You can also wire speakers in a combination of series
If each speaker is 4 ohms, this combination will give you a total of 4 ohms impedance for the circuit.
Left two speakers are in series: 4 + 4 = 8
Right two speakers are in series: 4 + 4 = 8
Left pair and right pair are in parallel: (8x8)/(8+8) = 4