Transcript interfacing assistive devices with cochlear implants

FM Systems
for School Aged Children
Linda Thibodeau, Ph.D.
Advanced Hearing Research Center
Callier Center for Communication Disorders
University of Texas at Dallas
Copyright by Linda M. Thibodeau
2005
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Supportive information
May be obtained at the
Website of Linda Thibodeau
www.utdallas.edu/~thib
Copyright by Linda M. Thibodeau
2005
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Welcome to this lecture on FM Systems!
I hope you will find this
information interesting and
rewarding as you learn of the
significant differences that can
be achieved with
FM Systems!
Copyright by Linda M. Thibodeau
2005
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OVERVIEW
1. Rationale for use of FM Systems
2. FM Systems
3. FM Evaluation Procedures
4. Use of FM Systems
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2005
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Let’s start with the Rationale for using
FM Systems.
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2005
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1. Rationale for use of FM Systems
A. Signal-to-Noise Ratio
B. Typical Classroom Noise
C. Audio Demonstration of
Classroom Noise
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A. Signal-to-Noise Ratio
A major problem for all persons with hearing loss is….
Listening in Noise !
The problem is described by the
signal-to-noise ratio or SNR.
The amount of “Signal,”
what you WANT to hear
. . .compared to. . .
“Noise”,
ANY sound you don’t want to hear.
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2005
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In a large group, distance and
noise can be a problem.
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This results in a poor
signal-to-noise ratio.
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i.e. the intensity of the noise at
the listener’s ear is greater than
the signal of the speaker.
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A poor S/N ratio is -10 dB
 the noise is 10 dB more intense than the signal
70 dB
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2005
80 dB
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A good S/N ratio is +20 dB
 the signal is 20 dB more intense than the noise
70 dB
90 dB
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So...ideally we want to have a
positive S/N ratio and a
constant signal level regardless
of distance between the
speaker and the listener.
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We can accomplish this by
placing a microphone on the
speaker and delivering the
sound directly to the listener.
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2005
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B. Typical Classroom Noise
Optimal noise level
for a class with students with
hearing loss would be
30-35 dBA,
yet the typical level is about
60 dBA.
Average conversational speech is
about 60 dBA, which means the
SNR is often 0 dB!
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The optimal SNR for teaching
students with hearing loss would be
+15 dB,
(the teacher’s voice is 15 dB more
intense than the background noise).
However, the typical SNR in
classrooms is only about
+5 to – 7 dB!
Copyright by Linda M. Thibodeau
2005
(ASHA, 2005)
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Effects of Noise on Speech Recognition
Finitzo-Heiber and Tillman (1978)
measured the effects of noise and
reverberation on speech recognition
scores with 8 to 12 year old
children with
Normal Hearing and Hearing loss .
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In a soundbooth:
No Noise, Little Reverberation
Children with Normal Hearing scored
95% - Only missed 5% of words
Children who were Hard of Hearing scored =
83% - Only missed 17% of words
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In a situation similar to a typical classroom:
SNR of +12 dB:
SNR of 0 dB:
Normal
Hearing
83%
48%
Hard of
Hearing
60%
28%
These results suggest that children with
hearing loss may only be hearing about
one fourth of speech in a typical
noisy classroom.
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2005
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C. Audio Demonstration of Classroom Noise
Click on each loudspeaker to hear:
Typical Classroom Noise
A teacher reads a story in a
classroom with a typical SNR
Same teacher reads a story in
an optimal SNR provided by
using an FM System
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2005
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Now let’s look at the operation and
design of FM Systems in our
second section of the lecture.
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2005
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2. FM Systems
A. Introduction to FM Technology
B. Transmitters/Microphones
C. Receivers/Sound Transducers
D. Cochlear Implants and FM Systems
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A. Introduction to FM Technology
FM Systems use a frequency-modulated
signal to transmit the speech through the
air similar to an FM Radio station.
The system involves a microphone and
transmitter on the speaker and a receiver
for the listener with some type of
sound transducer.
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All FM systems have these partsMicrophone
Transmitter
Receiver
Sound Transducer
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FM Transmission Process
1) Speaker talks into
microphone which
generates rapid
fluctuations of
voltage
4) Electric and
Magnetic field
fluctuations travel
as electromagnetic
waves
7) A filter selects
the frequency of
interest
2) Voltage
fluctuations are
passed to a
transmitting
antenna
5) Electromagnetic
waves produce
fluctuations in
voltage at a
receiving antenna
8) The voltage
fluctuations in that
frequency range are
sent to the
acoustic transducer
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2005
3) Voltage fluctuations produce
fluctuations of
electric and
magnetic fields
around the antenna at
a specific frequency
6) The voltage
fluctuations
are amplified
9) The transducer
converts the voltage
fluctuations into
sound waves to
go to the ear
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Transmitting Frequencies
Typically each transmitter is assigned a frequency,
also called a channel. These may be coded by numbers,
colors, or letters. The channel component may be
called an oscillator.
Examples:
Number Color
Letter
Trans. Freq.
#1
Red/Gray
A
72.000-72.025
#2
Brown/Gray
B
72.025-72.075
There may be as many as 40 different channels used
in a school.
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2005
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Now let’s look more closely at the
Transmitter/Microphone features….
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B. FM Transmitters/Microphones
Descriptive Categories
1) Microphone Type
2) Microphone Location
3) Channel Options
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FM Transmitters/Microphones
Microphone Type:
The microphone characteristics can vary.
Omni-directional Microphonepicks up sound from all around
Directional Microphonepicks up sound primarily from the top
Multi-Directional Microphonepicks up sound from all around OR
focused area
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2005
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FM Transmitters/Microphones
Microphone Location:
All Transmitters are worn on the body, but the
microphone placement may vary.
On the Body
On the Head
On the Lapel
On the Cheek
(also called Boom mic)
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2005
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FM Transmitters/Microphones
Channel Options on the transmitters:
Single, but fixed-Oscillator channel set at
the factory and cannot be changed
Multi-Frequency
Manual frequency selection-Oscillator
can be removed and changed to another
frequency
Wireless frequency selection-Channel
is changed digitally
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2005
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Wireless Channel Changeability
1) Direct Frequency SynchronizationPressing a button on the transmitter sends a signal to
the receiver to synchronize the channel
Ex. Phonak MLxS with Campus S
2) Automatic Frequency SynchronizationWalking near a plate on the wall that contains
transmitter changes the channel to a preset number
Ex. Phonak MLxS with Wall Pilot
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Automatic Frequency SynchronizationStudents wearing Phonak MLxS walking past
Wall Pilot as they enter classroom to get
synchronized to the correct frequency for that
class.
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2005
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OTHER OPTIONS - Transmitters
Programmable-Allows the channels to be set digitally via
a connection to a computer.
Audio Input Jack-An input jack for the audio signal from
another source such as a tape player, VCR, or
computer.
No FM/Low Battery Lights-Alerts the users that the
batteries or FM switches should be checked.
Talk Over-Allows the microphone to be active
even when the transmitter is connected to another
audio source such as VCR
Mute Switch-Allows the microphone to be
deactivated so conversations can be private.
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2005
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Now let’s look more closely at the
Receiver/Sound Transducer features….
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2005
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C. FM Receivers/Sound Transducers
Descriptive Categories
1) Type-Relationship to Personal
Amplification/Cochlear Implant
2) Receiver Location
3) Channel Options
4) Sound Transducers
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2005
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FM Receivers/Sound Transducers
1) Type-Relationship to Personal
Amplification/Cochlear Implant
There are two main types with respect to interacting with
Personal Devices:
Basic-Does not interface with Hearing aid or
Cochlear
Personal-Does interface with Hearing aid or
Cochlear Implant
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2005
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FM Receivers/Sound Transducers
2) Receiver Location:
Some FM Receivers interface with a personal
hearing aid worn at the ear? (i.e.one that the
student wears throughout the day)
Students and parents generally like this option!!!
Some are worn:
On the Body
On the Ear
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FM Receivers/Sound Transducers
3) Channel options on FM Receivers?
Single, but fixed-Oscillator channel set at the
factory and cannot be changed
Multi-Frequency
Manual frequency selection-Oscillator
can be removed and changed to
another frequency to match transmitter
Wireless frequency selection-Channel
is changed digitally by pressing a
button on the transmitter that is in close
proximity
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2005
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FM Receivers/Sound Transducers
4) Sound Transducers
Two Basic Categories:
Basic System-Child takes off personal hearing aid each
day and puts on the FM Receiver that picks up the
teacher’s voice AND acts like a hearing aid.
Personal System-Child keeps the personal hearing aid
on all day and the FM Receiver is interfaced through
one of three arrangements.
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2005
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FM Receivers/Sound Transducers
Basic System Options
Button Earphone with Body-worn FM system
Ear Level FM Receiver with limited power
Soundfield Speaker to set on desktop or
mounted on the wall
FM Amplifier with Behind the Ear hearing aid
Personal System Options
Neckloop with Personal Aid on T Switch
Direct Audio Input with Personal Aid
Silhouette with Personal Aid on T Switch
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Let’s look at some illustrations of these
different types of sound transducers!
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Button Earphone with Body-worn FM system
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Basic Ear Level FM Receiver with limited Power
For Persons with Normal hearing, Mild loss,
Auditory Processing Disorder
EduLink
by Phonak
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2005
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Soundfield Speaker to set on desktop or
mounted on the wall
Desktop Speaker
Wall Mounted
Speakers
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FM Amplifier with Behind the Ear hearing aid
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Neckloop with Personal Aid on T Switch
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Direct Audio Input with Personal Aid
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Silhouette with Personal Aid on T Switch
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OTHER OPTIONS - FM RECEIVERS
Programmable/Digital-Allows the features of the
receiver to be set via a connection to the
computer which results in more precise control of
the FM signal.
Audio Input Jack-Allows a direct electrical connection
to a VCR, computer, or tape/CD player.
No FM/Low Battery Lights-Warning lights to indicate
the switch settings and/or batteries need
checking.
Microphones-When the FM receiver is not interfaced
with a personal hearing aid that has a
microphone, a microphone will be needed on the
FM receiver to pick up the sounds nearby the
student but at a lower level than the teacher’s
voice.
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2005
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Now let’s consider interfacing FM System with
Cochlear Implants….
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2005
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D. Cochlear Implants and FM Systems
A child may receive a cochlear implant when they receive
no benefit from a hearing aid. After a surgical
procedure, they receive sound stimulation through
electrical impulses applied directly to the auditory
nerve. FM systems can be used with cochlear implants
to provide that optimal SNR.
The same FM Transmitters and some of the same FM
Receivers can be used.
Electrical Coupling of the FM Receiver to the Cochlear
Implant can occur in two arrangements:
Patch cords connect FM Receiver to Cochlear Implant
Direct Plug-in of FM Receiver
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Patch cords connect FM Receiver to
Cochlear Implant
Cochlear Implant
Ear Level Processor
Body Worn Processor
FM Receiver
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2005
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Direct Plug-in of FM Receiver
Cochlear Implant
Speech Processor
FM Receiver
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It is very important to
evaluate FM Systems to
ensure proper settings for
maximum benefit. Let’s
see how that can be
accomplished in our third
section of the lecture….
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2005
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3. FM Evaluation Procedures
A. Electroacoustic
B. Real Ear
C. Behavioral
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2005
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A. ELECTROACOUSTIC PROCEDURES
ASHA GUIDELINES FOR FITTING AND
MONITORING FM SYSTEMS (1999)
This document provides Recommended Measures to be
performed to compare response through amplification
settings with and without the FM system.
ELECTROACOUSTIC PROCEDURES
Performed by an Audiologist
Child need not be present, only need child’s
Hearing Aid (HA) and FM System
Very objective, efficient way to set systems
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First step is testing the child’s HA alone.
It is attached to a microphone and a sound is
delivered, and the output is measured and
graphed.
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Next the FM Receiver is attached
and the HA/FM system is evaluated.
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The output curves are compared to
verify that Curve #2 (FM + HA) shows
that the FM signal will be higher than
the Hearing Aid alone signal.
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B. Real Ear Procedures
Settings can also be verified by placing a small
tube microphone in the child’s ear canal and
measuring the sound level while
1) first wearing the HA alone, then
2) while wearing the HA + FM system
1)
2)
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C. Behavioral Testing with FM Systems
 Threshold Testing typically not
recommended due to lack of significant
information
 Speech Recognition Testing is more
meaningful
 Without FM System
 With FM System, with examiner wearing FM
transmitter
 Test each arrangement in Quiet and in
Background Noise if time permits
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2005
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Test Arrangement
Examiner Side of Test Booth
Student inside Test Booth
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Behavioral FM Verification
Case Illustration
Third Grader who resisted wearing FM system.
Testing done to show him benefits.
Hearing Aid Alone
Quiet
In typical classroom noise
90%
60%
Hearing Aid with FM
In typical classroom noise
Quiet
90%
100%
With the FM System, the speech recognition score
improved from 60% in noise to 90%!
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2005
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We’re now at the fourth, and final section
of the lecture….
Let’s consider some ABC’s of using FM
Systems in the Classroom!
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2005
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4. Use of FM Systems
A. Microphone Technique
B. Care and Use
C. Settings for Various Teaching Arrangements
D. Troubleshooting
E. Common Problems
F. Manufacturers
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A. Mic Technique
1. proper distance 6-8 in from mouth
(unless using boom mic, then 2 in)
2. don't stand near noise
3. turn off when leaving the classroom
4. antennae must hang free, not
wrapped around transmitter
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2005
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B. Care & Use
1. clean units with damp cloth
2. if put in prolonged storage - need
even temperature
3. annual electroacoustic checks
4. daily listening checks
5. keep in chargers when not in use
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2005
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C. Settings for Various Teaching
Arrangements
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2005
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Settings on FM Receivers
FM Receivers usually have switches that can
be set to send certain signals to the
listener:
FM Only-Sends only the teacher’s
voice
Environmental (ENV) Only-Sends
only the voices picked up by the
microphone on the FM Receiver
FM+ENV-Sends the teacher’s voice and the
environmental sounds around the student,
ideally the teacher’s voice is about 10 dB
more intense than the ENV signal
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1) Teacher lecture
Set Receiver to pick up FM Only Signal
I think they like
my tux!
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2005
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2) Class discussion led by the teacher
Set Receiver to pickup FM +
Environmental (ENV) Signals
I’m not sure
they’re listening.
How To Select
Hearing Aids....
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3) Independent work at desk
Set Receiver to pickup up ENV Signals
I’d rather be
shopping!
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4) Group work
Set Receiver to pickup ENV Signals
I’d rather be
fishing.
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D. Troubleshooting Works best when two
people check each
component
separately and the
add components
progressively
according to the
following steps:
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1. check FM receiver in microphone
mode (as a body aid)
2. check FM receiver & transmitter in
FM mode
3. check FM receiver & transmitter in
FM & Microphone mode
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4. check FM Receiver & transmitter &
personal aid (boot with loop silhouette)
5. check personal aid alone.
6. annually check each component,
daily check entire system (#4)
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E. Common problems
1. setting volume controls - must be
determined by audiologist
2. matching oscillators between
transmitter and receiver
3. setting the mic switch
4. neckloops often noisy & inconsistent
signal
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5. changes in frequency response re: to
hearing aid alone when using direct
input or neckloop
6. access to audiologist who can
monitor
7. dead batteries
8. broken cords
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2005
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F. Manufacturers
Web pages are VERY helpful, but do not hesitate to
contact manufacturer to ask questions:
1.Phonic Ear
www.phonicear.com
2.Telex
www.telex.com
3. Comtek
www.comtek.com
4. AVR Sonovation
www.avrsono.com
5. Phonak
Copyright by Linda M. Thibodeau
www.phonak.com 2005
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SUMMARY
 The SNR can be significantly improved by
using an FM system.
 Because there are so many options, the
audiologist is responsible for selection and
fitting of FM systems and the necessary
orientation and counseling.
 Any connection of hearing aid or cochlear
implant with an FM system should be tested
in controlled conditions to determine benefit.
 FM systems must be monitored on a regular
basis by trained personnel under an
audiologist’s supervision.
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2005
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Last Minute Advice regarding using
FM Systems….
If you have a lot of tension and you get a
headache, do what it says on the
aspirin bottle:
"Take two aspirin"
and
"Keep away from children."
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2005
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REFERENCES
 American Speech, Language, and Hearing Association
(2005). Acoustics in Educational Settings: Technical
Report, ASHA Supplement 25, In Press.
 American Speech, Language, and Hearing Association
(1999). Guidelines for Fitting and Monitoring FM
Systems. ASHA Desk Reference, 2, 151-171.
 Finitzo-Hieber, T., & Tillman, T.W. (1978). Room
acoustics effects on monosyllabic word discrimination
ability for normal and hearing-impaired children.
Journal of Speech and Hearing Research, 21, 440458.
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Acknowledgements
Erin Schafer, M.S.
University of Texas at Dallas
Paul Dybala, M.S.
University of Texas at Dallas
Gary Overson, M.A.
University of Texas at Dallas
Jack Scott, M.A.
University of Texas at Dallas
Marcia Crouch, M.S.
Plano Regional Program for the Deaf
Amy Popp, M.S.
Cochlear Corporation
Sallie Frye, M.S.
Frye Electronics
Helmut Ermann
Phonak Hearing Aids
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