Chris15 is right about the volume control.
Taps just are where you can connect into the
transformer coil in different places to get a different wattage loading. They could be wires coming out of the transformers or maybe metal tags that you can solder wires to.
Here is an example showing both the physical
transformer and the schematic representation.
Pure Resonance Audio SD64T Transformer & more 70v-100v Transformers within Commercial Audio Accessories at www.ProAcousticsUsa.com
On the schematic the taps are those wires that lets us set different wattage levels to use on the primary side of the
transformer e.g. Orange (
wire colour) 4W(atts) is one tap, Brown 32W(atts) is another tap. (these are the wires at the back of the
transformer in the picture.)
So to set it up you decide what wattage you want,then on the primary side
wire that tap ( lead ) to the Signal (70V on back of amp) side of the 70V
line and
wire the black lead to the
ground side ( common on back of amp).
On the secondary side the two wires go the
loudspeaker. (these are the wires at the front of the
transformer in the picture.)
But since you have a volume control that has to be wired in somewhere. Chris will tell us if it is more likely in the primary side or secondary side.
But now you have seen what a 70V
transformer looks like you should be able to work out how your volume control is wired. Remember primary side has the more wires and they should be labeled with the different wattages. The primary side will just have the two wires coming out.
So you need to identify the taps on your speakers. So find the
line coming from the amp then see which
wire goes to the Com side and the other lead should go to one of the leads marked with a wattage
rating. Then add up the wattage used on both speakers and take away from 60 Watts to work at how many more watts of speakers you can add. Don't push it all the way to 60 Watts as there are losses so maybe use 55 Watts as totaled allowed. Chris will tell us the typical figure used to allow for these losses.
Since you already have both speakers working you know you could move one without overloading the
amplifier.
Stock pot just means a standard potienometer (also known as a variable
resistor) used for a volume control. The
stock part just means it has a resistance value that is commonly used for this job.
Hope that helps.
Brent
The various
transformer taps are there to allow you to set the volume effectively for a given area. Individual volume controls in a normal office paging
system aren't always included, so you tap different speakers at different
power levels to try and get the coverage (volume
etc.) patterns you are after. You don't need as much
power in a small room, say a storeroom or bathroom as you do in say a school classroom. So you might tap the storeroom at say a
watt and the classroom. This is partly because you can't change the master volume to fix issues
in one place without it changing everything else. Please let us know if the whole concept of tapping still doesn't make sense.
By a
stock pot, I mean something you can get at Radio Shack or whatever other retail electronics
outlet you choose as an item off the shelf.
I don't know how speakers with internal controls are wired, but I would be putting the volume control on the
line side. There are two ways to do it, depending on whether you want to have off as a setting. Before you go and say why wouldn't you, there are some applications where you don't want the user to be able to completely turn the
speaker off, rather just subject it to background noise.
If people want me to talk more on volume controls (and ask) I will, but I think that's enough before I start boring you.
As to spare capacity. On a certain Australian brand, the generally accepted loading figure is 120W constant on a 100W amp. Most things are overengineered. Older gear you can be less sure of. You also balance the factors depending on the likelihood of expansion and need to increase taps later. It would be unwise in a
greenfield install to leave less than say 25% spare capacity, a number in
line with things like distribution boards.
Remember that at 100V, a 500W
line has an
impedance of 20 ohms. So an
ohm or two of resistance is not dire. Especially because it's not appropriate at that
point to treat the
line as a lumped
impedance, you will have a greater
power loss on the sections of cable closer to the amp and as you
pass through each (ceiling)
speaker you
drop part of the total load and thus you have less
current continuing along the main
line and thus less cable loss.
As to the original question, with a 60w amp, it is unlikely (but possible) that your
current speakers are tapped to 30w each. I would expect 5-10w is more likely. That being the case you can easily add another
speaker or speakers. You might be better off adding 2 new ones to serve the extra rooms rather than needing to patch a hole in the ceiling from whence you remove one of the existing speakers... If you've got a volume control on it, you can turn it off if you don't want it on...
