That really helps! It sounds like you have a mixed distributed
speaker system with (7) 8" ceiling speakers each with a maximum 5
Watt, 25/70V
transformer and (2) J.W. Davis speakers which apparently do not use transformers but about which I can find nothing online (I know of J.W. Davis but can't find anything on that particular model).
The amp sounds like a QSC Model 1200 and there are a few questions that might help understand better how the
amplifier is actually being used. To which input connection(s) on the rear of the
amplifier is the feed from the audio
mixer physically wired? Next to the inputs and above the
barrier strip on the rear of the
amplifier is an eight position input programming
dip switch, how is that set? How are the
gain controls above the input connections on the rear panel set? How is the output wiring connected, is it wired to one set of red and black binding posts or is it connected to both red binding posts and not to either black post (the latter reflects bridge
mono operation)? Also related to bridge
mono operation is the
mono bridge
switch located next to the inputs and below the
barrier strip, is it in the "Bridge" or stereo position?
You mentioned that the three lines (the two booth speakers and the speakers back
stage) were all tied together, are they literally all connected directly to the back of the amp with all three red wires on one binding post and all three black wires on the other?
This may be difficult, but if you can easily access the JBL ceiling speakers, the
transformer attached to the
speaker should have several different color wires coming out and a little chart on the top of the
transformer showing what those represent. The wiring coming in should attach to two of those internal wires, one going to the common
wire and the other to one of the other wires connected to the
transformer. Knowing what the
transformer says the connection used is (e.g. 5W/70V or something like that) could help. This is not as critical as some of the other information so don't spend a lot of effort if it is difficult to do.
When you say you measured 45 Ohms, was that with a voltmeter or an
impedance bridge? Audio is an AC signal and speakers are a complex load, while a simple DC resistance reading may help in identifying an open or short it does not really reflect the actual AC
impedance. However, if the 45 Ohms was measured with an
impedance bridge then it could be very useful information.
Sorry for all the questions but it sounds like you have a
system that was either very carefully designed to support a specific load and thus sensitive to any changes or very poorly designed, which that is depends greatly upon the answers to some of these questions.