Recording - July 2013 - 59

and the load impedance is high. In the case of headphones, bridging has long
been standard, with amplifier output impedances at least ten times lower than
that of the headphone input impedances. This arrangement is ideal, ensuring
high fidelity and minimum degradation in frequency response and distortion.
In recent years, the paradigm of impedance bridging has been challenged.
The issue is that older headphones are quite high in impedance (hundreds of
ohms) and powerful amplifiers are required to drive them to loud levels. Not
surprisingly, these higher Z models can tax modern portable music players,
quickly draining their batteries. With battery life an important selling point,
manufacturers answered by lowering headphone impedance. These newer
models, with impedance typically in the 16 to 50 ohm range, create higher
sound pressure levels without requiring more voltage.
Unfortunately, there are several side effects to lower headphone impedance. Sound quality is one, as frequency response can suffer and distortion
figures can rise when amplifiers are asked to deliver higher levels of current.
Another problem is unique to recording studios. With high-impedance cans,
multiple pairs can be fed off the same amplifier output simultaneously without
affecting performance. When several low-impedance headphones are connected at the same time, however, the total circuit impedance can drop below
bridging, drawing more current from the amplifier than available. This can
drive the amp into clipping, which not only sounds bad, but can blow headphone drivers, and in extreme cases, the headphone amp itself.

The AKG K702 is an open-back headphone, while the Audio-Technica
ATH-M50 is a closed-back design. Each has its advantages in sonics
and practical use.
Impedance & you
So what does all this complicated impedance stuff mean to you, the
everyday audio engineer? The first thing to note is that today’s world is
filled with headphones of many different impedance values. Higher-Z models can sometimes sound better, provide flexibility with old and new amplifiers, and allow the running of multiple pairs simultaneously off the same
amp output. Lower-impedance phones, on the other hand, are louder and
therefore are ideal for iPods and other portable music players.
These impedance differences can make their greatest impact when recording multiple musicians on the same tracking date. Unless a studio has many
of the exact same headphone models, different musicians will inevitably end
up wearing cans of varying impedance, fidelity, and loudness. This can
make headphone mix creation difficult, especially if musicians are sharing
the same amplifier and individual level adjustment is impossible. With this in
mind, it is important to know the differences between the headphones you
own and save the loudest pairs for the musicians needing to monitor at the
highest levels, such as drummers and horn players.
It’s all in the feel
Regardless of the delineations between open-back and closed-back, highimpedance and low-impedance, comfort and personal taste are the two

most important factors when choosing a pair of cans.
Concerning comfort, two fancy words are used to
describe the physical design of phones. Circumaural
headphones employ earpieces that surround the ear
and supra-aural headphones sit on top of the ear. In
general, ear-surrounding (circumaural) cans are more
popular in studio environments, as they typically offer
better bass response and less leakage to and from the
outside world. Supra-aural headphones offer other
advantages such as being lighter, easier to transport,
and less likely to overheat the ears. The bottom line
regarding comfort is that everyone’s ears are shaped
differently, and you should always test drive a set of
cans before purchasing. Over of the years, I have
encountered phones that feel great for hours while others take mere minutes to cause discomfort.
Personal taste is also a significant factor when
selecting headphones. A few years ago I spent some
time at a retailer comparing different models. I was
amazed how much sound quality varied between
pairs, ranging from pleasing to distasteful. Of course
my opinions are subjective, and I know other professionals that completely disagree with my eventual
headphone choice. So what do you do?
As a general rule, it’s probably best to search out a
pair with relatively flat frequency response, especially
if your intention is to use the phones for checking
mixes. With that said, it’s even more important that
you like the sound of your headphones, or otherwise
you’ll avoid using them. To prevent this scenario, when
shopping for cans, I suggest bringing along a CD or
iPod loaded with a reference playlist of recordings
you know well and think sound great. Listening to reference material can really help in identifying the headphones you prefer.
Ears, not eyes
Before completing a headphone purchase, consider
these last tips. First off, don’t trust the marketing. Just
because a well-known artist puts his name on a set of
cans, or just because you’ve seen dozens of teenagers
sporting headphones of a particular brand or color, there
is no guarantee that those models are the best choice.
Headphones are among the few pro-audio devices that
share mass marketing with everyday consumers. Don’t
trust the hype—use your ears, not your eyes!
Also, do your best to determine the strength and reliability of any headphones before purchasing.
Checking reviews online and demoing models in
stores might reveal critical weaknesses. Vetting cans is
important, as headphones see a fair share of physical
stress: we sweat on them, sit on them, leave them in
hot cars, stuff them in backpacks, and repeatedly
knock them off chairs. Cheap headphones are typically light and fragile and usually don’t survive long in
recording studios. Features that imply durability
include removable cables, so replacement is easy
when a cable gets mangled, hard-shell cases, and
replaceable foam ear pads.
It’s tricky to balance audio quality, durability, comfort, and technical considerations like impedance, but
it can be done. The key is to end up with one or more
headphone models in your studio that give you confidence and comfort as you work. Good luck!
Eric Ferguson (ferguson@recordingmag.com) spent a
dozen years as a freelance audio engineer in Los
Angeles, and is now on the faculty of the New England
School of Communications (NESCOM) in Bangor, ME.
RECORDING July 2013

Recording - July 2013

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