Handbook for Sound Engineers

1562 Chapter 43

background music or other audio program material to
speaker-equipped locations. The Bogen PI35A is
designed to meet highpower paging and intercom
requirements with features suitable for applications with
mixed noise environments (construction, retail stores,
small factories, parking garages, etc.). A 20 W intercom
amplifier features a voice-shaped frequency response
for intelligibility. A 35 W program amplifier is used for
program material and/or emergency announcements.

Program material from microphones, a CD player, or

other background music source can be used. Distribu-

tion is accomplished by simple push-button selection.

Emergency announcements take precedence over

program distribution and are accomplished with a single

push-button selection. A time signal can also be sent to

all stations. Optional paging facilities permit emergency

all-call paging from a remote telephone, or interphone

or microphone. Telephone paging captures system

priority and overrides all system functions except the

emergency page feature.

A room selector panel is provided to select intercom

and program functions for each station. Calls from

stations are initiated through call-in switches in the

various rooms and are announced at the control center

by light and tone annunciation. The system provides a

25 V balanced output and operates from a 120 Vac,

60 Hz source. The system consists of a master control

panel and a twenty five-station room selector pane. A

number of options are available including room call-in

switches, call-in adapter modules for existing older

call-in switches, two-wire call-in adapters, and various

styles of transformer-coupled loudspeakers.

43.1.2 Matrix Systems

Not too many years ago, all intercoms used a mechan-

ical switching matrix to call and to route the voice

signal. Systems were simple, wires came from a central

system and went out to the individual masters and

submasters. Switches were multipole and carried signal

and voice. Often the voice line was shielded to elimi-

nate hum and stray noise pickup, however, on inexpen-

sive systems unshielded lines were used and the

frequency response of the receiver was limited to

200 Hz–4 kHz to eliminate noise and hum.

While these systems are still used today, many have

been replaced with digital matrixes and electronic

switching. These systems use low voltage/low power

Figure 43-2. Master/slave, master/master, and intermixed
intercoms.

Master

Master Master

Master

Master Master

Master Master

Slave Slave

Slave

Slave Slave

Master/slave

Master/master

Intermixed

Figure 43-3. Bogen P135A twenty five station intercom.

Courtesy Bogen Communications, Inc.