Understanding impedance: amps and speaker cabinets

[Tim Farrant]

Tube amps are more critical than solid state ones in terms of what load they see. This is why you find switches on the back to select the right impedance.

If you have 2x 8 ohms cabs connected to 1 amplifier, the parallel load will be 4 ohms. If you have 2x 16 ohm cabs connected to 1 amp, the load will be 8 ohms. If you have a 16 ohm cab and an 8 ohm cab connected, the load will be 5.3333333333 ohms.

2x 4 ohm cabs (not really very common) will give you a load of 2 ohms - most gat amps will not lke this - too low.

Is this what you are asking?

As for speaker cables, the heavier the better. 2.5mm sq speaker flex is good for 4 ohms over distances of 10m. Higher loads (16ohms) and you can get away with 1.5mm sq (sorry - we're metric in NZ!).


Cheers
Tim.

[redddog]

What's the worst case scenario if you were to have 2 - 8 ohm cabs hooked up to the 8 ohm speaker out on the amp?

Will it blow up something?

[wehateyourhate]

Originally Posted by redddog

What's the worst case scenario if you were to have 2 - 8 ohm cabs hooked up to the 8 ohm speaker out on the amp?

Will it blow up something?

its possible to damage either the speaker or amp. the speaker voice coil can heat and blow. on the amp any number of things can go wrong down to and including bnlown transformers...

[Jackie Treehorn]

Tim-- Thanks for the reply. Actually, I don't know exactly what I'm asking, so let me put it another way:

I have an amp that has 3 speaker outputs-- two are 8 ohms and one output is 16 ohms. Say I want to drive two cabinets with the amp. One cabinet is an 8 ohm input and the other is 16 ohms. What's the safest/best-sounding way to drive them? Use two different speaker cables (8-ohm output to the 8-ohm cabinet and 16-ohm output to the 16-ohm cabinet)??