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

Supportive information Website of Linda Thibodeau May be obtained at the Website of Linda Thibodeau www.utdallas.edu/~thib Copyright by Linda M. Thibodeau 2005

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

Copyright by Linda M. Thibodeau 2005 OVERVIEW 1. Rationale for use of FM Systems 2. FM Systems 3. FM Evaluation Procedures 4. Use of FM Systems Copyright by Linda M. Thibodeau 2005

Let’s start with the Rationale for using FM Systems. Copyright by Linda M. Thibodeau 2005

1. Rationale for use of FM Systems A. Signal-to-Noise Ratio B. Typical Classroom Noise C. Audio Demonstration of Classroom Noise Copyright by Linda M. Thibodeau 2005

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. Copyright by Linda M. Thibodeau 2005

In a large group, distance and noise can be a problem. Copyright by Linda M. Thibodeau 2005

This results in a poor signal-to-noise ratio. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 i.e. the intensity of the noise at the listener’s ear is greater than the signal of the speaker. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 A poor S/N ratio is -10 dB the noise is 10 dB more intense than the signal 80 dB 70 dB Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 A good S/N ratio is +20 dB the signal is 20 dB more intense than the noise 70 dB 90 dB Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 We can accomplish this by placing a microphone on the speaker and delivering the sound directly to the listener. Copyright by Linda M. Thibodeau 2005

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! (ASHA, 2005) Copyright by Linda M. Thibodeau 2005

(the teacher’s voice is 15 dB more intense than the background noise). 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) Copyright by Linda M. Thibodeau 2005

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 . Copyright by Linda M. Thibodeau 2005

95% - Only missed 5% of words 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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

second section of the lecture. Now let’s look at the operation and design of FM Systems in our second section of the lecture. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 2. FM Systems A. Introduction to FM Technology B. Transmitters/Microphones C. Receivers/Sound Transducers D. Cochlear Implants and FM Systems Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005 13

Copyright by Linda M. Thibodeau 2005 All FM systems have these parts- Microphone Transmitter Receiver Sound Transducer Copyright by Linda M. Thibodeau 2005 14

Copyright by Linda M. Thibodeau 2005 FM Transmission Process 1) Speaker talks into microphone which generates rapid fluctuations of voltage 2) Voltage fluctuations are passed to a transmitting antenna 3) Voltage fluctua- tions produce fluctuations of electric and magnetic fields around the antenna at a specific frequency 5) Electromagnetic waves produce fluctuations in voltage at a receiving antenna 4) Electric and Magnetic field fluctuations travel as electromagnetic waves 6) The voltage fluctuations are amplified 8) The voltage fluctuations in that frequency range are sent to the acoustic transducer 9) The transducer converts the voltage fluctuations into sound waves to go to the ear 7) A filter selects the frequency of interest Copyright by Linda M. Thibodeau 2005 16

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005 17

Now let’s look more closely at the Transmitter/Microphone features…. Copyright by Linda M. Thibodeau 2005

B. FM Transmitters/Microphones Descriptive Categories 1) Microphone Type 2) Microphone Location 3) Channel Options Copyright by Linda M. Thibodeau 2005

FM Transmitters/Microphones 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 Copyright by Linda M. Thibodeau 2005

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) Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

Wireless Channel Changeability 1) Direct Frequency Synchronization- Pressing a button on the transmitter sends a signal to the receiver to synchronize the channel Ex. 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 number Ex. Phonak MLxS with Wall Pilot Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005

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. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 Now let’s look more closely at the Receiver/Sound Transducer features…. Copyright by Linda M. Thibodeau 2005

C. FM Receivers/Sound Transducers Descriptive Categories 1) Type-Relationship to Personal Amplification/Cochlear Implant 2) Receiver Location 3) Channel Options 4) Sound Transducers Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

FM Receivers/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. Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 Let’s look at some illustrations of these different types of sound transducers! Copyright by Linda M. Thibodeau 2005

Button Earphone with Body-worn FM system Copyright by Linda M. Thibodeau 2005

Basic Ear Level FM Receiver with limited Power For Persons with Normal hearing, Mild loss, Auditory Processing Disorder EduLink by Phonak Copyright by Linda M. Thibodeau 2005

Soundfield Speaker to set on desktop or mounted on the wall Desktop Speaker Wall Mounted Speakers Copyright by Linda M. Thibodeau 2005

FM Amplifier with Behind the Ear hearing aid Copyright by Linda M. Thibodeau 2005

Neckloop with Personal Aid on T Switch Copyright by Linda M. Thibodeau 2005

Direct Audio Input with Personal Aid Copyright by Linda M. Thibodeau 2005

Silhouette with Personal Aid on T Switch Copyright by Linda M. Thibodeau 2005

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. Copyright by Linda M. Thibodeau 2005

Now let’s consider interfacing FM System with Cochlear Implants…. Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

Patch cords connect FM Receiver to Cochlear Implant Ear Level Processor Body Worn Processor FM Receiver Copyright by Linda M. Thibodeau 2005

Direct Plug-in of FM Receiver Cochlear Implant Speech Processor FM Receiver Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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…. Copyright by Linda M. Thibodeau 2005

3. FM Evaluation Procedures A. Electroacoustic B. Real Ear C. Behavioral Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005

Next the FM Receiver is attached and the HA/FM system is evaluated. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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) Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 Test Arrangement Examiner Side of Test Booth Student inside Test Booth Copyright by Linda M. Thibodeau 2005

Behavioral FM Verification Case 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%! Copyright by Linda M. Thibodeau 2005

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! Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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 Copyright by Linda M. Thibodeau 2005

C. Settings for Various Teaching Arrangements Copyright by Linda M. Thibodeau 2005

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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 1) Teacher lecture Set Receiver to pick up FM Only Signal I think they like my tux! Copyright by Linda M. Thibodeau 2005

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.... Copyright by Linda M. Thibodeau 2005

3) Independent work at desk Set Receiver to pickup up ENV Signals I’d rather be shopping! Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 4) Group work Set Receiver to pickup ENV Signals I’d rather be fishing. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 D. Troubleshooting - Works best when two people check each component separately and the add components progressively according to the following steps: Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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) Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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 www.phonak.com Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005

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." Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 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. Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005 Acknowledgements Erin Schafer, M.S. University of Texas at Dallas Paul Dybala, M.S. Gary Overson, M.A. Jack Scott, M.A. 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 Copyright by Linda M. Thibodeau 2005

Copyright by Linda M. Thibodeau 2005