Forum Proceedings

Technology Area

Infrared and Inductive Loop Assistive Listening Systems were identified by researchers, manufacturers and end-users as technology areas that could benefit from technological innovation and refinement. They believed that the development of improved infrared and inductive loop systems would meet important user needs and represent significant business opportunities for this industry segment.

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Market Need

The general function of hearing aids is to pick up sound from the environment with a microphone, process this sound (e.g., compress, expand, amplify, filter, etc.) and deliver it to the user's ear through a speaker and earmold. Advanced hearing aids use signal processing algorithms (to remove certain types of undesirable sound) and directional microphones, which are somewhat more sensitive to sound sources in front of the user than to their sides or back. However, even advanced hearing aids provide limited benefit for users trying to pick up a remote sound source in a noisy or reverberant environment. Hearing aids can be fitted with a telecoil (T-coil) capable of picking up an electromagnetic signal. T-coils were designed to facilitate telephone conversation by picking up the electromagnetic fields produced by the speaker diaphragm coil in phone handsets. T-coils can also be the receiver for inductive loop Assistive Listening Systems (described below). Unfortunately, it is estimated that only 30% of modern hearing aids sold in the U.S. incorporate a telecoil (Self Help for Hard of Hearing, 1999b).

The general function of Assistive Listening Systems (ALS) is to bring a remote (essentially `noise free') sound signal into the direct-proximity of the user's ear. A television (e.g. with audio jack) or remote microphone might be the source for such sound signals. ALS's process the remote signal and then transmit this signal via a wireless link. These wireless links commonly use infrared light (`invisible light' whose wavelength is `longer than' the red light that we can see), inductive (electromagnetic) fields or frequency modulated (FM) radio waves. The receiver for the wireless link can be part of the hearing aid (e.g. built-in FM receivers or T-coils that pick up inductive transmissions) or a hearing aid accessory (e.g. an external FM receiver; AVR Sonovation; Phonak). Alternatively, the receivers can be completely separate from the hearing aid. In some cases, users wear a FM or IR receiver whose sound output is through headphones or earphones. Other FM or IR receivers process and retransmit the signal via an inductive neck loop whose signal is picked up by the hearing aid T-coil. Large assistive listening system can receive inputs from a number of remote sources (e.g., multiple microphones, sound systems, sound mixing tables, etc.).

Many people appear to be unaware that Assistive Listening Systems are available or may not understand that they can be used in conjunction with hearing aids to increase communication clarity (Self Help for Hard of Hearing, 1999a).

Audiologists and hearing aid dispensers could have an important role educating their patients about ALS technology, its appropriate use and availability.

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 persons could benefit from hearing aids and Assistive Listening Systems. A large majority of these people (approximately eighty-percent) have chosen not to make use of available technologies. This leaves more than 16 million people with substantially correctable hearing loss who are not seeking treatment, or addressing their hearing loss by other means.

According to the 1990-91 National Health Survey study, 3.6 million people (eighteen percent) who identified themselves as having hearing problems use hearing aids. ^* Use of hearing aids is highest among the 18 years of age and older groups whose hearing loss became significant after the age of 19. In 1999, hearing aid sales in the United States were estimated at 1.9 million units. ^** Revenue from hearing aid sales reached $1 billion in 1993 and is currently estimated to be $1.43 billion (5.2% compound growth rate; Frost & Sullivan, 1994). The USA presently generates 39.3% of hearing aid sales, Europe has 34.5%, the Pacific Rim has 14.3%, while the rest of the world accounts for 12.1% of all revenue.

Assistive Listening Systems have general market potential beyond the needs of people with hearing disability. For the hearings impaired market, an Advance Data Report from the National Center for Health Statistics reported that in the U.S., approximately 874,000 persons who are 'hard of hearing' use amplified telephones, ALSs, and other hearing technologies (not including hearing aids; National Center for Health Statistics, 1997). This figure represents less than 5% of those persons who could benefit from such technologies. ALS are used as private, noise free communication channels. For example, infrared and FM Assistive Listening Systems are common in educational settings, museums, conference rooms and many other settings. ALS also have great potential for people who are blind.

The United States population is aging, with more people living into their 70's and 80's. All of these persons are potential consumers of assistive hearing technology. The aged population is expected to grow until the year 2036 when this population is expected to reach its maximum level. The world population is also following a similar growth trend.

The Americans with Disabilities Act (ADA) has increased the availability of assistive listening technologies for employment, education, and access to public buildings and transportation. ALS can be permanently installed or set up on request although this last option does not ensure timely access. Of course, the assistive listening system must also be properly maintained (e.g., receiver batteries charged) in order to serve the user's needs.

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Basis for Discussion

Assistive listening systems bring a remote essentially noise free sound signal directly to the hearing impaired listener across the intervening reverberant and noise filled acoustic space. Assistive listening systems extend the hearing range of these individuals.

Directional hearing aids attenuate peripheral sounds and focus on sounds directly in front of the listener. These devices provide better understanding of speech in noise when the speaker is close by but provide little benefit when the speaker is distant. Used in conjunction with hearing aids, wearable and hand-held "directional beam-forming microphone arrays" further improve the perception of close by speakers.

Assistive Listening Systems are classified by the wireless link between a distant transmitter and body worn receiver. The three most common technologies use infrared light, inductive (electromagnetic) fields and radio waves to establish this link.

This discussion focuses on systems using infrared (IR) and inductive loop (IL) technologies. Inductive loop systems have been in place for many years. The IL transmitter is commonly a loop of wire around a listening area. The IL receiver is a coil of wire often inside the hearing aid itself (telecoils or T-coils). The great benefit of IL systems is that a hearing aid user does not require a separate receiver. Unfortunately, most hearing aids in the U.S. are not equipped with telecoils. In addition, the telecoil orientation with respect to the inductive field may impact the quality of signal reception.

Infrared systems use an infrared `heat source' as their transmitter. Receivers must generally be in line-of-sight to this transmitter. This feature provides a great benefit there is no spillover of communication between infrared systems in adjacent rooms. Infrared assistive listening systems are generally used indoors where sunlight cannot interfere with reception.

Improvements to and application extensions of inductive loop and infrared assistive listening technology will provide important benefits for end-users and significant business opportunities to manufacturers.

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Current Technology

Most ALS have a single sound source (e.g. public address system, TV audio output jack, etc.) and one or more listeners. For some systems, the user can switch between sound sources (e.g. multiple microphones) or mix signals from different sources. With the exception of gain control (roughly equal amplification across all frequencies) and signal compression (wide input signal excursions are kept within some dynamic range) most ALS do not further process the sound signal.  Typical environments for ALS include service counters, conference rooms, auditoriums, classrooms, courtrooms, churches and temples, theaters, museums, arenas and sport stadiums, retirement and nursing homes and hospitals. The following sections discuss conventional inductive loop, 3-D inductive loop and infrared Assistive Listening Systems in more detail.

Conventional Induction Loop Systems (Architectural and Transportation Barriers Compliance Board, 1999; Bakke, Levitt, Ross, & Erickson, 1999)

This technology converts the acoustic signal into electromagnetic fields produced as electric current which passes through a wire loop placed around a listening area. In general, the user must remain within the loop area in order to receive the transmission. The inductive loop ALS can be permanently installed or installed on an as-needed basis. Portable inductive loop systems are available for use with small groups of listeners and can be stored in a carrying case and set up as needed.

For a typical system, a speaker talks into a microphone connected to a loop amplifier. The acoustic energy of the speaker's voice is changed to an amplified alternating electrical current that is sent through a loop of wire placed around the reception area (e.g., home, conference and class rooms, churches, nursing homes, theaters, courtrooms, etc.). As electrical current passes through the wire loop the electrical energy is transformed into electromagnetic energy. The electromagnetic field "induces" a corresponding electrical current in the hearing aid telecoil (essentially another loop of wire). This electrical current 'travels through' the hearing aid to the hearing aid's speaker. The speaker transforms the electrical signal back into an acoustic signal (sound) that is delivered to the ear.

Microphones are the most common input device for inductive loop systems but these systems may also receive their input from other sources (e.g., a television's SCART connection, sound systems, special doorbells, telephone ringers, etc.). In large halls, there may be multiple microphone positions, along with alternative sound sources such as tape machines and audio-mixing equipment interfaced to the system. Pocket, hand-held, and ear level (similar in form to a hearing aid) inductive receivers are available. These devices output the sound signal through headphones (with or without a hearing aid in place) or earphones.

Permanent installation of the inductive loop wire often requires grooving the floor for cable placement. This may be difficult, costly or impractical (e.g. historical sites, vinyl floor covering, etc.). To solve this problem, a flat insulated cable with adhesive backing has been developed. A plastic (PVC) cap can be placed over the cable for increased protection and durability.

3D Induction Loop Systems (Frost & Sullivan, 1994; National Center for Health Statistics, 1997)

The 3D inductive loop systems use a special "loop processor" and "loop mats" rather than a single loop enclosing the reception area. The electromagnetic fields produced by a 3D-loop system substantially reduce the orientation dependent sensitivity of a standard telecoil receiver. Field spillover for a 3D-loop system is also substantially reduced relative to the conventional inductive loop system. Installing loop mats six feet apart essentially eliminates the spillover effects. 3D-loop systems are much less common and generally more difficult to install than conventional loop systems.

Infrared (IR) Systems (Frost & Sullivan, 1994; National Center for Health Statistics, 1997)

This technology converts the acoustic signal into infrared light radiated from infrared emitters focused onto the listening area. Infrared light has a 'longer wavelength' than red light (wavelength determines the perceived color) and is invisible to human eyes. The infrared light signal will reflect well from many but not all surfaces. Depending upon the environment then, the user (actually their infrared receiver) may or may not need to be in the "line-of-sight" to the emitter. Infrared ALS can be permanently installed or installed on an as-needed basis. Portable infrared systems are available for use with small groups of listeners and can be stored in a carrying case and set up as needed. Infrared transmitters for in‑home use can be plugged into the audio jack of a television or stereo.

For a typical system, the speaker talks into a microphone transforming the acoustic signal into an electrical signal. The electrical signal may be processed (e.g., input signal compression) before driving an infrared emitter. For large venues, infrared ALS employ large emitter (heater) panels. The infrared signal is picked up by the infrared receiver and converted back into an electrical signal. The transmitted infrared signal is typically frequency modulated (FM). This electrical signal drives headphones or earphone speakers. Alternatively, the electrical signal can be retransmitted via an inductive neck loop to be picked up by a hearing aid T-coil or provided as a direct audio input (DAI) to the hearing aid.

Infrared transmissions do not travel through walls or other solid surfaces. There is no signal spillover and privacy is ensured. Some infrared systems use multi-frequency receivers that support independent, non-interfering communication channels. This is useful (for example) with multilingual translation and multilingual environments. Infrared wireless headphones are especially useful for television listening. Sound input to an in-home infrared transmitter from the audio jack plug on the TV, or a microphone placed near the TV speaker.

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Statement of the Problem

The following discussion is based upon issues raised during interviews and panels involving researchers, manufacturers and end-users.

Induction Loop Systems

For conventional inductive loop systems, the orientation of the electromagnetic field is dependent upon ones position relative to the loop. In the center of the loop, the field is perpendicular to the plane in which the loop lies. As one moves about the looped region, the field orientation changes somewhat. A telecoil picks up the signal best when the local electromagnetic field is perpendicular to the plane in which the telecoil lies. The user must reposition their head (and maintain this position) in order to orient the hearing aid telecoil for optimal reception.

• The electromagnetic field produced by a conventional loop system spreads somewhat beyond the region enclosed by the loop. This is problematic when adjacent regions are "looped." In such cases, users may pick up signals from adjacent looped regions.
• In principle, inductive loop systems have significant advantages over infrared and FM Assistive Listening Systems. These advantages include convenience for hearing aid users with built‑in telecoil receivers, elimination of the cost for separate receiver units, and decreased system maintenance (e.g. charging receiver batteries). Unfortunately, it is estimated that only 30% of modern U.S. hearing aids are fitted with telecoils ‑though in many European countries, the percentage is much higher. For general applications, separate receiver units must be purchased and maintained. Inductive (telecoil) receivers are also susceptible to interference from ambient electromagnetic fields (e.g., fluorescent light fixtures, power cables, electric motors, etc.). Building structural elements (e.g., steel girders) and environmental objects (e.g., steel seats) can affect the shape, strength and local orientation of the electromagnetic field.
• 3D-loop systems are much less common and generally more difficult to install than conventional loop systems.

Infra-Red (IR) Systems

Infrared ALS generally cannot be used in direct sunlight and are subject to interference from fluorescent lighting. Infrared receivers are required for everyone and these receivers require administration and maintenance. Infrared systems that use neck loops are also subject to electromagnetic interference. Portable infrared transmitters are available that can run for hours between battery charges.

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Issues to Consider

The Need

• What are the important, unmet (or poorly met) user needs related to infrared and inductive loop Assistive Listening Systems?
• What populations or demographics (e.g., degree of hearing loss, characteristics of hearing loss, cause of hearing loss, age, etc.) are most affected by these needs/problems?
• In which environments and for which activities is this need or problem most significant?
• What accommodations (or behavioral changes) do hearing impaired persons make in order to function in these environments and accomplish these activities?

State-of-the-Practice

• What infrared and inductive loop products are used by, or prescribed for, hearing impaired persons in order to address these problems or needs?
• What are the strengths (e.g., performance, cost, etc.) of these products?
• What are the weaknesses (e.g., performance, cost, etc.) of these products?

Future Technology and Products

• What significant technical improvements are needed?
• What technical barriers (e.g. environmental factors, power consumption, size, etc.) must be overcome in order to achieve these technical improvements?
• What breakthrough technologies (not present in current products) might better address the identified needs and problems?
• What technical barriers (e.g. environmental factors, power consumption, size, etc.) must be overcome in order to achieve these technical breakthroughs?

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References

Architectural and Transportation Barriers Compliance Board. (1999). Table A2: Summary of Types of Assistive Listening Devices and Systems. Available: http://www.access-board.gov/bfdg/texta2.htm [April 25, 2000].

Avrsono Company. (2000). Extended-Ear. Available: http://www.medicine-news.com/articles/devices/phonak.html [March 29, 2000].

Bakke, M, Levitt, H, Ross, M, & Erickson, F. (1999). Large Area Assistive Listening System: Review and Recommendations, Final Report to United States Architectural and Transportation Barriers Compliance Board. Jackson Heights: RERC on Hearing Enhancement.

Frost & Sullivan. (1994). World Audiology Product Markets. Available: http://www.frost.com [March 29, 2000].

National Center for Health Statistics. (1997). Advance Data: Vital Statistics of the Centers for Disease Control and Prevention (292). Hyattsville, MD: National Center for Health Statistics.

Phonak, A. (2000). Biomedical Device Manufacturers - Medicine News. Available: http://www.medicine-news.com/articles/devices/phonak.html [March 29, 2000].

Self Help for Hard of Hearing, I. (1999a). SHHH Position Statement: Hearing Assistance Technologies. Available: http://www.odc.state.or.us/ tadoc/hoh1.htm [April 25, 2000].

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

^* The study included non-institutionalized persons over the age of three.

^** Report published by the Hearing Industries Association Statistical Report, ending December 31, 1999. Numbers were based upon data supplied by 37 companies that agreed to participate in the report. Within this number the total number of hearing aids can be further broken down to: Behind-the-Ear (372,000 units), In-the-Ear (893,000 units), Completely-In-the-Canal (195,700), In-the-Canal (385,700), Body Aids, Eyeglasses, and others (53,200). Exports from the USA were estimated at 500,000 for this same time-period.

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