Switching Units - Q. What are the benefits of series vs parallel wiring?
Answer:
The switches which have more than two sets of speakers use a combination
of series and parallel switching to achieve the minimum impedance of 4 Ω
no matter what combination of speakers are switched on.
For the two way
switches, there is a choice between exclusively series or parallel
versions. If you have 8 Ω speakers (and a 4 Ω min amp) you should always
use the parallel switch. If you have 4 Ω speakers and a 4 Ω min amp you
should always use the series switch.