GLOSSARY--Definitions widely used in speaker systems (1976)

A/B test--A listening test in which two similar audio devices (or program sources) are compared by rapidly switching between them while the rest of the system is unchanged. except for relative volume adjustment if needed.

acoustic or air suspension-- See "speaker enclosure."

baffle--Panel on which a loudspeaker is mounted; sometimes used colloquially to refer to the complete enclosure, especially when it is a fully sealed box.

Balance--As used in speaker parlance, the term "balance" refers to suitable pro portions of low, middle, and high frequencies that are reproduced by the speaker system amply but not in such a way that one portion of the total musical spectrum dominates or is slighted.

bass reflex--See "speaker enclosure." biamplification Use of separate amplifiers to handle highs and lows that are first divided by an electronic crossover circuit. The "bass amplifier" drives the woofer, while the "treble amplifier" drives the tweeter, in a two-way speaker system. A further refinement of this idea is "tri-amplification" in which the total audio spectrum is divided three ways and fed to three amplifiers, each of which energizes its own driver in a three way speaker system. The electronic crossover is inserted after the normal preamplifier stages and it in turn feeds the individual basic or power amplifiers.

Performance claims made for this type of hookup include improved damping, more effective coupling of amplifier power to speakers. and reduce IM distortion.

channel--A single, complete through path, as from microphone to loud speaker.

channel balance--See "balance." channel separation The degree to which stereo channels are kept apart from each other. Expressed in decibels; the greater the number, the more the separation.

compliance--In speaker parlance, the ability of the speaker to vibrate in accordance with the signals from an amplifier.

"High compliance" speakers. also known as "long-throw" speakers, are typically used in air-suspension systems.

cps--Abbreviation for cycles-per-second (of frequency), an obsolete term.

Now called hertz, abbreviated Hz.

crossover--A frequency at which other frequencies below and above it are separated. A crossover or dividing network, for instance, separates the highs and lows in a woofer/tweeter speaker system.

damping--A speaker's ability to control "ringing." Ringing is an undesirable tendency of the speaker to continue to respond after the driving signal has been removed. Excessive ringing causes distortion and a blurring of transient quality. A well-damped speaker overcomes this tendency. Speaker systems that load to a room via port or horn openings are inherently better damped than sealed-box systems. The latter depend on special construction of the voice-coil for their damping, and in addition seem to benefit from high damping factors in the driving amplifier.

damping--factor The ratio of load impedance (the speaker load) to an amplifier's internal impedance. A ratio of 10 is generally considered normal for high fidelity use; most of today's amplifiers because of their internal solid-state circuitry--typically have damping factors well over 10.

decibel--Abbreviated dB, this is a unit of change in the intensity of a signal. An increase is expressed as a + number of dB; a decrease, as a- number. No change is stated as 0 dB. Zero dB also is the starting level or reference level from which changes are measured. The smallest change the ear can detect is said to be 1 dB. A two-to-one change in loudness, as heard by the ear, is given as 10 dB. A two-to-one change in electrical power is 3 dB; a two-to-one change in voltage is 6 dB.

difference--The signal energy representing the differences in information between the signals in two or more stereo channels. A difference signal is produced when stereo signals differing in electrical polarity or in intensity are mixed together in opposing polarity ("A"-"B").

DIN--Letters stand for Deutsche Industrie Norm and designate performance standards followed in Europe as well as the type of unitized connecting plug and its mating socket in which a number of pins and holes enable more than one function or more than one channel to be handled by a single connector.

dipole--Also known as doublet, this term describes a loudspeaker that radiates equally from both sides of its sound-producing element; such a speaker has no nominal front or back.

directivity--A tendency of a loud speaker to concentrate its sonic output in a beam, thus sounding stronger on axis, and progressively weaker off axis. This tendency, when pronounced, can lend the sound a harsh sheen and actually is classified as a form of distortion. Since directivity tends to increase as frequency rises, it becomes a problem in the upper midrange and highs. "Omnidirectional" (or more correctly multidirectional) speakers use some kind of technique to avoid beaming and to radiate the middles and highs in a more uniform dispersion pattern.

distortion--Any measurable or audible difference between the audio signal fed into an audio device or system and the signal coming out of it. Distortions of various kinds are always present to some degree in every audio component, but careful design can keep them sufficiently low as to be inaudible or barely so. See also "doubling," "harmonic distortion," "IM distortion," "phase."

doubling--A speaker's tendency to distort in the bass region by producing harmonics of bass tones rather than the pure tones. Doubling typically increases as frequency is lowered and/or as the speaker is driven harder. Freedom from doubling is one of the hallmarks of good low-frequency response.

driver--A single loudspeaker or "speaker element" without its enclosure or baffle; any of the individual speakers used in a speaker system.

dropout--In speaker parlance, this term refers to relative losses of certain tones when the output of a speaker system is lowered in volume.

dynamic range--The span of volume between loud and soft signals, expressed in dB. A speaker's ability to cover the normal dynamic range of program material is one of the hallmarks of its accuracy as a sound reproducer.

efficiency--A ratio, often expressed as a percentage, of signal output to input; often used to estimate the power needed to drive a loudspeaker, and in effect the same as the "sensitivity" of a loud speaker.

equalization--Altering the frequency response deliberately for a desired effect. There are special auxiliary net works or devices which, inserted into a playback system before the loudspeaker and/or power amplifier, may be used to modify the system's sound to compensate for variations in program material, room acoustics, and the response of individual components in the system. These devices can do so more precisely and more effectively than conventional tone controls.

feedback--Return of part of an output signal to an earlier stage. Controlled electrical feedback, of specific types and amounts, is used in amplifier circuit design and in special speaker/amplifier systems. "Acoustic feedback" describes the spurious return of part of a speaker's output to the system input to cause noise and distortion. A typical form is a live microphone picking up sound from speakers being used for sound-reinforcement or public-address work, or as monitors in recording. In a home music system, a similar type of acoustical feed back occurs when the phono pickup senses some of the output from the speaker. This signal then is amplified along with the desired signal to cause harsh noises. Acoustical feedback of this type usually is cured by increasing the distance between speaker and turntable.

folded horn See "speaker enclosure." frequency response A speaker 's ability to reproduce a range of tones accurately. To be meaningful, a statement of frequency response should include specific dB variations from flat response (i.e., ± a number of dB), and also should state the sound-pressure-level (in dB/ SPL) at which the measurement was made (e.g., 90 dB/SPL).

ground A point of zero voltage, also known as "earth" in Britain; the "common" or "negative" terminal in speaker hookups.

harmonic A tone whose frequency is a multiple of another, lower-frequency tone (fundamental). Musical sounds are comprised of a fundamental and a number of harmonics.

harmonic distortion The addition of spurious harmonics to the signal. Expressed as a percentage; the lower the number, the better--although audio experts disagree as to the importance of harmonic distortion in loudspeaker output.

hertz Abbreviated Hz, this term has replaced "cycles-per-second." Hz Abbreviation for hertz, meaning cycles-per-second of any periodic phenomenon such as audio or radio frequencies.

IM abbreviation for "intermodulation" and most commonly used to denote "intermodulation distortion," q.v.

impedance--Total load presented to a circuit or signal-handling device. Electrical impedance in ohms is opposition to alternating current; it is the load on a source of alternating voltage, and consists of "pure resistance" combined with inductive and/or capacitive reactances.

The electrical impedance value of most speaker systems used in high fidelity is 8 ohms; a few are of 4 ohms, and some are of 16 ohms. The lower the impedance (the less ohms) of a speaker. the more power it draws from an amplifier.

Impedances, or loads, connected in series are additive (e.g.. two 8-ohm speakers in series become a I6-ohm load). Impedances in parallel are sub tractive (the same two 8-ohm speakers in parallel become a 4-ohm load). To determine the net impedance of dissimilar loads in parallel, use the formula:

Z= , Z, + Z.,. etc.

Thus, for example. a 16-ohm and an 8-ohm speaker in parallel present a total impedance of 5 1/2 ohms. "Acoustic impedance" refers to the load of air "seen" by a speaker as it vibrates to produce sound in a given environment. Because of the interaction of acoustical load and speaker. changes in the former can make the same speaker sound different.

input--In speaker parlance, the signal from an amplifier that is applied to the speaker to he converted to sound.

infinite baffle See "speaker enclosure."

intermodulation (IM) distortion The introduction of spurious signals as the result of interaction between two or more simultaneously reproduced tones, causing a smearing or veiling of the sound. Expressed as a percentage; the lower the number, the better. IM in speakers has been postulated as a serious cause of a form of distortion, although there is as yet no widespread agreement on how it should be measured. On the other hand, there is wide agreement that the use of more than one driver (e.g. woofer and tweeter) to reproduce the full audible spectrum is a way of reducing IM.

k Abbreviation for kilo.

kHz Abbreviation for kilohertz, which is one thousand hertz. Thus. 3 kHz means 3,000 Hz.

kilo One thousand (1.000).

labyrinth See "speaker enclosure."

level The intensity or amplitude of a

load See "impedance."

long-throw speaker See "compliance.”

m Abbreviation for milli.

M Abbreviation for mega.

matching In speaker parlance, the term refers to correctly mating a speaker system to an amplifier in terms of power requirements and capability, and at the recommended impedance.

mega One million (1,000,000).

micro One-millionth (1/1,000,000).

mil One one-thousandth ( 1 /1,000) of an inch. Tape thickness, stylus size, and wire diameter are usually stated in mils.

milli One-thousandth (1/1,000).

monitor A "monitor" speaker is any speaker used for listening critically to a signal that is being primarily directed to some other purpose, such as recording or broadcasting. What constitutes a "monitor" speaker is largely a matter of personal choice on the part of a recording or broadcast technician; in general, the term has come to mean an accurate speaker with high power capabilities.

μ (mu) Abbreviation for micro.

octave The musical interval between two pitches whose fundamental frequencies differ by a ratio of 2 to 1. Thus, 440 and 880 Hz constitute an interval of one octave. Similarly, 10,000 Hz and 20,000 Hz span one octave.

omnidirectional A term that has come to signify a speaker's ability to spread or disperse the sound evenly throughout the listening area. Strictly speaking, there is no truly "omnidirectional" speaker; a more accurate term would be "multidirectional" or "multi-planar."

peak A maximum instantaneous amplitude in a signal. The opposite of a "peak" is a "dip." The absence of peaks and dips is a desirable aspect of speaker response; an excess of peaks and dips lends an uneven, ragged quality to the reproduced sound. A broad peak or dip covering an appreciable portion of the tonal range can lend an artificial "coloration" to the reproduced sound.

phantom A signal carried by or reproduced through two sources in such a manner as to "appear" from another source. In two- and four-channel stereo reproduction, sounds which appear to come from between the loudspeakers are said to be "phantomed."

phase A part of a signal with respect to its relative timing vis-à-vis other parts.

Phase distortion refers to the displacement of this time relationship. Moderate amounts of phase distortion are said to be objectionable in that they lend the re produced sound a "canned" quality and detract from the speaker's transient response and its ability to reproduce inner musical detail.

An "out of phase" condition is said to exist when the individual drivers in a multiple speaker system are not vibrating in step with one another; i.e., one is "pushing" while another is "pulling." Two speaker systems, as entities, are said to be "out of phase" when one system as a whole is "pushing" while the other is "pulling." Out-of-phase hookups cause loss of bass tones and a wavering of the stereo image.

power When used in connection with loudspeakers, the term refers to the amplifier power recommended for driving the speaker as well as the maximum amplifier power it is safe to feed to the speaker. The term "acoustic power" refers to the signal output provided by the speaker and is expressed as a sound measurement rather than an electrical measurement.

resonance A tendency for a speaker, while being driven, to emphasize particular tones.

reverberation A slight, tapering prolongation of sounds due to multiple reflections in a large auditorium. It differs from echo, which is (acoustically) a sudden return of sound rather than a smooth decay.

ringing A tendency for a component to continue responding to a no-longer-present signal. See also "damping."

rms Root mean square; the effective value of a signal that has been expressed graphically by a sine wave.

rolloff A gradual diminishing of signal amplitude over a portion of the frequency response.

sensitivity For loudspeakers, this term has the same meaning as "efficiency."

signal Electrical energy generally; in audio, the electrical replica of intelligence.

sine wave In effect, a pure tone of a single frequency, used in testing and as a carrier wave to be modulated with a signal.

speaker enclosure A structure or cabinet specifically designed to house a loudspeaker in order to load its output to the listening area and to generally aid in its response. A bass reflex system uses a critically dimensioned port (auxiliary opening) to help smooth and extend the bass response. An infinite baffle totally encloses the speaker to suppress its rear wave, thereby permitting the speaker to respond down to its inherent resonant frequency. An acoustic or air-suspension system is relatively smaller than the previous types and uses a very loosely suspended woofer whose resonance is raised to the audible range and whose diaphragm motion is controlled by a critical amount of air trapped within the en closure. A folded horn adds a constantly expanding horn structure to the front and/or rear of a diaphragm to couple its output, via "acoustic transformer" action to the room. A transmission-line system (actually a variation of the former labyrinth system) loads a diaphragm with a critically dimensioned duct that smooths the response and helps extend the low-frequency range.

A "tower" enclosure describes a speaker enclosure that is designed as a vertical structure in which drivers may be installed in a vertical array, or so positioned as to radiate their energy upward, or from more than one side, etc.

sum The combination of two electrical signals of the same electrical polarity; the total electrical energy produced by combining the two signals of a stereo program. If the two speaker systems of a stereo setup are placed one atop the other, they will produce an "acoustical sum" (monophonic version) of the stereo program.

transient response Ability to respond to percussive signals cleanly and instantly without "ringing."

transmission-line speaker See "speaker enclosure."

tweeter Loudspeaker designed for high frequencies.

woofer Loudspeaker designed for low frequencies.

Z Symbol for impedance, q.v.

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(High Fidelity, 1976)

Also see:

HOW SPEAKERS WORK

MANUFACTURERS' DIRECTORY--Names and addresses of speaker companies.

BUYER'S GUIDE TO SPEAKER SYSTEMS--A complete listing of available models from various manufacturers giving important design and performance features, sizes, prices.