How to properly power your speakers

So you’ve just bought a swanky new pair of speakers and can’t wait to listen to them, but setting them up has become a frustrating riddle. What do you do? For most people, that means using the included speaker wire in the box. However, not all speakers come with this, and if you want to wire up a home theater: the situation is a little more complicated. We’re here to tell you not to panic: we can help you learn everything you need to know from powering your speakers to impedance matching them.

Ensuring that your speakers work with maximum efficiency, volume, and minimum distortion isn’t difficult these days, but there are a few insider tips worth knowing. Here’s everything you need to know about how to power your speakers properly.

Active vs. passive speakers

Speakers ship in two distinct types: Active and passive. Active speakers are the most common in the consumer market, and these use their own power supply and amplifier to power the speakers themselves. If you have active speakers, you can simply plug them in, and stop reading here (unless you’re curious of course)!

Smart home and Bluetooth speakers are always active, as they require power for their additional features. Bookshelf speakers are often active too, although you still have to plug the secondary speaker into the primary one. But if your speaker has a power cable: it’s active, and handles everything we’re about to talk about for you.

The second type are passive speakers, which tend to occupy the higher end of the market. Passive speakers don’t have their own power supply, so there’s no power cable attached to them. Instead, you’ll find a couple of jack sockets or wire connectors on the back of each speaker that you’ll need to plug into an amplifier (or home theater receiver). All speakers and headphones require a certain amount of power in order to make them function, but the main difference with passive speakers is that they don’t already have an amplifier inside them like active speakers do.

It’s up to you to figure out which amplifier to buy and how to hook everything up. That’s where this guide comes in.

Impedance matching is key

Speakers are essentially circuits that follow the basic rules of resistance and impedance. Matching the correct impedance ratio maximizes the power transfer from the source (amplifier) to the load (speaker). Failure to match these correctly can result in under-powered speakers and low volume, or worse: an overheated and failing amplifier.

Don’t worry if you never took Electronics 101, we’re not going to need to do any math. Audio engineers have made the whole process simple enough.

So start with, locate your speakers’ manual, and look for something called the speaker impedance (in ohms Ω). You’ll usually find this measurement on the back of your speakers, too. Typical values are 4Ω, 6Ω, and 8Ω, with the latter being the most common for home speakers. Lower impedance values like 4Ω are generally reserved for very high power setups.

Match your speaker’s impedance to your amplifier’s corresponding output channel. Simple.

Next, check out your amplifier and find the corresponding impedance information. This will be labeled on the back by the connector for the left and right speakers. So if your speaker is 4Ω you’ll want an amplifier with a 4Ω rated output connection. Yes, it’s really that simple!

However, amplifiers differ in their level and range of support. It’s uncommon these days, but some amplifiers support only one impedance rating. Others may have multiple connectors for different impedances, and some have just one port that supports a range of values. It’s always best to research your amplifier beforehand to make sure it’s compatible with your speakers.

If you can’t get an exact matching, play it safe by plugging your speakers into a higher impedance port rather than risk overloading your amplifier. For example, if you have a 6Ω speaker but just 4 or 8Ω amp connections available, plug into the 8Ω one.

A word on wiring

After buying an expensive speaker system, it’s temping to fine tune your listening experience. There’s a whole market selling overpriced speaker cables, promising superior sound but with no scientific backing. Save your money and stick with the cables that ship with your speaker. As we’ve shown, even a wildly-impure zinc alloy coat hanger sounds perfectly fine powering speakers. The main benefit to getting oxygen-free copper is that it won’t corrode over time, but the conditions required for it to corrode are extremely unlikely to begin with.

Where you do need to pay attention is if you opt to wire up multiple left and right speakers to a single amplifier channel. In this instance, you’ll need a little bit of math to calculate the combined impedance of all the speakers connected to each channel.

For serial connections, this is very simple as impedance adds. Two 4Ω speakers connected in series have an impedance of 8Ω, two 6Ω speakers become 12Ω, and so on. Connecting speakers in parallel is more complicated, as impedance actually reduces for each speaker connected. You’ll need the formula 1/Ωtotal = 1/Ω1 + 1/Ω2 + 1/Ω3 + …

For example, two 4Ω speakers in parallel have a combined impedance of 2Ω. Or a more complex connection of two 4Ω and one 6Ω speakers have an impedance of just 1.5Ω. This is important to know, as parallel connections can easily load down your amplifier, causing it to overheat or shut off.

Pay attention to power

Just like the impedance rating, speakers each have a power rating in watts (W) too. You’ll find this in the manual, and possibly on the back of the speaker too. Likewise, amplifiers also have a maximum power rating. This is often quoted in watts-per-channel (WPC).

Opting for an amplifier with a slightly lower power rating than your speakers ensures that you won’t blow them out at max volume. Not that you’ll likely ever push home speakers that hard, as good pairs tend to have a high rating. Instead, you’ll save money opting for an amplifier with a power limit that suits your listening purpose.

You’d be surprised by how little power most speakers actually need to sound loud in your living room.

To do so, you’ll need to consider your loudspeaker’s sensitivity (in dBSPL), the listening distance from your loudspeaker, and your desired volume (70-80dB is usually plenty). Plug them into an online calculator like this to get you in the right ballpark.

You’d be surprised by how little power most speakers actually need to sound decently loud. Just 10W to 20W is more than enough for most modest listening spaces. Generally speaking, a 50W amplifier is more than enough for home listening with plenty of headroom. Although you may want 75W or more for a multi-channel home cinema setup. Of course, distortion and frequency characteristics are just as important when looking for a good amplifier, so don’t let power be your only deciding factor.

Putting it all together

There’s a lot of info there, but powering passive speakers isn’t that complicated. Fortunately, the industry has mostly become standardized, catering for a more plug and play mentality. Even so, there are a few key tips to make sure your new purchase works at peak performance.

• Make sure your amplifier can handle your speaker’s impedance. Check the spec sheets and match up your speaker to the matching amp channel.
• Buy an amplifier that suits your power needs. More watts aren’t always better, especially for small rooms and speakers.
• Triple check your impedance math when connecting speakers in serial or parallel.
• Avoid cable snake oil, stick with what’s in the box.

With all that in mind, you’ll have no problem powering your speakers properly.