Parallel Load References
The following is a quick reference listing of some commonly used parallel loads: (Avoid the ones that go lower than output impedance rating of your power amp.)
Two 16-ohm speakers = 8 ohm
Two 8-ohm speakers = 4 ohm
Two 4-ohm speakers = 2 ohm
Three 16-ohm speakers = 5.33 ohm
Three 8-ohm speakers = 2.67 ohm
Three 4-ohm speakers = 1.3 ohm
Four 16-ohm speakers = 4 ohm
Four 8-ohm speakers = 2 ohm
Four 4-ohm speakers = 1 ohm