Why an Assistive Listening System?
Background noise and reverberation, or simply distance to the sound source, degrade intelligibility much faster for hard of hearing people, whether they wear hearing aids or not. Thus, hard of hearing people are prevented from participating on equal terms with hearing people in larger assembly areas which are not equipped with assistive listening systems. Even the best in digital sound systems technology, combined with the best in digital hearing aid technology, cannot solve the intelligibility problems the hard of hearing people are faced with. In recognition of this, requirements for making assistive listening systems and devices available in places of public accommodation were included in the Americans With Disabilities Act (ADA) signed into law in July of 1990.
The International symbol for hearing accessibility adopted by the United States Access Board.
The purpose an Assistive Listening System?
The purpose of an assistive listening system is to transmit sound as directly as possible to a transducer in the hard of hearing person's ear. The simplest way to achieve this is to use a small personal amplifier with a microphone and an extension cord. The microphone is simply placed near the sound source. The user wears a headset or neckloop and can adjust the loudness on the amplifiers volume control. However, hard wired systems like this are not practical in places of public accommodations. Apart from personal body worn systems, they practically all have been replaced by modern wireless systems as shown below the guidelines.
Guidelines to ADA and CBC/DGS Compliance
Americans with Disabilities Act (ADA) and California Building Code (CBC) - Department of General Services (DGS)
Many government web documents contain hundreds of pages that do not relate to Assistive Listening Systems (ALS). Therefore it can often be difficult to find what you are looking for. To save you time, we have provided shortcuts and excerpts to most relevant pages. This information is intended as a guideline for ADA and CBC/DGS compliance only. It should not be used as a substitute for legal advice. It is recommended that you obtain legal advice that is specific to your application as some information provided could be outdated and/or may not reflect current legal developments.
Americans with Disabilities Act (ADA)
The Americans with Disabilities Act (ADA) was signed into law on July 26, 1990, by President George H.W. Bush. The ADA is one of America's most comprehensive pieces of civil rights legislation that prohibits discrimination and guarantees that people with disabilities have the same opportunities as everyone else to participate in the mainstream of American life -- to enjoy employment opportunities, to purchase goods and services, and to participate in State and local government programs and services.
ADA Help Pages as they relate to Assistive listening Systems and Devices
California Building Code (CBC - DGS)
Both the Americans with Disabilities Act (ADA) and the California Building Code (CBC) require public facilities to provide equal access to people with disabilities, including those individuals who have difficulty hearing. However, there are differences in the codes, in particular to receiver requirements and how the codes applies to public facilities, houses of worship, and premises occupied by California Department of General Services (DGS).
CBC & DGS Help Pages as they relate to Assistive listening Systems and Devices
Wireless Technologies and How They Work
Today there are three basic wireless technologies available which provide different methods of transmission: FM broadcast technology, Infrared light technology (IR), and Induction loop technology. No single technology is best for all applications. Each type has its own advantages, problems and limitations. All three types of assistive listening technologies can easily and successfully be used for personal and commercial applications alike, as long as their individual limitations are observed.
FM Broadcast Technology.
In principle, FM systems designed for hearing assistance application work just like commercial FM broadcast systems operating in the 88 to 108 MHz range. However, in the United States, the FM systems operate at FCC-designated frequency bands in the rage from 72 to 76 MHz and from 216 to 217 MHz. Since each FM system may use its own broadcast frequency, several systems can operate simultaneously at one location without interfering with one another. However, unlike the loop system, the FM system requires a special receiver for each person, whether s/he has a hearing aid or not. There are several listening options available for FM receivers. The most common for public facilities are headphones and neck loops for T-coil users.
Infrared Light Technology (IR).
Infrared light can be used for signal transmission in same fashion as with FM transmission. An infrared system consists of two or three basic components: a modulator and an emitter which often are combined, and a receiver. The audio signal is conveyed onto a sub-carrier in the modulator which in turn is converted into infrared light by the emitter. The receiver detects the IR signal and converts it back into the original audio signal. However, unlike FM transmission and induction loop technology, infrared light cannot pass through walls. Therefore, infrared light transmission is ideal for facilities operating several systems simultaneously in different rooms in that all receivers can be identical with no need for frequency coordination.
As with FM technology, each person must use a receiver, whether or not s/he has a hearing aid. Receiver types include lightweight under-the-chin style, over-the-head receivers for 360-degree reception and body-pack style. The same listening options are available for the body-pack style receivers as for the FM receivers.
Induction Loop Technology (Teleloop - Hearing loop - Room loop)
This technology is based on electromagnetic transmission and has the unique advantage that the signal is received directly by the user's hearing aid when it is equipped with a T-coil (telemagnetic pickup coil). It is commonly referred to as a telephone switch. An induction loop system consists of an amplifier and a discrete wire (the loop) that runs along the perimeter of the room. When the loop amplifier receives a signal from an audio source such as a microphone or PA system, the sound is received wireless by the user's hearing aid without the need for an additional receiver as is required by all other technologies. Induction receivers are available for hearing impaired people without hearing aids or without the T-coil feature.
A similar summary of assistive listening devices and systems can also be found in the ADA Accessibility Guidelines (ADAAG) A.4.33.7 Types of Listening Systems - Table A2. Please note that the ADA chart was reprinted and modified from an earlier Centrum Sound publication. However, the basic content does not differ from the above.
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