1520 Chapter 40
assistance messages, and automatic store closing
announcements—all with a single announcer. In addi-
tion, this type of repeater can also play existing back-
ground music through, thereby eliminating the need for
customers to purchase a cassette with recorded music.
40.4.8 Museum Applications for Message
Repeaters
Message repeaters with multiple inputs are ideal for
museum displays that require several messages associ-
ated with a single display. For example, messages that
are tailored to either adults or children, short messages
or detailed messages, or multiple language messages.
Museums can be exciting with interactive displays
and audiovisuals replacing the static placards of the past.
Today visitors are accustomed to a multimedia environ-
ment where programming captures their attention with
entertainment mixed in with an educational message.
The original museum audio systems included narra-
tions and sound effects. Loudspeakers were mounted in
front of the exhibit, often at knee level. The source was
often continuous loop tapes that could not be rewound
and they ran continuously so if the listener came in
during the message he or she would have to listen to the
end before the beginning. If the tape had automatic stop
at the end of the narration, the listener could push the
start button and hear the message from the beginning. Of
course anyone coming in after the dialogue was started
would have to listen to the end before restarting it. Often
multitrack playback tape machines were used so the
listeners could pick their language of choice. While not
the best system, it was a step beyond placards.
Around 1957, visitors carried a reel-to-reel tape
recorder over their shoulder. With this system they not
only heard the message but also got their exercise for
the day.
40.4.8.1 Inductive Loop Systems
Another early system, and still used by some museums
today, is to transmit the signal on a wire inductive loop
antenna that surrounds the audience area. The listeners
wear a receiver and earpiece and as long as they are
within the boundary created by the loop, they can hear.
As they step outside of the loop, the signal disappears.
They can then go to the next exhibit, step into its loop,
and hear the dialogue. An advantage of the system is it
is simple and reliable and works with hearing aids. The
drawbacks are:
- Poor frequency response making it useful only for
voice. - As the signal is analog and operates much like an
AM radio station, the volume and sensitivity vary
with the distance of the listener to the loop. - Affected by external electrical noise such as light-
ning, electric motors, and SCR lamp dimming
circuits. - Requires a wire loop around the area of interest,
sometimes rather difficult to install and hide.
For more information on magnetic induction loop
systems, see Chapters 41.2 and 42.2.140.4.8.2 Infrared SystemsAnother type of system by Sennheiser and others uses
infrared (IR) transmission. In this system the message is
transmitted via wireless infrared using amplitude and
frequency modulation processes. They come in either
narrow band for multichannel setups or wideband for
high quality.
The area of reception is confined to line-of-site or an
individual room. Through reflections, however, it can
bounce around corners into other unwanted areas. While
they can cover large areas effectively, they are limited
when it comes to multiple exhibits in a confined area.
Another problem with IR is its poor operation in the sun
or very bright areas.
Dual channel systems normally operate subcarriers
of 95/250 kHz or 2.3/2.8 MHz. The emitters are placed
around the room to give even coverage and they may be
daisy-chained for easy installation.
For more information on infrared systems, see Chap-
ters 41.3 and 42.2.5.40.4.8.3 RF SystemsToday RF systems are most often used, making the
systems much more versatile and simpler to install.
These systems range from simple to quite complex. The
following systems are only a smattering of what is
available but give an indication of the features avail-
able.
Acoustiguide has been in business for over 50 years.
Its major system is the Acoustiguide 2000 Series and
includes three AG 2000 players—the Wand, the Mini,
and the Maxim.
All three systems use MP3 and Windows Media
Audio 4.0 for full production sound, and their own soft-
ware called Vocoder for voice only.