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As printed in Hearing Health, volume 20:2,
Summer 2004
By Nannette Nicholson, Ph.D.
When you talk while you are wearing your hearing aids,
does it sound to you like you are in a barrel? If so,
know that you are not alone. Hearing aid wearers with
mild or moderate hearing loss report this phenomenon
all the time.
Hearing your voice as hollow, boomy or as if you were
in a tunnel is what is known as the occlusion effect.
It is caused by the ear canal being blocked, or occluded,
by an earmold or a hearing aid shell. To experience
occlusion without hearing, say the vowel sounds “ah,”
“ee” and “oo” while blocking
both ear canals with the fingertips or by pushing the
cartilage in front of the ear over the ear canal. Notice
how the vowels sound much louder and with more of an
echo than they do when the ear is unobstructed.
An earmold or earshell seals the ear canal, increasing
sound pressure and trapping air in the canal. When you
talk, it causes the trapped air particles to move or
vibrate like a drum, resulting in speech sounding louder.
The tighter the seal, the louder the sound. People with
mild or moderate hearing loss in the low tones can easily
hear this subtle change in sound pressure but those
with greater degrees of loss may not experience this
sensation.
Hearing aid manufacturers have long been working on
solutions to this aggravating problem. They have found
that one sure way to reduce the effects of the sound
pressure from trapped air in the ear canal is to vent
the canal, allowing air to pass through from the outside
portion of the earmold to the inside where the air is
trapped.
Researchers have determined that the larger the vent,
the higher people rate the acceptability of their own
voice. Typically, a two to three millimeter vent is
needed in order for hearing aid users to find the sound
of their voice acceptable. However, as vent size increases,
so does annoying feedback.
Feedback is the whistling sound that occurs when an
earmold or earshell is not sealed tightly enough. Amplified
sound slips back through to re-enter the microphone
of the hearing aid, resulting in a squeal similar to
one from a sound system when someone comes too close
to a microphone.
Two ways to reduce feedback are to reduce the gain/amplification
of the hearing aid or to tighten the seal of the earmold.
Neither is an acceptable solution, though, because reducing
the gain makes understanding speech more difficult and
tightening the seal of the earmold results in occlusion.
This is obviously a “Catch 22” for hearing
aid wearers and the engineers who have struggled to
find a way to reduce both irritants.
The good news is that newly released products appear
to have the answer. The emerging solution couples digital
signal processing strategies that “sense”
and reduce the opportunity for feedback before it occurs
and “open” venting systems are also designed
to reduce the effects or occlusion. These new venting
systems are also designed to guard against feedback.
One is the collection vent that has a smaller opening
on the outside of the mold than the one on the inside,
allowing in to “collect” the trapped air
and funnel it out of the ear. Another venting system
consists of deeply seated earmolds that come in contact
with the bony portion of the ear canal to dampen vibrations,
reducing the drum sound.
If you are bothered by occlusion with your hearing
aids, you may want to visit with your hearing healthcare
professional about the possibility that innovative products
like these may provide a solution.
Bernafon’s answer to occlusion
is Openfit™, a collection vent
and adaptive feedback cancellation strategy that detects
the presence of feedback and subtracts it from the incoming
signal. Combined with SymbioXT’s two millisecond
processing time, digitally amplified sound is heard
before unamplified sound traveling through the vent
and the aid’s programming software compensates
for the loss of low-frequency energy usually associated
with a larger vent.
Oticon reports success with its OpenEar
Acoustics®, a venting system coupled with
digital signal processing, digital feedback control
and low-frequency gain compensation. It can be applied
to most of Oticon’s digital aids – including
value-priced and high-end models.
Phonak has the Perseo™
Open, a product line designed to eliminate
occlusion for steeply sloping high frequency hearing
loss delivering optimal performance and wearing comfort.
Phonak’s OpenSound® technology
is available in the company’s other aids as well.
ResoundsAir™ by GNResound,
a mini-BTE digital hearing aid for people with high
frequency hearing loss, is designed to address occlusion
and feedback with a unique venting design that reduces
the plugged up sensation while enhancing high frequency
amplification.
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