Attenuation pot on secondary side of output trans?

[disorder]

My work was getting rid of this old wall mount PA speaker that has an output transformer connected to the back of the speaker. The box has an external pot that is wired up to the secondary side (speaker side) of the output transformer. I was going to assume the pot is wired as a voltage divider with the speaker connected across the "lower" resistor of the divider but this transformer has three connections on it (center tap?) which convolutes things for me. Any ideas how this might be accomplished?

[antonis]

I should vote for "impendance matching" but it's safer to know the internal wiring.. 

[Hatredman]

http://www.belden.com/blog/broadcastav/All-About-70-volt-Speaker-Systems.cfm

https://www.parts-express.com/resources-70-volt-system-beginners

http://www.alectrosystems.com/audio/Distribution/70volt.htm


--
Scarlett Johansson uses a Burst Box with her Telecaster.