What Speaker Impedance Means and Why It Matters

For almost every speaker or set of headphones you can buy, you'll find a specification for impedance measured in ohms (symbolized as Ω). Seldom do the packaging and included product manuals explain what impedance means or why it matters to you.

Impedance is like great rock 'n' roll. Understanding everything about it is complicated, but you don't need to understand everything to "get" it.

About Speaker Impedance

When talking about things like watts, voltage, and power, many audio writers use the analogy of water flowing through a pipe because it's an analogy that people can visualize and relate to.

Think of the speaker as a pipe. The audio signal—your music—acts as the water flowing through the pipe. The bigger the pipe, the more easily water can flow through it. Bigger pipes also handle more volume of flowing water. A speaker with a lower impedance is like a bigger pipe in that it lets more electrical signal through and allows it to flow more easily.

As a result, you see amplifiers that are rated to deliver 100 watts at 8 ohms impedance or 150 or 200 watts at 4 ohms impedance. The lower the impedance, the more easily electricity (the signal or music) flows through the speaker.

A lot of amplifiers aren't designed to work with 4-ohm speakers. Using the pipe analogy, you can put a bigger pipe in, but it'll only carry more water (audio) if you have a pump (amplifier) powerful enough to provide the extra flow of water.

Does Low Impedance Guarantee High Quality?

Using lower-ohm speakers without equipment that can support them may cause you to turn the amplifier all the way up, which can damage the equipment.

Take almost any modern speaker and connect it to any modern amplifier, and you'll have more than enough volume for your living room. So, what's the advantage of a 4-ohm speaker versus a 6-ohm or 8-ohm speaker? Not a lot—just that low impedance sometimes indicates the amount of fine-tuning the engineers did when they designed the speaker.

The impedance of a speaker changes as the sound goes up and down in pitch (or frequency). For example, at 41 hertz (the lowest note on a standard bass guitar), the impedance of a speaker might be 10 ohms. At 2,000 hertz (the upper range of a violin), the impedance might be just 3 ohms. The impedance specification seen on a speaker is just a rough average.

Some of the more exacting speaker engineers like to even out the impedance of speakers for consistent sound throughout the whole audio range. Just as someone might sand a piece of wood to remove the high ridges of grain, a speaker engineer might use electrical circuitry to flatten the areas of high impedance. This extra attention is why 4-ohm speakers are common in high-end audio but rare in mass-market audio.

Can Your System Handle It?

Before you buy a 4-ohm speaker, make sure the amplifier or receiver can handle it. It may not be clear, but if the amplifier or receiver manufacturer publishes power ratings in both 8 and 4 ohms, you're safe. Most separate amplifiers without a built-in preamp or tuner can handle 4-ohm speakers, as can most high-end A/V receivers.

A relatively inexpensive receiver might not be the best match for 4-ohm speakers. It might function OK at low volume, but crank it up, and the amplifier might not have the power to feed the speaker. The receiver may shut itself off temporarily, or you may burn up the receiver.

About the Impedance Switch

Some amplifiers and receivers feature an impedance switch on the back that you can use to switch between ohm settings. The problem with using this switch is that impedance is not a flat setting, it is a curve that varies. Using an impedance switch to "match" your equipment to your speakers intentionally cripples the full capabilities of your amplifier or receiver. Leave the impedance on its highest setting and buy speakers that match your equipment's impedance settings for the best performance.

Impedance of Car Speakers

In car audio, 4-ohm speakers are the norm. That's because car audio systems run on 12 volts DC instead of a 120 volts AC. A 4-ohm impedance allows car audio speakers to pull more power from a low-voltage car audio amp. Car audio amps are designed for use with low-impedance speakers. So crank it up and enjoy.