Simplifying electrical circuits
The schematic is a bit confusing, because the 2nd loudspeaker is drawn "upside-down" with its driving signal connected to its lower terminal. It might be more clear (but take more space) if you draw it this way,







simulate this circuit &ndash; Schematic created using CircuitLab

There is nothing more to simplify. You can use mesh or nodal analysis to complete the analysis of the circuit.

The speakers are neither in series nor in parallel. They are just sharing a ground node.