What Is a Headphone Amp and Do I Need One?
The rise of mobile music devices, like MP3 players, smartphones and tablets, has mostly been for the better. Today’s audiophile can store literally thousands of songs their pocket and enjoy them with just a few taps of a touchscreen.
If you’re serious about music, however, you may be disappointed by the audio quality your mobile device manages – particularly when paired with high-end headphones. The solution is to pair your mobile device with a portable headphone amplifier, a small device that can greatly improve your listening pleasure.
What’s An Amp, Anyway?
I’m sure you’ve heard the term amp before, but you may have never needed to learn about what it does. Only audiophiles working with high-end audio setups regularly worry about details like these.
Amp is, of course, short for amplifier, and the name is an accurate description of what an amp does. The amplifier increases the power of an audio source so that it can properly drive bigger, louder equipment. Home theaters sometimes use an amplifier (usually in a receiver) to power big speakers, and bands inevitably need amps to power massive concert speakers.
A headphone amp is simply a smaller version of this same concept. The smallest are barely the size of a solid state hard drive, while the largest are around the size of CD-ROM drive, but they all accomplish the same goal.
Why Might You Need One?
The connection between the amps which power concerts and a pair of headphones isn’t obvious. You might think headphones easy to power, and compared to other audio equipment, that’s true. But a smartphone (or MP3 player, or tablet) is exceptionally small and must manage power usage carefully. This means some mobile devices don’t provide the power required to drive high-end equipment.
Headphones are essentially a set of speakers rigged to fit on your head and comfortably over your ears. Like all speakers, they need power, which is provided (in this situation) by a 3.5 millimeter audio jack. If the power provided by the jack is not enough to fully drive the speakers you’ll find them strangely quiet and feel that certain aspects of the experience, such as strong bass, are missing. This occurs because headphones, unlike most electronics, don’t switch off when they receive insufficient power. They work – but not as well as they could.
The power you’ll need to drive a headphone can be inferred by its impedance. A set with high impedance (like the Sennheiser HD800, which is rated at 300 Ohms) requires more voltage to produce a given volume than those with low impedance (like the Denon AHD-2000, which is rated at 25 Ohms). You will probably benefit from a headphone amp if your headphones are rated beyond 32 Ohms, but you likely don’t need an amp unless you use a set rated at 100 Ohms or greater.
Your ears, however, should be the final judge. Those that aren’t as loud as you’d like almost certainly aren’t receiving as much power as they should. If unsure, try the same pair with a home theater receiver or other powerful audio source to see if volume improves.
Note, also, that all of this talk only applies to on-ear headphones. In-ear headphones, also know as earbuds, work differently and require far less power, so an amp isn’t needed to extract the most from them.
What About Quality?
An amplifier can increase the quality of your listening experience, but it’s not guaranteed to do so, and you may have a very difficult time telling the difference between a headphone amp and a smartphone that already provides enough power to drive your set. Tests of the iPhone 5 and other popular smartphones show portable devices work well compared to a dedicated amp – not better, but well enough for all but the pickiest audiophiles.
You’re only likely to run into an issue if the output impedance of your device is too high relative to the impedance of your headphone. In general, a device’s output impedance should be no more than 1/8th the impedance of the headphone it’s paired with. Unfortunately, determining this ratio can be difficult because most smartphone and tablet manufacturers don’t publish the audio output impedance of their devices. You’ll have to rely on audiophile reviews, when available.
I Need An Amp — What Do I Buy?
Most headphones don’t need to be amplified when used with an iPhone or other portable device. This is purposeful; headphones used to have higher impedance, on average, than they do today. Manufacturers have adjusted the way they build headphones to ensure they work reasonably well with mobile hardware.
If you’ve found you do need an amp, however, (perhaps you want to use your Sennhesier HD800s on a plane, for example) you’ll want to pick up something that’s slim yet powerful. You should aim for an amp that can provide at least 500 milliwatts of power and has as very low output impedance (preferably a couple Ohms or less).
FiiO’s E12 is a popular example. Rated at 850mW and featuring a built-in battery that can last up to six hours, this $129 amp can power virtually any headphone on the market and boasts an output impedance below 1 Ohms, yet can fit in your pocket. This is a great pick for audiophiles.
Alternatively, you could go with something smaller and lighter, like the FiiO E11. This unit is rated at only up to 300mW of output, so it won’t fully drive the beefiest headphones around, but it’s great for mid-range audiophile gear and is only $65.
If you want something more exotic, and more compact, check out the V-Moda Vamp Verza. Unlike other amps, which stand alone, the Vamp is designed to strap onto an iPhone, iPod, Android smartphone or similar device, which results in a more compact form-factor. The device can output up to 150mW of juice and lasts up to 7 hours. The downside, though, is the price; it’s a whopping $600.
Understanding amps is a bit difficult, but in all likelihood it’s not a quest you need to embark on. If your headphones are already almost too loud to tolerate at maximum volume, you don’t have an amp problem. You only need to worry about purchasing one if you have a high-impedance, audiophile set.
Do you use an amp? If so, what headphones do you use it with? Let us know in the comments.