The pursuit of audio excellence can be something of a rabbit hole. Broach the subject with any sound engineer worth their salt, and you’ll likely find yourself sitting through a series of lectures on the ideals of sound quality. Tone may be subjective, but no audiophile will deny the function and appeal of a discrete headphone amplifier.
Impedance Matching
Walk into any audio electronics store and you may be overwhelmed by the variety there is with headphones alone.
There are high-impedance headphones, which typically see more utility in studio and audiophile settings, owing to the nature of their drivers and circuit design. Then there are the low-impedance headphones that are conceived with portable battery-powered music players like smartphones in mind.
What is important to remember is that a headphone’s impedance level (measured in ohms) should be matched by the power that’s delivered by an amplifier. This is regardless of whether it’s inbuilt like the one inside your smartphone, or an external one. Improper matching can result in excessive power use, distortion and noise problems.
Generally speaking, the higher the headphone’s impedance, the more voltage you’ll need to drive them. This generally translates conveniently to the need for more “powerful” headphone amplifiers.
Imagine a garden hose
A good analogy to consider is that of a hose: a pair of high impedance headphones are like a hose with a small nozzle, which requires more force (i.e. voltage) to push adequate water (i.e. audio signal) out. A more powerful amplifier will have more voltage on tap to do so, pun fully intended. High-impedance headphones carry a rating that ranges anywhere between 100 and 600 ohms. Most portable devices, however, will not have the voltage swing necessary to drive them. The result? Inadequate volume, compromised sound quality, and unfulfilled potential.
Usually, it helps to have an amplifier that’s more powerful than what’s necessary. The extra headroom that’s available in terms of “unused” voltage comes into play with demanding music like bass-heavy tracks or intricate orchestral music, which have wider voltage swings even if played at the same perceived volume. Regardless of music genre, the bump in voltage provided by good headphone amplifiers can result in an audible improvement in clarity, detail and dynamics.
Low Impedance and Sensitivity
Does this then mean that low-impedance headphones will have no use for headphone amplifiers? Not entirely. Returning to our analogy, a pair of low impedance headphones are like a “hose” with a wide nozzle. It does require less force to push “water” through, but maintaining an adequate flow necessitates a large volume of water (i.e. current). In this case, a more powerful amplifier helps by supplying enough current to let a pair of low impedance headphones perform to their full potential.
The last thing to consider is sensitivity (or efficiency), which measures the volume produced by a pair of headphones at a specific power rating, expressed in decibels (dB). Sensitivity ratings are typically in the range of 90 to 105 dB; anything falling below 95 dB is considered insensitive. These headphones will require more voltage and current to perform well.
What about wireless headphones? They come with integrated amplifiers, so there are no aftermarket options, unfortunately.
Headphones themselves are undoubtedly the most crucial part of any personal audio system, but the headphone amplifier follows closely behind. Ultimately, pairing a set of headphones with an amplifier is all about maximising the former’s performance. You just need the right trampoline to get there. If you use wired headphones at home, plugging them into an external amplifier instead of directly into the output jack of your laptop, desktop, or music player could just open up a new listening experience.
