FMs and ALDs

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FMs and ALDs

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

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