FMs and ALDs
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Transcript of FMs and ALDs
![Page 1: FMs and ALDs](https://reader036.fdocuments.us/reader036/viewer/2022062406/559247871a28abda358b47e2/html5/thumbnails/1.jpg)
Assistive Devices
Objectives Describe effects of FM system on speech
perception Recommend appropriate assistive listening
devices for a given child.
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Assistive Devices - FM
ANSI Standard 12.60 - Classroom acoustics
Noise no greater than 30 dB-A
Reverberation time (RT60) no greater than 0.6/0.7 s
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Assistive Devices - FM
60 dB room noise 4’ away: 66 dB
+6 SNR 8’ away: 60 dB
0 SNR 16’ away: 54 dB
-6 SNR
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Assistive Devices - FM
Mic 1’ to mouth 60 dB room noise
1’ away: 78 dB +18 SNR
1’ away: 78 dB +18 SNR
1’ away: 78 dB +18 SNR
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Assistive Devices - FM Types
Microphones Lavalier
Boom
Handheld
Receivers Self contained
Direct audio input to CI or HA
Induction Neckloop T-Coil
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FM Microphone Styles
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FM Receivers
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Soundfield FM
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Desktop FM
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Conundrum of the FM v. HA/CI Microphone
FM only – only teacher’s voice is audible FM+Mic – teacher plus environment audible
For severe/profound loss, also own voice is audible
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Adaptive FM
FM system automatically adjusts level of hearing aid/CI microphone
Subjectively preferred
Better performance on speech recognition
(Thibodeau 2010)
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Troubleshooting FM
Transmitter and receiver must be on same channel
Both need to be charged Cables need to be connected
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Bluetooth adapters
Music
Music or
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Other ALDs
Closed/open captioning
Vibrating alarm clocks Flashing alerts
phone, doorbell Amplified telephone Phone relay
Voice Carry-Over TTY relay IM relay (AT&T and AOL Instant Messenger)
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Factors affecting classroom understanding
Distance
Directionality
Reverberation
Noise
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Signal to noise ratio
Affected by Noise and DistanceDistance
Directionality
Reverberation
Noise
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Critical distance Where indirect
sound level equals direct sound level
Distance
Directionality
Reverberation
Noise
Indirect energy
Direct
energy
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Critical distance
Within 1/3 of critical distance Direct energy 10
dB above indirect
Distance
Directionality
Reverberation
Noise
Within 1/3 of critical distance
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Distance
Directionality
Reverberation
Noise
Critical distance
More than 3x the critical distance
Beyond 3x critical distance Direct energy 10
dB below indirect
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Distance
Directionality
Reverberation
Noise
Critical distance
Directional microphones are only effective within critical distance!!