How to Choose the Right Amplifier for Your Speakers

By: Michael Perez (Audio Arkitekts)

It has always been good practice to purchase speakers that best match ones listening style. Selecting speakers is an undertaking in and of itself. Once you find your holy grail speakers, you will need to power them somehow. This is a ubiquitous question many people in the industry get from folks first starting in the world of high-fidelity audio and perhaps stepping away from the conventional Bluetooth speaker or stereo boombox. For people who do not know the science behind it all, it could become a disastrous combination of speaker and amplifier.

The first step is to check your new speaker’s specifications.

The manufacturer will write out this little section on the website in words and acronyms you may not understand at first. So, what do you do with this? At least for me, it looked like hieroglyphics the first time I encountered this little box of science and math. However, this little box will be essential for finding an amp for those new speakers you bought. So, we will begin by discussing the speaker’s efficiency, which is measured in decibels or dB if you are reading the spec sheet. Companies measure the efficiency of a loudspeaker by placing a microphone one meter from the speaker and then providing the speaker with one watt of power. So, if you stand one meter from your speaker and input 1 watt of power from your amplifier, which results in 86 dB of sound, then the speaker sensitivity is 86dB. Doubling the wattage input into the speaker will result in approximately 3dB of volume increase. In this case, 2 watts of power results in 89dB, 4 watts of power will produce 92dB, and so on. At 10 watts of power, you would be producing about 96dB of volume. That’s about as loud as a Boeing 737 one nautical mile away before landing. Always consider that you will lose approximately 6 dB of sound every time you double the distance between yourself and the speaker. Usually, speakers range in efficiency or sensitivity from about 85 dB, considered very inefficient, to 105 dB, which is very efficient when measured in decibels. For example, a loudspeaker that measures 90.5dB like the KLH Model Five doesn’t necessarily need a powerful amplifier to fill your room with sound since with around 20 watts of power; you will be able to play them at volumes you’d be more than comfortable with. This is the big misconception with amplifiers and companies that tout enormous amounts of watts per channel; it is simply the fact that you will more than likely never listen to or use even half the watts they’re rated at. You would probably blow your speaker or your eardrums before reaching that high of wattage. So, if you bought a speaker with horrible efficiency, don’t worry. This isn’t a bad thing, per se. You’ll have to find an amplifier to give the speaker the right power to drive them to their full potential. It may be a bit more expensive, but it’s available. Most speaker manufacturers are making their speakers with decent efficiency since most stay within that high 80s to low 90s in decibel range.

Many audiophiles prefer the sound of tube amplifiers because they have a bit of distortion that causes the feeling of warmth to come across its sonic signature. Most of these low-wattage amps, like Nelson Pass’ First Watt SIT 3, only provide 18 watts per channel; however, paired with really efficient speakers, this amplifier can provide a beautiful sound that isn’t easily matched by many amplifiers in the industry. At the same time, if you pair this same amplifier with inefficient speakers, it may not play as well as expected because of its limitation in pumping copious amounts of watts and volts into a pair of power-hungry loudspeakers. Let’s say you are using Vincent Audio’s SP-332 Power Amplifier, which can provide up to 150 watts of power per channel at 8 ohms. I think it is safe to say this hybrid amplifier, which utilizes both solid state and tube amplifier topology, can drive most speakers you would throw its way. Watts and power are very matter of fact and rely on knowing the speakers’ efficiency.

What are ohms?

I mentioned ohms earlier because the impedance of a loudspeaker is also something you need to consider when pairing your speakers with an amplifier. A speaker’s impedance is measured in ohms, which directly refers to a circuit’s opposition to the flow of electrical current. This is another moment where you must look at the speaker’s specifications and find the speaker’s nominal impedance. The resistance is called ‘nominal impedance’ for speakers, as the actual impedance changes based on the frequencies of sound you are playing at the time. Usually, loudspeakers will have a nominal impedance of eight, six, and four ohms. The most important thing to remember is the lower the ohms; the more current is coming through. If you have a speaker output labeled “minimum of 4 ohms,” you can connect one 4-ohm speaker or two 8-ohm speakers to that output. If you were to connect two 4-ohm speakers to that output, it would overload the amplifier and probably destroy it. So making sure your amplifier can handle the ohms listed on your speaker’s specs is an essential factor to consider when deciding on an amplifier.

How many speakers will you be connecting to the new amplifier?

Something you will already know beforehand, depending on whether you’ll be setting up a home theater or just a simple two-channel listening environment.

Most basic home theaters will run five speakers and a subwoofer to help recreate a theater-like environment and provide a full range experience. In this case, you will need to buy an Audio/Video Receiver or AVR. An AVR has many functions and features that will consolidate your entertainment needs into one device. For example, if you have a television, media streamer, Blu-Ray Player, and Gaming Machine, most new AVRs will allow you to connect them via an HDMI cable into your AVR. The receiver will then process the sound and picture, sending the video signal to your flat screen or projector and the audio signal to its internal amplifier, which will power all five speakers. Five speakers are modest for some home theater enthusiasts. The advent of Dolby Atmos and full surround sound has driven the cinephiles of the world into a feeding frenzy to fit more and more speakers into their environment. However, five speakers are a good place to start, and you can always move up from there. The AVR will be your media hub and amplifier for all audio/video needs.

Suppose you are just running two speakers, primarily for music. In that case, you’ll need a two-channel amplifier with enough power (watts) and match the nominal impedance (ohms) to allow your speakers to play at their finest capacity.

As if this was not confusing enough for someone starting out, the next step would be to decide what class of amplifier you want to use in your system. There are several classes of amplifiers; however, the most typical are Class A, A/B, and D.

Class A amplifiers are found more in the realm of high-end home audio. The part of the amplifier responsible for converting the input voltage into output power is always on, making these amplifiers relatively inefficient because whatever voltage they do not use turns into heat. It’s constantly consuming energy. It is also the heaviest and most expensive amplifier out of the group. Why is this so sought after by audiophiles? Well, because the sound they produce is considered to be the best quality amongst all classes of amplifiers. If you’ve never heard a proper Class A amplifier, I think you should head over to a Hifi shop or a friend’s house who has one because they sound pretty nice.

A class A/B amplifier is a bit different where it is not always off but not always on. It is a compromise without sacrificing too much of the sound quality of a Class A amplifier, with better efficiency and lessening the price compared to its Class A counterpart. I did a poll recently within my YouTube community and 56% preferred class A/B because of its balance of value and sound quality.
Class D amplifiers are becoming a more popular and widely used type of amplifier among the lower-priced offerings. Even higher-end brands are starting to adopt Class D since its quality has evolved quickly over the years. They are highly efficient, can be made much smaller and lighter, produce less heat, and are the least expensive. A huge misconception is that Class D stands for digital, which it DOES NOT; it is just another amplifier class. Over the years, they have evolved into a fantastic sounding option for your sound system, and I imagine we will see these a lot more often in the coming years in more high-end applications.

Choosing your amplifier is an important decision because, in my experience, they do have different sonic signatures, even within the same power ratings and classes. A company’s engineering team will do their best to ensure a pleasant sonic experience; nonetheless, not all amplifiers are made the same or designed the same way. This creates slight distinctions in the sound they produce. Some are warm and pleasant, and some can come across as cold or shrill. It’s always best to do your due diligence when making your final decision. This can be a purchase that may very well last you decades, as many amplifiers from the 1970s and 1980s are still circulating in the used market today and work great. Plan for this purchase to be an excellent match for your current speakers, but also future-proof yourself by purchasing an amplifier that can match well with speakers you will likely upgrade to.