SPA 608 - Lundeen©

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Assistive Listening Devices

• Purpose = reduce the effects of– Distance– Background noise– Reverberation

• Solution:– Pick up signal at its source– Transmit signal directly to listener

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ALD Types

• Hard Wired - connection from sound sourceto receiver– Sound source (mic, TV, stereo, etc.)– Receiver (headphones, hearing aid with DAI)

• Wireless– Radio Frequency– Light (Infrared)– Loop Induction (Loop)(Electromagnetic)

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Hard Wired System

• Advantages– High fidelity– Inexpensive

• Limitations– Restricted mobility

Directaudio input

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Radio Transmission

FM88 – 100 MHz72 – 76 MHz = hearing assistanceChannels10 wide-band (WB)40 narrow-band (NB)

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Radio Transmission

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Infrared

Transmit sound throughlight waves to receiversworn by users. They aretypically found incourtrooms, movietheaters, and playhouses.They are susceptible tointerference from brightlight.

SPA 608 - Lundeen©

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Induction Loop

• Audio signal is routed through a wire“loop” which produces anelectromagnetic field picked up by thehearing aid telecoil

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Telecoils (T-coil)

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Induction Loops: Small Area

Neckloop

Direct audioinput

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Induction Loop: Wide Area

• Oval Window

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ALD ComparisonLoop

AdvantagesLow-techInexpensive

LimitationsPortabilityCross-talkInterference

InfraredAdvantages

Privacy

LimitationsInstallationCostlyOccasionalinterference

FMAdvantages

Portability & freedomof movementIndividualizedtransmission

LimitationsModerate costBroadcast rangeOccasionalinterference