Just to clarify, here are examples of "series" and "parallel" wiring.
Series wiring raises the impedance of the speaker circuit, and this is an easier load for an amplifier to drive. Total sound output will generally be not as loud with this type of load. (Less output wattage)
Parallel wiring lowers the impedance of the circuit, this is a more difficult load for the amplifier to drive, some amplifiers are OK driving lower impedance, but there is always a limit. Sound output will generally be louder with this type of load. (more output wattage)
Speakers are resistance loads, like a resistor. You could actually put a resistor in place of a speaker, problem is, it wouldn't make any sound, just heat.
Generally you don't want to test the load handling of an amplifier by just dropping the resistance of the speaker load until it blows, that is unless you have an infinite supply of amplifiers.
Hope this helps. Sorry the two examples are of not the same impedance speakers, but if the second example had 4 ohm speakers, the load to the amplifier would be 2 ohms.