|
ADA Accessibility Guidelines for Buildings and Facilities (ADAAG)
3.5 Definitions.
Assembly Area. A room or space accommodating a group of individuals for recreational, political, social, civic, or amusement purposes, or the consumption of food and drink.
4.1.3. Accessible Buildings:
New Construction. Accessible buildings and facilities shall meet the following minimum requirements;
(19)* Assembly areas
(b) This paragraph applies to assembly areas where audible communications are integral to the use of the space (e.g., concert and lecture halls, playhouses and movie theaters, meetings rooms, etc.). Such assembly areas, if (1) they accommodate at least 50 persons, or if they have audio-amplification systems, and (2) they have fixed seating, shall have a permanently installed assistive listening system complying with 4.33
For other assembly areas, a permanently installed assistive listening system, or an adequate number of electrical outlets or other supplementary wiring necessary to support a portable assistive listening system shall be provided. The minimum number of receivers to be provided shall be equal to 4 percent of the total number of seats, but in no case less than two. Signage complying with applicable provisions of 4.30 shall be installed to notify patrons of the availability of a listening system.
4.30 Signage.
4.30.7* Symbols of Accessibility.
(4) Assistive Listening Systems.
In assembly areas where permanently installed assistive listening systems are required by 4.1.3(19)(b) the availability of such systems shall be identified with signage that includes the international symbol of access for hearing loss (see Figure 1).
4.33 Assembly Areas
4.33.6* Placement of Listening Systems.
If
the listening system provided serves individual fixed seats,
then such seats shall be located within a 50 ft (15 m) viewing
distance of the stage or playing area and shall have a complete
view of the stage or playing area.
Figure 1: International Symbol of Access
for Hearing Loss
4.33.7* Types of Listening Systems.
Assistive listening systems (ALS) are intended to augment standard public address and audio systems by providing signals which can be received directly by persons with special receivers or their own hearing aids and which eliminate or filter background noise. The type of assistive listening system appropriate for a particular application depends on the characteristics of the setting, the nature of the program, and the intended audience. Magnetic induction loops, infra-red and radio frequency systems are types of listening systems which are appropriate for various applications.
Figure 2: An induction Loop (IL) System
Figure 3: An FM System
Figure 4: An Infrared (IR) System
DOJ Title II rule
DEPARTMENT OF JUSTICE
Office of the Attorney General
28 CFR PART 35
[Order No.]
Nondiscrimination on the Basis of Disability in State and Local Government Services
AGENCY: Department of Justice.
Action: Final Rule.
Subpart A -- General
{35.104 Definitions
Auxiliary aids and services includes—
(1) Qualified interpreters, notetakers, transcription services, written materials, telephone handset amplifiers, assistive listening devices, assistive listening systems, telephones compatible with hearing aids, closed caption decoders, open and closed captioning, telecommunications devices for deaf persons (TDD’s), videotext displays, or other effective methods of making aurally delivered materials available to individuals with hearing impairments.
Subpart E – Communications
{35.160 General.
(a) A public entity shall take appropriate steps to ensure that communications with applicants, participants, and members of the public with disabilities are as effective as communications with others.
(b)(1) A public entity shall furnish appropriate auxiliary aids and services where necessary to afford an individual with a disability an equal opportunity to participate in, and enjoy the benefits, of a service, program, or activity conducted by a public entity.
(2) In determining what type of auxiliary aids and service is necessary, a public entity shall give primary consideration to the requests of the individual with disabilities.
AND TITLE III:
PART 36 NONDISCRIMINATION ON THE BASIS OF DISABILITY BY PUBLIC ACCOMMODATIONS AND IN COMMERCIAL FACILITIES
Sec.36.303 Auxiliary aids and services.
(a) General. A public accommodation shall take those steps that may be necessary to ensure that no individual with a disability is excluded, denied services, segregated or otherwise treated differently than other individuals because of the absence of auxiliary aids and services, unless the public accommodations can demonstrate taking those steps would fundamentally alter the nature of the goods, services, facilities, privileges, advantages or accommodations being offered or would result in an undue burden, i.e., significant difficulty or expense.
(b) Examples. The term “auxiliary aids and services” includes – (1) Qualified interpreters, notetakers, computer-aided transcription services, written materials, telephone handset amplifiers, assistive listening devices, assistive listening systems, telephones compatible with hearing aids, closed caption decoders, open and closed captioning, telecommunications devices for deaf persons (TDD’s), videotext displays, or other effective methods of making aurally delivered materials available to individuals with hearing impairments;
[…]
(c) Effective communication. A public
accommodation shall furnish appropriate auxiliary aids and
services where necessary to ensure effective communication with
individuals with disabilities.
The
technical assistance provided in this Bulletin is intended
solely as informal guidance; it is not a determination of the
legal rights or responsibilities of
entities subject to titles II or III of the ADA. |
The landmark Americans with Disabilities Act (ADA), enacted on July 26, 1990, provides comprehensive civil rights protections to individual with disabilities in the areas of employment (title I), State and local government services (title II), public accommodations and commercial facilities (title III), and telecommunications (title IV). Both the Department of Justice and the Department of Transportation, in adopting standards for construction and alterations of places of public accommodation and commercial facilities covered by title III and public transportation facilities covered by title II of the ADA, have issued implementing rules that incorporate the Americans with Disabilities Act Accessibility Guidelines (ADAAG), developed by the Access Board. U.S. Architectural and Transportation Barriers Compliance Board BULLETIN
#8B: ASSISTIVE LISTENING SYSTEMS FOR INSTALLERS How do assistive listening
systems (ALS’s) differ from ordinary public address (PA)
systems? In some
respects, this is the key question. Certainly, PA systems are
assistive listening systems. That’s what they are designed to
do: help people hear. In a PA system, the sound waves travel
from one or more loudspeakers to the people sitting in the
audience. Ordinarily, for most people and in most circumstances,
and without minimizing the technical skill required to determine
the appropriate loudspeaker locations, this is all that is
required. For normally hearing people, the sound signals
emanating from the loudspeakers can be both heard and
understood. Unless the acoustical conditions and/or loudspeaker
installations are particularly poor, the fact that sound waves
have to travel some distance before listeners receive them is
not a particularly relevant concern for people with normal
hearing. No matter how well-placed the loudspeaker(s), however,
the perception of the air-borne speech signals will be difficult
for many people with hearing loss. The presence of background
noise or excessive reverberation times will compromise speech
intelligibility for most listeners, but people with hearing
impairments are particularly disadvantaged in such conditions. An ALS
differs from a PA system in that the sound signals delivered by
the ALS do not travel through acoustical space before arriving
at listeners. Thus they are not weakened by distance or degraded
by noise and reverberation during the transmission process.
Instead, these signals are transmitted via electromagnetic,
radio, or light waves to specialized receivers used by
listeners. What ALS’s do is to eliminate the last acoustical
leg of the signal transmission path. In essence, an ALS provides
hearing-impaired listeners with a parallel transmission path,
one that short cuts the usual delivery process. By
“bridging” the acoustical space between the source and the
listener, the impact upon the sound waves caused by distance,
noise, and reverberation can be circumvented. Why is it necessary to
“bridge” the acoustical space for hearing-impaired people
and not for those with normal hearing? It is
necessary here to emphasize the distinction between audibility
and comprehension. Certainly, the signals delivered by
loudspeakers can ensure audibility for almost everyone. And if
audibility is still a problem for people with hearing loss, the
question is often asked why hearing aids can’t provide what
they need? Isn’t that what hearing aids are supposed to do?
For a hearing-impaired person, however, loudness is just one
part of the listening equation. Of course they have to hear the
signal, with or without hearing aids, in order to understand it.
But for most people with hearing loss, the comprehension of
verbal messages takes more than audibility. Their comprehension
also depends upon the nature of their hearing losses. In the
most common type of problem, particularly affecting older
persons, hearing acuity is poorer at the higher frequencies than
the lower. However, the acoustic characteristics of speech that
allow listeners to distinguish between speech sounds occur
largely in the higher frequencies. Thus, the common complaint of
people with hearing loss, “I can hear but I don’t
understand”. That is, they can “hear” the low frequency
components of speech signals, and thus know someone is talking,
but cannot “understand” because many of the important higher
frequencies are being filtered out by their hearing loss.
Increasing loudness, by itself, will not measurably improve the
situation. In addition
to the filtering impact of the hearing loss, the nature of many
hearing problems is that the analytic powers of the cochlea are
also compromised. Thus, such people would have difficulty
resolving the separate components of complex acoustic signals
(as in a piano chord) or discriminating fine temporal
differences within speech sounds. For example, the distinction
between such voiced and voiceless sounds as /p/ and /b/ or /t/
and /d/ depend as much on detecting timing differences as it
does upon hearing the voiced components. Beyond a pure
sensitivity loss, then, and depending upon the specific site and
type of damage to the cochlea and the higher auditory pathways,
other psychoacoustic abnormalities may co-exist with diminished
thresholds and interfere with speech perception. What all
this means for people with hearing loss is that these auditory
pathologies interact with the external acoustic conditions in
such a way as to produce a disproportionate effect upon speech
perception. Indeed any distortion of the speech signal can have
this effect, such as that produced by people talking with
foreign accents, too fast, or with sloppy articulation. For
example, consider an optimal acoustical situation in which a
normally hearing person achieves speech perception scores of 96%
and a hearing-impaired person obtains an 84% score. Now add some
moderate degree of noise and/or reverberation and their scores
may drop to 88% and 40% respectively. The scores for the
normally hearing person drops 8% while that of the
hearing-impaired person is reduced by 44%. This example shows
the disproportionate effect of acoustical conditions upon the
speech perception ability of people with hearing loss. Increasing
the loudness of the signal will not remedy this situation; what
has to be increased is the signal-to-noise (S/N) ratio. There
have been lots of studies that demonstrate that it is possible
to compensate to some degree for this disproportionate effect by
increasing the S/N ratio. In effect, what we’re doing with an
ALS is attempting to replicate a perfect listening situation for
the hearing-impaired person, the one in which (in the example
above) a score of 84% was achieved. While we can’t always
provide the “perfect” signal, we can, through an ALS,
significantly improve its quality over that which would be
received via the loudspeaker system. What ALS’s
do for people with hearing loss, then, is to permit them to
function to the limits of their residual hearing capacities.
They do more than this, however. Often hearing-impaired people
are able, with a great deal of effort, and by expending a great
deal of energy, to understand the speech signals in large-area
listening venues. –They can get the message, but in doing so
they have to focus so intently on receiving the spoken message
that they have difficulty attending to what is being said.
Unlike people with perfectly normal hearing, they can’t really
relax and enjoy the experience. ALS’s will help them to do
this and preclude their leaving the venue tired and unhappy,
something that happens all too often. How many people in our
society can benefit from an ALS? The
statistics regarding the number of people with hearing loss in
our society vary depending upon the source and the criterion
used to define hearing loss. Most sources give this number as
falling between 24 and 28 million people, or about 10 percent of
the population. Hearing-impairment increases with age. It is
estimated that the majority of people over the age of 65 have
some degree of hearing impairment. Due to the increased
longevity and the aging of our population, the total number (and
the percentage) of people with hearing loss is likely to
increase in the future. There is little doubt but that most of
these people would be able to benefit from an ALS. While some
may benefit more than others, just about all people with any
degree of hearing loss should be able to obtain some advantages
from the system – if not in their actual comprehension of the
spoken messages, at least in the effort they have to make in
order to comprehend. We should also keep in mind that people
receiving direct assistance from an ALS are not the only ones
involved. People do not usually attend events by themselves. If
one considers those family members who would be accompanying the
person with a hearing loss, then it is apparent that the total
number of people potentially affected by the availability of
ALS’s is much greater than these already high figures. What are the statutory
requirements for ALS for specific venues? The
Americans with Disabilities Act of l990 (ADA) requires that
buildings and facilities be accessible to and usable by people
with disabilities. This includes communication access for people
with hearing loss. The
ADA Accessibility Guidelines (ADAAG), adopted as the ADA
standards for accessible design by the Department of Justice 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 (public sector) and title III (private sector) of the
ADA include requirements for effective communications with
people with disabilities that may require the installation of
fixed or portable ALS 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 ALS’s available to their congregants, not as a
matter of law but as a service to their people. What types of systems are
available? Basically
there are three types of large area ALS:
Induction Loop (IL):
In
the first type, the induction loop (IL) system, a loop of wire
encircles the listening area (or is embedded in a mat placed
under a rug) (see Figure 2). This loop of wire is connected to
the amplifier output of a Public Address (PA) system instead of,
or in addition to, the usual loudspeaker. Instead of sound
emanating from a loudspeaker, the IL system produces an
electromagnetic field around the wire. These electromagnetic
signals are accessed by hearing-impaired listeners through
telephone coils found in many hearing aids (about 30% of hearing
aids include “T” coils). While these “T” coils were
originally included in hearing aids to improve telephone
communication, they will respond to any electromagnetic field.
When the electromagnetic field emanating from the wire loop
intersects these coils, it “induces” an alternating
electrical current in the coil. This electrical current is then
processed by the hearing aid in the same way that it processes
acoustical signals reaching the microphone. The major advantage
of IL systems is that listeners whose hearing aids include
“T” coils always have their special ALS “receiver” with
them. All they have to do to get “tuned in” is switch their
hearing aids to the telecoil (“T”) position when entering a
looped area. A
few facilities that only include an IL system also provide
special telecoil receivers for people who do not use hearing
aids. These special receivers come in various shapes and sizes,
but all contain a wire coil to detect the electromagnetic field
and an amplifier to increase the signal level. A
number of problems have been associated with IL systems: these
include spill-over of the magnetic into adjacent areas (both
horizontally and vertically), susceptibility to stray
electromagnetic fields, variations in the electromagnetic field
within the loop, and issues related to the quality and physical
orientation of the telecoils. With a proper installation and
appropriate hearing aids all of these problems can be eliminated
or minimized.
FM: The
second type is the FM system. An FM assistive listening system
is simply a variation on the commercial FM radio. The signals
are “broadcast” by FM transmitters and picked up by
listeners using an “FM radio” tuned to the transmitting
frequency (see Figure 3). These “radios”, or special FM
receivers, must be made available by the facilities that use FM
ALS’s. The FCC has reserved the non-commercial 72MHz to 75MHz
and the 216 MHz to 217 MHz bands for auditory assistance
devices. The lower band is a non-exclusive band, which means
that interference from other users in the same frequencies may
occur (such as from emergency vehicles of various kinds). The
effective range of the lower FM band is a radius of about 300 to
500 feet, given the power limits set by the FCC (80 millivolts
per meter at 3 meters). The effective transmitting range of the
216-217 MHz band is approximately twice that of the lower band. There
are several potential problems with FM systems. The first is
that privacy is not possible. The FM signals do not stay
contained within the four walls of the enclosure. If privacy is
a consideration, then an FM system is not appropriate for that
facility. The second potential problem is the flip-side of the
first: radio signals originating outside of the facility can
enter the facility and interfere with reception. One cannot
prevent occasional interference, as when some emergency vehicle
in the area transmits on the same frequency used in the venue.
However, persistent interference can usually be overcome by
selecting alternate frequencies within the permitted bands. On
the up side, it is relatively easy with an FM system to ensure
adequate signal strength at all seat locations, even in the
largest venues.
Infrared (IR): The
third type of ALS is the Infrared (IR) light system. In an IR
system, audio signals from any source are conveyed to listeners
via infrared light waves (using Light Emitting Diodes) invisible
to the human eye. The light waves are picked up by a photo
detector diode contained within the “optical bubble” found
on every IR receiver. The receiver then extracts the original
audio information from the IR signal and delivers an amplified
version to the ears of a listener (see Figure 4). Ordinarily,
strict “line of sight” is necessary between an IR emitter
and the transparent lens on the receiver, but this can be
modified in rooms with light-colored surfaces (the IR waves are
reflected off them) or by adding additional emitters. Since IR
systems are light waves, they exhibit the advantages and
disadvantages of light waves. The IR signals are contained
within a room, thus ensuring privacy, and adjacent rooms in a
facility can use IR systems without fear of inter-room
interference. They are also not as subject to radio or
electromagnetic interference as are FM systems. However, outdoor
use if problematic because of the effect of sunlight (which
contains a great deal of infrared energy) and it is more
difficult to cover the largest venue with IR systems than with a
radio type system. All
IR systems require a radio-frequency (RF) sub-carrier as an
intervening step between the audio and the light waves. That is,
the audio signals first “modulate” the RF sub-carrier, which
in turn modulates the IR light signals. Until now, 95 kHz has
been the unofficial RF sub-carrier, permitting a person to use
the same IR receiver in different venues. Compatibility between
venues has always been a major advantage of IR systems. The
situation may now be changing because of the electromagnetic
interference at this frequency produced by the newer, more
energy efficient, fluorescent lights. Because of this, some
facilities are or may be switching to different sub-carrier
frequencies (250 kHz, 2.3 MHz) with their IR systems. This will
not be a problem for consumers as long as the facility provides
them with compatible IR receivers. However, switching
sub-carrier frequencies may affect those consumers who have, or
desire to, purchase a personal IR receiver. Since no commercial
IR receivers have the capability to detect all the possible
sub-carrier frequencies, it would not be practical for them to
possess personal IR receivers (unless they limit their
attendance to those facilities that provide compatible IR
sub-carrier frequencies) What principles govern the
selection of ALS’s for specific venues? It is always
a good idea for the installer (or the equipment distributor) to
consult with the provider prior to the selection and
installation of an ALS. When possible, a preliminary visit to
the facility is advisable. At the least, the installer should
obtain a detailed description of the facility, its operation,
and its unique needs prior to decision-making. Below are just
some of the considerations that you and the facility
representative should jointly consider: ·
Is
privacy a major consideration? Is it necessary that the events
taking place within a facility not be accessible to people
outside the enclosure? If so, then an IR system must be
employed. There are really no other alternatives. ·
Is
this an outdoor facility? (A racetrack would be a good example.)
In this case, an FM system would be the appropriate choice. ·
Is
this a large indoor facility, such as a really massive
auditorium with balconies, overhangs, and other nooks and
crannies? While a skilled person can satisfactorily install an
IR system in such locations, and it should not be ruled out, it
is easier to ensure adequate signal strength at all seat
locations with an FM system. However, this choice will be
influenced by the presence of electromagnetic interference from
outside sources, or the possibility of interfering with such
external users of radio systems as hospital and public safety
organizations. ·
Are
a large number of simultaneous events going to be taking place
in adjoining facilities? While there are a sufficient number of
potential FM carrier frequencies available to ensure
non-interference between rooms, and thus an FM system is a
possibility, it may then be necessary to provide FM receivers
that can be tuned to all the possible frequencies. How will the
audience respond to the necessity to change frequencies? Will it
cause difficulties if someone in one room can “tune in” to
events in a different room? If these possibilities may turn into
future problems, then an IR system is advisable. IR systems can
be installed in every room in a facility with no interference
between rooms. Furthermore, the same IR receiver can be used in
every room. ·
Is
it going to be necessary to use the same system alternately in a
number of different rooms (such as in a community center,
switching from one activity room to another)? Ordinarily, FM
system are somewhat more flexible and can be used both indoors
and out (as in a tour group). However, some IR systems are also
relatively easy to deploy, and portable units will work well in
the smaller activity rooms, though they will not operate as
effectively outdoors. ·
Is
there a possibility of radio interference within the auditory
assistance FM frequencies (72-75 MHz and 216-217 MHz bands).
This can be determined by using a frequency scanner to determine
the possibility of interference prior to the installation. If
the interference is likely to persist, and this is not amenable
to a change in carrier frequency (which most problems would be),
then an IR system would be the best bet. Except for a
few specialized locations (like schools for the deaf), IL
systems are rarely used in large listening venues. This is
ironic, since of all the ALS’s, they are probably, from the
viewpoint of the facility, the simplest system to provide. The
IL “receiver” is simply the telecoil in the person’s own
hearing aid, thus relieving the facility of the necessity to
supply and care for receivers. Unfortunately, since less than
30% of modern hearing aid include a telecoil, an IL system alone
would not provide auditory access for all the hearing-impaired
people in the audience. Specialized IL receivers are available,
but this defeats the major advantage of an IL system – its
convenience. What
are my target electroacoustic performance standards for the
signals emanating from the earphones? The
following recommended electroacoustic performance standards
reflect the results of a research project completed at the
Lexington Center’s Rehabilitation Engineering Research Center
(RERC) in 1998 and 1999. In conducting this study, the RERC
researchers opted to focus on the last stages of the
transmission process, i.e. the signals actually being delivered
to the earphones through ALS’s. By comparing the input to the
output, all the factors that ALS’s can impose upon an audio
signal would be subsumed. The complete project, as well as the
background “state of the art” paper can be accessed on the
Lexington Center website at www.hearingresearch.org. The primary
metric used to define the quality of the output signal was the
Speech Transmission Index (STI). Basically, the STI compares the
integrity of an audio signal at two different points in the
transmission process, e.g. at a talker’s lips or loudspeaker
compared to the same signal being delivered through the
earphones. It does this by measuring the “fill” between
adjacent peaks in a simulated or actual speech envelope. This
fill represents the addition of noise and reverberation to the
primary signal. The more the “fill”, the lower the STI. An
STI of 1.0 represents the source signal; anything less reflects
the amount of noise and reverberation added to the primary
signal. Measuring
the STI RERC
engineers developed a simplified software version of the
original STI. This can be used to measure the STI where the
input is either from a live microphone or from an audio track.
With live microphones, a test loudspeaker is placed at the
location of the talker. The output signal from the STI
measurement system is broadcast from the test loudspeaker,
picked up by the microphone, and passed through the ALS for
measurement. When an audio track is the source (such as in a
movie), the line output of the STI measurement system replaces
the audio track. In either case, the output of the ALS is
monitored either by means of a line output from the ALS, or via
earphones through a coupler of some kind (e.g., Zwislocki
coupler). The output from the ALS is connected to the STI
measurement system through the line input port of the
computer’s sound card. The person testing the system can then
run the software (available through the Lexington RERC) and in
about three minutes the STI measurement is complete. It is
important to note that the recommended STI is applicable in any
type of listening situation. It can be employed in the absence
of a sound system, simply by comparing the signal at a
talker’s mouth (the input) to that picked up at any point in
an enclosure (the output). Obtaining
the software. Detailed
information about the Speech Transmission Index Software,
including system requirements and equipment setup, may be found
at the following website: www.hearingresearch.org/STIinfo.htm.
The software itself may be downloaded from hearingresearch.org/stidownload.htm
or ordered on CD-ROM from hearingresearch.org/STI.htm.
Electroacoustic
targets. These
targets apply in all seat locations in every venue employing an
ALS. ·
We
recommend a minimum STI of .84 with any ALS in any large-area
listening situation. In our judgment, all facilities should
strive to exceed this minimal figure, in this and in all of the
other electroacoustic recommendations given below. ·
We
recommend a minimum Signal-to-Noise ratio of 18 dB. This result
is also based on the results obtained in the listening project
we conducted with hearing-impaired listeners. When the system is
being used with hearing-impaired children, we recommend that the
S/N be increased to 25 dB, to reflect the fact that children in
the process of learning auditory language require greater signal
saliency than adults who use the sound to recognize a previously
learned language system. ·
The
system must be capable of providing at least 110 SPL output, but
not exceed an output of 118 dB SPL. The assumption here is that
people who require greater signal levels would be employing some
kind of external coupling to personal hearing aids (acoustical,
inductive, or direct audio input). Are
all the possible transmission variables subsumed under these
electroacoustic targets? Yes. By
measuring the signal at the last stage in the transmission
process, i.e. the headphones, all the variables and factors that
can reduce signal quality would be included. For signals
originating from microphones, this would include microphone
position re the talker, type of microphone, and room acoustics
as well as any signal degradation occurring between the source
and the headphones. When any of the electroacoustic targets are
not met, the installer must troubleshoot the system, locate the
source of the problem, and correct the situation. It is
impossible to predict and anticipate all the factors that may
affect signal quality, and there is no desire to dictate the
details of an ALS installation to the professionals who install
them. By focusing only upon the electroacoustic targets,
installers would then be able to utilize their own skills and
creativity in ensuring that these criteria are being met. In
some instances, because of a clearly inadequate system, it may
be impossible to achieve the desired targets. In such a
situation, it would be incumbent upon the installer to utilize a
higher quality ALS, one with which the electroacoustic targets
can be met. What
types of pre-processing strategies are desirable? This is a
very difficult question to answer specifically. A number of the
participants in our focus groups suggested that the transmitted
signal be as transparent as possible, with any signal processing
strategies accomplished at the personal receiver level. However,
other participants pointed out that certain pre-processing
strategies may be inevitable, given the need to compensate for
wide input signal variations and to provide additional high
frequency emphasis when transmitting speech signals. This issue
was basically left unresolved. The danger of being too specific
in recommending certain pre-processing strategies is that it may
inhibit future product development by manufacturers who
constantly try to improve their products. As long as the
electroacoustic targets are met (or exceeded), installers can
exercise a wide range of pre-processing strategies to obtain the
desired targets. What
types of receivers and coupling arrangements are available? RF receivers
are about the size of a pack of cigarettes and feed either
headsets or earbuds. All include on/off switches and volume
controls. The receivers may be worn hung around the neck,
clipped to a belt or placed in a pocket. Those people who use
hearing aids may prefer to use a neckloop instead headphones or
earbuds. A neckloop operates on the same principle as the
large-area IL system; only it fits around the neck rather than
around a room. It is plugged into the receiver earphone jack and
transmits an electromagnetic field to a hearing aid telecoil.
For the individuals involved, “inductive” coupling is a
convenient way to use an ALS receiver, since it enables them to
continue to use their personal hearing aids. However, as noted
above, only about 30% of modern hearing aids include telecoils,
mainly because of size restrictions (they won’t fit into the
smallest hearing aids). Other hearing aid (behind-the-ear type)
or cochlear implant users may prefer to directly connect the ALS
receiver to their personal listening devices through a wire
cord. In these instances, users would ordinarily supply their
own patch cords. IR body pack
receivers are similar to FM receivers and employ the same
coupling arrangements (headphones, earbuds, neckloops,
patchcords). The major difference is that every IR receiver has
an “optical bubble” which collects the IR light wave for
processing by a photo-optical circuit. IR receivers are also
available in forms not available with FM receivers, such as
under-the-chin stethoscope units and self-contained headphones.
Stethoscope units place the electronics, volume control and
optical bubble in a single unit that dangles from a user’s
ears. Some of these units also include an output jack for
insertion of a neckloop. Is
it possible or desirable to mix and match transmitters from one
company to the receivers of another? Yes, it is
possible, as long as both transmitter and receiver function at
the same frequencies (FM or IR). Generally, however, it is not
desirable. Even though the same frequencies are being used,
there are issues of receiver sensitivity and bandwidth that can
affect the quality of the received signal. It is advisable,
therefore, to use receivers and transmitters from the same
company to preclude possible problems. On the other hand, many
consumers have purchased IR receivers that use the 95 kHz
sub-carrier and find themselves able to use the same receiver in
a number of different venues that employ this frequency (which
up to now has been a kind of de facto universal standard). One
of our recommendations to the Access Board dealt with the
desirability of developing a truly universal receiver, one that
could be employed in any facility employing any type of ALS
whatever the specific characteristics of the transmitter or the
coupling needs of the user. When and if such a device does
become available, then consumers would have the option of bring
their personal receivers to any venue that uses an ALS. How
many receivers should be made available? The number
of receivers should be equal to at least four percent of the
total number of seats available, with a minimum of two in any
facility with fixed seating of 50 or more. Changes have been
proposed that this number vary as a function of the number of
seats in a facility, and that a certain percentage of neckloops
also be made available for those patrons whose hearing aids
include T-coils. What
possible problems should I be aware of? There are
two types of problems to be considered, one type at the time of
installation and the other that may occur later. The presence of
interfering radio signals, in the event of an FM installation,
or interference from fluorescent ballasts with an IR
installation, are examples of the first type of problem apparent
at the time the ALS is being installed. In some locations, it
may be desirable to monitor the presence of potential radio
interference for some period of time, and to do this throughout
the facility, before making an FM installation. A frequency
scanner would be a useful device to employ. These problems can
be managed before the system is put into operation. When
extraneous radio signals of particular frequencies are found to
occur often, the installer has the option of shifting to another
radio frequency. The second
type of problem is one that often bedevils installers (as well
as providers and consumers). Some period after making what they
believed to be an excellent installation, they may get calls
from an irate provider who reports that their patrons are
complaining of poor or non-existent reception. After visiting
the facility and troubleshooting the problem, the installer may
find: ·
IR
emitters moved from their previous location because some
maintenance person or stage designer felt that they were
intrusive in some fashion. ·
Scenery,
curtains, or some other fixture placed between the audience and
an emitter and thus “shadowing” some of the IR light waves ·
Transmitter
system settings modified from the original ones (e.g. VU meter
readings below optimum level) ·
Radio
or electromagnetic interference from an adjacent facility, or
from within the facility, not present during original
installation ·
One
problem or another with the receivers (dead batteries, broken
cords, poor connectors, etc.) ·
Some
change in microphone usage (i.e. number, location, type) which
severely affects THE quality of THE signals reaching the
microphones. The
solutions in these examples are obvious. Facility personnel must
understand that the ALS installation is a permanent addition to
the venue, not to be tampered with for any reason, and how it
works with the basic sound system. The quality of an ALS
installation can be compromised at any point in the transmission
path by what may appear to be a simple adjustment or change of
some kind. When problems occur subsequent to the original
installation and the problems rectified, the technician should
retest the system to ensure that the electroacoustic targets are
once again being met. The
Rehabilitation Engineering Research Center on Hearing
Enhancement, website www.hearingresearch.org,
has a great deal of useful information on assistive listening
systems. Other resources include the technical assistance center
at Gallaudet University, www.tap.gallaudet.edu,
and the U.S. Access Board, www.access-board.gov.
The Access Board also services a toll-free technical assistance
number at 1-800 872-2253 (V) or l-800 993-2822 (TTY). If you
wish to field a complaint about the lack of functioning ALS/ALD,
contact the US Department of Justice at 1-800 514-0301 (V) or
1-800 514-0384 (TTY). Bulletin #8B September 2001 U.S. Architectural and Transportation
Barriers Compliance Board TEL:
(800)872-2253 TTY: (800)993-2822 |
