Difference between revisions of "Multiple Speaker Public Address and Intercom System"
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==== Using Transformers ==== | ==== Using Transformers ==== | ||
| − | The output connectors on the Amp serve only a single speaker, or | + | The output connectors on the Amp serve only a single speaker, or speakers in a series or parallel circuit of the same resistance. More complex speaker arrangements may be achieved with the aid of transformers. |
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| + | Transformers are not meant to be used local to the amp, but are to be used local to the speakers. One transformer is meant to be used per speaker, in a 1:1 ratio with the speakers. | ||
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| + | It is wrong to think that one transformer near the amp can be used to solve multiple speaker of multiple resistance configurations, as there is obviously already a transformer in the amp itself with leads going to the connectors of the different resistance ratings on the back of the amplifier. | ||
*Determine what type of transformer is needed. | *Determine what type of transformer is needed. | ||
Revision as of 19:54, 27 May 2007
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.
Contents
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
Using Transformers
The output connectors on the Amp serve only a single speaker, or speakers in a series or parallel circuit of the same resistance. More complex speaker arrangements may be achieved with the aid of transformers.
Transformers are not meant to be used local to the amp, but are to be used local to the speakers. One transformer is meant to be used per speaker, in a 1:1 ratio with the speakers.
It is wrong to think that one transformer near the amp can be used to solve multiple speaker of multiple resistance configurations, as there is obviously already a transformer in the amp itself with leads going to the connectors of the different resistance ratings on the back of the amplifier.
- Determine what type of transformer is needed.
There are several advantages to using transformers.
- connect speakers with different impedances without causing differences in output between the speakers.
- add or remove a speaker without having to recalculate the entire system's impedance.
- reduce signal loss on long distance wire runs (like 50ft or more)
The MPA-20 Amp uses a 70v system.
When using transformers, power from the 70v terminal is being supplied to the transformers to "localize" the amplification power to the speaker, when the transformer is at or near the speaker.
Without Transformers
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
Amplification
The Realistic MPA-20 is a 20 watt Solid State PA Amplifier sold by Radio Shack at one time.
