Grumpy_Mike:
I would not take too literally the + and - markings on the speakers. It all depends on the circuit of the amplifier output stage. When you measured the continuity did you do it in both directions? That is swap the leads around to make sure you were not going through a semiconductor PN junction.
However it is possible that the speaker is connected to the +ve rail of the supply and it is pulled down by the output stage. This will result in a square wave type signal.
For what I is worth I don't think your problems are with the 4.5V regulator either, mind you I think it will work just as well off 5V as 4.5V.So why not connect the speaker - to the arduino input pins and all the grounds together, would that not do it?
Mike - I REALLY value your help. Just wanted to say so.
I didn’t swap the probes when measuring continuity. Will do so when I get home.
Can I clarify? Did you mean to
A) connect the “speaker–“ to an input pin and tie the vreg ground to the arduino ground?
B) connect the “speaker–“ to an input pin and tie the speaker + to the arduino ground.
I agree the speakers will work equally well from 5v (I tried it and it works). But I am worried about overloading the ethermega (my Arduino variant) because I would be asking it to provide power for six LEDs, five wireless doorbell receivers, one servo and one ethernet ‘shield’.