Handbook for Sound Engineers

1564 Chapter 43

at each end with a 120: resistor. This keeps a proper
impedance of the line.

Any door entry system camera should be mounted so
the unit is not exposed to environmental extremes.
Sudden temperature drops, for instance, can cause the
camera to fog up and raindrops can distort the picture.
Lighting should be on the front of the person. Strong
backlight—i.e., sunlight or street lights—can cause a
silhouette image on the monitor, and fluorescent lights
can cause flickering. Taking these into account will give
a good picture under most conditions.
It is important that the door release button has
normally open contacts to activate an optional electric
door strike. The normally open contact assures that the
door will not open during a power failure.

43.1.4 Residential Intercom Systems

Residential intercom systems are used to talk between
rooms, or between a master unit and all other rooms, as
a door security system and for programming external
sources such as AM/FM or CDs to any or all rooms.
Because of the limitations of intercom systems, the
music is usually not in stereo and not of the quality of a
dedicated stereo system, but is quite adequate for back-
ground music. They also have the advantage that the
same source is heard as a person walks between rooms.
Normally residential intercoms are wall mounted, incor-
porate hands-free answering and include a privacy
switch. The systems can be master/slave, master/
master/slave, or all master.

43.1.5 Commercial Security Systems

A building security system assists security personnel in

the protection of the lives and property of all tenants,

employees, and visitors. People in parking areas, ramps,

tunnels, stairwells, and elevators should have access to

conveniently located, easily operated hands-free emer-

gency call-in stations.

43.1.5.1 Zone Paging

High-rise buildings and multibuilding complexes have

special needs for zoned public address announcements.

Buildings with controlled access need audio voice

confirmation and integration with CCTV cameras.

Elevators require intercommunication to security and

the lobby and communication to the elevator machine

room for maintenance, Fig. 43-6.

Variations of this type of intercom can be used for

campus security where there are multiple buildings,

parking lots, dorms, and walkways.

43.1.5.2 Security Audio Monitoring

Unfortunately, all too often crisis situations do develop

in the shadows of darkened areas or dimly lit passage-

ways. These are the areas where criminals tend to stalk.

These are also the places where a building’s highly vola-

tile power transformers, generators, and steam lines are

neatly tucked away. Security and maintenance personnel

can’t be everywhere. Even with the assistance of video

surveillance there are limits to the number of cameras

used and manpower to monitor them. Even in the best of

situations video cameras can’t see around corners,

through closed doors, or behind parked cars or trucks.

To eliminate problems with video only monitoring,

security system manufacturers have developed listening

devices and loud-noise triggering alarms. Although

these products seem to be moving security systems in

the right direction, they still have substantial limitations.

Listening devices are a great idea because they allow

security personnel to interpret and discriminate the

sounds they hear. Unfortunately, like video cameras,

they must continually be monitored to be truly effective.

There is also the question of open microphones being

construed as invading individual privacy.

Loud-noise triggering alarms have the problem of

discerning sounds, for instance, screams from laughter,

or the loud noise of a car engine starting up. Without the

ability to discern specific sounds and discard normal

background sounds, false alarms would render the

system useless.

Figure 43-5. Video coverage door stations. Courtesy
Aiphone Communications.

79

67

48

44

Camera

center

51 inches

Camera

center

60 inches¾

74

27

46

20 20

26 72 39

¾

¾

¾

¾

¾¾

¾

¾

¾

¾

¾

¾

¾

Top view

Side view

Fixed and nontilted

A. Pan and tilt. B. Wide angle lens.

¾