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How to Pick the Right Amp for Your Speakers (or Vice Versa)

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MArk.jpgAmplifiers and loudspeakers. Two devices that go together "like a horse and carriage," as the Sultan of Swoon would have said. After all, you can't have one without the other, assuming you actually want to listen to your music and movies in an actual room. But if speakers and amps were a Facebook couple, there's no doubt that their relationship status would be "It's Complicated."

Despite being quite dissimilar devices (one being an electrical device designed to increase the amplitude of a signal from a preamplifier or preamp stage; the other being a mechanical device designed to convert that electrical signal into acoustical energy), the performance characteristics and capabilities of both loudspeakers and power amplifiers are described using many of the same words: primarily, watts (both RMS and peak) and impedance (usually denoted as Ω, or ohms). As such, you might think it would be reasonably simple to match a speaker with an appropriate amplifier: make sure the numbers match, and you're in good shape, right? Well, sorta yes and sorta no. To understand why, we need to take a look at what those terms mean.

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But first, a caveat: this article is intended as a quick primer for beginners. As such, it contains a number of simplifications, many of them bordering on grossness. The goal here isn't to write the definitive treatise on the subject, but rather to give budding audio enthusiasts a foundation of knowledge on which to build. To keep things simple, we'll mostly be focusing on the characteristics of your typical solid-state amplifier and ignoring things like OTL (output transformerless) tube amps. Still, even a simple discussion of the relationship between speakers and amps can get a bit mathy; so, if you're merely looking for a cheat sheet to help you find a new amp for your favorite speakers (or vice versa), you can skip straight to the conclusion.

With that out of the way, let's discuss some of the common terms listed in the specifications for most amps and loudspeakers, and what those specs mean when shopping for components that play well together. Since wattage is the spec that most people look at first (and the only spec that some shoppers consider), we'll start there.

Watts It All About?
Pioneer-TS-A1375R-5.25-inch-Three-way-Speakers-Back.jpgWattage is a measure of electrical power described most simply as voltage (volts) times current (amps). But what does that mean when it comes to speakers? Despite conventional wisdom, it really isn't a good indicator of how loud a speaker will play. Instead, it's an indicator of how much power a speaker can physically take without distorting or physically breaking (whether that be from fried voice coils, blown speakers, or cooked crossovers).

An amplifier's rated wattage, by contrast, is calculated a little differently: by throwing numbers into a hat and pulling them out until one sounds impressive.

I'm kidding, of course. Mostly. The power output of amplifiers is usually listed as RMS and Peak. The former (which would be more simply described as continuous power) is calculated by playing a sine wave signal and measuring the average (root mean square) voltage and current that the amp can deliver without clipping (which is usually measured in terms of Total Harmonic Distortion, but can be seen on an oscilloscope as a flattening out of the curved tops and bottoms of a sine wave).

A good amplifier can, of course, deliver more powerful, albeit brief, bursts of clean energy than its continuous power output rating without clipping, and good speakers can likewise handle such brief bursts. How much more? It really depends on the speaker and the amplifier. I recently spoke with Larry Reagan, vice president of sales for Pro Audio Technology, about his company's LFC-24sm subwoofer, whose power-handling capabilities are rated as 1,000 watts (AES) / 2,000 watts continuous. When I asked him what that meant, exactly, he had this to say: "The AES test is 1,000 watts of constant pink noise for two hours straight. It's the Audio Engineering Society's torture-test rating. With real musical or movie content, the thing can handle up to 2,000 watts constant easily, but you could actually throw 10,000 watts at one of these things in one of those momentary bursts, and it wouldn't flinch."

Needless to say, what's true for subwoofers isn't necessarily true for all speakers, but what is undeniably true is that most everyone seems to have an opinion on exactly how much amplification you should feed a speaker given its rated power handling. And almost none of them agree. Some recommend an amp with a 10 percent higher RMS power rating than the speaker's continuous power-handling capabilities. Other suggest 1.5 times. Others still recommend doubling or even quadrupling the speakers' RMS power-handling rating.

Why such high recommendations? I think that notion comes from the mistaken belief that what blows up drivers is a lack of power, not an excess of power. It's easy to see why this canard is so commonly accepted as gospel, though. What's actually happening when an underpowered amp blows up a speaker is that the amp is being asked to deliver more voltage or current than it's physically capable of doing safely and cleanly, which sends the amp into clipping. And when an amp clips, it subjects your speakers to a not-insignificant amount of direct current. So, technically, if you've ever fried your speakers with too small an amplifier, the murder weapon was too much DC power, not too little AC power.

triton_detail_overview_image_new.jpgPerhaps that's why a number of knowledgeable speaker manufacturers have started to eschew RMS and peak power ratings in favor of a broader "recommended amplification" rating. GoldenEar Technology is one such company, so I called head honcho, Sandy Gross, to ask why his speakers are rated this way and how, exactly, the "recommended amplification" rating relates to RMS and peak power handling. "The truth is," he told me, "RMS and peak power specifications don't really relate to anything in terms of real-world listening material. You can blow up speakers with virtually any size amp, or you can use them safely with virtually any size amp, depending on how you drive them." To make his point, Sandy told me that he's currently driving his pair of GoldenEar Triton Two towers (which carry a recommended amplification rating of 20 to 500 watts) with a 22-watt-per-channel tube amp from Line Magnetic. "I had David Chesky over recently to listen to the setup, and he was blown away by how good it sounded," he told me. "I've even driven the Triton Two with amps as low as six watts per channel, and it did a pretty good job. You'd be surprised."

Click on over to Page 2 to find out why Resistance Is Not Futile, Sensitive Speakers and Wrapping Up . . .

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