A-B Test: A test between two components. For example, a test between two different pre-amplifiers. For the test to be scientifically valid the levels should be matched.

A: Common abbreviation for ampere (see ampere).

A/D: Analog/Digital; an integrated circuit device that converts analog signals to digital signals.

AB Switch: A coaxial cable switch capable of switching one cable to one of two branch cables, A or B.

ABX Comparator: A device that randomly selects between two components being tested. The listener doesn’t know which device is being listened to.

AC: Common abbreviation for alternating current.

Acoustic Suspension: A sealed or closed box speaker enclosure.

Acoustic: Pertaining to sound; usually refers to the specific characteristic sound in a particular place (e.g. cathedral acoustic; concert hall acoustic; listening room acoustic etc). See Reverberation also.

Aerial: An array of metal wire used primarily to help a radio or television tuner locate and tune into broadcast signals. A complex multi-element FM aerial or yagi is required in areas far from radio transmitters. It comprises reflectors and directors, as well as the standard dipole. AES/EBU: Balanced digital connection. For example, used to connect a CD transport to a DAC. The AES/EBU standard uses XLR type connectors.

Alignment: A class of enclosure parameters that provides optimum performance for a woofer with a given value of Q.

Alpha: Term used in sealed enclosure designs to mean the ratio of Vas to Vb, where Vb is the volume of the box you will build.

Alternating Current (AC): An electrical current that periodically changes in magnitude and direction; Electricity in the form of sine wave (ie. with positive and negative halves of a continuous waveform). Mains electricity is in the form of alternating current (AC).

Ambience: The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is said to be “live”; one without much reverb is “dead.”

Ambisonics: A recording/replay system developed in the Seventies to improve three dimensional stereo definition by means of a special microphone recording technique, encode/decode electronics and a multiple surround sound loudspeaker playback system.

Ampere (A): The unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohms Law.

Amplifier (Amp): A device which increases signal level. Many types of amplifiers are used in audio systems. Amplifiers typically increase voltage, current or both.

Amplifier classes: Audio power amplifiers are classified primarily by the design of the output stage. Classification is based on the amount of time the output devices operate during each cycle of signal swing. Also defined in terms of output bias current, (the amount of current flowing in the output devices with no signal).

Class A operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers are single-ended designs with only one type polarity output devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power.The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion.

Class AB operation allows both devices to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demands. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design. Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.

Class B operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is due to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio.

Class D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle.  Since the output devices are either completely on or completely off they do not theoretically dissipate any power.  Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times — a product we’re still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.

Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.

Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. Theefficiency of class H is comparable to class G designs.

Amplitude Modulation: A form of radio broadcast, (abbr: AM); literally means that the carrier frequency is modulated, or varies, in size (amplitude) according to the content of the transmitted signal.

Analog: Before digital, the way all sound was reproduced.

Anechoic: Non-reverberant. An anechoic chamber is an acoustically dead room designed primarily for the purpose of accurate loudspeaker measurement.

Aperiodic: Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but lower the Q of the system and reduce the impedance peak at resonance. Most restrictive ports are heavily stuffed with fiberglass, dacron or foam.

ATRAC: The system of data reduction used by Sony in its MiniDisc format.

Attenuate: To reduce in level.

Audio: A term used to describe sounds within the range of human hearing.  Also used to describe devices which are designed to operate within this range.

Audiophile: A person interested in sound reproduction.

Auxiliary Bass Radiator: A loudspeaker drive unit fitted to a box loudspeaker, coupled acoustically but not electrically to the input signal. Functions somewhat like a port or tuned tube in the loudspeaker cabinet supplementing bass output and aiding loudspeaker sensitivity.

AWG: American Wire Gauge; a wire diameter specification, the lower the AWG number the larger the wire diameter.

Back EMF: The rear electromotive force from loudspeaker drive units.

Baffle:   A surface used to mount a loudspeaker.

Balanced: Referring to wiring: Audio signals require two wires. In an unbalanced line the shield is one of those wires. In a balanced line, there are two wires plus the shield. For the system to be balanced requires balanced electronics and usually employs XLR connectors. Balanced lines are less apt to pick up external noise. This is usually not a factor in home audio, but is a factor in professional audio requiring hundreds or even thousands of feet of cabling. Many higher quality home audio cables terminated with RCA jacks are balanced designs using two conductors and a shield instead of one conductor plus shield.

Band-pass Enclosure:  A multi-chambered ported system.

Band-pass filter: An electric circuit designed to pass only middle frequencies.

Bandwidth: A range of frequencies defined by its highest and lowest limits. The audio bandwidth of human hearing has traditionally been defined as 20Hz to 20kHz. In pure electronic terms, the width of a communication channel, measured as frequency (in cycles per second, or hertz).  A channels bandwidth is a major factor in determining how much information it can carry.

Bass Blockers: Commercial name for auto-sound first order high pass crossovers (non-polarized capacitors), generally used on midbass or dash speakers to keep them from trying to reproduce deep bass.

Bass Reflex: A type of loudspeaker that uses a port or duct to augment the low-frequency response. Opinions vary widely over the “best” type of bass cabinet, but much has to do with how well a given design, such as a bass reflex is implemented.

Bass: The bottom octaves of human hearing.

Beaming:  A tendency of a loudspeaker to concentrate the sound in a narrow path instead of spreading it.

Belt-drive: Turntables fitted with a belt between the drive motor pulley and the record-supporting platter.  A belt is used to isolate the pickup cartridge from motor noise. It is traditionally regarded as the best way to maintain rotational speed stability at audio frequencies.

Bessel crossover: A type of crossover design characterized by having a linear or maximally flat phase response.  Linear phase response results in constant time-delay (all frequencies within the passband are delayed the same amount). Consequently the value of linear phase is it reproduces a near-perfect step response with no overshoot or ringing. The downside of the Bessel  is a slow roll-off rate. The same circuit complexity in a Butterworth response rolls off much faster.

Bi-amplify: The use of two amplifiers, one for the lows, one for the highs in a speaker system. Could be built into the speaker design or accomplished with the use of external amplifiers and electronic crossovers.

Bi-wiring: The use of two pairs of speaker wire from the same amplifier to separate bass and treble inputs on the speaker.

Bias: A high frequency AC signal applied to the record head of a tape recorder to help it record a wide bandwidth linear signal onto magnetic tape.

Binaural: Associated with a type of recording made using a dummy head fitted with microphones located at the position of the two ears. Replay of binaural recordings via headphones is considered to enhance a sense of ‘out of the head’ definition in contrast to the normal ‘inside the head’ sound using headphones.

Binding Post: A device for clamping or holding electrical conductors, such as wire, in a rigid position.

BNC: A type of connection often used in instrumentation and sometimes in digital audio. BNC connectors sometimes are used for digital connections such as from a CD Transport to the input of a DAC.

Boomy: Listening term, refers to an excessive bass response that has a peak(s) in it.
Bridged Mono Impedance = (Y / X)/2 .  Y = impedance of driver(s) (both drivers should be identical)X = # of drivers in circuit. One 4 ohm sub in bridged mono is equal to hooking up two 2 ohm subs in stereo, one to each channel.
Bridging:   Combining both left and right stereo channels on an automotive amplifier into one higher powered mono channel. When an amplifier is bridged, the impedance that the amplifier actually “sees” is calculated based upon the output of both stereo channels. Here is a simple formula to help define this:

Bright: Listening term. Usually refers to too much upper frequency energy.

Butterworth crossover: A type of crossover circuit design having a maximally flat magnitude response, i.e., no amplitude ripple in the passband. This circuit is based upon Butterworth functions, also know as Butterworth polynomials.

C: Symbol for capacitance and centigrade.

Cabin gain: The low frequency boost normally obtained inside a vehicle interior when subs are properly mounted.

Cantilever: Arm on which is fitted the stylus of a pickup cartridge.

Capacitance: A measure of reactance (units: Farad, pF, uF etc).

Capacitor:  A device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an AC current.

Cartridge: The small component fitted to the front end of a tonearm. Contains the stylus and electro- magnetic system required to track a vinyl record (LP or single) and feed output to an amplifier phono stage.  There are two main types of hi-fi pickup cartridge – the ‘moving magnet’ and ‘moving coil’.

Cassette deck: The machine required to play and/or record onto an audio cassette.

Cassette: Audio cassette or analogue cassette. Contains blank or pre-recorded tape on spools constrained within a case or cassette.

CD-ROM: Compact Disc Read Only Memory is an audio/video offshoot technology from CD. Now an established multimedia source, CD-ROM is now an accepted extra source for Macintosh and Personal Computers.

CDi: Compact Disc Interactive. An offshoot technology from CD, developed by Philips as an educational and entertainment format providing interactive still and moving pictures and audio sound.

Center Channel:  In home theater, sound decoded from the stereo signal sent to a speaker mounted in front of the listener, specially designed to enhance voices and sound effects from a movie soundtrack. Used in car audio to help offset skewed stereo imaging due to seating positions in the automotive environment.

Channel Balance: In a stereo system, the level balance between left and right channels. Properly balanced, the image should be centered between the left-right speakers. In a home-theater system, refers to achieving correct balance between all the channels of the system.

Chip: A silicon chip on which is etched a microcircuit. May perform a variety of functions from amplification to signal processing.

Clipping: The type of distortion caused by gross overload. The resulting loud, harsh and unpleasant sound may cause damage to a hi-fi system, particularly loudspeaker drive units. Clipping is so named because of its reference to the sharp truncation of the AC signal waveform.

Cms: Mechanical suspension compliance of a driver, consisting of the spider and surround.

Co-axial: A speaker type that utilizes a tweeter mounted at the center of a woofer cone. The idea being to have the sound source through the full frequency range become “coincident.”

Coaxial Driver: a speaker composed of two individual voice coils and cones; used for reproduction of sounds in two segments of the sound spectrum. See also triaxial driver.

Coherence: Listening term. Refers to how well integrated the sound of the system is.

Coloration: Listening term. A visual analog. A “colored” sound characteristic adds something not in the original sound. The coloration may be euphonically pleasant, but it is not as accurate as the original signal.

Compact Disc: The first commercially available digital audio playback format. Software is a 12cm diameter single sided silver disc containing digitally encoded signal to a 44.1kHz, 16-bit standard. Optical playback is by means of laser beam. Developed jointly by Philips and Sony CD has spawned a number of offshoot audio/video technologies such as CDi and CD-ROM.

Compliance:  The relative stiffness of a speaker suspension, specified as Vas.

Compression: In audio, compression means to reduce the dynamic range of a signal. Compression may be intentional or one of the effects of a system that is driven to overload.

Conduction: Electrical signal transmission.

Conductor: A material suitable for carrying an electric current.

Cross-talk: Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

Crossover Slope: High and low pass filters used for speakers do not cut-off frequencies like brick walls. The rolloff occurs over a number of octaves. Common filter slopes for speakers are 1st through 4th order corresponding to 6db/oct to 24db/oct. For example, a 1st. order, 6db/oct high pass filter at 100hz will pass 6db less energy at 50Hz and 12db less energy at 25Hz. Within the common 1st through 4th filters there is an endless variety of types including Butterworth, Linkwitz-Riley, Bessel, Chebychev, etc. Salesmen and product literature will sometimes make claims of clear superiority for the filter used in the product they are trying to sell. Since the subject fills books, suffice it to say that there is no one best filter, it depends on application and intended outcome. Good designers use the filters required to get the optimum performance from the system.

Crossover: A network of components, usually capacitor(s), inductor(s) and resistor(s) arranged on a circuit board inside a box loudspeaker to divide the incoming signal from a power amplifier into discrete frequency bands appropriate for each loudspeaker drive unit. In simple terms in a two-way loudspeaker, the crossover feeds treble to the tweeter and midrange/bass to the main cone drive

Current (I): The flow of electrical charge measured in amperes.

Cycles per second: More commonly known as one hertz.

Hertz (abbr: Hz): after the German who discovered the nature of audio frequencies. It is the speed of movement of a sine wave or cycle that determines its frequency, and in turn the musical pitch of a note.

D/A: Digital to Analog.

DAC: A Digital to Audio Converter. Converts a digital bitstream to an analog signal. Can be a separate “box” that connects between a CD Transport or CD Player and a pre-amplifier.

Damping (Damping factor, etc.): Refers to the ability of an audio component to “stop” after the signal ends. For example, if a drum is struck with a mallet, the sound will reach a peak level and then decay in a certain amount of time to no sound. An audio component that allows the decay to drag on too long has poor damping, and less definition than it should. An audio component that is overdamped does not allow the initial energy to reach the full peak and cuts the decay short. “Boomy” or “muddy” sound is often the result of underdamped systems. “Dry” or “lifeless” sound may be the result of an overdamped system.

Damping: A process whereby the amplitude of a vibration  or resonance is reduced. This may be required in tonearms or loudspeaker cabinets for instance. Resistors may be used in circuits to provide electrical damping. The pros and cons of damping have generated heated debate among audio enthusiasts.

DAT: Digital Audio Tape. This format introduced in the late Eighties makes use of a rotating drum containing a helical scan head similar to the sort used in video cassette recorders.  Unfortunately disagreement between the recording and hi-fi industries led to a refusal by the major record companies to produce pre-recorded DATs or to sanction the release of a non-copyright protected digital tape recorder hardware. By the time a copyright protection system had been agreed, DAT was dead on its feet as a mainstream consumer format, though it is widely used by professionals and semi-professionals today.

dB: Abbreviation for decibel.

DCC: Digital Compact Cassette is Philips’ backwards compatible digital cassette format. In addition to playing and recording Digital Compact Cassettes, DCC recorders also play standard analogue cassettes. Hence the term backwards compatible. DCC tapes work to 16-bit 44.1kHz sampling. It also features Philips’ PASC data reduction system. PASC selectively discards signals thought to be below the threshold of audibility. Soft signals audible in isolation may be masked by louder signals. In such circumstances PASC eliminates the masked signals.

Decibel: A measure of loudness (abbr: dB). The decibel scale is such that 3dB represents a doubling of amplifier power from say 50W to 100W), while 10dB represents a doubling of perceived loudness.

Diaphragm: The surface of a loudspeaker drive unit. Most moving coil bass drive unit diaphragms are cones while moving coil tweeters are invariably domes. Ribbon and electrostatic drive units are flat.

Dielectric: The non conducting space/insulation between two conductors in a cable.

Diffraction: A change in the direction of a wave front that is caused by the wave moving past an obstacle.

Digital: A sampled analogue waveform encoded in the form of on/off pulses. The frequency with which the analog waveform is sampled is its sampling frequency which, in the case of Compact Disc, is set at 44.1kHz (44,100 samples per second). The accuracy
of sampling is determined by the word length of each sample. For Compact Disc it is 16-bit. Modern professional digital recorders are capable of almost 24-bit resolution as of this date (12-15-96)

Diode: The thermionic diode invented in 1904, marks the start of the electronics era. It is the first device for controlling the flow of current in relation to applied voltage, and comprises two electrodes, the heated cathode (electron source) and anode (electron receptor).

Dipole: An open-back speaker that radiates sound equally front and rear. The front and rear waves are out of phase and cancellation will occur when the wavelengths are long enough to “wrap around”. The answer is a large, wide baffle or to enclose the driver creating a monopole.

Direct Current (DC): Current that moves in only one direction.

Directionality: The tendency in some loudspeakers to beam sound like a laser rather than radiate it equally in all directions. Horn, ribbon and electrostatic speakers tend to be more directional at high frequencies than well designed dome moving coil tweeters, a factor that in extreme situations can impose restrictions on listening and speaker position.

Dispersion: The spreading of sound waves as they leave a source. The spreading of sound waves as they leave a source.

Distortion: Any loss or addition to the audio signal is a distortion. Various amplifier distortions have been identified, the most commonly measured being intermodulation, transient intermodulation and harmonic distortion.

Dither: A low level random noise added to a digital signal to mask highly audible forms of digital distortion.

DIY: Abbreviation for Do – It – Yourself. In audio, the most common DIY is building speakers but some hobbyists build everything from pre-amps to amplifiers to DACs.

DMM: Direct Metal Mastering. An LP disc mastering process in which silvering and electroplating stages
are eliminated.

Dome Tweeter:  A high frequency speaker with a dome-shaped diaphragm.A high frequency speaker with a dome-shaped diaphragm.

Double (Dual) Voice Coil (DVC): A voice coil with two windings, generally used in woofers. Each voice coil can be connected to a stereo channel, or both voice coils can be wired in parallel or series to a single channel.

DSP: Digital Signal Processing. DSP can be used to create equalization, compression, etc. of a digital signal.

DTS: Digital Theater System. A multi-channel encoding/decoding system. Used in some movie theaters. Also now included in some home-theater processors. A competitor to Dolby Digital.

DVD: Digital Video Disc or Digital Versatile Disc. A relatively new standard that seeks to combine better-than-laser-disc quality video with better-than-CD quality audio in a disc the size of a CD. Requires special players. Seems to be a viable candidate to replace both Laser Discs and CDs, but the jury is still out.

Dynamic Headroom: The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 db.

Dynamic range: The range between the loudest and the softest sounds that are in a piece of music, or that can be reproduced by a piece of audio equipment without distortion (a ratio expressed in decibels). In speech, the range rarely exceeds 40 dB; in music, it is greatest in orchestral works, where the range may be as much as 75 dB.

Earth Loop: A source of hum audible through the loudspeakers, at mains frequency (or multiple thereof), and caused by failure to find a common single earth. Incorrect earthing of tonearms and turntables is perhaps the most common source of earth loops.

Earth: Sometimes called ground, earth is the zero reference point for electrical circuits including the mains electricity supply.

EBP: Efficiency Bandwidth Product. A guide that helps a designer determine whether a driver is more suitable for a sealed or ported enclosure. EBP of less than 50 indicates the driver should be used in a sealed, 50 – 90 indicates flexible design options, over 90 indicates best for a ported enclosure. EBP = Fs / Qes.

Echoic: Literally prone to echo. Hard surfaces in listening rooms will result in a lot of high frequency reflections and a generally echoic sounding acoustic. The technical term for this is a long reverberation time. It is to be avoided if possible.

Efficiency: A measure of the proportion of electrical energy fed to a loudspeaker that is turned into acoustic energy. Most loudspeakers are very low efficiency transducers (typically around 5 per cent).  Only horn loudspeakers manage a much higher efficiency (sometimes around 30 per cent).

Eigentone: A standing wave set up between two parallel room surfaces. The frequency of a standing wave is determined by the distance apart of the parallel surfaces. A listening room where the long axis is double that of the short axis is likely to have acoustics problems since the first standing wave will be augmented by one at twice the frequency. This second harmonic will be difficult for the ear to differentiate and the effect will be a pronounced and audibly intrusive bass resonance easily excited by music signals.

Electromagnetic induction: The process whereby an electrical current is induced in one of two ways. Either a magnet moves within a structure of coiled wires, or vice versa. It is the foundation stone or underlying principle of all moving coil loudspeaker drive units, moving coil cartridges and moving magnet cartridges.

Electronic Crossover: Uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers. Uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers.

Electrostatic Speaker: A speaker that radiates sound from a large diaphragm that is suspended between high-voltage grids.

Electrostatic: The electrical force induced when friction is applied between two nonconductive materials (eg plastic and paper). The principle has been applied to loudspeaker design. The Electrostatic loudspeaker works by applying a fixed or polarizing voltage to an electrostatically charged flat diaphragm mounted between two transformer coupled plates fed anti-phase signal.

EMI: Electromagnetic Interference.  External signals that disrupt the data being transmitted on the local area network or electronic device being operated.

Equalization: A correction made on playback of tape recordings to restore correct linear frequency balance.

Equalizer: Electronic set of filters used to boost or attenuate certain frequencies.

Euphonic: Pleasing. As a descriptive audio term, usually refers to a coloration or inaccuracy that non-the-less may be sonically pleasing.

Extension: How extended a range of frequencies the device can reproduce accurately. Bass extension refers to how low a frequency tone will the system reproduce, high-frequency extension refers to how high in frequency will the system play.

F3: The roll-off frequency at which the driver’s response is down -3dB from the level of it’s midband response.

Farad: The basic unit of capacitance. A capacitor has a value of one farad when it can store one coulomb of charge with one volt across it.

Fb: The tuned frequency of a ported box.

Fc or Fcb: The system resonance frequency of a driver in a sealed box. The system resonance frequency of a driver in a sealed box.

Feedback: Acoustic or structure-borne vibrations that interfere with the operation of audio equipment.  For example loud deep bass emanating from a loudspeaker may upset the performance of a turntable such that the pickup stylus reads the interference as bass signal. In extreme instances a loop of sound may be created resulting in high frequency instability; the more usual effect is a loss of clarity to the music signal. Bass becomes woolly and the rest of the signal unfocused. See also Negative Feedback.

Fiber Optics: Transmission of energy by light through glass fibers.  A technology that uses light as an information carrier.

Filter: An electrical circuit which blocks signal below or above a predetermined frequency. The filter rate may be shallow, steep, or in the case of a digital filter of ‘brick wall’ type.

Filter: An electrical circuit or mechanical device that removes or attenuates energy at certain frequencies. . An electrical circuit or mechanical device that removes or attenuates energy at certain frequencies. .

Flat Response: The faithful reproduction of an audio signal; specifically, the variations in output level of less than 1 dB above or below a median level over the audio spectrum.

Fletcher-Munson curve: Our sensitivity to sound depends on its frequency and volume. Human ears are most sensitive to sounds in the midrange. At lower volume levels humans are less sensitive to sounds away from the midrange, bass and treble sounds “seem” reduced in intensity at lower listening levels.

Free Air Resonance: The natural resonant frequency of a driver when operating outside an enclosure.

Frequency response: The measured accuracy within db limits of a piece of audio equipment. For instance, hi-fi loudspeaker manufacturers specify the tolerance limits (usually +/-3dB) of each model alongside the operating frequency range (typically 50Hz – 20kHz).

Frequency: The number of cycles per second (Hertz or Hz) of a vibration, resonance or sine wave. Audio frequencies range up to 20kHz (20,000Hz), though many experts believe humans may be able to detect far higher into the supersonic spectrum. Radio frequencies (RF) extend from around 70kHz into the MHz. FM stereo broadcasts are typically in the 87.5 -107MHz frequency bandwidth.  In some countries such as Japan, FM broadcasts are at a slightly lower bandwidth.

Front end: Traditionally used to designate the input stage of a radio tuner. More broadly it refers to the source component in a hi-fi system. This could be one of a number of product types from CD player and turntable to tuner and turntable.

Fs: The frequency of resonance for a driver in free air.

Full-range: A speaker designed to reproduce all or most of the sound spectrum.

Fundamental: The lowest frequency of a note in a complex wave form or chord.

Fuse: Protection device containing thin wire within glass case. The fuse wire will break under high stress conditions preventing overload of the component (eg Loudspeaker or amplifier).

Gain: To increase in level. The function of a volume control.

GHz: Gigahertz. 1,000,000,000 cycles per second.

Golden Ratio: The ratio of depth, width, and height based on the Greek Golden Rectangle. Often applied to speaker boxes or listening room design. The Ratio: W = 1.0, Depth = 0.618W, Height = 1.618W. The ratio of depth, width, and height based on the Greek Golden Rectangle. Often applied to speaker boxes or listening room design. The Ratio: W = 1.0, Depth = 0.618W, Height = 1.618W.

Grain: Listening term. A sonic analog of the grain seen in photos. A sort of “grittiness” added to the sound.

Grid: The perforated element in a triode tube (valve). The addition of the grid to the diode thermionic valve meant that in the triode, the first building block to the invention of an electronic amplifier had been discovered.

Ground Loop: The generation of undesirable current flow within a ground conductor, owing to the circulation currents which originate from a second source of voltage.

Ground: Refers to a point of (usually) zero voltage, and can pertain to a power circuit or a signal circuit. In car audio, the single most important factor to avoid unwanted noise is finding and setting a good ground.

Haas effect: If sounds arrive from several sources, the ears and brain will identify only the nearest. In other words, if our ears receive similar sounds coming from various sources, the brain will latch onto the sound that arrives first. If the time difference is up to 50 milliseconds, the early arrival sound can dominate the later arrival sound, even if the later arrival is as much as 10 dB louder. The discovery of this effect is attributed to Halmut Haas in 1949.

Harmonics:  Multiples of the fundamental sine wave frequency. A 50Hz sine wave has a second harmonic at 100Hz, a third harmonic at 150Hz, a fourth harmonic at 200Hz, a fifth harmonic at 250Hz and so on. The timbre of a musical instrument is defined by the complex mix of harmonics overlain on each note. In amplifiers, harmonic distortion is the addition of unwanted harmonics to the signal.  Total Harmonic Distortion is the summation of all harmonic distortions.

Harmonics: Also called overtones, these are vibrations at frequencies that are multiples of the fundamental. Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth. Each even-order harmonic: second, fourth, sixth, etc.-is one octave or multiples of one octave higher than the fundamental; these even-order overtones are therefore musically related to the fundamental. Odd-order harmonics, on the other hand: third, fifth, seventh, and up-create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasize odd-order harmonics tend to have a harsh, hard quality.

HDCD: High-Definition Compact Disc. A proprietary system by Pacific Microsonics that requires special encoding during the recording process. Some observers report HDCD discs as having better sound. To gain the benefits requires having special HDCD in your CD player.

HDTV: High definition television.

Head Unit: The in dash control center of a car audio system, usually consisting of an internal low powered amp, AM/FM receiver, and either a tape or CD player (or both).

Headroom: The ability of an amp to go beyond its rated power for short durations in order to reproduce musical peaks without distortion. This capability is often dependent on the power supply used in the design.

Hertz (Hz): A unit of measurement denoting frequency, originally measured as Cycles PerSecond, (CPS): 20 Hz = 20 CPS. Kilohertz (kHz) are hertz measured in multiples of 1,000.

Hi-Fi: Abbreviation of High Fidelity. Literally means honesty or truthfulness. In audio terms the context is accuracy to the original recorded signal, or more broadly authenticity to the composed music.

High-Pass Filter: A circuit that allows high frequencies to pass but rolls off the low frequencies. When adding a subwoofer it is often desirable to roll-off the low frequencies to the main amplifiers and speakers. This will allow the main speakers to play louder with less distortion. High-pass filters used at speaker level are usually not very effective unless properly designed for a specific main speaker (see impedance below).

Hiss: Audio noise that sounds like air escaping from a tire.

Home Theater: An audio system designed to reproduce the theater sound experience while viewing film at home. Minimally consisting of a Dolby Pro Logic® surround sound receiver, left and right front speakers, a center channel speaker, and two surround speakers. These plus optional subwoofer(s), surround speaker(s), and digital formats such as Dolby Digital® can enhance the viewing experience by drastically improving the sound quality of movie soundtracks.

Horn: A flared structure often used to assist a loudspeaker. Horn-loaded loudspeakers are considerably more efficient than ordinary moving coil loudspeakers in turning electrical into acoustic energy.

Hum: Audio electronic noise that has a steady low frequency pitch.

I2R: Formula for power in watts, where i=current in amperes, R=resistance in ohms.

IF: Intermediate Frequency to which RF signals are converted in a radio tuner.

Imaging: Listening term. A good stereo system can provide a stereo image that has width, depth and height. The best imaging systems will define a nearly holographic re-creation of the original sound.

Impedance: Impedance is a measure of electrical resistance specified in ohms. Speakers are commonly listed as 4 or 8 ohms but speakers are reactive devices and a nominal 8 ohm speaker might measure from below 4 ohms to 60 or more ohms over its frequency range.

Inductance (L): The capability of a coil to store energy in a magnetic field surrounding it. It produces an impedance to an ac current. Inductors are commonly used in audio as low pass crossovers.

Inductor: Solid state component with a particular Henry value.

Infinite Baffle: Sealed box loudspeakers work on the infinite baffle principle. The idea is to isolate the rear radiation and front radiation from a loudspeaker. In theory an infinitely large baffle board will perfectly achieve this goal.

Infrasonic (Subsonic) Filter: A filter designed to remove extremely low frequency (25Hz or lower) noise from the audio signal. Useful for Ported box designs.

Interconnects: Cables that are used to connect components at a low signal level. Examples include CD player to receiver, pre-amplifier to amplifier, etc. Most interconnects use a shielded construction to prevent interference. Most audio interconnects use RCA connections although balanced interconnects use XLR connections.

Jitter: The slight movement of a transmission signal in time or phase that can induce errors and loss of synchronization in high-speed synchronous communications.

kHz: 1000Hz or kiloHertz. or 1000 cycles per second.

kOhm: 1000Ohms or kiloOhm.

kWatt: 1000W or kiloWatt.

Lacquer: The soft disc cut on a lathe from the master tape. It is the first disc stage in the production of LPs. From the lacquer are made a number of negatives and positives before the negative metal stamper can be created to press vinyl discs.

Le: The inductance of a driver’s voice coil, typically measured at 1 kHz in millihenries (mH).

Line Level: CD players, VCRs, Laserdisc Players etc., are connected in a system at line level, usually with shielded RCA type interconnects. Line level is before power amplification. In a system with separate pre-amp and power-amp the pre-amp output is line level. Many surround sound decoders and receivers have line level outputs as well.

Line Stage: Another name for a preamplifier. A unit that controls the volume and allows for selection of various inputs
(CD player, Tuner, etc).

Line-Source: A speaker device that is long and tall. The line-source has very limited vertical dispersion, but excellent horizontal dispersion.

Linearity: A general term referring to the accuracy of response of an audio component in terms of a particular measured parameter, such as frequency response.

Load: Electrical resistance is often referred to as the load.

Lobing: Any time more than one speaker device covers the same part of the frequency range there will be some unevenness in the output. (Picture the waves from one pebble dropped into a calm pool vs. two pebbles dropped several inches apart.) Lobing means that the primary radiation pattern(s) is at some angle above or below the centerline between the two drivers. Good crossover design takes this into account.

Loudness: Perceived volume. Loudness can be deceiving. For example, adding distortion will make a given volume level seem louder than it actually is.

Loudspeaker: A device for converting electrical energy into acoustic energy.

Low-Pass Filter: A circuit that allows low frequencies to pass but rolls off the high frequencies. Most subwoofers have low-pass filters built in and many surround sound decoders have subwoofer outputs that have been low-pass filtered.

LP: Long Playing record. Usually a 12 inch diameter vinyl disc.

LW: Long Wave band (one of three AM radio bands, the other two being Short Wave and Medium Wave).

Magnetic flux: The measure of strength of a magnet. Unit of measurement is Gauss (G).

Magnetic-Planar Speakers: A type of speaker that uses a flat diaphragm with a voice coil etched or bonded to it to radiate sound. If the magnets are both in front of and behind the diaphragm, it becomes a push-pull magnetic-planar.

Mastering: The process of recording and mixing that leads to the production of a master tape and finished pre-recorded cassettes, LPs, Compact Discs, DCCs and MiniDiscs are mass produced copies derived from the mastering of studio mix.

Maximum power rating: A meaningless specification.

MHz: Megahertz (one million cycles per second).

Microfarads (mF): A measurement of capacitance.

Midbass: Mid frequency bass, usually frequencies just above the sub-bass range, from around 100 – 400 Hz or so.

Midrange: A speaker, (driver),  used to reproduce the middle range of frequencies.  A midrange is combined with a woofer for low frequencies and a tweeter for high frequencies to form a complete, full-range system.

Millihenries (mH): A measurement of inductance.

MiniDisc: A record/playback system developed by Sony using a small silver disc as software and a data reduction technology known as ATRAC. Seen by many as a rival to Philips’ Digital Compact Cassette. MiniDisc is incompatible with CD since it is a magneto-optical record/playback format.

Monitor: Loudspeaker used to gauge quality in a recording or broadcast studio.

Mono: Single channel record/replay standard. All commercial recordings were mono until the early Fifties
when stereo was introduced.

Monopole: Any speaker that encloses the backwave of the speaker device even though part of this backwave may be released via. a port or duct. The primary radiation at most frequencies will be from the driver front. If the driver is not enclosed it becomes a dipole.

MOSFET: Metal Oxide Semiconductor Field Effect Transistors. Used in most modern, quality car audio amplifiers in the power supply (and sometimes in the output stage). MOSFET’s run cooler than normal bipolar transistors, and have a faster switching speed.

Moving coil: Operating principle of moving coil loudspeakers and pickup cartridges. Wound around a permanent magnet a loudspeaker’s voice coil is fed electrical input signals. The resulting electro-motive force induced in the coil forces the loudspeaker
diaphragm to move. In the cartridge, the mechanical movement of the pickup stylus translated to the moving coils located next to a fixed permanent magnet causes the production of an analogous electrical signal.

Moving magnet: An alternative and cheaper form of pickup cartridge to the moving coil is the stylus assembly moves in precise relation to fixed coils causing the generation of analogous electrical signals.

Muddy: Listening term. A sound that is poorly defined, sloppy or vague. For example, a “muddy” bass is often boomy with all the notes tending to run together.

Multibit: A type of digital to analogue conversion in which ladder resistor networks are used to read the 14, 16, 20, or 24-bit words of a digital bit stream.

Muting: To greatly decrease the volume level. Many receivers and pre-amplifiers have a muting control which allows the volume level to be cut way down without changing the master volume control. Great for when the phone rings.

mV: Millivolt. (1000mV = 1V); 1000uV = 1mV).

Near field: The region within approximately two meters of the loudspeakers. Listening tests conducted in the near field reveal different aspects of a loudspeaker’s performance compared with listening in the far field.

Negative feedback: An amplifier circuit configured so that the output signal is fed back to be compared with the input signal and any error signals cancelled. Easier to imagine than to achieve the desired results without unwanted side effects.

Noise: Any unwanted sound other than the signal. Examples include tape hiss, electronic noise generated by amplifier circuits, earth loop induced hum, and random hums, hiss and spurious electronic clicks and pops (e.g. from static electricity on vinyl records).

Nonlinearity: What goes into a system comes out changed by its passage through that system-in other words, distorted. The ideal of an audio component and an audio system is to be linear, or nondistorting, with the image on one side of the mirror identical to the image on the other side.

Octave: An octave is a doubling or halving of frequency.

Ohm: The electrical unit of resistance.  The value of resistance through which a potential difference of one volt will maintain a current of one ampere.

Ohm’s Law: Stated V=IR, I=V/R, or R=V/I where V is voltage, I is current, and R is resistance.

One-bit: Also known as BitStream, one-bit digital to analogue conversion is an alternative method to multi-bit d/a conversion developed to improve low level signal resolution.

Out of Phase: When speakers are mounted in reverse polarity, i.e., one speaker is wired +/+ and -/- from the amp and the other is wired +/- and -/+. Bass response will be very thin due to cancellation.

Output impedance: The source impedance an amplifier presents to a loudspeaker. The lower the source impedance the greater difficulty a loudspeaker will have in feeding Back EMF to the driving amplifier, and the greater the level of control the amplifier will be able to exert over the loudspeaker.

Output: The audio signal exiting a component.

Overload: A condition in which a system is given too high of an input level. A common cause of distortion or product failure.

Overtones: See Harmonics. P = Volts^2 / Impedance.

Parallel/Series: All electrical components can be connected in series or in parallel. Their effect on signal may reverse depending on the type of connection. An inductor connected in series with a woofer will provide a simple low pass filter. A capacitor connected in series with a tweeter will provide a high pass filter. An inductor connected in parallel with a series capacitor will help create a 12dB/octave high pass filter for a tweeter. A capacitor connected in parallel with a series inductor will help create a 12dB/octave low pass filter for a woofer. Band pass filters can be created by means of a series capacitor and series inductor, or by a mixture of series and parallel capacitors and inductors.

Passive Crossover: Uses inductors (coils) and capacitors to direct proper frequencies to appropriate drivers. These crossover systems can be simple (First Order = 1 component @ -6 dB/octave slope) to complex (Fourth Order = 4 components @ -24 dB/octave slope).

Passive Radiator: A device that looks just like an ordinary driver, except it has no magnet or voice coil. A passive radiator is usually a highly compliant device, with a similar cone material and surround found on regular active drivers. The radiator must usually be at least as large (or larger) than the driver it is aligned with. The passive radiator is tuned to Fb and used in place of a port.

Passive: A component unconnected electrically to the signal source, such as an Auxiliary Bass Radiator. Or a component unconnected to a source of mains power, such as a passive pre-amplifier which acts purely as a source signal switching/routing device providing control functions for a power amplifier.

PCB: Printed Circuit Board.

PCM: Pulse Code Modulation. A means of digital encoding.

Pe: Driver’s rated RMS power handling capability.

Peak output: Sudden bursts of power are required in response to certain types of music. Loud drum beats and percussive piano playing demands a high peak output power from an amplifier. Failure to do so causes signal compression, resulting in a squashed,
thick sound as if the drum sticks or piano hammers are made of sponge.

Peak:  The maximum amplitude of a voltage or current.

Pentode: Commonly used valve type. Contains cathode, anode, grid and two further electrodes.

Phase Coherence:  The relationship and timing of sounds that come from different drivers (subs, mids, tweets) mounted in different locations.

Phase Distortion: A type of audible distortion caused by time delay between various parts of the signal.

Phase: Measured in degrees up to 360, as in a circle, phase refers to points in a sine wave cycle. The crossover point between positive half of the cycle and negative half cycle is 180 degrees. If the left channel is shifted by 180 degrees relative to the right channel, and identical information is fed to both channels, assuming the two loudspeakers are perfect and turned
to face each other, the signal will be self-canceling. No sound should be audible. If a system is connected out of phase, music signals fed through a normally positioned pair of loudspeakers will sound unfocused with a monotonous undifferentiated bass. It is easy to accidentally connect a system out of phase by wiring the positive lead of one channel to the negative socket. If both channels are accidentally connected this way, the system will be in-phase, but strictly speaking in reverse phase. Some amplifiers feed a reverse phase signal to the loudspeakers. Users should check the  manufacturer’s owners’ manual for optimum mode of connection. Some products are fitted with a phase inverter switch to enable direct comparison.

Phono stage: The extra equalization and gain stage required to amplify signal from a pickup cartridge to line level.  The RIAA equalization is necessary because bass signals are compressed to allow them to be cut onto vinyl records. There would be insufficient space otherwise. Moving magnet cartridges, which typically deliver output in mV (for 5cm/sec standard acceleration) require less amplification than most moving coil cartridges which deliver output typically in uV for the same acceleration standard.

Pilot tone: The 19kHz tone carrier tone on which stereo sum and difference signals are broadcast. It is removed
by the stereo decoder of FM tuners.

Planar Source: Most electrostatics and magnetic planars have a large surface area. Think of a wide board dropped flat onto the water surface. The sound can be extremely coherent, but the listening window is effectively limited to being directly on-axis of both the left and right planar speaker.

Point-Source: Most multi-unit loudspeakers try to approximate a point-source. Think of a pebble dropped into the water and the expanding wave pattern away from impact. Obviously it is difficult to integrate multiple point-sources into a truly coherent expanding wave. The best designs do quite well with careful driver engineering and crossover development.

Polarity: The difference between positive and negative.

Ported Enclosure:  A type of speaker enclosure that uses a duct or port to improve efficiency at low frequencies.

Potentiometer: The device used to provide volume level setting. Ideally a potentiometer is a variable resistor. Often
shortened colloquially to ‘pot.’

Power (P): The time rate of doing work or the rate at which energy is used. One equation for Power:

Power amplifier: The amplifier required to drive a loudspeaker.

Power output: The amount of power, usually measured in watts per channel, delivered by a power amplifier or integrated amplifier to loudspeakers. The rated maximum rms or continuous sine wave power output is a less relevant indicator of the dynamic range capability of an amplifier than its peak output power capability or its peak current delivery measured in Amps. Amplifier power output is usually specified relative to an 8 Ohm resistive load. However the majority of loudspeakers present a load that varies according to audio frequency, rising at loudspeaker drive unit resonant frequency but often decreasing
elsewhere across the bandwidth. Impedances lower than 4 Ohms require an amplifier to have considerable current drive capacity.

Power Supply: Electronic components deriving their power from a mains source require a transformer, smoothing capacitors and rectifier to turn the mains AC into a stable DC rail voltage.  Amplifiers in particular are heavily dependent on a stable rail voltage. However components as varied as CD players, DACs and turntables also benefit from well configured power supplies often as separate items.  Power supplies can be a useful retrofit upgrade.

Preamplifier: Another name for a line stage. A unit that controls the volume and allows for selection of various inputs (CD player, Tuner, etc).

Presence band: The middle range of audio frequencies to which the ear is most sensitive. Typically taken to mean
the 1-4kHz frequency range.

Printed Circuit Board: (Abbr: pcb). The board onto which a conducting track and solid state components – resistors,
capacitors and the like – are mounted. pcbs may be single sided or double sided, fitted vertically or horizontally.

Push-pull: Most common type of amplification that amplifies the negative and positive sides of the waveform separately. Allows for much higher power output than single-ended.

PWM: Pulse Width Modulation. A form of digital recording which makes use of the width of a digital pulse.

Q: The sharpness of a peak.

Quadraphonic: Four channel audio. Various rival quadraphonic audio formats including QS, SQ and CD4 were proposed in the Seventies. Many broadcast companies experimented with four channel FM transmission, the BBC, for example, favoring a format known as Matrix H. No quadraphonic format survived as a viable commercial entity into the digital age.

R: Symbol for resistance or resistor.

RCA Connector: “Phono” plugs, used primarily as low-level connections between Phonographs/CD players/Tuners/Recievers/Amplifiers

Reactance: A frequency selective resistance. Inductance and capacitance are the two forms of reactance.  The combination of resistance and reactance is impedance.

Receiver: An audio component that combines a pre-amplifier, amplifier(s) and tuner in one chassis. A Dolby Prologic Receiver also contains a Dolby Prologic decoder for surround sound.

Rectification: An essential process in the conversion of AC to DC by means of a half wave rectifier, a form of diode which is a key element in a power supply.

Resistance: Pure resistance is measured in Ohms. Resistance in the form of resistors blocks the flow of electric current in a linear or non frequency selective manner.

Resonant frequency: Any system has a resonance at some particular frequency. At that frequency, even a slight amount of energy can cause the system to vibrate.

Reverberation Time: The time it takes for a sound generated in a room to drop to 60dB below its original level. It is a measure of the size and reflectivity of the room boundary surfaces.

RF: Radio Frequency. Typically frequencies upwards of 70kHz through to MHz.

RFI: Radio Frequency Interference.  The disruption of radio signal reception caused by any source which generates radio waves at the same frequency and along the same path as the desired wave.

Ribbon Speaker: A type of speaker that uses a pleated conductor suspended between magnets. Most true ribbons are tweeters only. Sometimes confused with magnetic-planar speakers.

RMS: Root Mean Square. RMS qualifies an amplifier power output specification to signify continuous power output as opposed to peak or transient power.

Roll-off (cut-off): The attenuation that occurs at the lower or upper frequency range of a driver, network, or system. The roll-off frequency is usually defined as the frequency where response is reduced by -3 dB.

Rumble: Turntable rumble is a very low frequency noise caused usually by main bearing noise. It is usually a sign of poor bearing lubrication.

SACD (Super Audio Compact Disc): A dual-layer 12cm disc developed by both Philips and Sony. This new dual layer disc employs a 1-bit Direct Stream Digital (DSD) for higher resolution audio with upwards of six channels while the second layer adheres to the two channel 16-bit/44.1kHz compact disc standard.

Satellite: A satellite speaker is usually fairly small, and does not reproduce the lowest frequencies. Usually meant to be used with a woofer or subwoofer.

Screening: A form of protection of conducting cable from radio interference.

Sd: The effective piston area of a driver. The effective piston area of a driver.

Sealed enclosure: An air tight enclosure that completely isolates the back wave of the driver from the front. Very tight, defined sound (with Qtc = 0.707) with very good transient response and power handling.

Selectivity: The ability of a radio tuner to select or separate stations transmitting on nearby frequencies. By reducing the IF (intermediate frequency) bandwidth to sharpen selectivity, there may be a tradeoff in the form of increased distortion. Some sophisticated tuners provide switchable selectivity so that when two adjacent stations are required to be separated, users may do so by choosing narrow IF selectivity, at other times reverting to wide selectivity to benefit from the natural reduction in distortion.

Sensitivity: A measurement of how much power is required for a loudspeaker to achieve a certain output level. The general standard used is on-axis SPL (Sound Pressure Level) at 1 watt input, 1 meter distance.

Separation: Stereo separation is a measure of the success in isolating left and right channel stereo signals. The higher the dB specification the better.

Series/Parallel: See Parallel/Series.

Signal-to-noise (SN) Ratio: The range or distance between the noise floor (the noise level of the equipment itself) and the music signal.

Sine wave: Continuous waveform of a particular frequency (cycles per second).

Sine wave: The waveform of a pure alternating current or voltage. It deviates about a zero point to a positive value and a negative value. Audio signals are sine waves or combinations of sine waves. The waveform of a pure alternating current or voltage. It deviates about a zero point to a positive value and a negative value. Audio signals are sine waves or combinations of sine waves.

Single-ended: Type of amplification often, (but not always), using vacuum tubes. Typically low power output, low damping factor and relatively high distortion. Single-ended enthusiasts claim that the sound quality is more “real.”

Smoothing capacitor: An important component in a power supply, the smoothing capacitor(s) eliminate(s) unwanted ripple, the remains of the positive half cycle of AC mains following rectification.

Sound Pressure Level (Spl): Given in decibels (DB) is an expression of loudness or volume. A 10db increase in SPL represents a doubling in volume. Live orchestral music reaches brief peaks in the 105db range and live rock easily goes over 120db.

Sound Waves: Sound waves can be thought of like the waves in water. Frequency determines the length of the waves; amplitude or volume determines the height of the waves. At 20Hz, the wavelength is 56 feet long! These long waves give bass its penetrating ability, (why you can hear car boomers blocks away).

Soundstage: A listening term the refers to the placement of a stereo image in a fashion that replicates the original performance. A realistic soundstage has proportional width, depth and height.

Speaker Level: Taken from the speaker terminals. This signal has already been amplified.

Spectral balance: Balance across the entire frequency spectrum of the audio range.

Spider: The flexible material that supports the former, voice coil, and inside portion of the cone within the speaker frame.

Square wave: A waveform designed to simulate a transient impulse such as that of percussion instrument. Derived from a sine wave, a square wave can be shown by technical analysis to contain a multitude of harmonics. It is a very difficult test of hi-fi equipment and therefore particularly useful.

Standing wave: A buildup of sound level at a particular frequency that is dependent upon the dimensions of a resonant room, car interior, or enclosure. It occurs when the rate of energy loss equals the rate of energy input into the system. This is what you hear when you listen into a sea shell.

Stereo: Literally means solid. Usually taken to refer to two channel stereo, though developments in digital
audio will facilitate multichannel stereo.

Stylus: The needle part of a cartridge, the tip of which makes contact with a vinyl record. Elliptical, and super-elliptical tipped styli are preferable to conical styli (found only on the  cheapest, most unsophisticated cartridges.

Subwoofer: A speaker designed exclusively for low-frequency reproduction. A true subwoofer should be able to at least reach into the bottom octave (20-40Hz). There are many “subwoofers” on the market that would be more accurately termed “woofers”.
Surround (suspension): The outer suspension of a speaker cone; holds the diaphragm in place but allows it to move when activated. Usually made of foam or rubber.

Surround Sound: Sound extracted from the stereo signal sent to smaller rear or side speakers used in a home theater.

Tetrode: A four electrode tube (valve) based on the triode.

Thiele/Small parameters: The numbers that specify the behavior of drivers, as defined and analyzed by two engineers, Neville Thiele and Richard Small.

THX: Refers to a series of specifications for surround sound systems. Professional THX is used in commercial movie theaters. Home THX specifications are not published and manufacturers must sign non-disclosure waivers before submitting their products for THX certification. Manufacturers that receive certification for their products must pay a royalty on units sold.
Timbre: The quality of a sound that distinguishes it from other sounds of the same pitch and volume.  The distinctive tone of an instrument or a singing voice.

Total harmonic distortion (THD): Refers to a device adding harmonics that were not in the original signal. For example: a device that is fed a 20Hz sine wave that is also putting out 40Hz, 80Hz etc. Not usually a factor in most modern electronics, but still a significant design problem in loudspeakers.

Tracking: The ability of a cartridge to track the record icrogroove. A down force or tracking force is applied by a counterweight on the end of the tonearm to which the cartridge is attached. An appropriate side force (bias) is also applied to ensure the cartridge is not dragged towards the center of the disc.

Transducer: A device that converts one form of energy to another. Playback transducers are the phono cartridge, which changes mechanical vibrations into electrical energy, and the loudspeakers, which change it back, from electrical energy coming from the amp to mechanical movement of the diaphragm, causing audible pressure changes in the air.

Transient response: The ability of a component to respond quickly and accurately to transients. Transient response affects reproduction of the attack and decay characteristics of a sound.

Transients: Instantaneous changes in dynamics, producing steep wave fronts.

Transistor: There are numerous types of transistor, all designed to amplify an electrical signal. The most common form used today is the bipolar transistor. There are also j-fets, mosfets hexfets and many other generic types with particular applications.

Transmission Line: Also referred to as a T-line. A type of bass cabinet in which the back wave follows a relatively long, usually damped path before being ported to the outside. T-lines are usually rather large and costly cabinets to manufacture. Opinions vary widely over the “best” type of bass cabinet, but much has to do with how well a given design, such as a transmission line is implemented.

Transparency: Listening term. An analog that can be best “pictured” in photography. The more “transparent” the sound, the clearer the auditory picture.

Tri-wiring: The use of three  pairs of speaker wire from the same amplifier to separate bass, midrange and treble inputs on the speakers.

Triode: The first electronic amplification device. Invented in 1907 by Lee de Forest who called it the audion, the triode is a diode with an extra perforated electrode, the grid, whose function is to vary the amount of current flowing from anode to cathode.

Tuning Frequency: The helmholtz resonant frequency of a box. Also refers to the resonant frequency of other types of systems.

Tweeter: High frequency loudspeaker drive unit. Usually a dome diaphragm moving coil unit of either doped fabric or plastic construction.

Unbalanced: A form of cable and electrical circuit in which only one half of the positive/negative signal is referred to a zero reference earth.

Unity gain: A circuit with unity gain will not increase or decrease the volume level.

V: Symbol for Volt.

Valve: Known as tube in America, the thermionic valve is the earliest form of electronic amplification.  At its simplest in the form of a triode, the valve comprises an evacuated glass case containing three electrodes (conducting elements), the cathode, anode and grid.

Vas: The equivalent volume of compliance, which specifies a volume of air having the same compliance as the suspension system of a driver.

Vb: The total box volume, usually in cubic feet or liters. Used specifically in sealed and ported designs.

Vf: The front volume of a bandpass design. The front volume of a bandpass design.

VHF: Very High Frequency. The early terminology for FM radio broadcasts.

Voice coil:  The wire wound around the speaker former. The former is mechanically connected to the speaker cone and causes the cone to vibrate in response to the audio current in the voice coil.

Volt: Unit of electricity (Abbr: V).  A unit of electrical “pressure.”  One volt is the amount of pressure that will cause one ampere of current to flow through one ohm of resistance.

Volume: Subjective term for loudness; more accurately the signal level setting of an amplifier.

Vr: The rear volume of a bandpass design.

W: Symbol for watt or wattage.

Warmth: A listening term. The opposite of cool or cold. In terms of frequency, generally considered the range from approx. 150Hz-400Hz. A system with the “proper” warmth will sound natural within this range.

Watt: A measure of electrical power defined by Current multiplied by Volts (A X V).

Wattage: Is the unit of power used to rate the output of audio amplifiers. For a wattage number to have meaning the distortion level and impedance must also be specified.

Wavelength: The distance the sound wave travels to complete one cycle.  The distance between one peak or crest of a sine wave and the next corresponding peak or crest. The wavelength of any frequency may be found by dividing the speed of sound by the frequency. (Speed of sound at sea level is 331.4 meters/second or 1087.42 feet/second).

Woofer: Low frequency or bass loudspeaker drive unit.

Wow and Flutter: Measures of speed instability, typically of turntables and cassette decks.

X: Symbol for reactance.

XLR: A type of connector used for balanced lines. Used for microphones, balanced audio components and the AES/EBU digital connection.

Xmax: The maximum linear cone excursion of a driver, measured in inches or millimeters. Caution; this should be specified as linear excursion one way, but many manufacturers list the the total excursion both ways which falsely doubles the value!

Y-Adapter: Any type of connection that splits a signal into two parts. An example would be a connector with one male RCA jack on one end, and two female RCA jacks on the other end.

Z: Symbol for impedance.

Zobel Filter: A series circuit consisting of a resistance and capacitance. This filter is placed in parallel with a speaker driver to flatten what would otherwise be a rising impedance with frequency

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