Biomedical Engineering Reference
In-Depth Information
skill level of the installer. There are quite a
few residential installation packages that
cost $100 to $300, which can be installed
quite easily by the consumer with a little
planning, comfort with connecting elec-
tronics, and typical household tools.
These small residential kits are perfect
for living rooms and bedrooms, and they
have installation instruction manuals.
Figure 7-8 shows the basic components
and the relative ease of installation of a
residential induction loop system kit
with a small amplifier box, power supply,
~100 feet of 20- to 22-gauge wire to loop
a room, and red and white audio cables
to connect to a television. Some of these
residential installation kits may offer a
small microphone port that could be used
for a small public address system. For
these small residential loop systems, the
installer should minimize trips and falls
by securing the wire loop to the inter-
section of the floor and wall, or taping it
down underneath the bed, couch, carpet,
or rug. Although not as common, the
loop could be elevated to the intersection
of the ceiling and wall or be hidden above
acoustic tiling. To maximize the magnetic
signal, the wire loop should be above or
below head level. Residential loop system
users should be aware that individuals on
floors above or below the loop may also
be able to “listen in” with their telecoils.
If the individual with hearing loss does
not have his or her own hearing aids or
implants with telecoil, a portable induc-
tion loop receiver can be purchased and
used with a standard pair of headphones
or earphones.
Induction loop systems for larger
public and commercial areas such as
meeting rooms, places of worship, the-
aters, lecture halls, auditoriums, sports
arenas, and performing arts venues may
cost anywhere from $1,000 to upwards
of $150,000. The cost will depend on the
size and construction of the room and
whether the installation will be in a new
facility or in one that requires retrofit-
ting to bury the wire loop into the struc-
ture. Generally speaking, installation for
a preplanned new facility, or one that is
already being remodeled, will be cheaper
than retrofitting. These installations will
require professionals who are specially
trained to connect the loop system to
existing audio systems, while minimizing
electromagnetic interference (EMI) and
maximizing the capabilities of the loop
system. These goals are met by conform-
ing to IEC60118-4 (International Elec-
trotechnical Commission, 2006), which
specifies the frequency response, field
strength, background noise, and various
subjective tests. The IEC standard pro-
vides an average reference of 100 mil-
liamps per meter (or 100 mA/m) with
a peak output of 400 mA/m. What this
means is that when a loop system can
produce an average output of 100 mA/m,
then the acoustic equivalent is about 70 dB
SPL. These values are important in the
selection, programming, and verification
of telecoils in hearing aids. In very large
rooms, there will often be more than one
loop and more than one amplifier. Fur-
thermore, the individual loops may be
placed into patterns that preserve sound
quality while minimizing “null zones” or
“dead spots.” For example, if there are sev-
eral fixed rows of seats, a single wire can
be “figure-8” looped around each row.
