Maybe you want to build a wall of cabs yourself and take the upgrade route like I did. Maybe you need some help with wiring said cabs. I am here to offer my guidance, grasshopper.
A typical 4x12 cabinet is rated at 16 ohms. The conventional wiring is called series-parallel, and the speakers themselves are each 16 ohms. Fig. 1 shows how to connect four 16-ohm speakers in a series-parallel configuration. This is your classic 4x12 schematic. Red is positive (+) and black is negative (-).
Fig. 1 — Image courtesy of Weber Speakers
The 4x12 cabinet is sometimes referred to as a half-stack, and players routinely connect two of them to a single amp to create a full stack. A 4x12 cab is typically 16 ohms, so when you connect two of them together in parallel, the total load becomes 8 ohms. Most amplifiers on the planet can run an 8-ohm load, so this is desirable. I should mention that, for some reason, many venues aren’t happy when you show up with a full stack.
Note: Some 4x12s have an 8-ohm rating and contain a quartet of 8-ohm speakers. This is still series-parallel wiring, so following this diagram will still work.
Always be sure your amp head is set to the total load. So, for example, if you have two 16-ohm cabs for an 8-ohm total, then set your amp to 8 ohms. You could also use two 8-ohm cabinets for a 4-ohm total load. In that case, just set your head to 4 ohms.
You never want to connect cabinets of different impedances because an amp does weird stuff when it sees a mismatch. If you were to connect a 16-ohm cab and an 8-ohm cab to a head, then you would have a 5 1/3 repeating-ohm total load, but the 8-ohm cab will get twice the power of the 16-ohm cab, which doesn’t sound awesome. If you have differing impedances, use separate heads for each cab and simply set them to their respective cab’s impedance. That will sound awesome.