Parallel speaker wiring question - Model Railroader Magazine

Parallel circuits reduce the resistance of each circuit, counterintuitively.  

If you had a bucket of electricity and punched two holes in it (positive and negative) you'd get water leaking at a certain rate and pressure. Punch two more holes in and you increase the flow and reduce the back pressure. 

That's why you need to match total impedance of the two speakers to the power capability of the decoder sound signal output to the impedance that one speaker provided. 

Like punching four new smaller holes in the electricity bucket to match the total size of the two holes you were planning to put in. 

The wires feeding the speakers can be joined up anywhere from the solder pad on the decoder to the connections at one of the two speakers as long as they are connected in parallel.