What is a headphone amp? This is a completely fair question even for non-beginners. Most of us are familiar with the small headphones that come with our smart phones and MP3 players. Even when we encounter headphones that are big like studio versions they are typically only like that in appearance and are still on the consumer level. Even beyond that, many headphones that could benefit from an amplifier can still be used without one at low volumes and you'd never know the difference. But eventually in the professional music industry you run into a headphone amp... Just what is it and why do we need them?
Even once a person discovers headphone amps, they usually first encounter the snake oil audiophile type that are meant to misinform and syphon money out of your pocket, attempting to charge as much as $20,000 and more for some gear that can get the job done for $200 and even less at times.
So what's the truth?
The reality is completely different than some people would have you believe. An amp that's over 20 to 50 times the price of your headphones will not be able to boost the quality of the audio any higher than the headphones are capable of producing.
It's always and only about two things:
That's it. No amp can out-perform the headphones. No electronics are producing electricity so "dirty" that it effects the ability of the headphones to function properly. We have too many standards and regulations for that.
What it really has to do with is sufficient power, and that has to do with how the headphones are built.
A headphone amplifier is simply a device that delivers electrical power to headphones. In modern times, they are tiny and inexpensive. They are hidden everywhere, from your iPhone to your TV and your car stereo. So why do we see giant amplifiers powering giant speakers in stadiums during concerts?
That's your hint... "giant." To keep the explanation simple at first, in the present the main use for amplifiers is to deliver a lot of power to operate gigantic woofers at high volumes. The larger a woofer (speaker cone) is, the more power it takes to drive it at the same volume as a smaller woofer. To push the big boy up to volume 10 will take a lot more voltage than their smaller counterparts will at the same volume.
These teeny earbuds we use today are about as small as it gets. It takes so little power to drive them that we can run them off of a single lithium battery on our phones for 10 hours straight while still doing other things like browsing the web.
So how come many people can plug in huge circumaural headphones like the ones above into a small CD player or MP3 player and still listen?
Because big earphones can be powered at low volumes by today's tiny amps. When turned up louder, they will begin to distort at the peak volumes with insufficient power. Most people don't notice and don't have true studio headphones.
There is a third element we haven't mentioned yet that's the true "problem causer" and the reason we need headphone amps:
Impedance is the reason that the best set of studio headphones on the planet might sound horrible at 70 dB in your Walkman while your $10 gym earbuds sound great. Try seeing which sounds better at 80-90 dB when each receives enough voltage for their respective impedances.
As mentioned in our article on the best studio headphone amplifiers...
The issue is one of quality at every volume, not just high volumes.
When we talk about quality, we're talking about performance across the entire frequency spectrum. Today's small amps might power a big set of headphones fine in the high and mid-range, but really struggle to produce any bass. So you have no bass. Or you turn it up only to discover that there is now bass only it's completely distorted.
Think of the flow of electricity as water flowing through a garden hose. The volume of water flowing through at any given time is equivalent to current. This is impacted by the size of the nozzle. If you have a nozzle the same diameter as the hose then the current flows freely. But if you put your thumb over the opening or screw on a nozzle with a small hole at the end, the current slows down.
The water still comes out but at a restricted rate. It may not be enough to drink from, fill your swimming pool, or feed the grass. The size of the nozzle is inversely proportional to the amount of impedance, meaning a small nozzle is high impedance and a huge one is low impedance. It is a form of resistance.
All old headphones have high impedances and the music studio industry still builds their headphones like this, and for good reason. It allows them to deliver more precision by using more coils in the drivers of the headphones. The last piece of the puzzle is voltage, which can be thought of as the pressure of the water trying to spray through the nozzle.
If you have a small nozzle (high impedance) then you need more pressure (voltage) to push the same volume (current) of water (power) through the nozzle.
And there's the catch. Today's headphones are purposefully built with low impedance so batteries don't run out on our mobile devices too fast. They are built this way so that they demand less power. Therefore the headphone amps in most devices are built to supply little power, which happens to be enough for modern headphones.
But they can't supply enough voltage to overcome the impedance of studio headphones enough to drive the woofers with enough power!
And that's why we need better headphone amplifiers for our studio headphones.
When it comes to the chassis (the physical container of the electronics), you have three main types:
The portable kind are designed to be slim and fit into your pocket. They accept audio from your smart phone or MP3 player and then deliver the power to your headphones through a battery. They have to be recharged after some time. These only drive one set of headphones at a time.
Desktop headphone amps typically drive one or two sets of cans but can have up to four outputs and even a set for studio monitors. They are larger and are designed to sit on your desk where you can reach the volume knob.
Lastly there are the rackmount variety that are designed to be racked into your normal 19 inch wide rack with the rest of your studio signal processing gear. These usually have four to six headphone jacks each and can be daisy-chained to one another to double or triple the number of outputs.
Each of these usually perform one of the following purposes better than the other, although the mid-tier to high-end options do both fantastically. These purposes are:
So why are there these two purposes?
A professional audio mixer needs to hear every single detail at varying volumes to make sure every element of a song or sound track is perfectly balanced. They don't need this done in 8 sets of cans, just one. And they need it done well. The same goes for fans of music who don't want to compromise quality at all (and this is how lots of people end up getting scammed).
People using headphone amps for this purpose will often choose a desktop amp. As long as you don't buy the cruddiest options out there, you end up with a lot of convenient features. You can switch between one or two sets of reference monitors and headphones, change volume, mute, drop to mono, and much more. Some even have remote controls, which is always fun.
The second purpose is to power a lot of headphones at once. You might have a band of six people in for recording, plus yourself, assistant, and their producer and everyone needs to hear what's going on. Enter the rackmount amp!
At this stage of recording you don't need top-notch quality, just a ton of power. You also need the ability to speak to the band members through their headphones from a distance. And the most convenient feature besides talkback is the "More Me" feature. This routes each members' vocals or instrument back into their own headphones and allows them to control the volume for that independent of everyone else's inputs. It saves you tons of time and annoyance having to tweak everyones' levels for comfort. They can do it themselves.
Portable headphone amps can be taken on the train or bus to work and be used at work for pleasure listening. Desktop and Rackmount amps are for mixing, mastering, and recording in the studio. High quality options can range from $200 to $2,000+ depending on the quality and number of channels. Nobody in their right mind's spends the $15,000 on one channel on some flashy desktop amp with vacuum tubes sticking out everywhere. That's just marketing meant to part a fool from his money.
The reason professionals need amps designed specifically for headphones has to do with delivering enough power to overcome the high impedance of studio headphones so there's no distortion or an impacted frequency response.
Please check out our suggested headphone amplifiers and studio headphones to get an idea of what's reasonable and what to expect in each price range. Dig in deep into the technical details of headphone impedance with the NwAvGuy.
And now you know the complicated answer to the question, "What is a headphone amplifier?" Go forth and be merry!