Speaker question

[Dedman]

I'm thinking of building a 2x12 speaker cab and had a crazy idea of wiring it so it could function as a single 2x12 with one input or as 2 separate 1x12's with 2 separate heads feeding a speaker each. My question is how do I wire it to keep the impedance at 8ohms? or do I even need to? (thinking of using 50w Celestions, probably a cream and green)

[AndrewA]

Hey Dedman, Its entirely possible to do. Each speaker should be 8 ohms and can be connected individually to 2 jacks on the back to connect to 2 amps. BUT 2 x 8ohm speakers joined together either make 4 ohms when joined in parallel (usual method) or 16 ohms joined in series. The good thing is most amps will run fine into 4 ohms (check the amp stats first). You could put a switch on the back to join them together, or some jacks even come with a switch that would automatically join them if you plug into that particular jack.

[Hobastard]

Most amps have 2 output sockets. Probably just have an input for each speaker and use 2 leads from one amp or 2 amps with a lead each.

[Simon Barden]

We'd need to know what the amps are you're talking about. Solid state or valve? But as AndrewA said, whatever value impedance speakers you use (and they would need to be the same), when connected in parallel, the overall impedance the amp sees will be halved, and if connected in series, the overall impedance the amp sees will be doubled.

Solid state amps are normally happy driving into a wide range of loads, with 4 ohms being a typical minimum load for a guitar amp, and the power output of the amp decreasing as the load impedance increases. When one of these amps has a couple of output jacks, then (unless its a stereo amp with an output per channel) these will normally be wired in parallel.

Valve/tube amps have an output transformer and need to be correctly matched to the load impedance. They normally have several outputs, each output designed for a specific load impedance or combination of (similar) load impedances e.g. a connection to the 8-ohm transformer tap if two 16-ohm cabs are connected. It is very important to select the right connection or you can do serious damage to your output valves and output transformer.