Assistive Listening

Assistive listening systems (ALSs) are devices designed to help people with hearing loss improve their auditory access in difficult and large-area listening situations. Typically, these devices are used in such venues as movie houses, theaters, auditoriums, convention centers, and stadiums, where they are piggybacked on a public address system.  They may also be used in smaller listening locations like courtrooms, museums, classrooms, and community centers.

Even though a public address (PA) system is in use, sound signals have to travel from the loudspeaker(s) to the listener’s seating position.  Depending upon the particular site, this distance may be anywhere from a few feet to well over a hundred feet.  Whenever sound signals travel acoustically, they lose volume over distance and are subject to distortion and masking from background noise and reverberation.

The sound signals delivered by the ALS do not travel through acoustical space before arriving at listeners’ ears.  Thus, they are not weakened by distance or degraded by noise and reverberation during the transmission process. Instead, signals are transmitted via electromagnetic, radio, or light waves to specialized receivers used by listeners.  An ALS eliminates the last acoustical leg of the signal transmission path, providing listeners with hearing impairments with a parallel transmission path that short-cuts the usual delivery process.

It is important to note that ALSs are not intended as substitutes for hearing aids but as supplements to hearing aids.  ALS can also be used to improve functional hearing abilities for people who don’t use hearing aids.  Assembly facility operators may need to provide more than one type of device in order to serve all audiences.

Audibility and comprehension are not the same. One of the most frequent complaints voiced by people with hearing impairments is that they hear someone talking without understanding what is being said. Even in what appear to be adequate listening conditions, people with hearing loss may struggle to understand.  In rooms with excessive noise and reverberation, comprehension can become impossible.  While hearing aids can restore some of the reduced loudness caused by a hearing loss, they cannot separate the primary signa – the desired sound – from the undesired background noise.  In fact, they amplify both.  Thus, hearing aids cannot improve the speech-to-noise ratio (S/N), which is the intensity level of the speech signal relative to background noise.   People who have hearing loss need high S/N ratios to comprehend sound signals.

ALSs work to overcome the deleterious effect of the intervening acoustical conditions by bypassing them.  They deliver the desired sound signal directly to the listener’s ear, which increases the speech-to-noise ratio.  This permits people with hearing loss to function to the limits of their residual hearing capacities.

ALSs do more than improve basic speech perception capabilities in large-area listening situations.  Often people with hearing impairments are able, by expending a great deal of energy and effort, to understand speech signals in such places. They can get the message, but they have to focus so intently on receiving the spoken message that they have difficulty attending to what is being said. Unlike people with normal hearing, they may not be able to relax and enjoy an entertainment experience or focus effectively for long periods of time in an education setting. The use of ALSs can minimize this listening fatigue.

The Americans with Disabilities Act of 1990 (ADA) requires that buildings and facilities be accessible to and usable by people with disabilities. This includes communications access for people with hearing loss.

The ADA Accessibility Guidelines (ADAAG), adopted as the ADA standards for accessible design by the Department of Justice (DOJ) in 1991, require that certain newly constructed and altered assembly facilities be designed and constructed to include assistive listening systems (see the sidebar for ADAAG scoping and technical provisions). In addition, DOJ regulations implementing title II (covering the public sector) and title III (covering the private sector) of the ADA include requirements for effective communication with people with disabilities that may require the installation of fixed or portable ALSs in existing assembly facilities (see sidebar).

The ADA does not cover private clubs and entities that are operated and controlled by religious organizations.  However, many houses of worship make ALSs available to their congregants, not as a matter of law but as a service to their people, and club facilities used by other organizations must support ALSs required for meetings and performances.

Consumers who use assistive listening devices report dissatisfaction with the quality of many systems provided in assembly areas.  Device use rates and patterns may have been artificially depressed due to the lack of effectiveness and/or compatibility of many systems now installed.   Demographics suggest that use of ALSs will increase as our population ages.  It is likely also that current technologies will advance as new requirements are implemented.

± - What is an Inductive Loop System?

± - How do Induction Loop Systems work?

It is well known that when an alternating current is passed through a wire, a magnetic field is generated around the wire. If a second wire is brought within this magnetic field, a corresponding alternating current is created within the second wire. In technical language, a current is said to be "induced" in the second wire. Hence the term "induction". This particular electromagnetic principle is the basis on which electrical motors, electrical generators and transformers operate.

An induction loop system "induces" hearing aid telecoils or an Induction Loop Receiver in the same way. An Induction Loop System consists of an amplifier and a loop. The amplifier is connected to a sound source such as a TV, a radio, a public address system or a dedicated microphone. It then amplifies this sound signal and sends it out, in the form of an alternating current, through the loop. The loop itself consists of insulated wire, one turn of which is placed around the perimeter of the room in a simple loop system. When the alternating current from the amplifier flows through the loop, a magnetic field is created within the room. The magnetic field "induces" the hearing aid telecoil or the Induction Loop Receiver.

If a hearing aid user switches to the T or MT position on their hearing aid or if an individual is wearing an Induction Loop Receiver, the telecoil in the hearing aid or Induction Loop Receiver picks up the fluctuations in the magnetic field and converts them into alternating currents once more. These are in turn amplified and converted by the hearing aid or the Induction Loop Receiver into sound. The magnetic field within the loop area is strong enough to allow the person with the hearing aid or Induction Loop Receiver to move around freely in the room and still receive the sound at a comfortable listening level.

While this principle is well known and appears straightforward, in practice only well designed constant current driven amplifiers coupled with correct loop design, can provide the pure, undistorted sound necessary to satisfy both the listeners and the regulators demands. AMPETRONIC designs and manufactures the finest, commercial quality constant current driven induction loop amplifiers available and provides technical support to ensure correct loop design.

± - What are the advantages of Induction Loop Systems?