Copyright by Linda M. Thibodeau 2005 1 FM Systems for School Aged Children Linda Thibodeau, Ph.D....

Copyright by Linda M. Thibodeau 2005

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FM SystemsFM Systemsfor School Aged Childrenfor School Aged Children

Linda Thibodeau, Ph.D.Advanced Hearing Research Center

Callier Center for Communication DisordersUniversity of Texas at Dallas


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Supportive informationMay be obtained at the

Website of Linda Thibodeau

www.utdallas.edu/~thib


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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!


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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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Let’s start with the Rationale for using FM Systems.


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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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In a large group, distance and noise can be a problem.

In a large group, distance and noise can be a problem.


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This results in a poor signal-to-noise ratio.

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.

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 dBA poor S/N ratio is -10 dB

the noise is 10 dB more intense than the signal

80 dB80 dB70 dB70 dB


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A good S/N ratio is +20 dBA good S/N ratio is +20 dB

the signal is 20 dB more intense than the noise

90 dB90 dB

70 dB70 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.

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.

We can accomplish this by placing a microphone on the speaker and delivering the

sound directly to the listener.


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B. Typical Classroom Noise

Optimal noise level for a class with students with

hearing loss would be30-35 dBA,

yet the typical level is about 60 dBA.

Average conversational speech is about 60 dBA, which means the

SNR is often 0 dB!

(ASHA, 2005)


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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!

(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:

Normal Hard of

Hearing Hearing

SNR of +12 dB: 83% 60%

SNR of 0 dB: 48% 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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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 inan optimal SNR provided byusing an FM System


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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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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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Microphone

Transmitter

Receiver

Sound Transducer

All FM systems have these parts-


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1) Speaker talks intomicrophone whichgenerates rapidfluctuations ofvoltage

2) Voltage fluctuations are passed to a transmitting antenna

3) Voltage fluctua-tions produce fluctuations of electric and magnetic fields around the antenna ata specific frequency

4) Electric and Magnetic field fluctuations travel as electromagneticwaves

5) Electromagneticwaves produce fluctuations in voltage at a receiving antenna

6) The voltage fluctuations are amplified

7) A filter selectsthe frequency of interest

FM Transmission Process

8) The voltage fluctuations in that frequency range aresent to the acoustic transducer

9) The transducerconverts the voltagefluctuations intosound waves togo 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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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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Microphone Type:The microphone characteristics can vary.

Omni-directional Microphone-picks up sound from all around

Directional Microphone-picks up sound primarily from the top

Multi-Directional Microphone-picks up sound from all around OR

focused area

FM Transmitters/Microphones


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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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Channel Options on the transmitters:Single, but fixed-Oscillator channel set at the factory and cannot be changed Multi-FrequencyManual frequency selection-Oscillator can be removed and changed to another frequency

Wireless frequency selection-Channel

is changed digitally


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Wireless Channel Changeability

1) Direct Frequency Synchronization-Pressing a button on the transmitter sends a signal to the receiver to synchronize the channelEx. Phonak MLxS with Campus S

2) Automatic Frequency Synchronization-Walking near a plate on the wall that contains transmitter changes the channel to a preset numberEx. Phonak MLxS with Wall Pilot


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Automatic Frequency Synchronization-Students 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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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 activeeven when the transmitter is connected to another audio source such as VCR

Mute Switch-Allows the microphone to bedeactivated so conversations can be private.


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Now let’s look more closely at the Receiver/Sound Transducer features….


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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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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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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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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 closeproximity


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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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Basic System OptionsButton Earphone with Body-worn FM systemEar Level FM Receiver with limited powerSoundfield Speaker to set on desktop or

mounted on the wallFM Amplifier with Behind the Ear hearing aid

Personal System OptionsNeckloop with Personal Aid on T SwitchDirect Audio Input with Personal AidSilhouette 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

EduLinkby Phonak

For Persons with Normal hearing, Mild loss, Auditory Processing Disorder


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Soundfield Speaker to set on desktop or mounted on the wall

Wall MountedSpeakers

Desktop Speaker


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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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Now let’s consider interfacing FM System with Cochlear Implants….


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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 ImplantDirect Plug-in of FM Receiver


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Patch cords connect FM Receiver to Cochlear Implant

Cochlear ImplantEar Level Processor Body Worn Processor

FM Receiver


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Direct Plug-in of FM Receiver

Cochlear ImplantSpeech 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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3. FM Evaluation Procedures

A. ElectroacousticB. Real EarC. Behavioral


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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 system1) 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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Test Arrangement

Examiner Side of Test Booth Student inside Test Booth


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Behavioral FM VerificationCase Illustration

Third Grader who resisted wearing FM system.Testing done to show him benefits.Hearing Aid Alone

Quiet 90% In typical classroom noise 60%

Hearing Aid with FM In typical classroom noise 90%Quiet 100%

With the FM System, the speech recognition score improved from 60% in noise to 90%!


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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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4. Use of FM Systems4. 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 TechniqueA. 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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B. Care & UseB. Care & Use

1. clean units with damp cloth 2. if put in prolonged storage - need

even temperature3. annual electroacoustic checks4. daily listening checks5. keep in chargers when not in use


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C. Settings for Various Teaching ArrangementsC. Settings for Various Teaching Arrangements


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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 themicrophone 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 lecture1) Teacher lecture

Set Receiver to pick up FM Only Signal

I think they likeI think they likemy tux!my tux!


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2) Class discussion led by the teacher 2) Class discussion led by the teacher

Set Receiver to pickup FM + Environmental (ENV) Signals

I’m not sureI’m not surethey’re listening.they’re listening.

How To SelectHearing Aids....


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3) Independent work at desk3) Independent work at desk

Set Receiver to pickup up ENV Signals

I’d rather beI’d rather beshopping!shopping!


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4) Group work4) Group work

Set Receiver to pickup ENV Signals

I’d rather beI’d rather befishing.fishing.


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D. Troubleshooting - 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 problemsE. Common problems

1. setting volume controls - must be determined by audiologist

2. matching oscillators between transmitter and receiver

3. setting the mic switch4. neckloops often noisy &

inconsistent signal


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5. changes in frequency response re: to hearing aid alone when using direct

input or neckloop6. access to audiologist who can

monitor7. dead batteries8. broken cords


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F. ManufacturersF. Manufacturers

Web pages are VERY helpful, but do not hesitate to contact manufacturer to ask questions:

1. Phonic Earwww.phonicear.com

2. Telex www.telex.com

3. Comtek www.comtek.com

4. AVR Sonovationwww.avrsono.com

5. Phonakwww.phonak.com


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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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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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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, 440-458.


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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 ErmannPhonak

Hearing Aids


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