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Cheap PA System

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Anonymous
December 13, 2004 7:21:19 PM

Archived from groups: rec.audio.tech (More info?)

I am a teacher in a small Christian School in Florida, and we need an
extremely cheap PA system for the classrooms. I have very little
knowledge in audio, but I used to play with speakers and adaptors to
add speakers as a kid. The difference here is that the distance is
greater (300 feet) and they will probably need a way to easily connect
or disconect the speakers to address specific classrooms. There are 11
classrooms, but probably the hall will need a couple of speakers too.

I have been trying to search the internet for a project or more
technical information about how to make your own PA system. I would
appreciate any information about the kind of speakers I need, the kind
of cables I need, and if it is necesary to buy some kind of amplifier.
If you have an idea of how to do this, please email me and let me know.

More about : cheap system

Anonymous
December 14, 2004 4:49:25 PM

Archived from groups: rec.audio.tech (More info?)

tuxtlequino wrote:
> I am a teacher in a small Christian School in Florida, and we need an
> extremely cheap PA system for the classrooms. I have very little
> knowledge in audio, but I used to play with speakers and adaptors to
> add speakers as a kid. The difference here is that the distance is
> greater (300 feet) and they will probably need a way to easily connect
> or disconect the speakers to address specific classrooms. There are 11
> classrooms, but probably the hall will need a couple of speakers too.
>
> I have been trying to search the internet for a project or more
> technical information about how to make your own PA system. I would
> appreciate any information about the kind of speakers I need, the kind
> of cables I need, and if it is necesary to buy some kind of amplifier.
> If you have an idea of how to do this, please email me and let me know.

Having a system that can connect to individual rooms makes it
complicated enough that you'll probably want to get an outside
contractor to do the installation, and it sounds like that would be too
much for your budget. That kind of system would involve individual
speaker wires to each room and some sort of switching device as well as
some kind of amplifier and microphone. It's complicated enough that
unless it's installed correctly it could be a big headache if/when
something goes wrong.

If you can go with all rooms all the time it's very simple with what is
known as a '70 volt system,' one pair of wires daisy chained to each
speaker and connected to the 70 volt output on the amp. Bogen and TOA
are companies that make 70 volt amplifiers I've used in this type of
installation, eBay has them listed just about all the time. The
speakers require a transformer or need to be specifically for 70 volt
systems, maybe ebay...?

Check local libraries for 'Sound System Engineering' by Davis and Davis.
I have the first and second editions, they have information on 70 volt
systems.

One idea I had and haven't fully thought through (so watch out!) is
using GMRS or family service radios, put each room on a different
channel, have the radio in each room scan between it's channel and a
general 'all announce' channel that's used when all places need to be
addressed. Potential problems are the tiny speaker in the radio (maybe
use an extension speaker), batteries running down (keep it hooked to the
charger), interference from other, non-school users of the same radio
frequencies (use the tone access function). Potential positives are the
teacher in each room can talk back to the office or to other rooms and
the system works when the power goes off because the radios have
batteries. It's free advice, worth what you paid ;-)

-Galen
Anonymous
December 14, 2004 4:49:26 PM

Archived from groups: rec.audio.tech (More info?)

tuxtlequino wrote:
> I am a teacher in a small Christian School in Florida, and we need an
> extremely cheap PA system for the classrooms. I have very little knowledge
> in audio, but I used to play with speakers and adaptors to add speakers as
> a kid. The difference here is that the distance is greater (300 feet) and
> they will probably need a way to easily connect
> or disconect the speakers to address specific classrooms. There are 11
> classrooms, but probably the hall will need a couple of speakers too.

Define what YOU mean by "PA system"?
Do you mean separate sound reinforcement in each classroom?
Do you mean some kind of central announcement/signal (bell?)
system that covers all the rooms?
Do you mean some kind of selective 2-way commiunication
system (where the office can talk to an individual classroom)?

Specialty equipment is made just for these different kinds of
systems, but hard to suggest without better definition. Perhaps
you should start at what problem you are trying to solve? You
may be jumping into "solution space" with the wrong premise.

> I have been trying to search the internet for a project or more technical
> information about how to make your own PA system.

What kind of budget do you have for this project?
Do you have a licensed electrician that can do the
installation? Note that in public buildings, especially
schools, etc, most localities are very picky about the
way wiring is done. Licensed electricians, permits,
inspections, etc.

> I would appreciate any information about the kind of speakers I need,

You are unlikely to get much useful information without
a better description of what you are trying to do.

> the kind of cables I need,

Depends on what you are trying to do, but also depends on
the type of construction, and the regulations in your area.

> and if it is necesary to buy some kind of amplifier.

It will almost certainly require some sort of amplifier(s?).
You also didn't mention what you are trying to distribute
or what the source is?

> If you have an idea of how to do this, please email me and let me know.

Newsgroups like this work by holding conversations in
public. That way you can get additions/corrections from
others if bad or ignorant advice is offered. It also helps
"lurkers" just reading to learn things. That is the purpose
of these newsgroups.
Anonymous
December 15, 2004 2:42:44 PM

Archived from groups: rec.audio.tech (More info?)

It is possible to address individual rooms quite simply on 70V line.
For multi-channel, each speaker has a rotary switch connecting it (and
its transformer) to different 70V lines. This used to be used for
multichannel radio to hospital and hotel bedheads.

Simpler is to have a single channel setup, with switch / volume control
on the speakers to turn them off when the programme is not wanted in
the classroom. If an additional pair of wires is run, and a relay is
used at each speaker, all speakers can be turned to maximum for
all-call and emergency announcements, class change pips, etc. Google
for 'volume restoration relay'.

Owain
!