Audio Systems: PA System, gauge wire, power amps

Question
Hello Cleggsan

I am wiring up a PA system for my local church and am trying to connect 6 speakers to my amplifier. I do not have the model number but it bascially consists of one set of terminals at the back of the amp with which to connect all speakers to.
Two speakers run down the left hand side of the church and two down the right and the other two in other rooms.
First of all, can the two sets running down the sides of the building be run as a radial circuit ie cable to first speaker (+ & -) then looping out to second speaker or does each speaker need its own feed?
Secondly what is the best way to connect 6 sets of speaker cable into two small terminals?
Any help will be greatly appreciated!
james

Answer
I need to know the model number or technical details of the amplifier.  The very most important thing to know is the impedance matching scheme.  If it is a typical transistor amp it is likely a 4 or 8 ohm output which means you must try to match that  with the speaker load - at least do not go below that load or you will damage the amp.  If you go above it you don't get full power from the amp.

Second big thing is to get the sound level you need for the various speaker locations.

There are two ways to solve this problem:

ONE:  separate amplifiers for each zone.  This way each zone has its own volume control and can easily be adjusted as needed.  But you need separate wires to each speaker/zone.  And, it still must be impedance matched.

Amplifiers are very inexpensive now days and sometimes two or three lower power amps will cost no more than one big one.   Then the speakers can be connected to the amplifier that is suited for that zone.  The wiring is low voltage and does not  need to be in conduit in most cities (check the zoning requirements) and small gauge wire can be used for short runs up to 100 feet. In your case, since you have alreay acquired an amplifier you may wish to design around option TWO below.

TWO;  old fashioned but very cost effective way is 70v or 25v line.   The amplifier needs its output connected to a transformer that will bring the audio  voltage up to 25v or 70v.  Each speaker is connected to a transformer at its end that brings the 25v or 70v line down to the power level you want for that zone.  The transformer has taps on it that allow the choice of 1/2 watt, 1w, 10w, etc.   This usually requires the wires to run in conduit due to wiring codes, but only one wire is necessary.

Tutorial on 70v system is here:

http://www.docstoc.com/docs/2479185/70-Volt-Cheat-Sheet

and here:

http://www.soundinstitute.com/article_detail.cfm/ID/101

Design ideas:

http://www.yorkville.com/default.asp?p1=6&p2=17&p_id=73


Here you can find some prices for various constant voltage transformers and accessories;

http://www.thefind.com/instruments/info-70-volt-transformer

But you can google for many more such variationns.

Hope this helps you design a good system for your facility.