Handbook for Sound Engineers

Intercoms 1563

and because the signal is digital, seldom require
shielded lines.
Matrix systems can control upwards of 256 station
units and can have as many as 7170 stations by tying
more than one exchange together.
Because they are digital, it is easy to set them up
with quick dial single or double digit dialing of often
used numbers, connect them with outside C/O or PBX
lines, and record a customized outgoing message for
callers and record their response, retrievable at any
master. Because they are telephone system compatible,
they are capable of supporting a DTMF generating,
single line telephone instrument (telephone, autodialer,
fax machine, etc.). Interconnections are through twisted
pairs of copper wire or through fiber-optic cable.
Many of these systems are programmed with a
computer. Through simple programming, only selected
stations can be given access to special functions—i.e.,
paging, telephone calls, priority calls, external sources,
etc. Compression circuits and/or automatic leveling
circuits can be adjusted for individual units as well as
their overall level.

43.1.3 Apartment Security/Intercom Systems

Apartment systems are usually point-to-point and are
used for the visitor to contact the apartment owner for
access into the building and then into the apartment.
This system consists of a master panel outside the main
access door to the building and slaves in each apart-
ment, Fig. 43-4.

The outside master panel must be waterproof and
vandal proof so the outside unit panels and buttons must
be made of strong material such as aluminum, stainless
steel, or LEXAN®. The microphone/loudspeaker grill
must be indestructible and shed water, preferably a
continuous part of the panel and the loudspeaker must
be waterproof. The panel must be fastened to the wall
with vandal-free mounting hardware. The outside

master panel consists of a microphone/loudspeaker and

a means of contacting the person of choice. This can be

accomplished by a series of push buttons that connect

the visitor to the desired apartment or it may be a twelve

button telephone panel that connects the caller to the

suite through digital circuitry.

A power supply and amplifier is mounted inside

where it is out of the elements. Only one amplifier and

power supply is normally used for a system because

only one conversation goes on at the same time. The

door opener usually operates on 3–6 Vdc or 8–16 Vac.

The apartment loudspeaker station consists of a

microphone/loudspeaker unit, a talk button, a listen

button, and a door release button.

The more sophisticated security systems include a

video monitor for improved safety. The outside door

panel includes a camera and the indoor units include a

4 inch flat screen monitor. A pan and tilt capability

improves security as it can scan a large area. Because

the camera is behind a glass, the visitor cannot see

where it is aimed so the visitor cannot hide from it. With

today’s technology, wide angle cameras are possible,

eliminating the need for the more expensive and

complicated pan and tilt. The cameras require very good

low light level operation as most access is in the

evening or at night. One lux sensitivity is normal. Most

systems do not require coaxial cable between the

cameras and the monitors.

Self-contained video door answering systems are

rapidly becoming today’s replacement for the common

doorbell. They are a simple-to-install answer to the

growing need for entry security in both small businesses

and homes. Some use the same two wires as a doorbell,

often using existing wiring in older buildings, and

simplifying installation in new construction.

An example is a system where one pair carries an

FM modulated signal with both audio and video, and a

second pair operates the door releases shown in Fig.

43-4. In this system the door unit incorporates a high

resolution infrared CCD (charge-coupled device)

camera with 250,000 pixels, providing a clear, sharp

picture down to one lux of light.

By using a wide angle lens, an overall viewing area

of 39 inches × 27 inches at 20 inches away can be

attained, Fig. 43-5. For more coverage, a PanTilt door

station can be used, Fig. 43-5. This allows for a

coverage of 72 inches × 36 inches at 20 inches.Like

any transmission system, cabling is important. The

system was designed to operate with two wires such as

typical bell wire. Coaxial cable or two separate wires or

multicable will affect picture quality. If the cable has

more than one pair, the other pairs should be terminated

Figure 43-4. Audio/video entry security system. Courtesy
Aiphone Communications.