What Speaker Impedance Means and Why It Matters

Stack of various speakers
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For almost every speaker or set of headphones you can buy, you'll find a specification for impedance measured in ohms (symbolized as Ω). But the packaging or included product manuals tend to never explain what impedance means or why it matters!

Fortunately, impedance is kind of like great rock'n'roll. Trying to understand everything about it can be complicated, but one doesn't need to understand everything about it to "get" it. In fact, the concept of impedance is a rather simple one to grasp. So read on to find out what you need to know without feeling like you're taking a graduate-level course at MIT.

It's Like Water

When talking about things like watts and voltage and power, a lot of audio writers use the analogy of water flowing through a pipe. Why? Because it's a great analogy that people can visualize and relate to!

Think of the speaker as a pipe. Think of the audio signal (or, if you prefer, the music) as the water flowing through the pipe. The bigger the pipe, the more easily water can flow through it. Bigger pipes can also handle more volume of flowing water. So a speaker with a lower impedance is like a bigger pipe; it lets more electrical signal through and allows it flow more easily.

This is amplifiers can be seen as rated to deliver 100 watts into 8 ohms impedance, or maybe 150 or 200 watts into 4 ohms impedance. The lower the impedance, the more easily electricity (the signal/music) flows through the speaker.

So does that mean one should buy a speaker with lower impedance? Not at all, because a lot of amplifiers aren't designed to work with 4-ohm speakers. Think back to that pipe carrying the water. You can put a bigger pipe in, but it'll only carry more water if you have a pump powerful enough to provide all that extra flow of water.

Does Low Impedance Mean High Quality?

Take almost any speaker made today, connect it to almost any amplifier made today, and you'll get more than enough volume for your living room. So what's the advantage of, say, a 4-ohm speaker versus an 8-ohm speaker? None, really, except one; low impedance sometimes indicates the amount of fine-tuning the engineers did when they designed the speaker.

First, a little background. The impedance of a speaker changes as the sound goes up and down in pitch (or frequency). For example, at 41 Hz (the lowest note on a standard bass guitar), the impedance of a speaker might be 10 ohms. But at 2,000 Hz (getting into the upper range of violin), the impedance might be just 3 ohms. Or it could be reversed. The impedance specification seen on a speaker is just a rough average. The way the impedance of three different speakers changes with respect to the frequency of sound can be observed from the chart at the top of this article.

Some of the more exacting speaker engineers like to even out the impedance of speakers for more consistent sound throughout the whole audio range. Just as one 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 is why 4-ohm speakers are common in high-end audio, but rare in mass-market audio.

Can Your System Handle It?

When choosing a 4-ohm speaker, make sure the amplifier or receiver can handle it. How can one know? Sometimes it's not clear. But if the amplifier/receiver manufacturer publishes power ratings into both 8 and 4 ohms, you're safe. Most separate amplifiers (i.e., without a built-in preamp or tuner) can handle 4-ohm speakers, as can probably any $1,300-and-up A/V receiver.

I'd be hesitant, though, to pair 4-ohm speakers with a $399 A/V receiver or a $150 stereo receiver. It might be OK at low volume, but crank it up and the pump (amplifier) might not have the power to feed that bigger pipe (speaker). Best case, the receiver will shut itself off temporarily. Worst case, you'll be burning up receivers faster than a NASCAR driver wears out engines.

Speaking of cars, one last note: In car audio, 4-ohm speakers are the norm. That's because car audio systems run on a 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. But don't worry: Car audio amps are designed for use with low-impedance speakers. So crank it up and enjoy! But please, not in my neighborhood.