Baffle. The front mounting surface of a speaker enclosure. That surface also serves to suppress emission of the opposing-phase sound waves produced by the backs of speaker cones, making the baffle a significant enclosure element.

Banana Plug. A single-wire plug having expanded metal contacts that provide spring tension when inserted into a mating banana jack. Provides quick connection ease and is particularly useful in applications requiring frequent change. Generally the simplest interconnect solution, however, somewhat less reliable than the lock-down connection of a binding post.

Band. A frequency range of operation, such as the AM and FM bands of commercial radio or the multiple operating bands of a CB transceiver.

Bandpass. Passing a specific band of frequencies defined by upper and lower cutoffs, as with a bandpass filter. In equalizers, such filters commonly separate an audio signal into multiple frequency bands for separate control of response characteristics within each band.

Bandwidth. A frequency range of response most commonly defined by an upper frequency limit. However, bandpass responses, such as those of speakers and equalizers, are defined by both upper and lower limits.

Basket, Speaker. A speaker's mechanical frame that suspends the speaker cone(s). Also serves as a basic mounting bracket but adapter brackets may be required for specialized installations, such as encountered in cars.

Bass. The lower frequency range of the audio sound spectrum (drums, explosions, etc.) spanning the frequency range of around 20 Hz to 200 Hz. Primarily reproduced by woofers and subwoofers in audio systems.

Bass Boost. Increased bass signal for greater low-frequency sound. Often found in headphones where size restrictions limit the internal speaker size, restricting bass response.

Bass Reflex. A woofer enclosure having a tuned port for enhanced bass response. The tuned port is a tubular enclosure opening that is dimensionally tuned to enhance a narrow frequency range.

Battery Memory. A residual-charge characteristic of some battery types that prevents complete recharge until full discharge has occurred. Reduced operating time following charging may indicate this condition. To overcome the problem, some battery chargers offer the option to fully discharge such batteries prior to recharge.

Bi-directional. In two directions, as in the two-way communication permitted by intercom systems.

Binding Post. A versatile connector jack that accepts banana plugs and provides screw-down wire connection for either wire lugs or a thru-shaft wire insert. Typically located on the backs of speakers or amplifiers.

Bipolar. Bipolar junction transistor, as often used in the power output stages of audio amplifiers for its superior high-power efficiency.

Bitmap. A digital image storage format used by digital cameras and some video display drivers. As the name suggests, a bitmap identifies a digital word with a physical location.

BNC. A bayonet-style locking connector for coaxial cable connections commonly used for the higher frequency radio and video signals. Provides a highly-reliable low-loss connection consistent with the requirements of RF coupling.

Boost. Signal gain generally supplied within a selected band of frequencies. Often applied in audio to compensate for the restricted bass response of small speakers like headphones or simply to accentuate bass response.

Bridgeable (Output). An amplifier output capable of driving loads such as speakers that are connected in bridge configurations. Requires two output connections to the load for each bridge drive. (See also Bridged Power).

Bridged Power. The output power of an amplifier when driving a speaker connected in a bridged, as opposed to grounded, configuration. Bridged drive of a speaker potentially quadruples the power drive supplied.

BSM. Best-Stations-Memory station selector presets. A car radio feature that permits programmed assignment of specific radio tuning frequencies to selector buttons.

B/W. Black and White.

Camcorder. Camera/recorder; specifically, the video combination. A camera that records on video tape.

Capacitor. An electronic component that presents a frequency dependent impedance which decreases in proportion to frequency. Commonly used to shunt unwanted high-frequency signals or to block the coupling of DC voltages.

Car Cord. Adapter cord for power supply from a car cigarette lighter socket to a portable electronic device.

CATV. Cable TV.

CB. Citizen Band. A two-way radio broadcast band assigned for unlicensed public use.

CCAW. Copper-Clad Aluminum Wire.

CCD (Charge-Controlled-Device). A semiconductor element commonly used for electronic light detection or imaging. Converts the photon energy of light to electrical charge for electronic processing.

CCTV. Closed-Circuit TV.

CD. Compact Disc; a digital audio disc.

CDR. Recordable CD, typically a record-once disc.

CD-RW. Re-Writable CD, capable of multiple re-recordings as opposed to the single recording capability of a CDR.

Center Channel. An audio sound channel derived from the combined signals of the left and right channels for greater surround effect. A center channel fills in the sound presence between left and right.

Center Frequency. The midpoint frequency of a bandpass response. That frequency specified for a bandpass filter response.

CH. (See Channel)

Channel. One signal path, such as one of the two composing a stereo signal or one of the three containing the bass, midrange and treble segments of an audio signal. Also, a broadcast frequency as in TV and CB transmission.

Channel Separation. Signal isolation between channels such as between the two channels of a stereo system. Greater separation adds depth and spatial sense to audio playback.

Circumaural (Headphones). Ear surrounding; covering the ear. The circumaural configuration blocks ambient audio interference. In contrast, Open-Air headphones admit ambient sound.

Class A Operation. Transistor operation with continuous bias under all load and signal conditions for low distortion and greater bandwidth. While less power efficient, this operating mode avoids the transistor turn-off distortion introduced by the more efficient Class B operation. The reduced distortion of Class A operation most often benefits amplifier output stages. There, wide ranging current demands would routinely exercise the turn-off distortion of Class B bias.

Clipping. A form of distortion in which an amplifier limits or clips signal peaks. Commonly occurs when an amplifier is overdriven beyond its rated output level, resulting in output swing up to limit imposed by the power supply voltage. Results is severe audible distortion.

CM. Common-Mode. Common to the two lines of an electrical connection. Coupled noise often occurs as a common-mode signal on the two line of a differential connection. Common-mode rejection removes such error signals without disturbing the desired differential signal.

COAX. Coaxial; having a common center axis as with the two conductors of a coax cable or coax connector.

COAX Cable. A cable having two coaxial conductors with the outer conductor serving as an electrical noise shield for the inner one. Presents a well-controlled characteristic impedance to preserve matching for optimum signal transfer. The best solution for coupling low-level antenna or dish signals to TV sets and VCRs. Requires the installation of COAX connectors at the ends of each cable run.

COAX Speakers. Two speakers serving different frequency ranges internally joined on a common axis for space and mounting efficiencies. Typical combinations include a tweeter and midrange speaker having a common center-mounted driver.

Coaxial. Having a common center axis as with the two conductors of a coax cable. The coaxial structure of such cable makes the outer conductor an electrical shield for the inner conductor and controls the cable's impedance.

Coil. An inductor; an electronic component whose impedance increases with increasing frequency. Useful in blocking the transmission of higher-frequency signals such as in blocking high-frequency coupling from woofers.

Common-Mode Rejection Ratio. An attenuation factor for signals common to two lines which rejects coupled noise. Twisted-pair wires present signals benefiting from this rejection by equalizing the parasitic coupling affecting the two wires of the pair.

Compander. A signal dynamic range compressor/expander; often used for noise sensitivity reduction. Compressing the dynamic range increases the magnitudes of the lower level signals, which are the ones most sensitive to noise error. Recorded in this form, signals remain less sensitive to tape noise. Re-expanding the dynamic range later restores the signal in the absence of that noise source.

Component Video. The separate Red, Green and Blue signals that are normally combined in the composite video signal. As separate signals, they can directly drive a monitor without the need for the normal combining and later separation to avoid the signal degradation of that added processing.

Compress Ratio. The degree of signal compression produced by a limiter. Ideally this ratio would be infinite to totally block signal transmission above the limit threshold. However, practical constraints restrict this compression to around 20:1.

Cone. The conical diaphragm of a speaker. That portion of a speaker surrounding the central driver.

Constant-Q Response. Having constant selectivity (response sharpness). One of several responses achieved with bandpass filters, the constant-Q alternative typically provides a flatter overall response in the passband.

Continuous Adjustment. A continuously variable or linear adjustment, like that of a potentiometer, as opposed to the discrete step adjustments of a switch. The continuous adjustment typically provides greater adjustment resolution since switched adjustments remain limited by the number of switch positions practical.

Continuous Power. In a speaker system, the maximum average-operating power permissible. A speaker can withstand greater momentary power excursions, like those of music peaks, but a greater power continuously would potentially produce damage.

Converter (Power). Converts an input power line voltage to a different output power line voltage. In a frequent application, such a converter reduces the 240V line output common in Europe to the 120V common in the U.S. This conversion permits the operation of electronic products intended for the U.S. from European power sources.

Crest Factor. The ratio of peak instantaneous power to the average power. Most speakers can accept short term power peaks that significantly exceed the continuous power rating, as expressed by crest factor. No speaker damage will result as long as the average power remains within the speaker's rating.

Crossover. A transition frequency separating two regions of operation, such as the crossover frequency of a speaker system between bass and midrange or between midrange and treble. Crossover networks divide audio signals into these separate frequency ranges to permit individual response adjustments within the ranges and to separate the signals driving the corresponding speaker elements.

Crossover Frequency. (See Crossover).

Crossover Network. A multiple bandpass filter that separates an audio signal into frequency ranges such as bass, midrange and treble for separate signal control and for separate drive of woofer, midrange and tweeter speaker elements

Crossover Slope. The response roll off rate before or after the crossover frequency, typically 18 dB/octave. This slope defines the response selectivity of the crossover in separating its output frequency bands. High selectivity is desirable for isolation of specific frequency bands to their corresponding speaker elements.

Crossover, 3-Way. A crossover network supplying three frequency-separated outputs (bass, midrange and treble) for separate signal control and drive of woofer, midrange and tweeter speaker elements.

Crossover Type. Crossover classification by the response roll off rate before or after the crossover frequency. This defines the response selectivity of the crossover in separating two frequency bands. Typically 18 dB/octave, indicating a three-pole response roll off. (See also Crossover Slope.)

Crosstalk. Parasitic coupling between signal channels. At audio frequencies, crosstalk normally results from ground loops introduced by the use of one ground return for more than one high-current signal path. In one example of crosstalk avoidance, separate ground return lines for the two speakers of a stereo system avoid such cross coupling.

CRT. Cathode Ray Tube; the picture tube of a TV set or computer monitor.

Crystal-Controlled (Oscillator). Highly-stable frequency control achieved with a quartz crystal. Used in precision radio tuning where the frequency of a reference oscillator serves a reference standard.

CUL. Canadian Underwriters Laboratory. An electrical standards setting body equivalent to Underwriters Laboratory of the U.S.

Current Feedback. A signal control technique that reduces distortion by sensing an output signal current, comparing it with the input signal and supplying gain to correct any distortion difference. The type of control realized with the feedback winding of an autotransformer.

Cut. Signal attenuation applied within a selected frequency range. An equalizer tuning function much like a bass or treble control but spanning a more selective frequency range. The opposite of Boost.

Cutoff. The upper or lower limit of a frequency response where that response drops 3 dB from its midrange level.

Daisy Chain Connection. Connection of multiple devices in series on a common line. Used in applications such as intercom, the common-line series connection greatly reduces wiring requirements for installations spanning greater distances.

D/A converter. Digital-to-analog converter, as used to convert the digital signal of a CD to an analog audio signal. The precision and dynamic range of this conversion depends upon the number of bits resolved by the D/A converter. 16 bits represents the standard for high performance audio applications.

DAC. (See D/A converter.)

Damping Factor. A measure of the ability of an electronic circuit to prevent the introduction of extraneous signal resonances. A damping factor of 1.0 or greater assures the suppression of such resonances. In audio applications, adequate damping is particularly important in speaker and speaker enclosure responses because mechanical resonances there would disturb response flatness.

DAT. Digital Audio Tape. With this storage format, signal recording in digital form extends the high dynamic-range and low-noise benefits of CDs to tape.

dB (decibel). A logarithmic unit of relative signal level. For signal power, P(dB) = 10log(P1/P2) represents the power level P1 as compared with reference level P2. Differs from dBu in that the latter is referenced to a reference P2 level of 0.775Vrms.

dB/Octave (dB/Oct). Frequency response roll off rate or slope. This slope reflects the selectivity or response sharpness of equalizer passbands. 6 dB/octave represents the basic single-pole response roll off and 18 dB/octave represents a highly selective, three-pole response characteristic.

D-Bass. Dynamic bass. A boosted bass response producing increased low-frequency content for greater woofer output. Produces a more dynamic and encompassing sound for action videos.

DB-9. A 9-pin, D-connector configuration frequently used for computer equipment interconnections like those required for computer control of audio signals.

DB-25. A 25-pin, D-connector configuration frequently used for computer equipment interconnections like those required for computer control of audio signals.

D-Bass. Dynamic bass. A boosted bass response producing increased low-frequency content for greater woofer output. Produces a more dynamic and encompassing sound for action videos. (See also Bass Boost.)

dBu. The dB signal level relative to a reference level of 0.775 Vrms. [dBu = 20log(es/0.775).] Differs from dB in that the latter only provides a relative measure of two arbitrary signal levels.

DB-9. A 9-pin, D-connector configuration frequently used for computer equipment interconnections like those required for computer control of audio signals.

DB-25. A 25-pin, D-connector configuration frequently used for computer equipment interconnections like those required for computer control of audio signals.

DC. Direct Current or zero frequency, reflecting a voltage or current that, unlike an AC signal, does not vary with time. Power supplys and batteries deliver DC supply voltages for electronic equipment.

Diaphragm. The cone or dome of a speaker that vibrates in response to signal drive, producing sound pressure waves. The fabric portion of a conical speaker or the dome itself in a dome speaker.

Differential Input. An input signal connection between two input lines rather than between a single line and ground; as commonly used for coupled noise rejection.

Digital. Signal representation thru a series of either 1 or 0 (on or off) states. Contrasts with analog representation where signal amplitudes exist at any level. In audio, the digital encoding of CD and DAT sources expands dynamic range and suppresses noise.

Digital-to-Analog Converter. (See D/A converter.)

DIN. (Deutsche Industrie Norman) A German standard that defines mechanical configurations such as those of some older European audio connectors.

Directivity (Microphone). Response pattern. Expresses the geometric shape of the region of sensitivity surrounding the microphone in terms such as omnidirectional or cardiod. A narrow directivity like cardiod better separates a desired sound signal from background noise as generally desired in single voice use. A wide directivity like omnidirectional best serves applications involving multiple sound sources at varied locations, such as those produced by an orchestra.

Directivity (Speaker). The sound radiation pattern or the way output sound waves spread from a speaker. In general, a wide horizontal spread and a narrow vertical spread best serve audience spatial configurations or a varying listener position within a room.

Discrete Output. Output stage(s) formed with individual discrete transistors. For the higher-power output stages of amplifiers, discrete transistors provide greater power handling and more performance alternatives than those included in integrated circuit components.

Dispersion. The sound radiation pattern or output spread of a speaker (Directivity) over a given angle. (See also Directivity)

Distortion. Signal wave shape deviation from the original. (See THD) To some degree, all electronic equipment inherently distorts signals due to non-ideal responses. For a given audio element, Total Harmonic Distortion serves as a quantitative measure of such response deviations. (See also THD.)

Distortion, Harmonic. A measure of the distortion content of a signal as represented by equivalent harmonics of that signal and specified as a percentage of the signal amplitude. While the equivalent harmonics represented do not actually exist in the signal, their summation would reproduce the distortion component of the signal. Further, filter separation of the signal into its fundamental and harmonic frequencies yields the harmonics for identification and measurement comparison with the fundamental.

DNR. Digital Noise Reduction. The application of digital signal processing (DSP) algorithms to reduce the effects of noise.

Dome Tweeter. A tweeter having a dome rather than cone shaped diaphragm for wider sound dispersion. Tweeter response with a conventional cone diaphragm lacks the spatial dispersion afforded lower frequency signals and a dome diaphragm compensates for this limitation at the tweeter's higher frequencies.

Double-Sided Board. A printed circuit board having components mounted on both of its sides for increased compactness.

Downfiring Speaker. A speaker that projects its acoustic signal downward rather than outward. Sometimes preferred for woofers and subwoofers to achieve sound spreading through floor reflections. That spreading avoids the localized effect of conventional front firing speakers for greater surround effect.

Double-Sided Board. A printed circuit board having components mounted on both of its surfaces for increased compactness. Multi-layer boards increase the number of interconnect planes for even greater compactness.

DPI. (Dots-per-inch.) A measure of video image resolution. Electronic video signals are composed of a multitude of pixels or dots each having color and brightness attributes. The greater the density of dots or DPI, the smaller the dot size and the sharper the resulting image.

DRAM. Dynamic Random Access Memory.

Driver. In a speaker, the voice coil that drives the internal speaker vibration. Basically an electromagnet, the driver produces vibration in the speaker cone in response to its audio drive signal.

Dropout. Signal loss during tape playback often due to mechanical shock or vibration. Particularly important in portable tape players.

DSP. Digital Signal Processing. The application of digital signal-processing algorithms primarily to reduce the effects of noise but sometimes to produce special sound effects.

DSS. Digital Satellite System. A dish antenna and decoder combination that receives satellite-coupled TV transmission.

DTS. Digital Theater Surround. A surround sound implementation having greater bandwidth potential.

Dubbing. Adding a second audio signal to a first signal as in sound-on-sound recording. The second signal does not override the first but rather adds to it. Dubbing can, for example, add background music to a vocal dialog.

DV. Digital Video. DVD based video. ( See also DVD)

DVC. Dual voice coil. A type of audio speaker having separate voice coils for two frequency ranges. Separate coils permit optimizing each for the specific frequency segment it serves. In this way, one speaker fills the function of two others such as a tweeter and a midrange. However, this combination inherently introduces compromises not found with the two independent speaker alternative.

DVD. Digital Video Disc. A high-capacity video equivalent of a CD containing both video and audio recordings for video (TV) playback. Sometimes produced with dual-layer or double-sided discs.

Dynamic Headroom. The separation between a maximum signal excursion and the maximum allowable. For audio speakers, this defines the separation between the maximum-recommended operating level and that at which degradation occurs.

Dynamic Range. The span between minimum and maximum signal levels as determined by noise and power limitations, respectively. The noise reduction of 16 bit DSP potentially expands this range to 96 dB, however, speakers and headphone responses then impose a final limitation.

Dynamic Range Compression. Low-level signal amplification and high-level signal attenuation applied to raise signals well above the background noise level without exceeding maximum amplitude levels. Used to reduce the significance of tape noise. Requires signal re-expansion in the playback process.

Dynamic Speaker. A speaker having a permanent magnet for damping voice coil motion and for returning the voice coil to its neutral position. The most common speaker type for woofer and midrange applications.

EL. Electro-Luminescent. An illuminated display often found in auto radios that employs electro-luminescence rather than an incandescent bulb to light the display.

Electronic Crossover. A crossover network formed with active rather than passive filters for greater response shaping control. The gain introduced by the active elements provides impedance isolation between crossover sections, removing interdependences that otherwise compromise individual section responses. (See also Crossover Network.)

EMI. Electromagnetic interference. Electrical interference coupled by magnetic fields like the car radio noise sometimes produced by the car's ignition system. Can also result from parasitic coupling from transformers.

EP. Extended Play. A lower-speed tape recording mode that extends recording time. Frequently included in VCRs to accommodate longer recording requirements. However, the lower speed also reduces recording quality.

EQ. (See Equalizer)

Equalizer. A multi-band audio bandpass filter having individual gain or attenuation controls for each band. Adjusting the controls shapes the overall frequency response to add emphasis or reduction of various signal frequencies, controlling the character of the overall sound result. Essentially a multi-band tone control.

Equivalent Input Noise. Output noise divided by the circuit gain. This input representation permits direct comparison of noise and signal levels for qualitative evaluation.

ESR. Electrical Series Resistance. The parasitic resistance of a capacitor. Presence of that resistance makes the capacitor non-ideal and limits its ability to remove electrical transients and noise. ESR becomes most significant at higher frequencies as the falling capacitive impedance then makes the parasitic resistance a greater proportion of the capacitor's impedance.

Excursion. The physical distance traveled by a speaker's voice coil in producing its sound output. Greater excursions correspond to greater output volume, as incorporated in long-throw woofers.

F-type connector. An economical coaxial connector commonly used for TV antenna or cable connections. Similar to a BNC connector but lacking its locking feature.

Feedback. Supply of a portion of a circuit's output signal to the circuit input for comparison with the input signal and the generation of an error correction signal. Commonly used to reduce distortion in amplifier stages. The underlying principle of the autotransformers sometimes used in amplifier output stages.

Ferrofluid. A particle filled oil that heat sinks a speaker's voice coil to its magnet for cooling. Metallic oxide particles in the fluid enhance the thermal conduction of the heat sinking. That heat sinking economically extends the speakers power capacity.

FET. Field effect transistor. A lower-distortion but lower-gain alternative to the bipolar transistor. Often used for higher-power amplifier output stages and higher-impedance receiver input stages. Less effective than bipolar transistors in amplifier gain stages.

FF. Fast Forward. A rapid advance feature of tape players and recorders. Similar to Rewind but in a forward direction and generally slower to permit selective bypass of tape sections. Sometimes combined with AMS (Automatic Music Sensor) to permit fast forward advance to the next recorded track.

Filter. An electronic circuit that selectively separates a band of signal frequencies, such as a low-pass filter for the separation of the low-frequency components of an audio signal. Filters serve as the basic element of equalizers where multiple filter channels permit frequency response tailoring.

Filter Slope. The response roll-off rate outside the filter passband. The greater the roll off, the higher the filter selectivity. Crossover networks commonly provide 18 dB/octave response roll offs for a high degree of discrimination between adjacent frequency bands.

FM. Frequency Modulation; as in FM radio broadcast. Signal modulation of a carrier signal through variation of the carrier’s frequency. This contrasts with the amplitude modulation of AM broadcast. Noise interference more directly affects signal amplitude and, thereby, AM radio signals, giving rise to the demand for higher fidelity through FM broadcast. However, the higher carrier frequencies allocated to the FM band typically result in a shorter effective transmission ranges.

F&R. Front and Rear, as in car audio volume balance.

4k bit. 4000 bit memory element, where a bit represents one digit of a digital word.

Freq. Frequency.

Frequency. The rate of repetition of a signal in cycles per second. Higher audio frequencies correspond to treble tones and lower ones correspond to bass. Radio frequencies define station locations within a broadcast band.

Frequency Range. A range of frequencies between high and low end points. A passband or bandwidth. Individual speaker elements like woofers, midranges and tweeters serve different frequency ranges within the overall audio frequency range. (See also Frequency Response.)

Frequency Response. The range of signal frequencies supplied by an amplifier or reproduced by a speaker or microphone as specified by the upper and lower bounds of the frequency range in Hertz (Hz). Typically, 20Hz to 20kHz encompasses the full range of human hearing and separate audio speakers generally serve different segments of this range.

Front/Rear Fader. A front-to-rear balance control, as commonly used in car audio systems to achieve volume balance between front- and rear-mounted speakers. This control simultaneously increases volume in one location while reducing it in the other. Analogous to the more common Left/Right balance control of general audio systems.

FRS. Family Radio Service.

F-type connector. An economical coaxial connector commonly used for TV antenna or cable connections.

Full-Range Speaker. A single speaker, often incorporating multiple speaker elements, intended for the full audio range. Offers a more compact and economical solution but this combination speaker can not match the combined performance of a woofer, midrange and tweeter.

g. Gram(s). A metric unit of weight. (Approximately .035 ounces)

Gain. Amplification factor. Gain increases signal magnitude for greater sound volume or improved radio and TV reception. Commonly provided by an amplifier in audio or by an antenna in radio and TV.

GHz ( Gigahertz). A measure of signal frequency expressing thousands of million cycles per second.

GND. Ground. The zero reference point from which a voltage or voltages are measured. In the most basic case, earth ground. In electronic systems, generally the chassis or case of the system.

Ground Loop. A crosstalk producing condition in which the ground line currents from one signal produce voltage drops that add to another signal path. Star connection returns of all grounds at a common point avoids such parasitic interference.

GUI. Graphical-User-Interface. An icon-based software interface.

Halogen. An inert gas sometimes contained in strobe light enclosures.

HDF. High Density Fiberboard. An economical wood composite alternative often used for speaker cabinets when combined with a veneer finish. The high density of the fiberboard inhibits case resonances well but HDF lacks the durability and beauty of a solid hardwood.

HDTV. High-Definition TV. A higher resolution television system with twice the resolution of standard TV.

Headroom. The separation between a maximum rated signal excursion and the maximum allowable. For an audio speaker, the power level separation between a continuous operating capability and the higher level for which short term excursions can be handled without damage.

Hi8. A video tape format.

Hi&lo Pass. High and low pass, as in speaker crossover networks. Frequency response bands separated by the high-pass and low-pass filters of tone controls and equalizers to isolate treble and bass signals for separate control. (See also High Pass and Low Pass.)

High Pass. Passing only higher frequencies, such as the high-pass filters that provide treble control in audio equipment. Crossover networks and equalizers also incorporate high-pass filters to separate or control the treble component of audio signals.

Hi-lo or Hi/Lo. High-low. (See also Hi&lo Pass, High Pass and Low Pass.)

Hipass. (See High Pass)

Horn. A high-frequency speaker. (See also Tweeter)

Hot Shoe. Camera strobe mount including a firing control connection. Provided for mounting an external strobe without the need for a separate, wire connection from the strobe to the camera.

HP. (See High Pass)

HPF. High-pass filter. (See High Pass)

Hz (Hertz). A measure of signal frequency expressing signal cycles per second. Typically, 20Hz to 20,000Hz encompasses the full range of human hearing.

IEEE 1394. A high-speed digital data-transfer interface standard for applications such as streaming video. Often used with digital camcorders.

Impedance. The electrical characteristic of an electronic device that reflects the voltage developed in response to a current supplied to the device. Speakers typically display a low 4 ohm or 8 ohm input impedance to accept high power drive from reasonably low signal voltages. Microphones typically present a high output impedance to develop a sufficiently high signal voltage from their low internal power generation.(See also Impedance Matching.)

Impedance Matching. Matching the driven load impedance to that of the source for maximum power transfer, as typically implemented with transformer coupling.

IMPP. Injection Molded Polypropylene. A common form of rigid plastic.

Imaging. Acoustically portrayed location produced by a playback sound source, primarily through stereo effect but also through relative sound intensity. The stereo effect communicates left/right position and the sound intensity communicates relative distances.

Impedance. The electrical characteristic of an electronic device that reflects the voltage developed in response to a current supplied to the device. Speakers typically display a low 4 ohm or 8 ohm input impedance to accept high power drive from reasonably low signal voltages. Microphones typically present a high output impedance to develop a sufficiently high signal voltage from their low internal power generation. (See also Impedance Matching.)

Impedance Matching. Matching a driven load impedance to that of the source for maximum power transfer, as often implemented through transformer coupling for impedance transformation. A feature incorporated in many in-wall volume controls through transformer tap selection. Becomes especially important where multiple speakers share a given audio signal line, as each speaker added alters the net load impedance.

IMPP. Injection Molded Polypropylene. A common form of rigid plastic.

Inductor. An electronic element whose impedance increases with frequency. Sometimes used to decouple woofers from high-frequency signals by placing the inductor in series with the speaker's signal line. In such applications, the inductor's parasitic resistance must be much less than the speaker impedance to avoid significant signal loss.

Infrared. Light at frequencies below the red end of the visible spectrum. Often used for signal coupling in wireless headphones and in TV remote controls. Use of infrared light distinguishes the signal coupling light from normal room lighting. Infrared also provides a more economical control link than the RF alternative but it remains limited to line-of-sight coupling.

In/Out. Input/Output.

Input Impedance. That impedance presented by the input of an electronic device, as commonly expressed in ohms. Amplifiers typically present high input impedances to limit loading effects on their signal sources. Speakers most commonly present low input impedances to accept higher drive power. Most speakers have an 8 ohm input impedance, although 4 ohm and 16 ohm types exist for different applications.

Input Sensitivity. The minimum input signal level reliably detected by a device, such as that required by the input of an amplifier. Generally, the internal noise level of the device sets this minimum signal requirement.

Insertion Loss. Signal loss as a result of the insertion of an element in a line.

Inverter. A power converter; as commonly used to derive line-power backup from batteries. Inverters chop a battery's DC output voltage into time varying segments to produce an AC power signal.

In-wall. Designed for installation within a wall, as with in-wall speakers. In-wall speakers offer great placement flexibility and unobtrusive space demands but can not match the fidelity achievable with enclosure mounted speakers. By design, those enclosures enhance a speaker's acoustic result while a wall installation will more likely degrade it.

IR, I/R. (See Infrared)

ISO. An international standard that defines film speed ratings.

Isolated Mounting Legs. Equipment support legs that electrically isolate a case from unwanted ground connections that could introduce ground loop interference.

Isolation Transformer. A transformer used to break hum producing ground loops by permitting different input and output ground references. This isolation interrupts ground current paths that could otherwise couple ground reference differences into the signal path.

JPEG. A digital image compression format.

Kapton. A high-temperature electrical insulator film sometimes used in woofer voice coils.

kb (kilobyte). Thousand bytes where a byte is a unit of digital memory. For a digital camera, the number of kb of memory determines the number and resolution of the images that can be stored.

Kevlar. A high-strength, heat-resistant fabric sometimes used for speaker diaphragms in higher priced models.

kHz (kilohertz). A measure of signal frequency expressing thousands of cycles per second. (1 kHz = 1000 Hz). Audio signals extend up to 20kHz.

kohm (kilo-ohm). A measure of electrical impedance expressing thousands of ohms.

KVA (Kilovolt-Amp). An electrical power-rating product of voltage and current specified for an uninterruptable power source. Dividing that product by the line voltage, (110V in the USA, 220V in Europe) yields the output current rating of the power source.

LAN Local Area Network. A computer interconnection network for limited connection distances.

Lavaliere Design (Microphone). Clip-on; as with a lapel mic.

LCD (Liquid Crystal Display). An energy-efficient high-resolution display. Most often produces black characters on a light green background in audio equipment but capable of multi-color.

LCR. Left, Center, Right

LED (Light Emitting Diode). A semiconductor diode that generally serves as an electronic indicator light to display the on/off states of equipment functions, usually in red, yellow or green.

Li-Ion. Lithium Ion; a long-life battery material combination.

Limiter. An amplitude limiting clamp used to prevent signal overload.

Limit Threshold. That signal level at which a limiter initiates signal compression.

Line Input. A high level signal input that bypasses an amplifier's initial gain stage to accommodate line level signals (1 to 2 Vrms). An input that accepts the higher output signal presented by another amplified source.

Line Out (Line Output). An amplifier monitor output that bypasses the amplifier’s variable and power gains. This output remains unaffected by volume control variations and free of the distortion introduced by later power stages.

Lithium Ion (Li-Ion). A long-life battery material composition.

Low Cut. The low-frequency cutoff of an AC response. Attenuates signals having frequencies below that of the low cutoff. The opposite of Low Pass. Low cut filters, for example, remove bass signals from the tweeter drive.

Low Pass. Passing lower frequencies, such as the low-pass filter that provides bass control in audio equipment. In that application, the filter separates the bass components from the audio signal for separate volume control. The opposite of Low Cut. Analogous to the High Pass filters used to separate high frequency audio signals for treble control.

Low Pass Filter. A filter that passes only signals below its cutoff frequency. In audio, such filters sometimes remove midrange and treble components from woofer or subwoofer drive signals.

Low-Q. Having a broader frequency response and less susceptibility to electronic resonance. A desirable amplifier and speaker characteristic that avoids the potential for exaggerated responses from resonance and peaking.

LP crossover. A Low-Pass crossover frequency or filter network that separates bass components from the overall audio signal. One of the signal separation boundaries of a crossover network.

LPF. Low-pass filter.

L/R. Left/Right.

LUX. A unit of measure of light intensity.

m Meter

mA (Milliamp). 0.001 amp. One thousandth of an amp.

Magnetic Gap. The space in a speaker's magnetic field where the voice coil is suspended. This gap must be large enough to accommodate the voice coil's displacement but small enough to retain high magnetic field strength across the gap.

Magnetic Oil (Ferrofluid). A particle filled oil that heat sinks a speaker's voice coil to its magnet for cooling. Metallic oxide particles in the fluid enhance the thermal conduction of the heat sinking.

Magnetic Shielding. Shielding against electromagnetic interference such as that produced by transformers and speaker magnets. To be effective, the shield must have a high magnetic permeability as well as a high electrical conductivity. Steel posses both of these qualities while aluminum, although an effective electrostatic shield, lacks the permeability required for magnetic shielding.

mAh. Milliamp-hour. The current-time rating of battery capacity which equals the product of the current drain and the time duration of the drain. Dividing the mAh rating of a battery by the current drain of a device it powers yields the sustainable time of the battery supply.

MB. Megabit; one million bits of digital information.

MDF. Medium-Density-Fiberboard. A denser version of particle board often used for speaker cabinets because of its combination of economy and resonance damping qualities.

Memory Effect. A characteristic of some rechargeable batteries in which residual internal effects prevent full re-charge of the battery, particularly when the battery has not been fully discharged. For a battery powered device, reduced operating time between charges potentially indicates memory effect rather than battery degradation. In such cases, complete discharge may restore operating time.

Metal Particle Tape. Audio/Video tape having a metal particle layer for improved high-frequency response. The high permeability of the metal particles used to coat such tape permits reducing the particle size to extend frequency response.

MHz. (Megahertz). A measure of signal frequency expressing millions of cycles per second. TV signals and many radio signals are commonly broadcast in the MHz range.

Mic. Microphone.

Midrange. The intermediate frequency range of the audio spectrum between bass and treble. Also, a speaker designed to reproduce that range.

Milliamp. One thousandth of an amp (.001A).

MiniDisc. A 2.5" CD for compact/portable applications.

Mini Phone Connector. A 1/8" diameter plug-and-jack connector commonly used for headphones.

Mixer. An audio or video processor that combines two or more source signals in an output signal. Separate controls typically permit tone and volume control over the contribution of each source signal to achieve an optimum tone balance.

mm. Millimeter(s). (Approximately .04 inches; 1" = 25.4mm)

Modular. Contained in a variety of separate enclosures or cases as opposed to within one common enclosure. Modular audio systems typically consist of separately cased signal sources, amplifiers and speakers.

Modulator (Video/Audio). An electronic signal processor that combines a video/audio signal with a carrier signal for distribution. A later demodulator removes the carrier following transmission to restore the original signal. Analogous to radio transmission.

Mono (Monaural). Monophonic; single-channel audio.

MOSFET. Metal-oxide-semiconductor field-effect-transistor. Often used for higher current or lower distortion in power-driving amplifier stages.

MPEG. A digital image compression format.

Multi-Channel. Supporting multiple signal paths or channels, such as from an amplifier to multiple speakers.

Mute. To silence or cut off a signal. A feature used in CB radios to quiet the output in a standby mode.

mV. (Millivolt). 0.001 volt. One-thousandth of a volt.

Natural Resonance. The natural frequency of vibration of an object as determined by the object's physical dimensions. Natural resonance occurs in an object when struck by an audio wave having a wavelength equal to an even fraction of one of the object's dimensions. Then, the object vibrates in synchronization with that wave producing extraneous harmonics. Damping these harmonic vibrations requires the use of rigid, heavier materials for speaker enclosures.

NC. Noise Cancellation. A feature added to some headphones that removes ambient noise interference through signal cancellation.

Neodymium. A magnetic alloy alternative to ferrite for speaker magnets. Neodymium's greater magnetic field density reduces size for compact speaker applications and headphones.

NiCad. Nickel-Cadmium. A rechargeable battery material combination. Economical but subject to a memory effect that can eventually prevent full recharge.

NiMH. Nickel-Metal-Hydride. A rechargeable battery material combination having much greater capacity and none of the memory effect of NiCad equivalents.

NM. Normal-Mode. Between the two lines of an electrical connection.

NR. Noise Reduction. (See also NC.)

NTSC. National Television Standards Committee or the color TV standard governing the transmission signal format used in the USA and Japan.

OEM. Original-Equipment-Manufacturer.

OFC. Oxygen-Free Copper. Copper wire that provides lower line resistance for reduced parasitic line drops.

Ohm. The unit of electrical impedance, equaling an element's voltage drop divided by its associated current.

Omnidirectional Pickup. Responsive in all directions as with omnidirectional microphones that respond to sound input from any direction, as opposed to directional microphones. (See also Polar Pattern.)

Open-Air (Headphones). Open space design partially vents and receives acoustic energy to avoid the image restricting confinement of totally isolated stereo signals. However, in the process, the open-air design does emit sound to the surrounding environment.

Optically Isolated. Employing optical isolation between system components to prevent ground loop interference. Particularly effective because the conversion to optical transmission breaks all electrical conduction loops.

OS. Operating System (computer).

OSD. On-Screen Display. Often used to display an operating menu for TV channel selection and audio system control.

Output Impedance. That impedance presented by the output terminals of an electronic device, as commonly expressed in ohms. Lower output impedances facilitate higher power transfer to a load.

Overload Protection. Internal protection against damage from signal overload. Typically activated by sensing current level or temperature in output transistors.

PA. Public Address.

PAL. Phase Alternation by Line. A European TV broadcast signal standard.

Panhead. The position-adjustable mounting head of a photographic tripod. Permits free-moving left-to-right and/or up-down rotation or panning of a mounted camera.

Particle Board. Wood chips and glue pressed into board shape to provide an economical alternative to natural wood. Its uniformity and rigidity make it well suited for low resonance speaker cabinets. (See also MDF.)

Passive Radiator. An undriven, secondary woofer diaphragm used for improved low-frequency response.

PCB. Printed Circuit Board. The board on which electronic components are combined and interconnected to form an electronic circuit.

PCM. Pulse-Code Modulation. Signal encoding through modulation of a carrier pulse width. A signal encoding technique used in digital audio and some switching power supplies.

Peak Limiters. Signal amplitude limiters that clip or terminate response at a higher signal level beginning at a limit threshold.

Peak Power. In a speaker system, the maximum instantaneous operating power. A short term capability, this power level exceeds the continuous rating to accommodate signal transients.

PEI. Poly-Ether Imide. A resilient speaker cone material.

Phantom Mode. A surround sound alternative that diverts the low-frequency center channel signal to the main speakers. Used in the absence of a dedicated center channel speaker.

Phase Delay. An undesirable time shift of audio signals most pronounced at higher frequencies. Readily produced by bandwidth limitations, this delay is the source of phase distortion which degrades audio clarity.

Phase Linearity. The absence of phase delay.

Phase Reverse. A speaker drive option that reverses signal phase to permit sound synchronization with another speaker. One switch position will produce in-phase sound waves from the two speakers that compliment each other. The other position will produce out-of-phase waves that acoustically subtract to degrade sound. Listening tests while switching will determine the correct setting for synchronization.

Phase Shift. Time delay introduced in an electrical signal. Produces phase distortion in audio signals of higher frequencies. Most often the result of amplifier bandwidth limitations.

Phase Shift, Variable. Control over signal phase shift in stereo playback to vary the apparent image location. The associated time delay introduced in one channel of a stereo signal varies the apparent location of sound coincidence or the acoustic image. Phase delay in one channel makes its image further away than that of the other channel to alter the composite image location.

Phone Connector. A ¼" diameter plug-and-jack connector commonly used for headphones.

Phono Plug. A low-cost coaxial cable plug commonly used on audio and other low-frequency cables. Also called an RCA plug.

PIP. Picture-in-Picture. A small, secondary image screen displayed in one corner of a primary TV image. Selecting an alternate channel for the secondary image permits monitoring one channel while viewing another.

Pixel. An individual dot component of a dot-matrix video image. In color video, each of many thousands of pixels displays in red, green or blue to contribute to the localized screen color. Adjacent pixel colors visually mix to define the composite color perceived.

PLL. Phase-Locked Loop. A frequency-selective feedback loop used for electronic tuning within radio and TV receivers. Provides high-selectivity channel tuning with microelectronic compatible components. Bypasses the need for lossy, large inductor elements in tuning circuits.

Polar Pattern. The spatial responsivity pattern of a microphone. This describes the shape of the region surrounding the microphone that produces the greatest response. Different microphone designs respond to different patterns for different applications. For example, cardiod patterns provide very directional responses suitable for selectively receiving a single audio input. Omnidirectional patterns capture sound from all directions to detect surrounding sounds as well.

Polarity Switch. A phase reverse switch included on some amplifiers to permit phase reversal in a speaker drive. Used to check for speaker phase synchronization. Synchronized speaker drive produces additive sound waves while unsynchronized waves tend to produce canceling effects. In the absence of a polarity switch, simply reversing the two wire connections at one speaker produces the same effect but the time required then makes synchronization more difficult.

Polymer. A synthetic chemical compound, like plastic.

Power. The amount of electrical energy supplied or consumed by a device, such as supplied from an amplifier to a speaker or consumed by the amplifier from the power line, as specified in Watts (W).

Power Amplifier. An amplifier dedicated to higher output power levels but often lacking preamp sensitivity and control functions. Generally used in conjunction with a dedicated preamp to fulfill these other requirements. Such a combination permits largely independent optimizations of input and output features to best serve more sophisticated applications.

Power, Bridged. Power available to a bridge-connected load (speaker). When permitted by the amplifier, the bridge connection of a speaker drives it between two opposing output swings. This drive doubles the speaker’s overall voltage swing to potentially quadruple the drive power. Higher impedance speakers in conjunction with higher power amplifiers most likely realize the full bridged-drive benefit. However, amplifier output power limitations may independently restrict this benefit to a drive power doubling, depending upon the specific conditions of the application.

Power, Full-Bandwidth. That power delivered over the entire specified bandwidth. At higher frequencies, amplifier output power generally becomes restricted by a large-signal bandwidth limit that is distinct from the commonly specified small-signal bandwidth. Larger signals encounter a slew rate limit or maximum rate-of-change that imposes this added restriction. However, the amplifier remains capable of delivering the full bandwidth at a reduced power level.

Power Handling. Power capacity such as the input power rating of a speaker. Sometimes separate short term and long term specifications define this capacity with considerably higher short term ratings that accommodate music transients.

Power Inverter. A DC-to-AC power converter for powering AC devices from a battery source. These inverters transform a DC input voltage into an AC output voltage capable of powering devices designed for line power operation. Often used as a computer’s uninterruptable power source or UPS. Typically restricted in output power capability to short duration demands.

Power Output. The maximum power output available such as from an amplifier output. Higher power output is important for the accurate reproduction of audio signal peaks even if not fully utilized at the average volume level.

Power, Peak. In a speaker system, the maximum instantaneous operating power. A short term capability, this power level exceeds the continuous rating to accommodate signal transients. However, this short term rating does not reflect the more restricted continuous power capability.

PPS. Polyphenylene Sulfide. A type of plastic used in electrical insulation.

PTT. Push-To-Talk. A CB radio feature that leaves the radio in the receive mode until depressing the PTT button switches it to the transmit mode.

Pre-Amp. Pre-Amplifier. A low-level signal amplifier typically used in conjunction with a power amplifier. Pre-amps provide initial signal gain and often include response tuning controls. However, they most often require the addition of a power amplifier for speaker drive.

PTC. Positive-Temperature-Coefficient, as in electronic overload protection devices. Signal current passing through the resistance of a PTC device produces power dissipation that causes temperature rise. In response, the device’s resistance increases to reduce the current flow to a safe level.

Punch Bass. Bass boost. Increased low-frequency audio signal drive to accentuate bass components and/or to compensate for restricted low-frequency speaker response. Especially effective with headphones as size restrictions then preclude the use of lower-frequency transducer elements.

PVC. PolyVinyl Chloride; a flexible plastic often used for wire insulation.

PWM Power Supply. Pulse-width modulated power supply for high power efficiency. A type of switching power supply that increases the power available in response to power demand rather than consuming a high standby power.

PWR. Power.

Q Control. Response selectivity control. Varies the roll-off sharpness of a filter passband to control the selectivity of the band. Higher Q sharpens the response for greater frequency selectivity.

RCA Connector. An economical, coaxial cable plug/jack combination commonly used for audio and lower-frequency video signals. Couples signal and ground thru inner and outer conductors, respectively. Sometimes color coded by function such as signal (red/yellow/white) and ground (black).

RCA Inputs/Outputs. Signal connections presented with RCA connectors. These connectors are economical, plug-in coaxial types commonly used in audio and component video applications.

Regulated. Controlled or stabilized, as in a power supply output that remains insensitive to the varying load demands produced by signal variations. Power supply regulation is typically specified as the percentage variation in rated output voltage produced by regulation error in conjunction with a specified load current demand.

Release Time. The time required to deactivate a limiter following a signal