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Glossary

Analog
Generally, a mechanism that represents data using a continuously changing variable. In audio, usually a voltage that continuously tracks and represents sound pressure level.

Balanced Headphones
Balanced headphones are headphones that have been wired for balanced-drive, or 'differential drive' operation. Normally headphones have three connections: a left and right signal that is connected to the + side of the driver coil and then a common return for the - side of the driver coil. This common connection and its contact and other resistances to ground allow a small amount of cross-talk between channels to develop. Balanced headphones have four connections with a normal and inverted audio signal driving the = and - side of the driver coils for each channel. Balanced headphones require special four-channel balanced headphone amplifiers. The design completely removes the opportunity for crosstalk at the headphones and effectively doubles the slew rate of the amplifier/headphone system, providing a significantly cleaner sound.

Behind-the-neck
Behind-the-neck headphones are also called 'neckband' headphones. These have a headband that fits behind the neck rather than over the head. They are most commonly used in exercise or active-use applications since they're quite stable during movement. Fashionistas like them when they don't want to muss up their hair, or when wearing a hat or helmet.

Bright
A descriptive audio term meaning generally that a sound has strong treble. Would be harsh or tizzy in the extreme.

Circumaural
Literally meaning "around the ear," circumaural headphones have larger ear pads that completely surround the ear, and earcups that completely enclose or cover the ear.

Closed
Closed or closed-back headphones are also commonly called 'sealed' (or sealed-back headphones) and are designed to block out environmental noise using a passive acoustic seal. Full size closed headphones provide about -10dB to -15dB of isolation, mostly in the mids and higher frequencies. Smaller on-ear closed headphones provide somewhat less isolation dependent on their design and the shape of your ear. In-ear headphones are a closed design in which the earpieces 'seal' within the ear canal like earplugs to prove about -25dB or more outside noise attenuation. In-ear headphone usually provide the best isolation and noise-blocking of any headphone type. Noise-cancelling headphones are closed designs that add battery-powered electronics to attenuate ambient noises better than a normal 'passive' earcup seal could provide.

Coaxial
Many HeadRoom digital to analog converter (DAC) products have a "coaxial digital" input. This is a 75 Ohm S/PDIF digital audio input. The word "coaxial" specifically refers to 75 Ohm cables which typically use a coaxial construction, which refers to a center conductor and an outside conductor which completely surrounds the center conductor. Both conductors share the same center axis and are therefor called "co-axial."

Coherent
A descriptive audio term when all spectral components of the audio are passing through the system at exactly the same time. When audio is coherent, imaging is precise and stable with instruments clearly defined and natural sounding. When incoherent, may become edgy and hard sounding, lacking image depth.

Crossfeed
An electronic circuit that serves to make the audio image on headphones more like that heard on speakers. It takes the signal from each channel, delays it for a few hundred microseconds, and crossfeeds it over to the opposite channel to mimic the acoustics of the left speaker sound reaching the right ear and vice versa. It both improves the audio image on headphones and reduces listening fatigue.

DAC
A DAC is a Digital to Analog Converter. Music is stored as a series of numbers on CD's and in computer files. Each number represents a sample of the instantaneous voltage value of the audio signal at a point in time. Samples are taken many thousands of times per second (44,100/sec for CD's), and have a resolution of 16 or 24 bits typically. A DAC takes this stream of digital numbers from a CD player or computer and converts it to an analog electrical signal that can be amplified and used to drive headphones or speakers.

Damping Factor
Typically the input impedance of a speaker/output impedance of the amplifier. An 8 Ohm speaker driven by a power amplifier with an output impedance of 0.8 Ohms would have a damping factor of 10. Typically, damping factors of 10 or more are considered good.

dBr
"Amplitude (dBr)" is listed on the Y axis of HeadRoom frequency response measurement data. "dBr" stands for Decibels- relative. The graph is showing the amplitude of each frequency's response relative to the amplitude of the other frequencies, not the actual number of decibels measured at each frequency.

Diamond Buffer (Walt Jung)
HeadRoom headphone amps employ a discrete component output power amplifier using a circuit based on the Walt Jung-designed "Diamond Buffer." This circuit has the basic advantages of near-zero input/output offset; lower input bias current; and reduced distortion due to better load isolation. Our HeadRoom implementation is pushed fairly hard into Class-A bias, and is an extremely hardy design able to drive loads of widely varying characteristics.

Digital
Generally a system using binary data (ones and zeros) to represent information. In audio, a digital signal is a series of binary numbers that represent the sound pressure level sampled in a series over time.

Digital Inputs
Any input to a digital to analog converter (DAC); for example USB, or S/PDIF Toslink optical or coax digital inputs.

Distortion
Any new feature in a signal due to some imperfection in the device through which it passes. For example, putting in a 1000 Hertz tone, and getting a small amount of 2000 Hertz tone out along with the original 1kHz tone.

Driver
The element inside the headphone that converts an electrical signal into sound pressure that is heard by the ear. Most headphones use a dynamic driver which is a coil of wire suspended in a magnet and attached to a diaphragm, much like a very small speaker cone. Other popular headphones use planar magnetic or electrostatic driver types.

Ear Headphone
Ear headphones are always called in-ear headphones by us, but can be referenced by numerous terms including: in-ear monitor, IEM, ear canal headphones, earphones, and canal-phones. In-ear headphones are inserted into and seal the ear canal, and provide the highest amount of isolation from outside noise of any headphone type including noise-canceling headphones. There are two types of in-ear headphones: deep sealing and shallow sealing. With deep seating in-ear headphones the tip of the earphone goes in about half the length of the ear canal and seats in the bony section of the ear canal; this type provides about -23dB of isolation. Shallow seating types seal closer to the entrance to the ear canal and provide about -15dB of isolation.

Earbud
Earbud headphones are the ones that come with iPods or smartphones. Earbuds have small earpieces that are positioned in the small cupped area (concha) around the outer entrance to the ear canal in your outer ear (pinna). They most commonly simply rest in the concha, but some have attachments or ear clip features to improve wearing stability. Earbuds are all typically fairly similar in size, but they should not be mistaken for in-ear headphones, which seal in the ear canal like a true earplug and can typically sound much better than earbuds.

Earpad
Otherwise known as supra-aural or on-ear headphones, earpad headphones have ear-pieces are sometimes literally flat pads against the ear, but can also be shallow bowl shaped, or deeper ear cups that are too small to fully surround the ear.

Earphones

HeadRoom always calls this type of headphone 'in-ear headphones," but they are also known by numerous terms including: in-ear monitor, IEMs or ear canal headphones. In-ear headphones are inserted into and seal the ear canal just like an earplug, and thus provide the highest amount of isolation from outside noise of any headphone type including noise-canceling headphones. There are two types of in-ear headphones: deep sealing and shallow sealing. With deep seating in-ear headphones the tip of the earphone goes in about half the length of the ear canal and seats in the bony section of the ear canal; this type provides about -23dB or more of isolation. Shallow seating types seal closer to the entrance to the ear canal and provide about -15dB of isolation.

Efficiency
Headphone efficiency is the measure of the relation ship between input signal level and how loud the headphones play. This can be a rather confusing measure and can be expressed in numerous ways: dB/Watt; dB/mW; dB/Volt. Some in-ear headphones have very high efficiency (~120dB/mW); difficult to drive full size headphone may be in the 90dB/mW; headphones to be driven by portable players should have about 95dB/mW or better efficient, and a 100 Ohm or lower impedance.

Filter Switch
This switch engages a filter that makes the sound slightly brighter (more highs). It is there to compensate for the crossfeed which causes in increase in low frequencies. The amount of increase in low frequencies is dependent on how much information is common to the left and right channel; the more common information the more the bass will boost through the crossfeed. Over time, our electronics circuits have gotten faster, and we've found less bass emphasis occurs when the crossfeed is switched on, and we have found the need to use this switch is substantially less.

Frequency Response
A systems gain at various frequencies. "Flat" frequency response is when the gain is constant at all frequencies. For example, a gain of two at both 20 Hertz and 20kHz, and at all frequencies in between.

Full size
Also called "circumaural," full-size cans have large earcups that completely cover the earlobes on most wearers.

Gain Switch
A coarse volume control for headphones of differing impedance. Roughly, set to low for 10 to 50 ohm; medium for 50 to 200 ohm, and high for 200 ohm and up. Headphones vary widely in their impedance and efficiency. In order to have the amplifier volume control operate somewhere between the 12 o'clock to 3 o'clock to achieve a normal listening level with the wide variety of headphones commonly encountered, a gain switch is used to adjust the gain range over which the amplifier operates.

Harmonic Distortion
Distortion artifacts that are exact integer distances higher in frequency than the originating tone, usually a result of non-linearities in the transfer function of an analog electronic device. For example: 1kHz might yield a little distortion at 2kHz, 3kHz, 4kHz, 5kHz, etc. Typically, it is thought the even harmonics (2, 4, 6, 8) sound better than odd harmonics (3, 5, 7, 9). This is somewhat true, but a gross oversimplification of the subject.

Headphone Amplifier
A headphone amplifier is a miniature audio power amplifier specifically designed to drive the miniature audio drivers in headphones. Headphone amplifiers work essentially identical to power amplifiers used to drive speakers except they are much lower power and need to be capable of driving a wider range of impedance (~20-600 Ohms) than speaker amplifiers (4-8 Ohms). Headphone amplifiers typically range between 0.1 to 1 Watt, and about 0.2 to 2 Ohms output impedance.

Headphone Efficiency
A measure of how much energy it takes to drive headphones to a given listening level. Can be stated in numerous ways but generally in the form of: dB/volt or dB/Watt.

Headphone Sensitivity
see Headphone Efficiency

Image Depth
The ability of an audio system to portray sounds in front of, and behind each other. Essentially, front to back imaging. Audio systems typically trade off a punchy sound for a deeply layered sound; a very few do both well.

Image Width
The left to right width of the audio image. Typically within the boundary of the left and right speaker in a two channel audio system, but may be all around in a multi-channel (surround-sound) system.

Imaging
This refers to the ability of the headphone to reproduce the perceived spatial locations of the sound source(s) and instruments, both laterally and in depth. An image is considered to be good if the location of the performers/instruments/sound can be clearly located; the image is considered to be poor if the location of the sounds are difficult to locate.

Impedance
The sum of both resistive and reactive impeding forces of a load. Headphone impedance commonly changes with frequency, and would become somewhat inductive or capacitive at different frequencies.

In Ear Monitor 
Another term for In-ear headphones but also commonly known as IEMs, ear canal headphones, earphones, and canal-phones. In-ear headphones are inserted into and seal the ear canal, and provide the highest amount of isolation from outside noise of any headphone type including noise-canceling headphones. There are two types of in-ear headphones: deep sealing and shallow sealing. With deep seating in-ear headphones the tip of the earphone goes in about half the length of the ear canal and seats in the bony section of the ear canal; this type provides about -23dB of isolation. Shallow seating types seal closer to the entrance to the ear canal and provide about -15dB of isolation.

Input Impedance
The effective resistance of the input to a device. Essentially, how hard a load it is to drive. Most good electronics have an input impedance in the many thousands of ohms, and are easy to drive.

Isolation
The ability of a pair of headphones to block outside/ambient sounds so that the listener can hear the music on the headphones more clearly. Can be measured as a broad band reduction in amplitude in a single number in dB; or shown as a graph indicating the amount of attenuation over the audio spectrum.

Laid Back
A descriptive audio term meaning a headphone presentation that has a sense of ease and distance; i.e. in the tenth row instead of the first row of an audience. Generally meaning that it lacks aggressive high frequencies; slightly soft sounding.

Linear Amplifier
A broad category of electronic amplifiers with very linear gain curves. Usually solid state, class A/B push/pull amplifiers. Generally as opposed to single output device, class-A amplifiers that have more non-linear gain curves.

Liquid Sounding
A sense that the sound is a coherent and a naturally integrated whole that effortlessly bounces along. Maybe somewhat colored and lush; is the opposite to the terms 'dry' and 'lean' sounding.

Listening Fatigue
The result of your brain having to struggle to properly place (localize) sounds in an artificial listening environment like speakers and headphones. Generally much worse on headphones, and can be minimized with use of the HeadRoom crossfeed circuit.

Lush
Descriptive audio term usually attributed to vacuum tube audio gear which produces a relatively large amount of even-order harmonic distortion. This type of distortion is often pleasant to the ear, and produces a rich, warm ambiance to the sound.

MAP

Stands for "Minimum Advertised Price" enforced by manufacturers. Read on for more pricing information related to MAP.

Noise Cancelling

An electro-acoustic system which uses a microphone in the earpiece and an electronic circuit to produce a signal which is fed into the headphone which counter-balances and cancels outside/ambient noise to provide acoustic isolation. Typically a battery-powered design due to the electronics housed inside the headphones.

Op-Amp
An Operational Amplifier is technically an electronic amplification circuit with an inverting and non-inverting input and an output, ready to be configured to act in a variety of different ways using various methods. Commonly, Op-Amp is used to describe a type of integrated circuit chip that performs these functions.

OPA 627
An audio op-amp Previously a Burr-Brown, but now a Texas Instruments

Open
Open back headphones have the back of the earcups open or vented. This leaks more sound out of the headphone and also lets more ambient sounds into the headphone, but gives a more natural, airy or speaker-like sound and more spacious "soundstage" - the perception of distance from the source.

Optical
Optical, when used on the HeadRoom website, most often refers to a digital audio connection which uses light instead of an electricity to pass a signal. Optical cables (sometimes called Toslink cables) use a clear plastic fiber internally to pass the light on which the digital signal is carried. These connections have the advantage of not carrying an electrical signal and may help prevent ground loops and transfer of noise, and are immune from RF interference. Unfortunately, optical cables can vary widely in quality; we recommend using higher quality optical cables for runs longer than three feet.

OTL Tube Amps
OTL means "Output Transformer-less." Tube amplifiers typically use transformers to convert the high-voltage/low-current signals at the tube output into the low-voltage/high-current signal needed to drive the speaker. OTL amps use capacitive coupling, or D.C. coupling instead.

Output Impedance
The effective resistance seen by a load as it "looks back into" the output of an amplifier. The lower the output impedance of an amplifier, the more it shorts out (damps) the energetic reactions of the load. Good solid-state headphone amps have about one Ohm output impedance.

Power Amplifier
A power amplifier increases the amount of energy in an audio signal from a low level to a power level high enough to drive a pair of speakers. Power amplifiers typically have a fixed gain (amount of amplification) and volume is controlled by a pre-amp or headphone amp prior to being sent to the power amp. Power amplifiers are typically rated in Watts delivered into 4 or 8 ohms. Typical power ratings for desktop speaker amplification is about 25-100 Watts into 8 Ohms. 750 Watts is about 1 horse power.

Power Supply
In audio, the circuitry that converts the A.C. wall voltage into usable D.C. supply voltages inside the device. "Stiff" power supplies are desirable, and are those that change very little as the current demand from other circuits change.

Punch
A descriptive audio term meaning an audio system's ability to deliver significant pressure changes while remaining musically coherent. An overly punchy system will often lack finesse to deliver depth of imaging.

Resonance
The characteristic of a physical systems ability to "ring." A bell is resonant. Electrical circuits can also "ring" as in an oscillator, but resonant circuits can also be used to create filters. Reducing unwanted resonance when driving headphones is generally accomplished though damping. Proper balance between the instability of resonance and reduced slew rate due to over damping is called "critically damped."

S/PDIF
S/PDIF stands for "Sony/Philips Digital Interconnect Format," and is an industry standard specifying the hardware connections (RCA, BNC, or Toslink) and "data link layer" protocols for digital audio transfer in consumer electronics. It is a sub-set of a larger standard for digital audio transfer, IEC 60958, which is also known as the "AES/EBU" standard.

Sealed
Sealed headphones are also called 'closed-back' headphones and are designed to block out environmental noise using a passive acoustic seal. Full size closed headphones provide about -10dB to -15dB of isolation, mostly in the higher frequencies. Smaller on-ear closed headphones provide somewhat less isolation dependent on their design and the shape of your ear. In-ear headphones are a closed design in which the ear-pieces seal in the ear canal providing about -23dB of outside noise attenuation, and are the highest isolation of headphone type. Noise-cancelling headphones are typically sealed designs with battery-powered electronics to attenuate ambient noise better than a passive closed-back seal could provide.

Self-powered (speakers)
Usually computer speakers which contain their own power amplifier, take a line input, and have their own volume control. There are, however, very good self powered speakers of all sizes and quality used by professionals and audiophiles alike.

Solid State
A broad categorization of active electronic circuitry that use transistors of various types (NPN, PNP, FETs, J-FETs, and analog integrated circuits) to provide gain. Usually used to differentiate against vacuum tube based designs.

Soundstage
The ability of an audio system to reproduce the position and sense of space in which the instruments and sound sources are placed. Good imaging is when you can "see" with your ears the players standing there.

Square Wave Response
An audio test signal which alternates between two D.C. levels. Used to visualize the systems ability to pass a wide range of frequencies in proper time-alignment.

Supra-aural
Literally meaning "on the ear," supra-aural headphones rest against the outer ear and are generically termed earpad headphones. Ear-pieces are sometimes literally flat pads against the ear, but can also be shallow bowl shaped, or deeper ear cups that are too small to fully surround the ear.

Transient Response
The ability of a system to rapidly change voltage and/or acoustic pressure, and settle properly to target voltage/pressure. Also related to high slew rate, and the ability of the system to pass all frequencies at the same rate.

Transistor
A small electronic device which can provide electrical signal gain in circuit construction. Manufactured using silicon or gallium arsenide semi-conductor materials in negatively and positively dopes crystal layers in a variety of structural configurations. Mainly segregated into bi-polar and field effect types.

Tube Amplifier
An audio amplifier using vacuum tubes in its gain stages.

USB
USB stands for Universal Serial Bus and is a standardized interface designed primarily for personal computers as a peripheral control interface, but may be used in other devices like gaming consoles and hand held portable devices. The USB standard is controlled by the USB Implementer Forum, Inc which is a consortium of industry players including Apple, HP, NEC, Intel, and Microsoft.

Warmth
A descriptive audio term meaning generally that the overall sound has more bass and less treble. Would be muffled or murky in the extreme.

Wireless
Wireless headphones replace the wire with an alternative method for getting the audio signal to the headphones. Most commonly this is done with analog modulation of 900MHz radio frequency transmission, but digital modulation of 900MHz RF, Bluetooth, KLEER, and infra-red systems are also available.

 

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