Impedance and Ohms Explained for Musicians

You just bought a shiny new cabinet for your amp. Excited, you hook it up and give it some juice. You begin to play – and your rig catches fire. Don’t let it happen to you! Knowing the basic electrical concepts of impedance and Ohms are critical for mixing and matching amplifiers and speaker cabinets.

What is Impedance?

To impede something is to get in the way of it – to hinder it. So think about an electrical current as a river. In a river, large rocks and boulders get in the way of the water, impeding the flow of the river. Impedance in an electrical sense works the same way – the flow of electricity is impeded by certain amounts. The amount by which an electrical current is impeded is quantified in Ohms

Then What Exactly is an Ohm?

An Ohm is a unit of impedance as described above. The more Ohms, the greater the degree to which the electrical current is impeded. Now, this is the important bit: A speaker must be of equal or higher impedance than an amplifier is rated for. This means an 8 ohm cabinet will work with an 8 or 4 ohm amplifier. Likewise, a 4 ohm cabinet can be hooked up to a 4 ohm amplifier. But hooking up a 2 Ohm cabinet to a 4 Ohm amplifier is a VERY BIG PROBLEM.

The reason being that the cabinet is pulling more power than the amplifier can safely provide – remember the speaker has less impedance than the amplifier is rated for.

So What does This Mean When I Connect Cabinets?

When you have one cabinet running off an amplifier, the amplifier will run at the cabinet’s impedance. When you have two cabinets running off an amplifier, the amplifier will operate at half the impedance. This is because the load now consists of two cabinets drawing from a single source. A greater amount of power needs to flow from the amplifier at twice the rate in order to supply two speakers simultaneously.

This means that if you connect an 8 ohm cabinet to an amplifier rated for 4 ohms, the amplifier will actually supply power at 8 Ohms. Connect two 8 Ohm cabinets, and it will operate at 4 ohms. Connect 3 cabinets and it will operate at 2 Ohms – OH NO!

Since the amplifier is only rated for 4 Ohms, this means that with three speakers connected, more power is being drawn than the amplifier can safely handle.

That’s where the fires start. Don’t daisy chain 3 speaker cabinets off a single amplifier. (Unless the amplifier is rated for 2 Ohms, of course.)

The Moral of the Story

If you draw too much power from an amplifier, you have a big problem on your hands that will damage your equipment. This is why we use the impedance rating system – to keep users drawing safe amounts of power from their amplifiers. Make sure your speaker cabinet is rated for an equal or higher impedance than your amplifier is rated for. Remember, impedance and ohms is just as important for musicians as it is for electricians.

Until next time,
Audiomunk