Glossary: Headphones

ENCYCLOPAEDIA HEADPHONICA

As you might expect, the world of high‑performance headphones and earphones has gradually adopted specialized terminology all its own. This article is provided in an attempt to make it easier for newcomers and veterans alike to navigate that world.

Some of the terms described here are in common use throughout the industry, while others are more specific to The Absolute Sound. Our publication does try to use terminology consistently, especially within our on-going series of headphone/earphone-related product reviews, so that this glossary will—we hope— help you get more out of past, present, and future The Absolute Sound content.

Balanced Armature Driver

A type of miniature drive unit frequently applied in earphone and CIEM designs, but also—much less frequently—used in full-size headphone designs. Balanced armature drivers feature extremely small can-like enclosures containing very small armatures wound with wire coils and suspended within a magnetic field. As audio signals are applied, the changes in the magnetic field across the coil cause the armature to rock back and forth, pivoting on its balance point or fulcrum. As one end of the armature is driven upward, the other end goes downward (much like a child’s ‘seesaw’ or ‘teeter-totter’ in motion). In order to produce sound, one end of the armature drives an actuator connected to an extremely small diaphragm, which flexes inward and outward as the armature moves up and down. Output from the diaphragm typically is routed to the listener’s ears via a sound outlet tube commonly called a ‘bore’.

Balanced Headphone Amplifiers

In the world of headphones and earphones—as in traditional audio—there are two distinct topologies of amplifiers available: single-ended amplifiers and balanced amplifiers. By convention, in a single-ended amplifier the ‘–‘ output terminal is tied to electrical ground, while the ‘+’ terminal carries the active signal. In single-ended headphone amplifier

applications specifically, outputs are typically delivered through a three-conductor jack sized to fit either a 6.35mm phone jack-type plug or a 3.5mm mini-jack-type plug. In either case, one of the conductors in the jack/plug serves as the ‘–‘ or ground connection, while the other two conductors serve, respectively, as the ‘+’ connections for the left and right audio channels.

In balanced (some would call them ‘differential’) amplifiers, internal circuitry is differently arranged so that in essence the amplifier has two equal but opposite halves; one handling the positive-going side of the audio signal and the other handling the negative-going side of the signal. Both the ‘+’ and ‘–‘ halves of the amplifier are referenced to electrical ground. As a result, the outputs of each amplifier channel will have three (rather than just two) connections for audio signals: a ‘+’ connection, a ‘–‘ connection, and a dedicated ‘GND’ or ground connection. In balanced headphone amplifiers, outputs are typically handled by two 3-pin XLR connectors (one for the left channel and the other for the right), where the 3-pins correspond to ‘+’, ‘–‘, and ‘GND’.

Note the multiple types of balanced output connectors on the front panel of the iFi Audio Pro iCAN fully-balanced headphone amplifier.

Bore

Many CIEM and some earphone manufacturers use the term ‘bore’ to describe the sound outlet tubes associated with balanced armature-type drivers. Sometimes the outputs of multiple drivers might be routed through a single bore tube. Thus, one might read CIEM descriptions that state something like this: “Ours is a four-driver, triple-bore in-ear monitor design.”

CIEM

CIEM is an increasingly popular acronym that stands for ‘Custom-fit In-Ear Monitor’. The key idea is that CIEMs, unlike universal-fit earphones, have custom-molded earpieces that are crafted to provide a precise custom-fit that exactly matches the contours of the individual wearer’s ear canals and outer ears (or pinnae).

In order to have a set of CIEMs made, prospective owners must first obtain, either through a qualified audiologist or through the CIEM manufacturer, a set of ear-mold impressions, or else have the interior surfaces of their ears digitally scanned. Either way, the ear-mold impression or digital scans are used to create molds from which the CIEM’s custom earpieces are made.

CIEMs like the Westone ES80 offer beautifully finished, user-specific, custom-molded earpieces.

Circumaural Headphones

Full-size headphones generally come in two forms: on-ear designs and around-the-ear designs. The word ‘Circumaural’ is the correct, formal term for ‘around-the-ear’ designs, where the ear pads surround the wearer’s outer ears, but do not rest directly upon them.

Clamping Force

The term ‘Clamping Force’ describes the amount of pressure that a given headphone design exerts in squeezing or pressing the left and right ear cups of headphones against the sides of the wearer’s head. There is no industry standard for such forces and listener’s tastes can and do vary on the matter. The key concept is to have sufficient force for the headphone to stay in place during listening (too little clamping force might make the headphone prone to slipping out of position or even falling off) but force low enough to allow comfortable long-term listening sessions.

Closed‑Back Headphones

Generally speaking, full-size headphone designs follow one of two possible configuration formats: open-back or closed-back designs. In closed-back designs, as the terminology suggest, the back sides of the ear cups are completely sealed or ‘closed’—making each ear cup much like the enclosure of an acoustic suspension-type loudspeaker, but in miniature. For obvious reasons, closed-back headphones do a better job of blocking out external noise than open-back headphones do. However, there is much debate on which design format— open-back or closed-back—makes for superior driver performance and all-around sound quality.

Closed-back headphones like the Sennheiser HD820 have ear cups completely sealed on the back side.

Diaphragm

Regardless of type, headphone and earphone/ CIEM drivers invariably have some sort of diaphragm, which is the moving element that actually produces the sounds we hear.

Some headphone/earphone diaphragms are much like miniature versions of the circular woofers, tweeters, etc. that most of us have seen in conventional dynamic driver-equipped loudspeakers; these tiny diaphragms operate like tiny pistons moving inward and outward to produce sound waves.

Other headphone/earphone diaphragms are thin, planar membranes whose entire surface area vibrates to produce sound, much as in full-size electrostatic or planar magnetic-type loudspeakers.

Finally, some headphone drivers used folded membranes whose pleated surfaces move somewhat like the bellows of an accordion to produce sound, much like loudspeakers fitted with ribbon-type or Heil air motion transformer (AMT) types of drivers.

Dynamic Driver (Moving‑Coil Driver)

Dynamic drivers (also sometimes called ‘moving-coil’ or ‘pistonic drivers’) are by far the most popular types of drivers for use in loudspeakers, headphones, and earphones (although many CIEMs use balanced armature-type drivers). The core elements of dynamic drivers consist of diaphragms (the cone or dome that actually moves to produce sound), voice coils (ring-shaped coils of wire wound on small, cylindrical ‘voice coil formers’) that are attached to the diaphragm, and magnets (which are usually cylindrical in shape with ring-shaped grooves called ‘voice coil gaps’ on top).

As a musical signal is routed through the voice coil, which is positioned within the voice coil gap of the magnet, the electromagnetic interaction between the voice coil and the magnetic field causes the voice coil/diaphragm to move forward and backward, thus producing sound.

Dynamic headphone drivers like the Beyerdynamics’ T1 Tesla headphone are built much like miniaturized dynamic drivers for loudspeakers.

Ear Buds

The term ‘ear bud’ is the slang expression for the sort of loose-fitting transducers worn in the outer ear, as typically supplied with smartphones, personal digital music players, etc.

Some people use the terms ‘ear bud’ and ‘earphone’ interchangeably, but we at Hi‑Fi+ see those terms as having distinctly different meanings. For us, the defining characteristics of ear buds are, first, that they are worn in the outer ear and not within the ear canal, and second, that ear buds almost always fit loosely and do not provide any sort of airtight seal with the ear canal. Note, please, that ear buds typically are voiced so that they sound normally balanced without requiring an airtight seal.

Ear buds such as the Urbanears Medis are meant to rest lightly in the wearer’s outer ear— not inserted into the ear canal.

Ear Cup

In full-size headphones, ear cups are the physical housings or ‘enclosures’ to which the headphones’ drivers are attached, and to which the headphones’ ear pads are attached.

Typically, signal wire connections to the headphone are also made through the ear cups. There are many different schools of thought on ear cup construction so that you will find ear cups made of wood, molded thermoplastics, composites, and metal.

Ear cups can be made of various materials, including polycarbonate, carbon-fiber, and a range of exotic woods.

Earphone

The Absolute Sound (and many manufacturers and enthusiasts) consider the term ‘earphone’ to be a contraction of the longer though more descriptive term, ‘universal-fit in-ear headphone’. For us, the defining characteristics of earphones involve the fact that, regardless of the earpiece configuration used, earphones are meant to be worn within the ear canal, with the assumption that a flexible set of ear tips (offered in various sizes) will be used to ensure a comfortable yet airtight seal between the earphone and the ear canal. The voicing of earphones presumes and indeed requires this airtight seal for proper tonal balance to be achieved.

Some people use the terms ‘earphone’ and ‘in-ear monitor’, plus the acronym ‘IEM’, interchangeably, but at Hi‑Fi+ we again feel these terms have distinct and different meanings.

As above, we define ear buds as typically loose-fitting devices worn in the outer ear, while ‘earphones’ are worn within the ear canal and require the aforementioned airtight seal within the ear canal in order to work properly, in the process achieving significant levels of noise isolation.

‘In-ear monitors’ and ‘IEMs’ are, strictly speaking, in-ear transducers worn for monitoring applications, but the practical reality is that the majority of listeners doing actual monitoring work tend to choose CIEMs (Custom-fit In-Ear Monitors) for the job, owing to their superior noise isolation and more sophisticated sound quality.

In our opinion, most earphone makers who call their products ‘IEMs’ are overreaching, probably in the hope that the ‘IEM’ label will confer upon their earphones some of the perceived ‘hipness’ and sophistication of true CIEMs.

By design, earphones are compact and use sound outlet tubes fitted with flexible ear tips designed to create a comfortable yet airtight seal within the wearer’s ear canals.

Earpiece

The term ‘earpiece’ refers to the physical housing or enclosure within which ear bud, earphone, or CIEM driver(s) and crossover networks (if any) are mounted and from which the sound outlet tube(s), if any, extend.

For obvious reasons, earpieces must be large enough to accommodate the intended driver or driver arrays, yet small enough and smooth enough to fit comfortably within the wearer’s outer ears. The physical shape of the earpiece must also allow for very wide variations in ear shapes and sizes, while at the same being easy for the wearer to grasp, to insert, or to remove.

As with headphone ear cups, there are many schools of thought on earpiece construction, so that shoppers may encounter earpieces made of wood, molded thermoplastics, composites, metal, acrylic materials, or even cold-cure soft-gel silicone.

Manufacturers go to great lengths to balance the demands of fit and functionality in high-performance earpiece designs.

Ear Pads

All types of full-size headphones feature ear pads that provide a comfortable, soft, and flexible interface between the headphones’ ear cup/driver assemblies and the wearer’s head.

Ear pads typically are shaped either as circular, oval, or ‘racetrack’-like rings, open at the center to allow the sound to pass through; pads may be covered in fabric, leather, faux leather, or any combination of those materials.

Ear Tips

Almost all contemporary universal-fit earphones come with several sizes of flexible ear tips designed to provide a comfortable but airtight seal between the earphone’s sound outlet tubes and the wearer’s ear canals (even a seemingly minor air leak can upset if not ruin the tonal balance of the earphone). The sole exception would be certain ear tip designs that provide built-in vents (e.g., some of the tips used for the Cardas Ear Speakers) though vented ear tip designs are comparatively rare.

Ear tips come in a variety of configurations with popular variations including single-, double-, and triple-flange designs, and round or ‘bell-shaped’ designs that might also include special features designed to enhance noise isolation. Ear tips are typically made of soft, silicone rubber, but some manufacturers have experimented with multi-layer ear tips, in some cases with noise isolation gel sandwiched between the inner and outer layers. Another popular variation involves ear tips constructed of compressible foam materials—a concept patented by the firm Comply Foam (which is a spin-off of 3M Corporation).

Modern universal-fit earphones, such as the Campfire Audio Solaris ship with extremely elaborate sets of ear tips.

Electrostatic Drivers

Electrostatic drivers feature diaphragms made of thin membranes typically constructed of polyester-like materials (e.g., polyethylene terephthalate or PET) to which an electrically conductive coating has been applied. These membranes carry a high voltage (typically greater than 500V) but very low-current charge and are suspended between two metal (or metallized), mesh-like electrode grids called stators.

In operation, high voltage (but again, typically low-current) audio signals are applied to the stators. By design, the stator pairs are configured so that at any time when musical signals are present, the stators will carry opposite charges (one carrying a negative ‘–‘ charge and the other a positive ‘+’ charge, and then vice-versa, as the audio signal flows back and forth).

As the charge on the stators varies in response to musical signals, the diaphragm is simultaneously attracted to one stator and repelled from the other, so that the diaphragm moves back and forth within the air gap between the stators, producing sound as a result.

Headband & Headband Frame

In a general sense headbands are the frames used on all full-size headphones that reach up and over the top of the wearer’s head, while holding the left and right ear cups in proper position for optimal sound and user comfort. Frames can be made of various materials including metal, molded thermoplastics, composites, or other materials.

One key aspect of any headband design will be an adjustment mechanism of some kind that will allow the frame to expand or contract as needed in order to accommodate the varying sizes of users’ heads. Two other key elements of any good headband frame will be the ear cup yokes and the headband pad or strap.

Ear cup yokes are the frame elements to which the headphones ear cup/driver assemblies attach. Some yoke designs are minimal while others are quite elaborate. Some minimalist yoke designs hold the ear cups in fixed, or very nearly fixed, positions, trusting in the springiness of the headband frame to provide sufficient flex for a decent fit. Other yoke designs allow ear cups to swivel (in horizontal and/or vertical axes) to obtain a better overall fit. Trade-offs can be involved either way. As a general rule, minimalist yoke designs tend to be more rugged—say, for headphones that might be worn while participating in action sports, while swiveling designs offer greater flexibility for purposes of fit but are somewhat more complicated to build and more prone to breakage should the headphone inadvertently be dropped.

The frame and yoke design of the HiFiMAN Susvara headphone allows ear cups to swivel in both horizontal and vertical axes.

Headband pads or straps are the ‘suspension system’ for the headphone, enabling the headphone’s weight to be spread across the top of the wearer’s head. One school of thought calls for padding the headphone frame itself to provide a soft, comfortable point of contact with the wearer’s head. A second school of thought, however, calls for a broad, flexible strap to be suspended, sometimes via elastic or rubber suspension rings, from the frame of the headphone (so that the weight of the headphone is borne, in part, by the suspension bands or rings).

For example, the MrSpeakers ETHER 2 uses a lightweight suspension strap to support the headphone’s weight for greater comfort.

Headphone

The term ‘Headphone’ refers’ to full-size headphones (as opposed to earphones or CIEMs) that are worn on the head, with ear cups that either fit around or alternatively rest upon the listener’s ears.

We at The Absolute Sound draw a distinction between headphones, which by definition are worn on and rest upon the user’s head, versus earphones or CIEMs, which are worn in the user’s ears but do not rest upon the top of the head.

Headphone Connector Plugs

There are a handful of physical connector types commonly used for connections between headphones and headphone amplifiers (or tablets, smartphones, etc.). One useful distinction, however, can be drawn between connectors designed for use with single-ended amplifiers vs. connectors designed for use with balanced amplifiers.

Single‑ended Connector Plugs: Single-ended connector plugs have three conductors—a ground “GND’ conductor (shared by both the left and right channels), plus two ‘+/–‘ signal conductors (one each for the left and right channels).

3.5mm, three‑conductor, mini‑jack plug: By far the most common connector for earphones/ CIEMs (but also for some headphones), the small, three-conductor 3.5mm mini-jack

plug is the type of connector used to plug headphones into iPods, digital music players, iPads and other tablets, and iPhones and other smartphones. Quite recently, some manufacturers have begun using pairs of 3.5mm sockets to support balanced stereo output connections.

3.5mm plugs are probably the most common in all of personal audio because 100 years of jack plugs makes them ubiquitous!

6.35mm phone/headphone plug: Think of this as a considerably larger scale version of the 3.5mm plug. The 6.35mm plug is typically used to connect full-size headphones to full-size desktop (but also some portable) headphone amplifiers. Like the 3.5mm plug, the 6.35mm plug provides three conductors (sometimes called the Tip, Ring, and Sleeve) and supports connections to single-ended amplifiers.

6.35mm plugs, like this ‘garden variety’ adapter plug, are essentially bigger, sturdier version of 3.5mm plugs.

Balanced Connector Plugs: Balanced connector plugs will typically provide four, or in some cases two sets of three, conductors— with separate ‘+’ and ‘–‘ conductors for each channel, plus a separate ground ‘GND’ conductors in some configurations.

Three‑Pin XLR connector plug: Three-pin XLR connector plugs are designed specifically for balanced signal connections and in headphone contexts are always used in pairs (one for each channel in a stereo pair of balanced mode connections). The three pins provide ‘+’, ‘–‘, and ‘GND’ connections for one channel: hence, the need for two plugs to provide stereo (two-channel) connections.

Traditional three-pin XLR plugs are among the most common balanced audio connectors in use today, although there are a handful of brands that use a single, five-pin plug.

Four‑Pin XLR connector plugs: Externally identical to three-pin XLR connector plug, internally four-pin XLRs provide separate ‘+’ and ‘–‘ signals for both the left and right channels.

RSA connector plugs: RSA connector plugs, named in honor of Ray Samuels Audio, are sometimes found on small, portable, balanced output headphone amplifiers. RSA connector plugs essentially function like miniaturized 4-pin XLR connectors. Interestingly “RSA connectors” were developed by the firm Kobiconn Connector for use in certain types of camera connections, but Ray Samuels was the first to use Kobiconn Connector as a balanced audio connector in compact, portable amplifiers.

Tiny four-pin RSA/Kobiconn plugs support balanced audio connections for devices where space is at a premium.

3.5mm, four‑conductor, mini‑jack plugs: A handful of manufacturers have offered amplifier and headphone cables that provide balanced output connections through comparatively uncommon, four-conductor (or ‘four ring’) 3.5mm mini-jack plugs (where the conductors are labelled Tip, Ring, Ring, and Sleeve).

2.5mm, four‑conductor, connector plugs: Yet another means of providing balanced output connections is via a comparatively new-to-the-market four-conductor (or ‘four ring’) 2.5mm plug. This plug is the chosen balanced-output connector for use with the popular Astell & Kern AK240 portable digital music player/headphone amp.

Hybrid Headphone & Earphone Designs

Headphone and earphone makers, as well as the team at The Absolute Sound, use the descriptor ‘hybrid’ to indicate that the product in question uses a mixed (or ‘hybrid’) combination of technologies. One good example would be the recently released oBravo HAMT-3 Mk II headphone, which employs the hybrid combination of the dynamic-type mid/ bass driver and a Heil air motion transformer-type mid/high-frequency driver. Another good example would be the PSB M4U 4 universal-fit earphone, which employs the hybrid combination of a dynamic mid/bass driver and a balanced armature-type mid/high-frequency driver.

Final Audio Design’s Sonorous VI headphone looks conventional enough, but it features a hybrid dynamic/balanced armature-type driver array.

Noise‑Cancelling Headphones & Earphones

The term ‘noise-cancelling’ as applied to headphones or earphones means exactly what it says: namely, that the headphones/earphones provide active circuitry that detects external noise and then applies (to the best extent possible) an equal and opposite signal designed to cancel out the noise. For this reason, some designers (and marketers) prefer the term ‘active noise-cancelling’.

PSB’s M4U 8 is one of the very few active noise-cancelling headphones that manages to offer serious, audiophile-grade sound quality.

Noise‑Isolating Headphones & Earphones

Recognizing that active noise cancelling headphone and earphones can potentially create scenarios where the intended sonic ‘cure’ (active noise-cancellation) turns out to be worse than the sonic disease (noise), some designers have instead chosen to work on designs that use purely passive means of isolation or blocking out external noise. Generally, these passive designs are called ‘noise isolating’ (as opposed to ‘noise-cancelling’) headphones or earphones.

On‑Ear Headphones

Unlike circumaural (around-the-ear) headphones, on-ear headphones feature comparatively small ear cups with ear pads designed to rest upon, rather than to surround, the wearer’s ears.

On-ear headphones like the Klipsch Reference On-Ear have smaller ear cups and ear pads than equivalent circumaural headphones.

Open‑Back Headphones

Open-back headphones feature ear cups that, by design, are open both on their front (that is, ear-facing) sides and on their back sides (so that there is virtually nothing—apart from protective grilles—but open air behind the rear sides of the headphone drivers. In many respects open-back headphones are analogous to dipolar loudspeakers in that they have rigid perimeter frames, or in this case ear cup housings, with no sealed enclosures behind the drive units at all.

For self-evident reasons open-back headphones offer little if any isolation from external noise. However, there is much debate on whether open-back or closed-back designs offer superior overall driver performance and sound quality.

Planar Magnetic Drivers

The loudspeaker manufacturer Magnepan first pioneered planar magnetic drivers and holds (or once held) many of the core patents on the technology. Therefore, today’s modern planar magnetic headphones could, in a sense, be regarded as ‘Magnepans writ small’. In planar magnetic drivers, the diaphragm consists of a very thin but strong membranes on whose surfaces are found conductive circuit traces typically arrayed in very precisely dimensioned serpentine patterns, with the conductive traces are spread over the entire radiating surface of the diaphragm. Many manufacturers use some form of Mylar-like material for their diaphragms, but at least one manufacturer (HiFiMAN) is using a radically thin, low mass ‘nano-material’ diaphragm.

Then, placed in close proximity to the diaphragm there is a precisely aligned grid or array of powerful magnets with deliberate open-air spaces between the magnets to allow sound waves to pass through. Some designers favor the concept of having magnet arrays positioned on both the front and rear sides of the driver diaphragm, while others favor having an array on one side only—usually the side facing away from the listener’s ears. Either way, as musical signals are applied to the conductive traces on the diaphragm, the diaphragm is attracted to and/or repelled from the magnet array(s), thus producing sound.

The planar magnetic drivers used in the Abyss AB-1266 TC are considered to be among the most revealing of any headphone produced today.

Ribbon Drivers

Ribbon drivers could be considered a specialized-case version of planar magnetic drivers, but with one critically important difference. In a ribbon driver, the entire diaphragm is made of conductive, thin-film, metal material, so that in a very real sense the diaphragm is—to borrow dynamic driver terminology—its own voice coil. In most cases the ribbon driver diaphragm will be corrugated or ‘pleated’ and then suspended in the presence of very strong magnetic field. As musical signals are passed through the ribbon diaphragm/conductor, the diaphragm interacts with the surrounding magnetic field, moving fore and aft to produce sound.

Signal Cables

As is true in full-size, loudspeaker-based audio systems, headphone/earphone-based systems can be and typically are very sensitive to the quality of the signal-bearing cables in use. If you have any doubts as to whether cable substitutions can influence sound quality, let us assure you cables can impact sound in quite audible and obvious ways (and no, you don’t need to be a ‘golden ear’ to hear their effects).

We haven’t the space to go into cable technologies at this time but suffice it to say that it is worth seeking out headphones and earphones that either ship with very high-quality signal cables in the first place, or for which high-quality, third-party, aftermarket cables are available. Over time, you may discover—as we have—that judicious cable changes can help unlock hidden layers of performance in your favorite transducers.

Some pundits say wire substitution can’t possibly make an audible difference, but bluntly they’re wrong. You can easily prove this point by visiting a good headphone shop, trying some cable substitutions, listening carefully, and then drawing your own conclusions.

It is also important to recognize that most headphone/earphone failures in the field are attributable to cable failures. The point is that it is simpler and cheaper to replace a set of signal cables than to have to go shopping for entirely new headphones or earphones.

In addition, in a desktop personal audio application, different USB cables can have marked changes on the performance of a DAC.

Supra‑aural Headphones

Although you might rarely if ever hear this phrase in common usage, the term ‘supra-aural headphones’ is the formally correct way to say, ‘on-ear headphones’.