Q: I’ve been playing my 100-watt head into a 4×12 speaker cabinet and have been pretty happy with the sound. But, I recently was given another cabinet and thought it would be awesome to set that on the other side of the stage. However, the new speaker says 4 ohms impedance, and my existing speaker is 8 ohms. Will this work?
A: It depends on your amp, but probably not. There’s a formula for determining impedance, and using it, you’ll see that your amplifier would likely fall below the minimum value that would be safe. Multiply the 4-ohm cab by the 8-ohm cab (4×8), and you get a value of 32. Then, add the two cabinet impedances (4+8=12). Now, divide 32 by 12, and you get 2.667. If your amp is rated at a minimum of 4 ohms (check with the manufacturer), a 2.667-ohm load could cause major damage – even a fire! As cool as it would be to have two speakers, this mismatch is a recipe for disaster! Always verify the combined, impedance of speaker cabinets to ensure that the overall impedance is safe.