Multiple Speaker Public Address and Intercom System

The amplifier is a Realistic MPA-20 Solid State Amp. This is used instead of an old stereo receiver due to longevity of operation. This unit must remain powered on 24/7 to facilitate as the amplification for the alarm siren as well as serving as a PA, Audio, and Intercom system.

Functions

Alarm

The Alarm component will produce a siren loud enough to resinate though an entire city block. If an intruder breaks into the residence, the alarm will cause enough attention that the intruder will surely leave before police arrive as the result of someone phoning the police in the neihgborhood.

Public Address and Music

Audio from various sources can be piped into the system. These sources include satilight TV audio, MP3 music, or a stereo receiver.

Intercom

This is tied into the home intercom system so that from any intercom station within the residence someone may be paged that is outdoors near the house.

Speaker System

There will be a hybrid of outdoor horn speakers, outdoor 2-way speakers, and indoor speakers all powered by the MPA-20 amplifier. Different audio levels will be needed for the various speakers.

The loudest speakers need to be the outdoor horn speakers, which serve as the main volume when the alarm siren is activated. The horn speakers are also ideal for voice, easy to hear over the sound of a lawnmower when being paged.

Moderately loud will be the 2-way outdoor speakers. Their purpose is to supply some level of musical fidelity as horn speakers are not able to produce a wide range of sound. However, they need to be limited as to prevent damage when the high powered siren is sounded.

The relatively quiet indoor speakers serve only to supplement the alarm and also music. These speakers not only need to be volume limited, but also require an off function.

Multiple Speaker Handling

The output connectors on the Amp serve only a single speaker, or speakrs in a series or parallel circuit of the same resistance. When using 3 or more speakers it becomes necessary to utilize a special transformer.

• Determine what type of transformer is needed.

Speaker Volume Control

This may be accomplished using a Potentiometer on each speaker. All the Potentiometers can be centralized in the same area as the amplifier and PA microphone.

• Determine what resistance value and type is necessary for the potentiometer.

10K Ohm potentiometer - seems to be what is used on RS home intercom