Often forgotten in the portable-music realm is the fact that headphones are speakers too. And like conventional floorstanding or bookshelf speakers, headphones benefit to varying degrees by using an amplifier. These devices increase the output voltage provided by portable devices like iPods and Android devices, increasing low-level dynamics and bass articulation. An amplifier won't make cheap headphones sound more expensive, but they will improve the results on any pair.
Although most headphone amplifiers are relatively small when compared to conventional home audio amplifiers, some are clearly designed for in-the-pocket use. Some of these are battery-operated, do-it-yourself affairs, some mounted in breath-mint containers. Other amplifiers sit on the desktop and use AC power, receiving the feed from a computer or portable audio device either through a 3.5 millimeter or USB connection. Either is capable of being carried along in a computer or camera bag for improved headphone performance in a hotel room or on vacation. For the ultimate in portability, some amplifiers are the size of a USB thumb drive. Although these aren't extremely powerful, they can improve the clarity of easy-to-drive earbuds or other efficient headphone types.
Headphones, like all speakers, rely on power to start and stop the delicate drivers that move the air, creating sounds. The more power that is applied, the more control over those drivers. In turn, listeners experience greater clarity at lower volume levels. As volume is increased during more spirited listening sessions, this increase in power translates into superior resolution. Vocals are more intelligible, while instruments formerly buried in the background are brought to the fore. Although results vary from amp to amp, nearly any model provides more output power than those found on portable music sources.
Cost Benefit Analysis
Dedicated audio enthusiasts may not be averse spending large sums to perfect their musical experience. However, if you primarily use a smartphone or MP3 players as your primary source, you may want improvement without breaking the bank. Headphone amplifiers range from less than a hundred dollars to a few thousand, depending on the headphones used and the desired results. If you use uncompressed audio files or direct CD rips on your portable devices or computer, the added detail and warmth achieved from using a quality headphone amplifier should pay noticeable dividends. If low-bitrate MP3s downloaded from various legal sources are the order of the day, increased detail may actually prove detrimental, as a headphone amplifier will also increase the clarity of noise and compression artifacts.
Some amplifiers feature more than a single headphone output pair -- important if you share a workspace or like to use different headphones for different musical genres. If you leave them all plugged in, the available power is reduced proportionally, but the added convenience may be worth it. Additionally, some amplifiers are part of devices called digital-to-analog -- or D/A -- converters, which take the output of a portable device or computer and process it for smoother sound. It is quite common to find headphone jacks on these devices, a nod to those who want to increase sound quality without adding further clutter to a busy desktop.
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