10. Watts and Ohms – an eternal enigma?

There is no question discussed more heatedly in online forums and networks than the question about watts and ohms: "What happens if I hook up an 8-ohm cabinet to a 4-ohm amp?" "Can I connect two 4-ohm cabinets to my 4-ohm amp, or will I kill my amp if I do that?" Here's some concrete and fundamental advice on this:

Using single cabinets with a valve amps:

• Make sure always to connect a cabinet with exactly matching impedance to a valve amp; otherwise, you may damage the amp.

Using single cabinets with a solid-state amp:

• If your amp is designed for a certain impedance, you must not connect a cabinet with lower impedance. For example, if your amp has an output impedance of 4 ohm, any speaker cabinet you connect to it must have at least 4 ohm.
• If you connect an amp and a cabinet, with the latter's impedance being higher than the amp's, your amp's output power will decrease correspondingly. For example, if you use an 8-ohm cabinet with a 4-ohm solid-state amp, you'll end up getting only 50%-60% of its maximum power!

Using several cabinets:

• If you connect the cabinets to the amp in parallel (and the sockets on the box are usually configured for this method), the cabinet's impedance needs to be divided by the overall number of connected cabinets. So, if you use two 8-ohm cabinets, your calculation should be "8 ohms / 2 boxes = 4 ohms total impedance." With three, it should be "8 ohms / 3 cabinets = 2.67 ohms total impedance."
• If you connect two cabinets with identical impedance serially one after the other (a bit of technical know-how is all you need to do this), the impedance values need to be added. Two 4-ohm speakers connected serially add up to a total impedance of eight ohms.