Here at The Master Switch, we don’t like complexity. It’s totally fine in a good whiskey, a doorstop novel, a piece of modern art. It is absolutely not okay when it comes to audio gear. The world of speakers, receivers, headphones and the like is full of potential pitfalls and confusing jargon already. If we have one mission on this site, it’s to make things as simple and as easy-to-follow as possible.

No subject has caused more headscratching or more confusion than the act of matching speakers to amps. How do you do it? What will happen if you get it wrong? What is wattage, resistance, sensitivity? Are you about to hit the ON button and send your amplifier exploding skywards in a fiery column? More importantly, why does there not exist an online guide that doesn’t require an electrical engineering degree to understand? Seriously. There are plenty of guides on this subject, but almost all of them assume a certain level of knowledge already. Believe us, we know. We looked.

Kill that noise. We’re going to change things. In this How To, we’re going to explain the process of matching speakers and amplifiers. We’re going to do it as clearly and simply as we can, and we’re going to assume that you know nothing.

Photo: Marcus Carlsson

Wattage and Impedance

Actually, back up for a second. Forget about that heading. We told you we’d assume you knew nothing, so let’s get the most basic stuff out of the way first. Skip this part if you know it already.

What is a speaker? A speaker is a device that transmits sound into the air. It’s usually boxy and recognisable, and most commonly comes in pairs, so they can produce stereo sound - or, sound from two channels. You can either get active speakers, which have their own power supply, or passive ones, which don’t, and which need an amp for power. For our purposes here, we’re going to be talking about passive speakers. Almost all modern hi-fi and bookshelf speakers are passive, anyway, so you shouldn’t have to worry about this. They are commonly connected to amplifiers with copper speaker wire, which is available at any electronics store, or on Amazon.

What is an amplifier? It’s a device that provides power to the speakers, and allows you to control their volume. It’s usually a squat, rectangular box with lots of controls on it. You get stereo amps (two channels only) and home theater amps (five, seven, sometimes even nine channels).

The problem here is simple. You can’t just plug any pair of speakers into any amplifier and expect things to work. The operation of both speakers and amplifiers depends on electrical power, and when you mess around with electrical power, things can get complicated. There are, very obviously, thousands of amplifiers and speakers available to buy, and they all come with different specifications. Things might work perfectly, or you could fry either your speaker or your amplifier, or you could get no sound at all, or you could get wildly reduced sound. Our job here is to make sure you get perfect sound, and we’re going to do it by focusing on a couple of product specs: wattage and impedance.

Let’s talk about wattage first. Wattage is simply a measure of power, of the amount of electricity something can take. It’s measured in Watts (W), hence the name, and we’ll talk about wattage and power interchangeably. Usually, an audio product will have two listings for wattage, because manufacturers love to make things confusing. There will be a listing for Peak Power, and another for RMS (sometimes referred to as Continuous Power or Program Power, because reasons). You can ignore Peak Power completely. Seriously, don’t even look at it. It’s irrelevant. All it means is the amount of power device can put out under certain conditions. What you need to focus on is the RMS. It’ll be much lower, but it’s the one we’re going to use.

All right. Got that? Good. Now let’s talk about Impedance. Very simply, this is the ability of something to resist electricity. Impedance (sometimes referred to as Resistance) is kind of important, as it allows a piece of electronics to function without exploding. A high Impedance means that not a lot of electricity can get through, while a low one means lots can get through. It’s measured in Ohms, often written using this symbol: Ω.

So: wattage is the power, and impedance is how well something can resist electricity. Even if you don’t fully understand the concepts here (although we imagine you do, because you’re smart enough to be reading this site, right?), all you have to know is those two specs. With those at your fingertips, you will be able to confidently match any speaker with any app. And we’re going to show you how.

Photo: Jan Hammershaug

Making The Match

The key thing to remember is this. An amplifier’s output wattage needs to be at least 50% more powerful than the wattage of the speakers.

So if, for example, I have a pair of speakers that are capable of putting out 200W, I would require an amplifier with at least 300W of power - because 50% of 200 is 100, and added together, and now were explaining basic maths and we’re sorry. Anyway. It doesn’t have to be exactly 50% every time; as long as it’s not less than 50%. It can quite comfortably be more. You could run those 200W speakers with a 400W amp, no problem. 

This is the most important thing. If you have speakers and an amplifier with equal wattage, you’re going to wear out your speakers quite quickly. If your amp has less wattage than your speakers, you’ll ruin them. But 50% additional power or more? You’re gravy. By the way, make sure that the amplifier's output wattage is rated as Per Channel. You need the same amount of power on each channel, because each channel will have a speaker attached to it.

(Another important side note: only try this with passive speakers. Active speakers come with their own power supply, and if you plug an amplifier into them in any way, they will go bang.)

Now, what about impedance? This is even simpler. They should be equal. An amp with 4Ω of impedance should be matched to a speaker with 4Ω. Most amps will work with 4, 8 and 16Ω speakers, as a kind of industry standard. As long as the numbers on both your speakers and your amplifier are the same, you’re good to go.

This is something you want to pay attention to. If your speaker impedance is lower than your amp’s, you’ll blow both of them. If it’s higher, you simply won’t be able to generate enough volume.

The way that wattage and impedance on an amp are expressed often looks something like this: 750W/4Ω. That means that the amp is capable of generating 750W at a 4Ω load. As long as your speakers have less power than that, as described above, and are also capable of a 4Ω load, you’re good to go. But pay attention: power loads vary at different impedances. So that same amp might put out, say, 500W at a 6Ω load. Match the impedance first, then look at power.

Photo: Jan Hammershaug

A Real-Life Example

OK. Theoretical math is all fine. But what if we want to put this into practice?

Pioneer SP-BS22-LRPick two bookshelf speakers: say, a pair of the Pioneer SP-BS22-LRs. This is a terrific speaker set that we’d be happy to have in our living room. But what amp should we use to power them?

The speakers have a maximum input power of 80W, and an impedance of 6Ω (Pioneer call it Nominal Impedance, but it’s the same thing, so don’t worry). So what we need here is an amplifier with at least 120W of power at an impedance of 6Ω. Let’s see if we can find one.

Easy as pie. We’ll go for the Yamaha A-S500BL stereo amplifier. It puts out 150W of power per channel at 6Ω, which more than satisfies our requirements here. By pairing these two, we’ll get sound that is clear, distortion-free, loud, powerful, and gorgeous. No blown speakers, no piddly volumes, just crystal audio.

See? Wasn’t that easy?

Yamaha A-S500BL

But Wait: What About Sensitivity?

So there is one last item on the spec sheet you need to pay attention to. It’s not nearly as important as wattage or impedance, but it’s a good measure of the kind of speaker you’re buying.

The item is Sensitivity. This refers to how loud speaker gets for every watt of power applied to it. The lower the sensitivity, the more power will be needed to drive the speaker. A speaker with a high sensitivity will be easier to power, and will sound better at low volumes.

You don’t need to pay too much attention to this. Most modern speakers usually have a sensitivity of between 85 and 95 decibels (dB), which is more than capable. Obviously, you want to go for the highest sensitivity possible, but it’s far more important to spend some time comparing wattage and impedance.

Photo: Christian Herzog

What Do I Do Next?

Go shopping. Duh.

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