When you connect a speaker to an amplifier, the impedance of the speaker is what determines how much power the amplifier can send to it. The higher the impedance, the more power the amplifier needs to send before it starts to cause distortion. In general, speakers have an impedance of around 8 ohms. ..
The Elements of Electricity
It’s tough to talk about ohms without mentioning the other elements of electricity. So, before we dive deeper into ohms, let’s take a look at all the elements of an electrical signal as it applies to audio.
There are four key elements to electricity: volts, amps, ohms, and watts. Voltage is the potential power of the signal, while amps measure the current, which you can think of as the rate at which that voltage flows. Ohms measure resistance, which, if you think of the signal as flowing water, is like the size of the pipe it’s flowing through. In our water analogy, you could think of voltage as being similar to water pressure.
What about watts? Watts measure the overall power, which is the voltage multiplied by the current. Increasing either the voltage or the current will raise the overall watts of a given system.
Now let’s see why the resistance, measured by ohms, is so important.
A Closer Look at Ohms
Because ohms measure resistance, as the number gets higher, the resistance goes up. The fact that a lower number equals a more powerful signal is a large part of the reason people can get confused when it comes to ohms in the first place.
Again, if you think of an audio signal coming from an amplifier like water pouring out of a spout, you can think of a speaker as a pipe. You can pump all the water you want into that pipe, but at a certain point, no more water can flow through that pipe.
Assuming that the amplifier and speaker are rated at the same resistance of eight ohms, everything works as it should. The amplifier isn’t going to attempt to pump out more than the speaker can handle.
But what happens when you have a mismatch? Say you’ve got an eight-ohm amplifier but a four-ohm speaker. In this case, the amplifier can’t provide enough current because the resistance is lower than its own. This is like pouring a one-liter bottle of water into a pipe capable of handling far more at a given time.
In some cases, this is fine. In others, the amplifier will attempt to pump out enough current to match the resistance of the speaker, which is lower than its own, and damage itself in the process.
Ohms in Speakers and Amplifiers
The vast majority of amplifiers and speakers you see for consumer use like home stereos or home theater systems come in four, six, or eight ohms. That said, you’ll most commonly see eight ohms used these days.
Many stereos and A/V receivers are fixed and are only meant to be used with speakers of the same impedance. You’ll encounter some receivers, especially more expensive models, that are fixed but can handle 100 watts at eight ohms or, for example, 200 watts at four ohms.
Other amplifiers have a switch built-in, usually on the back, that enables you to choose various impedance settings. That said, as A/V receivers continue to increase channel counts for home theater systems, we’re seeing fewer and fewer with this setting.
Higher-end A/V receivers may support four-ohm speakers, but this isn’t something you’ll see in lower-end models. If you aren’t positive that your amplifier can handle four-ohm speakers, make sure you stick with a matching impedance, which is often listed on the back of the receiver.
Audiophiles using tube amplifiers need to be especially careful when it comes to impedance, as tube amplifiers are more easily damaged by impedance mismatches. Use a speaker with too low of an impedance, and you can damage the speaker, while speakers with too high impedance will damage the amp.
Make Sure to Match
As we’ve already looked at, mismatches in resistance can damage your speaker or amp.
If you’re using a solid-state amplifier, which the vast majority of consumer electronics use, you can relatively safely use speakers with higher resistance than the amp. Eight-ohm speakers with a four-ohm A/V receiver, for example, should work fine.
That said, for the best results and the least worry of damaging anything, your best bet is to make sure that you’re using an amplifier and speakers with the same values. If you’re reading this before setting up a stereo or home theater system, be sure to take a look at our guide to home theater wiring.
