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ALDs- Aural Rehab SHS 5734

Notes from the lecture discussing Assistive Listening Devices by Dr. Hazelbaker
Course

Introduction To Aural Rehabilitation I (SPHHRNG 734)

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Academic year: 2019/2020
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Ohio State University

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Assistive Listening Devices

ALDs n Broad range of assistive devices n Three categories n Assistive listening devices (ALDs) n Telecommunication devices n Alerting Devices n Broadly defined, assistive devices are technologies (other than hearing aids and cochlear implants) that are designed to improve the communication abilities of individuals with hearing loss n Used to help HI listeners understand speech when listening conditions are less than ideal n When the SNR is poor because of background noise n When the person is listening from a distance n When reverberation is present n ALDs can be used in conjunction with a hearing aid or can be used in place of a hearing aid n Telecommunication devices are used to improve communication over the phone or to aid in understanding the signal coming from the TV n Some telecommunication devices provide an enhanced auditory signal (like a telephone amplifier) n Others provide a visual signal in addition to or in place of the auditory signal (like a TDD for the telephone or a closed caption system for the TV) n Alerting devices are used to alert individuals to acoustic stimuli they might otherwise miss ie: alarm clock, smoke detector, crying baby, or a ringing telephone n Most commonly used by individuals with a severe to profound hearing loss n Most common HA user problem: Listening in conditions that are less than ideal—at a distance, noise, reverberant conditions n These situations are difficult because: n Signal arriving at HA microphone is reduced in intensity (because of the distance it has traveled) n Signal is mixed with background noise present in the environment n Signal is degraded by reverberation n A HA alone (even advanced digital HA) cannot completely resolve these problems n Help in adverse listening environments by: n Placing the microphone of the system close to the signal of interest (e., the speaker’s mouth, the public address system) n Signal is then transmitted directly to the ear of the listener n The signal can be transmitted using a variety of technologies (hardwire, induction, infrared, or FM) n The ALD can be used with or without a HA n Two broad categories: hardwired and wireless

n Hardwired systems require a direct electrical connection (a wire) between the microphone of the system (at the signal of interest) and the receiver of the system (at the ear of the listener) n Wireless technologies transmit the signal from the microphone to the receiver without a direct electrical connection n Induction loop n Bluetooth (most common) n Infrared n FM n Can get group systems or personal systems n Group systems are designed to be used by multiple individuals at once: n Classroom n An audience n Personal systems are “owned” by an individual and are portable and move with the individual

Hardwire Systems n Hardwired systems typically consist of n A microphone that is placed near the source of the sound n An amplifier n A receiver that is at the ear of the listener n All the components are connected via hardwire n Personal hardwire systems work in much the same way—just on a smaller scale n The mic of the system is placed near the sound source (the talker, TV, etc.) n The signal is sent to the amplifier, where the volume can be varied using a volume control wheel n Amplified signal is delivered to the listener’s ear—typically using a lightweight headset or earpiece n Personal hardwire systems are often referred to as PASs (Personal Amplification Systems) n These devices can be used as an alternative to hearing aids n They are relatively low cost n They can have good sound quality n They are easy to operate and have large, accessible controls n A Personal Amplification System can be a good alternative for people who are bedridden or physically or mentally unable to operate a conventional hearing aid n Also useful for professionals who interact with HI individuals who may not own a HA n Strengths n Low cost n Can have good sound quality (one-to-one) n Simple to operate n Weaknesses n Must have a direct electrical connection between the sound source and the listener (confined movement)

n The light wave is transmitted throughout the listening area by special light-emitting diodes (LEDs) located on the front of the transmitter n The receiver for the system is typically a battery-powered headset—it uses a photodiode to pick up the infrared signal, which is demodulated and heard via headset (or via coupling to a HA) n DAI of BTE n Neckloop n Can be used as a large group system in theaters and concert halls n A single transmitter or several transmitters are strategically placed around the listening area to bathe the area with the modulated light waves n Listeners with hearing loss obtain headset receivers and sit anywhere in the audience that there is a direct “line of sight” between the photodiode on the receiver and the LEDs on a transmitter n Infrared systems are also available for personal use n The most common application of personal infrared systems is for TV viewing n The microphone of the system can be attached with Velcro fasteners to the speaker of the television (or can be obtained from the audio output jack if available) n The transmitter is placed on top of the TV—facing the viewing area n The listener wears the receiver and headset—or couples the output of the receiver to their HA n Advantages n Infrared systems typically provide exceptional sound quality n Infrared systems are the system of choice when confidentiality or copyright restrictions are a consideration—infrared light waves cannot penetrate walls or thick curtains n Disadvantages n Lack of portability, confined to certain listening area n Cannot be used outside due to interference from sunlight n The LEDs and photodiode must be “line of sight” n Reflected signal from solid surfaces may degrade sound quality n Large area systems need professional installation

FM Systems n FM systems have been used in classrooms since the late 1960s n In 1982, the FCC lifted the classroom-only restriction—this allowed FM systems to become available for personal and group use in public facilities, like places of worship and auditoriums n Today, these systems—both group and personal—are very popular, in large part due to their versatility

Group FM Systems: n A microphone is placed close to the sound source

n The FM transmitter of the system uses the electrical signal from the microphone to modulate a designated carrier frequency n The FM signal is broadcast over a broad area—usually several hundred feet n The listener uses an FM receiver to pick up and demodulate the signal, and then delivered to the listener’s ear via headsets or through a HA n Group systems found in classrooms and in many public facilities n In the classroom, the teacher wears a mic n The mic can be wired into a small battery-powered transmitter that is also worn or n The mic can be wireless and send a signal to an AC-powered transmitter n In public facilities, the electrical signal from the public address system is typically used as the input to the FM transmitter n The FM signal is broadcast through the listening area—so individuals can sit anywhere in the room n Listeners who wish to use the system use an FM receiver to demodulate the signal n In a classroom, the child will have their own receiver that is adjusted for their HL n In a public facility, the person can pick up a receiver that provides a broad frequency response and a manual volume control n The output from the receiver is delivered to the listener using headset or the listener’s HA

n FM Soundfield Systems: n Help improve the S/N, therefore these systems help all children hear better n It is hypothesized that this will be especially beneficial to children with fluctuating hearing loss due to otitis media, children with ADD, children with unilateral hearing loss n It is also hypothesized that this will help teachers fatigue—particularly vocal fatigue n The teacher wears a wireless mic that sends the signal to an AC-powered FM transmitter n The FM transmitter sends an FM signal throughout the room n FM receivers (attached to soundfield speakers) are located strategically around the room n The soundfield speakers broadcast the teacher’s voice throughout the room

DM (Digital Modulation) Systems n Most systems use digital signal modulation today n Carrier frequency isn’t an issue n Kids and their systems are “paired” to a teacher’s mic n When going to a different group, pair with a new microphone n Direct DM systems have been developed n Some practical problems still need addressed n Digital sound transmission and digital sound processing n Leads to fewer transmission dropouts and security in the transmission itself, since it is an encrypted digital signal.

n Receivers are downloaded into the HA

Telecommunication Devices n Devices designed to assist a person with hearing loss to communicate on the telephone and to follow television programs are broadly classified as “telecommunication devices” n Personal hearing aids can be used on the phone using either acoustic coupling or inductive coupling n In the acoustic coupling method, the listener simply holds the telephone receiver up to the microphone of the hearing aid n Positioning is normal for custom instruments—it works particularly well for CIC instruments n Positioning is toward the top/back of pinna for BTE instruments n Problems associated with acoustic coupling: n Feedback n Positioning can be awkward n In the inductive coupling method, the person activates the telecoil in the HA n For listeners who do not own HA, whose HA do not have a telecoil, or who have problems even using a HA compatible phone with a good telecoil, telephone amplifiers can be used n Telephones can be amplified in a variety of ways n The amplifier can be built into the telephone itself n The amplifier can be built into a replacement handset (simply replace the original handset with one that amplifies the signal) n The amplifier can be placed “in-line” between the telephone and handset n Many HI people cannot converse on a telephone even with HA or telephone amplifiers n Some have severe to profound hearing loss n Some have severe speech understanding problems n Some have severe speech production problems n TDD stands for Telecommunication Device for the Deaf (aka TTY “teletype” machines) n Some prefer the term Text Telephone (TT) since individuals other than those who are “deaf” often make use of the device n TDDs typically consist of three parts n A keyboard for typing the outgoing message n A coupler (or modem) in which the handset is placed to send and receive the message n A display where the incoming message is shown

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ALDs- Aural Rehab SHS 5734

Course: Introduction To Aural Rehabilitation I (SPHHRNG 734)

7 Documents
Students shared 7 documents in this course

University: Ohio State University

Was this document helpful?
Assistive Listening Devices
ALDs
nBroad range of assistive devices
nThree categories
nAssistive listening devices (ALDs)
nTelecommunication devices
nAlerting Devices
nBroadly defined, assistive devices are technologies (other than hearing aids and cochlear
implants) that are designed to improve the communication abilities of individuals with
hearing loss
nUsed to help HI listeners understand speech when listening conditions are less than ideal
nWhen the SNR is poor because of background noise
n When the person is listening from a distance
nWhen reverberation is present
nALDs can be used in conjunction with a hearing aid or can be used in
place of a hearing aid
nTelecommunication devices are used to improve communication over the phone or to
aid in understanding the signal coming from the TV
nSome telecommunication devices provide an enhanced auditory signal (like a
telephone amplifier)
nOthers provide a visual signal in addition to or in place of the auditory signal (like
a TDD for the telephone or a closed caption system for the TV)
nAlerting devices are used to alert individuals to acoustic stimuli they might otherwise
miss ie: alarm clock, smoke detector, crying baby, or a ringing telephone
nMost commonly used by individuals with a severe to profound hearing loss
nMost common HA user problem: Listening in conditions that are less than ideal—at a
distance, noise, reverberant conditions
nThese situations are difficult because:
nSignal arriving at HA microphone is reduced in intensity (because of the
distance it has traveled)
nSignal is mixed with background noise present in the environment
nSignal is degraded by reverberation
nA HA alone (even advanced digital HA) cannot completely resolve these problems
nHelp in adverse listening environments by:
nPlacing the microphone of the system close to the signal of interest (e.g., the speaker’s
mouth, the public address system)
nSignal is then transmitted directly to the ear of the listener
nThe signal can be transmitted using a variety of technologies (hardwire, induction,
infrared, or FM)
nThe ALD can be used with or without a HA
nTwo broad categories: hardwired and wireless

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