Theatre Design & Technology - Summer 1983 - 24

Are the hearing-impaired just the
people who wear aids? Not at all. Only about 20 percent of the hearingimpaired wear aids. Many people with
hearing losses are able to function in
close or face-to-face situations but are
lost in noisy or reverberant settings.
Even people who wear hearing-aids have
problems in reverberant rooms or where
there is a high background noise level.
Often the highly-prized acoustical qualities of our theatres and concert halls
operate against the needs of the hearingimpaired.
For years the only special assistance
offered to the hearing-impaired was provided by a few churches in the form of
headphones in a couple of pews down
front. In recent years new technologies
have been developed or adapted to meet
the special needs of the hearing-impaired
in public assembly spaces. The new
systems have one thing in commonthey are wireless. The user is no longer
restricted to a specially-wired seatevery seat is available and no special
ticketing is required. The user can sit
with family and friends.
There are four basic types of wireless
systems: magnetic induction, FM broadcast, AM broadcast, and infrared light.
Each has its own set of advantages, problems, and limitations. While there is
no single best system for every application, each system is simple to operate
and can probably be installed by the theatre's technical staff with little or no
outside help.
The system, no matter what type,
must have a pick-up of the stage sound.
In a fully miked show, this could be a
feed of the house sound mix from the
control console. 'Where the show is not
miked, there must be a special microphone for the hearing-impaired system.
It is \'ery important that the feed to the
system be of the highest quality possible;
it should be especially free of re\'erberation pickup and extraneous noi es. A
PZi\I-type microphone on the forestage
noor or mounted on an acoustical renector panel oyer the forest age would be
good for many hows. The usefulness of
the system for a hearing-impaired person depends in large measure on the
quality of the sound pickup going into
the system.

Magnetic Induction, sometimes
called a loop system, is one of the oldest
and most popular. The principal advantage of this system is that it can operate
directly into the user's hearing-aid without the need for a portable receiver,
which is required by all other systems. A
loop of fine wire is run around the seating area, usually under the carpet, and
connected to a small amplifier. The electrical current nowing through the loop
will create a magnetic field (as the primary of a transformer) that can be
picked up by a hearing-aid equipped
with a T-coil (liT" as in telephone).
About 60 percent of the hearing-aids in
the United States have these T-coils for
magnetic coupling with the earpiece of a
telephone. Portable receivers are
available for use by patrons who do not
have an aid with aT-coil.
There are several problems with the
loop system. lost buildings have other
magnetic fields that will be picked up by
the T-coil. Ordinary electrical wiring
will radiate a large 60 Hz field throughout the room, so the T-coil and the portable receivers are designed to have no response in the low-bass region in order to
avoid the 60 Hz hum. There are other
power-line-related noises that cannot be
filtered out-motors, dimmers, and nuorescent lamps are among the more
common. The size and shape of the
loop and the amount of nearby steel in
the building or in the seats will affect the
strength and uniformity of the magnetic
field. Quality of reception is also dependent upon the quality of construction of the T-coil in the hearing-aidmost manufacturers' quality control for
T-coils is very poor. All these factors
combine to provide reception that often
is of poor sound quality, noisy, and variable in volume depending upon the location of the listeners and how they turn
their heads.
The limited statistics available indicate that of the people who need hearing
assistance, only about 20 percent are
wearing aids and only 60 percent of
those aids are equipped with T-coils.
This suggests that only 12 percent of
those needing help are able to make use
of a magnetic loop through their
hearing-aids. It has been argued that the
majority of those without T-coils are

young children and the very old, and
therefore active theatre-goers are most
likely to have T-coils. Despite the comparatively limited availability of T-coils
and the several substantial limitations of
the magnetic loop system, it is popular
and has the support of many of the 2.5
million people who have T-coils.
The cost of a magnetic induction
loop system includes the cost of the amplifier, $500 to $700, and the labor of installing the wire loop. The receivers cost
as little as $50, depending upon the
brand. Until recently, the magnetic loop
was the least costly system. However,
advances in solid-state electronics have
made the broadcast-type systems very
competitive in price. And where there
are large areas to be covered, the magnetic loop is probably not as costeffective as a broadcast system.
FM Broadcast systems have almost
totally replaced magnetic loops in classrooms where hearing-impaired children
are taught, because the FM signal is normally free from noise and provides a
more uniform and reliable signal. The
sound quality is excellent. The coverage
range varies from 100 to 300 feet depending upon the amount of steel in the
building. The transmitter is not much
larger than a pocket radio and has a
short whip antenna attached. Transmitters are available for operation on house
current or by battery. While they are
completely portable, they can be permanently installed.
The Federal Communications Commission (FCC) has set aside a band of
frequencies for FM broadcasting to the
hearing-impaired. These frequencies
cannot be used for any other purposesuch as language translation systems or
wireless headsets for the stage crew. 0
license is required, although the manufacturer of the transmitter is required to
have FCC approval of the transmitter
design. The system requires no special
knowledge to install; sufficient instructions are provided by the manufacturers.
The receivers are fixed-frequency devices and cannot be tuned to any other
channel, nor can regular commercial
FM broadcasting receivers be used. The
receivers are small-mostly pocket size.
They operate with either of two output
devices: a small earphone, or a magnetic

USITT /Summer 1983/Theatre Design & Technology

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