This described test regimen will provide
significant information regarding occlusion.
Note: The assessment of the lateralization of
(BC) frequencies, indicates important
information regarding potential binaural vs.
monaural occlusion problems.

12.  The revealed improvement of low
frequency thresholds under occlusion is a
good indicator of how the client will react
to the sound of their own voice while
wearing hearing instruments.
 Also, the revealed differences between (BC)
SRTs under occlusion modify the Stenger
effect.

13.  An alternate test procedure used to
measure the output of a person's own
voice, in situations, while occluded,
involves the use of a probe microphone.
 Many speech components are measurable
using this measurement method.

14.  Three simple vowel sounds are
recommended due to their spectral
content. From highest to lowest frequency,
they are /i/ (as in eat); /a/ (as in ah); and /u/
(as in boot).
 Probe microphone measures, using these
simple vowel sounds, can provide a
valuable “comparison tool” when
evaluating the effect of vents or
object/material changes.

16. Since a vent is usually a separate air cavity in
a hearing instrument fitting, its’ individual
resonant and impedance characteristics may
be expected to change when constructed of
different (soft or hard) materials.

17.  The size and shape of the ear canal limits
the amount of room available for building a
vent.
 The canal direction and shape must be
considered as a part of placing/constructing
a vent.
 Otoscopic examination, looking through
the vent, can often reveal whether it is
open into the canal, striking the canal wall,
etc.

18. The fit of the coupling in the ear dictates the
presence of leakage around the shell or ear mold
of the instrument.
Contact between the earpiece and the ear itself,
as well as retention changes due to mandibular
movement, each play a crucial part in the degree
of potential occlusion involved in a hearing
instrument fitting.
Please Note: The presence of slit leaks may have
a positive or negative effect upon the occlusion
performance of an individual.

19. Standard vents are found in three traditional
configurations.
They are:
1. External vents
2. parallel vents
3. diagonal vents
Note: External and parallel vents operate on the
same principle, with the only real difference being
the use of plastic versus human ear canal walls to
achieve the vent space.

20. External Venting
 The external vent remains highly useful in
cases of drainage and relief of non-acoustic
occlusion effects.
 External vents probably provide the
greatest potential for relief of feelings of
pressure in the ear.

21. Parallel Venting
 Parallel vents remain the most popular
vent configuration, since they provide
potential low frequency sound reduction
with minimal high frequency loss, and
lower incidence of electro-acoustic
feedback.
 The parallel vent provides greater ease of
retention of the aid than is generally found
with the external vent.

22. Diagonal Venting
 The diagonal vent, which opens directly into
the sound bore, has been found to have a
higher incidence of feedback. In addition, it
causes reduction of the high frequency output.
 While not commonly used in ITE or ITC
fittings, the occurrence of a narrow canal tip
with a belled end, in which the vent and sound
bore emerge in very close proximity, can
create the same effect as an actual diagonal
vent.

23. Important Venting “tips” To Remember
VENT ALWAYS: Occlusion should be
addressed in every fitting—remember, ears
need to “breathe”.
In the age of high cut filters, notch filters,
phase shifting, and digital control, the fear of
feedback can be reduced along with feedback
itself.

24. Important Venting “tips” To Remember
 Given the array of electronic and plastic
technologies available today, there
remains little reason for unvented fittings,
unless the client expresses desire for such
an arrangement.
 Closing off the vent is actually a good first
step in acoustic modification.
 It is rare, but some clients prefer no
venting.

25. Important Venting “tips” To Remember
A VENT IS ONLY AS LARGE AS ITS'
NARROWEST OPENING: This is the guiding
principle behind select-a-vent and positive
variable vent systems.
A change in the diameter at one point in a
vent yields changes in the overall function of
the entire vent.

26. Important Venting “tips” To Remember
VENTING TO ADD LOWS? Like every other
physical object, a vent will have a resonant
frequency. While its general impedance is
minimal for low frequencies, a vent between
1 and 3 mm in diameter can cause resonant
increases in low frequency amplification.

27. Important Venting “tips” To Remember
The exact nature of such a low frequency
boost depends on a number of factors; but
may generally be summarized as follows: the
smaller the vent, the lower the resonant
frequency boost.

28. Considerations for Deep Insertion Fittings
Finally, in relation to occlusion effects, the
placement of a damping object in contact within
the bony meatus has the potential to alter the
temporal location of internal bone conducted
sounds.

29. Considerations for Deep Insertion Fittings
There are a number of concerns associated with
such fittings. The bony meatus is a highly
sensitive area, composed of extremely thin skin
over bone.

30. Considerations for Deep Insertion Fittings
 This area is filled with multiple neural plexi.
 The sensitivity of this region could (and does)
cause discomfort in wearing a deeply seated
hearing instrument.
 This situation is potentially aggravated by
movement from the temporal-mandibular joint.