The reason for the 70V (or the 110V, we use here) is because of the long runs of speaker wire involved.
All the transformer on the speaker does is isolate the speaker from the 70V line voltage and also match the speaker to the line, hence the tappings.

Well, not exactly. The main reason for a constant voltage system is (in order of importance):

1)To allow a number of speakers to be easily connected to the output of an amplifier without regard for impedance matching.

2)To allow the levels (wattage) of each speaker to be easily adjusted independently of the others. This is the reason for the taps, not impedance matching.

3)Allow longer wire runs and/or a smaller size wire as compared to a low impedance amplifier output/voice coil connection. Ohm's law still applies here and you still need to do voltage drop calculations especially with large wattages or long runs.

I ran my system in Cat-5e.

I really didn't need to hear that! [Linked Image]

-Hal

www.myphonetechs.com