Forum Proceedings

Summary

Manufacturers, researchers, clinicians and other stakeholders have identified technology needs in the field of Infrared Assistive Listening Systems (ALS). High priority technology needs include systems for small group communication, portable receivers, and portable transmitters. Component technologies including narrow spectrum IR diodes, low power transmitter / emitter diodes, environmentally sensitive "smart" diodes, and an improved modulator circuit were identified as critical for improving infrared systems.

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Market

It is estimated that more than 20 million people in the United States experience some form of hearing loss. Ninety to ninety-five percent of these people could benefit from hearing aids and assistive listening systems. A large majority of the people who would benefit from these devices (approximately 80%) have chosen not to use them. This leaves more than 16 million people with substantially correctable hearing loss who are not currently using assistive devices. Many of the people in this population choose not to use the devices because they are not satisfied with the performance of products currently available or are reluctant to wear an obtrusive device they feel is stigmatizing.

Assistive Listening Systems (ALS) bring a remote (essentially 'noise free') sound into the direct-proximity of the user's ear in order to amplify a selected sound source, overcome background noise, enhance listening in large public venues, and improve one-to-one conversations. Used in combination with hearing aids an ALS can provide optimal sound clarity and speech comprehension. ALS are categorized by the wireless communication protocol used to link the remote sound source and the body-worn receiver. Common ALS include frequency modulated (FM), infrared (IR), and inductive loop (IL) systems. The receiver can be directly associated with the hearing aid (built-in FM receiver, FM-boot, telecoil). Alternatively, some IR and FM receivers retransmit the signal via an inductive neck loop to be picked up by the hearing aid telecoil.

According to the Hearing Aid Compatibility Act of 1988, all telephones sold in the US should be compatible with standard hearing aid telecoils. However, it is estimated that only 30% of modern hearing aids in the US actually incorporate a telecoil. (A telecoil is an induction coil placed in a hearing aid that is designed to pick up fluctuating magnetic fields produced by coils in the telephone hand set, so that these signals can be amplified without interference; Self Help for Hard of Hearing, 1999). Persons with greater hearing loss often have BTE hearing aids with T-coils, while persons with less severe hearing loss often have smaller ITC and CIC hearing aids that lack T-coils. As a consequence, persons with more severe hearing loss are more likely to benefit from inductive loop systems.

The Americans with Disabilities Act (ADA) and the Telecommunications Act have increased the popularity and availability of assistive technologies for employment, education, and access to buildings, transportation and telecommunications. The ADA requires that any business (auditoriums, theaters, etc.) with 50 or more fixed seats in an assembly area must make ALS available for at least 4% of the seating capacity (The US Equal Employment Opportunity Commission, 1990). The market potential for assistive listening systems is much broader than the hearing aid market. People without hearing impairments are currently using ALS for museum tours, nature walks, improved listening at philharmonic concerts, and other "enhanced listening experiences."  Additionally, infrared technology used for high quality public address systems and for a multi-channel, multi-media entertainment venue poses a huge market opportunity for anyone able to develop these technologies.

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Current Technology

Infrared (IR) systems provide a personal communication channel between the speaker and the listener that shortens the "acoustical pathway" between speaker and listener and improves the signal-to-noise ratio. Wide area IR systems are available for one-to-many (single sound source / many listeners) communication. Personal IR systems are available for one-on-one (single speaker / single listener) communication. IR systems for many-to-many (natural, small group) communication are currently not available.

The basic IR system is composed of the transmitter (also called the modulator), the emitter and the IR receiver. The modulator processes the audio signal so that it can be transmitted via infrared light. The signal from the modulator (transmitter) is delivered to emitters composed of one or more infrared diodes that produce the IR light waves. The transparent lens found on every IR receiver contains an infrared photo diode that detects the IR light wave. The IR receiver then demodulates the RF sub-carrier and the audio signal is retrieved and amplified (Bakke, Levitt, Ross, & Erickson, 1999). Infrared systems use commercially available "off-the-shelf" components that are designed for other applications (e.g. FM radio electronics) and may have sub-optimal performance.

Most infrared systems have operated at 95 kHz and 250 kHz (with stereo reception) sub-carriers. More recently, 300 kHz, 2.3 MHz and 2.8MHz sub-carriers have been employed. Infrared systems cannot generally be used in direct sunlight (infrared "noise" overpowers the transmitted "signal").  Fluorescent lighting produces infrared noise (harmonics from fluorescent lighting with T-12 ballasts) that interferes with 95 kHz infrared systems (providing impetus for other sub-carrier frequencies to be used). Fluorescent lights are sometimes covered with an infrared absorbing material that is transparent to visible light. Infrared receivers use broad-spectrum diodes with pass band filters that are more subject to infrared interference (than narrow-spectrum diodes). Narrowly tuned diodes would benefit system design by reducing interference - provided that transmitters will not drift outside the pass band during normal operation. Strong infrared transmitters can interfere with the infrared receivers of other electronic devices, such as large screen video projectors or TV remote controls. Signal overlap between nearby infrared transmitters can cause interference that is worse at night when the infrared signals carry farther.

Infrared systems generally require line-of-sight between transmitter and receiver. It can be difficult maintaining the signal path when people change their position and orientation relative to the transmitter (e.g. people moving about at an outdoor conference). Many surfaces reflect infrared light and for indoor applications it is generally not necessary to maintain direct line-of-sight between transmitter and receiver. Infrared opaque "walls," make infrared systems relatively secure and private. In contrast, FM and inductive systems lack privacy and security because their transmissions cannot easily be contained within a confined region. Infrared receivers are immune to electromagnetic and inductive interference that effect FM and inductive loop systems.  Infrared systems can be used in electromagnetic sensitive environments (e.g. hospitals, airplanes) for which FM systems are unsuitable.

Wide area infrared transmitters are relatively simple to set up and use in meeting rooms, conference halls etc. A microphone is the most common input device but large halls often have multiple microphone positions, or alternative sound sources such as tape machines and audio-mixing equipment interfaced to the main transmitter (emitter) panel. Multi-microphone systems are somewhat more complicated to set up (wires and microphones) and use. Emitter panels can be permanently installed or portable and generally have an ovoid transmission pattern. Coverage depends on the size and shape of the room" If one panel is not sufficient then repeater panels are used to increase the coverage area. Multi-channel (each channel a different frequency) infrared systems (e.g. for multi-language translation) are readily available but expensive. Small infrared systems for in-home applications are generally inexpensive. Most wide area infrared systems require an AC power supply.

Portable (body worn) IR transmitters are available with sound field systems and wide area systems. The speaker can move freely about some local area where a receiver picks up the signal that is then output through speakers (sound field system) or relayed to a more powerful infrared emitter and retransmitted on a different frequency (wide area system). Portable IR transmitters are also used with personal communication systems for one-on-one communication in loud environments. Body-worn transmitters are generally powered by a rechargeable battery with between 2-20 hours of use between charges(depending on battery type).

Infrared receivers are available in stethophone, headphone and body worn variations. Stethophone receivers hang below the user's chin, the lens of the receiver diode faces forward and sound is output through the ear buds or an inductive loop. Body worn receivers are similar in size and appearance to body-worn FM receivers except for the forward facing diode lens, sound output is through headphones, ear buds or an inductive loop. These receivers sometimes include jacks for environmental microphones (for communication in the immediate area) but generally lack low power indicators. Body-worn transmitters are generally powered by a rechargeable battery with between 2-20 hours of use between charges (depending on battery type).

Wireless headphones (FM or IR) are gaining acceptance for home entertainment (e.g., TV, music, etc.) where a person needs a volume level that would disturb others. The transmitter receives its input from an audio jack (television, radio, etc.) or from a microphone placed near the sound source. The receiver can be located at the top of the headphones with approximate omni-directional reception or on the headphones themselves. Headphones (for all receiver types) can be worn over all but behind-the-ear (BTE) hearing aids. Universal infrared/FM receivers were on the market that (in principle) eliminated the need for multiple receivers, however FM receiver and "active microphone" performance were not considered to be acceptable.^*

Infrared systems from different manufacturers (even using the same sub-frequency carrier) are often not completely compatible due to differences in transmitter signal pre-processing (e.g. high frequency emphasis) and receiver signal post-processing and sensitivity. IR system standards (e.g. light level) are generally lacking. Setting up or installing an IR system may be straightforward but obtaining uniform and consistent signal strength is not (installers usually move about the reception area to evaluate reception quality).

Technology is currently under development in other industry sectors that may be applied to the assistive listening field. This includes technology developed for the military and systems developed for the blind. The Department of Defense (DOD) has developed high power diodes that can transmit over three miles in sunlight. DOD is also interested in transferring narrowly tuned diodes to the private sector. Other DOD-developed technologies include phototonics, smart diodes, advanced transmission technologies, dry lithium polymer and other battery innovations.

Talking Signs is an infrared system for the blind that uses an advanced front-end receiver circuit to reduce interference from sunlight while the transmitter has a smart power-saving diode. Another technology with good potential for ALS applications is telemetry recharging. A "plastic gun" recharges the battery without removing it.

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Technology Requirements

Users, manufacturers, clinicians, researchers, and other stakeholders have identified technology that will significantly improve the performance of ALS and expand the market for infrared ALS and related technology. Technology currently needed includes:

• IR systems for "natural" or small group communication
• A "universal" portable receiver
• A "universal" portable transmitter
• Narrow-spectrum IR diodes for portable receivers
• Low power IR diodes for transmitter/emitter
• Smart transmitter diodes that adjust power in a response to the environment
• An improved IR modulator circuit
• Improved batteries

The specific performance features for these technologies are listed below. Final product manufacturers and consumers are keenly interested in technologies that meet these needs. Both component and system solutions that enhance the lives of people with and without hearing disabilities present a significant business opportunity.

Infrared System for Natural Small Group Communication

• Consists of Receivers and Transmitters.
• Should use multi-frequency or signal path (range and direction) approach.
• Should isolate the speaker(s) and listener(s) in a "noise free cone" (imagine the speaker and listener in a Bell Jar ability to capture input properly")
• Should eliminate bill boarding effect (e.g. prevent persons at nearby tables" from listening in on conversations).
• Should be easy to use (e.g. portable, natural, little or no setup of transmitters, wires and microphones)

(Note: a System for Natural, Small Group Communication is essentially a combination of the characteristics found with the Universal Receiver and Universal IR Transmitter below.)

Universal Portable Receiver

• Should be priced so that individual users can own them (increased user convenience)
• Should be universally compatible (work with) any infrared transmitter.
• Should be multi-frequency (e.g. readily identify and receive transmissions for some set of predefined frequencies).
• Should detect and lock onto transmitter frequency (e.g. useful when changing environments; for small group communication systems)
• Should indicate who is speaking (user should not have to look around to see who is speaking, perhaps a visual display might indicate who is speaking).
• Should have a more natural way to "aim" the receiver (e.g. for small group communication, attached to eyeglasses, or a piece of [head worn] jewelry).
• Should have adjustable reception range (short range would help prevent billboarding during small group communication; long range would enable the user to hear someone speaking across the room).
• Should have user frequency selection capability (e.g. select among multiple channels carrying different languages).
• Should be compatible with other electronic devices (e.g. connect receiver to a tape recorder).
• Should support headphones, DAI, and inductive loop (universal output for persons with and without hearing aids).
• Should integrate FM and IR receivers (minimize equipment carried by persons with profound hearing loss).

[Note: please refer to problem statement on FM Systems for details on desirable FM receiver characteristics.]

• Should be immune (eliminated or greatly reduced) to infrared interference from sunlight, fluorescent lighting and bulb flashes.
• Should use narrowly tuned (narrow spectrum) diodes to reduce IR interference (e.g. sunlight, fluorescent lights, "flash bulbs)
• Should employ a "front-end circuit" that reduces the effects of sunlight (Talking Signs referenced)
• Should minimize sound leakage (i.e. don't annoy nearby listeners that do not have hearing impairments).
• Should be comfortable, convenient, and attractive (e.g. keep wires untangled, integrate receiver into jewelry (cufflinks, etc.) or headphones).
• Should be unobtrusive (currently "big black box hanging from your neck")
• Should have large and easy to use controls (ON/OFF, volume, etc.; especially important for elderly users.)

[Note: it was suggested that volume should not be under user control but rather could be preset by an audiologist.  This suggestion is not compatible with universal use by persons with - and without impairments.  It was also suggested that a separate credit card sized remote control could be employed.]

Infrared Transmitters (for both Portable and Wide Area Transmitters

• Should use a carrier frequency that fluorescent lighting will not interfere with (e.g. shift sub-carrier frequency away from 95 kHz)
• Should not interfere with other infrared devices (e.g. IR remote controls).
• Should have improved modulator circuit (e.g. FM modulators circuits now used)
• Should be compatible with other electronic devices (e.g. TV, radio audio output).
• Microphone should provide low noise input to the transmitter (i.e. signal quality at the receiver is limited by the signal quality from the transmitter.)

"Universal" Portable Infrared Transmitter (Emitter)

• Should use diodes with lower power consumption
• Should use "smart diodes" that limit infrared energy to "just what is necessary" for the environment (Talking Signs referenced)
• Should be smaller and lighter (current units are bulky, unaesthetic and interfere with vigorous physical activity)
• Should have short-range transmitters on aircraft (i.e. enable one-on-one communication without interfering with other users.).
• Should use batteries with reduced size, increased time between recharge, increased capacity, reasonable cost etc.

Wide Area Transmitter (Emitter)

• Should use more-powerful diodes
• Should have ON/OFF signage on (important for users - if the system is "ON" and nothing is received, users know there is a problem.)

^* Technology developers who are interested in Inductive Loop Technology solutions may also want to refer to the FM and Infrared Problem Statements. There may be opportunities to combine the technologies and leverage a multi-system solution for an expanded market share. New, innovative or revolutionary approaches that are independent of the technologies under consideration might provide the superior solution. Dr. Laszlo's comments introducing this section of the Proceedings are particularly relevant.

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References

Bakke, M, Levitt, H, Ross, M, & Erickson, F. (1999). Large Area Assistive Listening System: Review and Recommendations. RERC on Hearing Enhancement. Available: http://www.hearingresearch.org/LargeAreaALS.htm [December 1, 2000].

Self Help for Hard of Hearing, I. (1999). SHHH Position Statement: Telecoils. Available: http://www.odc.state.or.us/tadoc/hoh6.htm [April 25, 2000].

The US Equal Employment Opportunity Commission. (1990). Americans with Disabilities Act. Available: gopher://trace.wisc.edu/00/ftp/pub/text/ada_info/handbook/h_faq.txt [April 25, 2000]

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