Car Audio Glossary of Terms


AC: Alternating current. Energy that changes potential at a fixed or regulated rate. Both the electricity in a home, and a musical signal going to a speaker are forms of alternating current.

Active Crossover: A device built with components, such as operational amplifiers and transistors, that requires an external power supply.

Acoustical Energy: Energy created by sound waves.

Acoustics: A science dealing with the study of sound waves.

Advanced MOSFET OFR: A high-performance, amplifier power supply design that can efficiently provide the power needed by the amplifer, while running cool. Advanced MOSFET OFR power supplies are used in JBL mobile audio amplifiers to allow maximum headroom and drive difficult loads.

Ammeter: A device used to measure current flow.

Amperage: A unit of electrical current indicating the force through which energy is pushed through a conductor. Measured in amps.

Ampere: Unit of measurement used to determine the quantity of electricity flowing through a circuit.

Amplification: An increase in signal level.

Amplitude: The measurement of the power of a sound or electrical wave.

Analog: An electrical signal where the frequency and level vary in direct relationship to the original acoustical sound waves that created the signal.

Anode: The electrically positive terminal of an electronic device.

Apex Off-Axial Tweeter: Coaxial speaker design where the tweeter is located in the base of the woofer cone. Apex mounting equalizes signal path length differences of all frequencies handled by the speaker. This ensures all frequencies reach the listener's ear at the same time and improves stereo imaging.

Aquaplas: A strong lightweight cement developed for aerospace applications. Allows speaker cones to maintain their shape regardless of output level.

Attenuate: To reduce the force or volume of a signal.

Audio Frequency Spectrum: The range of human hearing commonly accepted as 20 Hertz (cycles) to 20,000 Hertz (cycles).

Audio Signal: The analog electronic representation of a sound wave.


Bandpass: Allowing a certain range or band of frequencies to pass through a system, while blocking or restricting others. In audio, this can be done electrically in a crossover, or mechanically as in a bandpass subwoofer box.

Baffle Board: The board to which speakers are mounted in a box.

Bandwidth: The upper and lower usable frequency limits of a device.

Barium Ferrite: A material capable of maintaining a strong magnetic force.

Basket: The outside frame of a speaker that supports the cone and the magnet.

Bass: Low-frequency audio signals below 500Hz.

Bass Reflex: A vented or ported speaker enclosure.

Bessel: A crossover design that places emphasis on phase and transient response over reducing ripple.

BL: The electrical motor strength of a speaker.

Boomy: Bass reproduction that has a noticeable peak in the midbass or upper bass region.

Boprene: A type of butyl rubber surround that has excellent damping characteristics and is extremely environmentally stable.

Bridging: Combining the outputs of two amplification channels to provide one more powerful channel.

Butterworth: A filter with a pass band allowing no ripple, but sacrifices steepness in the attenuation slope.

Bump Back Magnet: A magnet design that minimizes the chance for speaker "bottoming."

Butyl: A type of rubber used for speaker surrounds. Butyl has very good damping characteristics and is resistant to UV contamination from the sun.


Capacitance: The property of storing an electrical charge between two separate conductors.

Capacitor: An electronic device that can store energy and release it as needed. A capacitor works by resisting a change in voltage, making it useful in crossover circuits. Capacitors are rated in farads, or more commonly microfarads or millionths of a farad.

Cathode: The electrically negative pole of a device.

Channel: An amplifier section providing positive and negative signal information for a speaker. Two channels are used to process a stereo signal.

Chassis: The metal frame of a vehicle.

Chebyshev Filter: A crossover that allows some signal ripple in the pass band but allows an attenuation slope that is steeper than a Butterworth design.

Clamshell: Operating two subwoofers face to face on the same baffle board and electrically out of phase with each other. A type of "compound loading," it allows a subwoofer to operate in a smaller box.

Clipping: A distorted signal generated by an amplifier that is being operated over its capabilities. Clipping describes the actual "cutting off" of signal peaks of an electrical signal at the amplifier's power limit. This is the sound often heard when a system is played too loud and the sound starts to "break up." Clipping distortion is the most common source of speaker damage.

CMS: The mechanical compliance of a speaker suspension.

Common Sense Turn-on: The ability of amplifiers or outboard devices to be turned on by an incoming speaker-level signal.

Compliance: The volume of air in cubic feet that is equal to the compliance of the total suspension of a speaker.

Component Speaker System: Separating the units of a coaxial speaker into a tweeter and a woofer or midrange driver. This allows for better placement in a car environment, improving the stereo image.

Compound: Using two subwoofers coupled together in a small airspace. It allows a woofer to be used in a smaller enclosure. Compound loading can be done by clamshelling or positioning the woofers front to back.

Cone: The part of a speaker that moves.

Constant Bass: The ability of an active crossover to maintain a constant bass output regardless of the position of a system fader control.

Curvilinear Cone: A cone design pioneered by JBL that allows for better midrange and off-axis performance.


d: The system damping factor of a 4th order bandpass box.

Damping: The reduction of resonant energy in a speaker, or between a speaker and amplifier.

DC: Direct Current. Power derived from a battery or rectified source where electrons flow only in one direction.

DC Resistance: The resistance a device produces for a DC current. Direct measurement by a digital multimeter or a volt/ohm meter gives DC resistance.

Decibel: A measurement of sound pressure, or relative intensity of sound. It should be noted that decibels are logarithmic in nature. An increase of 10dB from a certain point represents a doubling of sound output. From an audio standpoint, doubling the sound output of a system will require 10 times the power.

dB: Decibel.

DMM: Digital Multimeter. A digital meter that "samples" electrical input to give very accurate readings of voltage, current, or ohms.

Diamond Pattern Surround: A patented method that JBL uses to control high-frequency resonances in single-piece titanium speaker diaphragms.

Dia: The usable piston diameter of a driver.

Die Cast Aluminum Baskets: Driver baskets that are cast from aluminum. Cast baskets are much stronger than stamped steel and allow for tighter production tolerances and precise driver operation under even the most demanding situations.

Differential Input Circuit: A circuit used by JBL amplifiers that re-creates a preamp-level signal from a high-level signal that is of preamp quality. This method produces a signal that is much lower in distortion than the methods commonly used in other amplifiers.

Diode: An electronic device that blocks current flow in one direction, but allows it in another.

Discrete Circuitry: The use of separate components such as resistors, capacitors, and diodes instead of ICs (Integrated Circuits) which "print" these components in microscopic size on a chip. Discrete components allow for tighter tolerances, and higher performance (especially in amplifier output stages), are less heat sensitive, and make better-sounding components.

Distortion: Sound that has been changed from the original performance. The three major forms of electronic distortion in audio are clipping distortion, harmonic distortion, and intermodulation distortion.

Driver: Another name for a speaker.

Dv: The inside diameter of a vent or port.

Dynamic Range: The difference between the loudest and softest sounds that can be reproduced by a device or format.


E-M: The electro-mechanical parameters of a loudspeaker.

EBP: The efficiency bandwidth product. (Fs/Qes)

Edgewound Ribbon Voice Coil: A practice pioneered by JBL where wire is flattened into a metal ribbon and then wrapped on edge to form a voice coil. This allows for the greatest amount of wire to be located in the gap, increasing performance.

Efficiency: The measure of an amplifier or speaker's ability to convert input power to work. Expressed as a percentage.

Electrolytic Capacitor: The most common form of capacitor consisting of a conductive film in an electrolyte. These are canister-shaped and come in the widest range of values. Stiffening caps are electrolytics.

Excursion: The amount of movement a speaker cone is capable of.

Extended Pole Piece: A design innovation that allows for increased excursion while decreasing distortion by operating the voice coil over a longer throw.


Fb: The resonant (tuned) frequency of a vented box. Expressed in Hertz (Hz).

Fc: The resonant frequency of a sealed box. Expressed in Hertz (Hz).

F3: The half power (-3dB) of a loudspeaker enclosure design. (Hz)

Fp: The free-air resonant frequency of a passive radiator. (Hz)

Fs: The free-air resonant frequency of a driver. (Hz)

Farad: The basic unit of capacitance. Outside of stiffening caps, the most common values of capacitors are in microfarads, or millionths of a farad.

Fill: Polyfill or something similar used to "stuff" a box. When placed inside a box, fill makes the box seem larger to the woofer, and helps break up standing waves within the box.

Flat Response: The ability of a speaker or amplifier to reproduce all points of the frequency band equally, without dips or peaks when referenced to the original input.

Free Air Resonance: The frequency at which a driver will naturally resonate.

Frequency: The number of vibrations or cycles completed by a signal in one second. Frequency is expressed in cycles, or more commonly, Hertz (Hz).

Frequency Response: The usable frequency bandwidth of a speaker, amplifier, or source unit. Usually stated as lower to upper frequency with a deviation in decibels, or relative loudness. Example: Frequency Response of 10Hz to 40kHz +/- 1dB.

Fuse: A device designed to protect other electronic devices by melting and opening the circuit when the system is drawing too much power.


Gain: The amount of amplification applied to a signal.

Gap: The space between the magnet and the pole piece in a speaker's motor assembly that houses the voice coil.

Generator: A rotating device that creates DC current.

Ground: Any place having an electrical potential of zero. In mobile audio, ground is typically used as the term for the vehicle chassis.

Ground Loop: A situation where electrical potential exists between two grounding points on the same vehicle.


Harmonic: A weaker overtone or undertone of a musical note that is responsible for the character or texture of the note.

Harmonic Distortion: Distortion that is harmonic in nature, following the natural harmonics of the original signal. This is the least noxious form of distortion.

Head Unit: A factory or aftermarket car radio, especially with CD or cassette.

Hertz (Hz): The basic unit of frequency. The number of full cycles completed by an alternating signal in one second.

High Current Design: An amplifier that is able to supply the electrical current demanded by a reactive, low impedance driver, while maintaining output voltage.

High Frequency: The highest audible frequencies. Generally accepted as those over 5,000 Hz.

High Pass Filter: A device or network of components that blocks low (bass) frequencies below a designated point, and allows high frequencies to pass.

High-Polymer Laminate: A type of speaker cone that consists of a natural substrate with a coating of a special polymer to reduce cone resonance and increase strength. HPL cones are extremely durable and keep their shape under extreme conditions, providing tight bass and excellent dynamics.


Imaging: The sensation, provided by a well-designed, high-quality audio system, that the performers on the recording are actually performing in real space in front of the listeners.

Impedance: The resistance of a device to the flow of alternating current. Often used to rate the resistance of a speaker's voice coil.

Inductive Coupling: Noise that is transmitted through a magnetic field to surrounding wires.

Inductor (Coil): An electrical component which increases impedance with an increase in frequency. Often used in passive crossovers, inductors are rated in henries.

Infinite Baffle: A speaker mounted in a board with no side or rear panels. Also called "free-air." Technically speaking, a speaker can be considered infinite baffle if it is in a sealed enclosure that is larger than the Vas of the driver.

Intercooling: A design feature of JBL's GTi subwoofers that draws cooling air into the motor structure and vents out heated air.

Intermodulation Distortion: Distortion created by a device that is not harmonic with the original signal. Since it is not harmonics of the original signal, intermodulation distortion is often described as "harsh and grating," and tends to be more noticeable than harmonic distortion. Intermodulation distortion is often the result of poor amplifier design or the use of excessive amounts of negative feedback in the circuit. Systems that are fatiguing to listen to often have high rates of intermodulation distortion.

Intermount: A speaker mounting system JBL has developed where a mounting ring is first fastened to the car and the speaker is fastened to the mounting bracket. This method not only allows for easier installation, but in the case of Intermount II, allows for the use of a larger cone in the speaker, creating added efficiency and bass response.

Isobaric: The mounting of two speakers in a way that will couple their output. This can be done by mounting the drivers in a back-to-front, or front-to-front (clamshell) arrangement with the drivers mounted out of phase with each other. This method of box construction allows the use of a smaller than normal box.


Joule: A unit of energy that equals one watt delivered in one second.


Kevlar Cones: Constructing speaker cones using Kevlar. Kevlar is an aramid fiber that is extremely strong and light, making it an excellent choice for speaker cones and bullet-proof vests.

Kirchoff's Current Law: All current entering a point in a circuit must equal the sum of all the current leaving that point.

Kirchoff's Voltage Law: The voltage applied to a DC circuit must be the same as all of the voltage drops within the circuit.

kHz: Abbreviation for kilohertz or thousands of Hertz or cycles.


Le: The inductance of a voice coil.

Lv: The length of a vent or port.

Loudspeaker: An electro-acoustic transducer that converts an electrical signal to audible sound waves.

Low Frequency: Generally refers to sound within the 40Hz to 160Hz band.

Low Pass Filter: A device or network of components that block high frequencies at a designed point, and allows bass frequencies to pass.


Mms: The mechanical mass of a loudspeaker diaphragm including air load.

Magnet: The device at the back of a speaker that provides a stationary magnetic field to attract or repel the voice coil as the signal passes through it.

Midrange Driver: A speaker that is designed to reproduce midrange frequencies, where most musical information lies.

Midwoofer: A speaker that is designed to reproduce the upper bass frequencies, typically between 80Hz and 200Hz. Small subwoofers are often used as midwoofers in order to integrate a larger woofer, or add midbass "punch."

Milliamps: Thousandths of an amp.

Mineral Filled Co-Polymer Cone: A very light and rigid cone material that combines high strength and exceptional damping characteristics. JBL uses this on the GTx subwoofer line for high SPLs and excellent transient response.

Multiple Power Supplies: Putting more than one power supply in an amplifier. JBL will often use multiple power supplies on large amplifiers to improve performance in difficult situations.


No: The reference efficiency of a driver with a half-space acoustical load.

Negative Feedback: The practice of returning some of an amplifier's, or amplifier stage's, output to its input 180 degrees out of phase. This has a tendency to reduce distortion and make an amplifier more stable. Too much reliance on negative feedback results in very high IM (intermodulation distortion) readings, and poor sonic performance.

Neodymium: A rare earth magnet that is 10 times stronger than standard ferrite magnets.

Nominal Impedance: The stated impedance rating of a speaker. This is used by a manufacturer to represent the load the speaker will provide to an amplifier.


Octave: A doubling or halving of frequency. Example: 80Hz is one octave above 40Hz.

Ohm: Basic unit for measuring resistance.

Ohm's Law: The basic relationship between current, voltage, and resistance. Ohm's law states that voltage = current x resistance, current = voltage/resistance, and resistance = voltage/current.


Pe: The maximum continuous (RMS) power-handling capability of a speaker.

Parallel Wiring: Connecting two or more devices to a common voltage point so that each device carries the full applied voltage.

Pass Band: The band of frequencies that a bandpass crossover or bandpass speaker enclosure will allow to pass.

Passive Radiator: Often called a "drone cone." A speaker with no motor assembly that resonates in response to a driven speaker in an enclosure. Passive radiators act very much like a vent or port in a speaker.

Peak: An emphasis on a relatively narrow band of frequencies, typically less than one octave in width.

Period: Amount of time required for one cycle of a sound wave to occur.

Phase: The timing of a sound or electrical wave. Phase is measured in degrees, from 0 to 360. 180 degrees would be perfectly out of phase and often causes signal cancellation in lower frequencies.

Parallel Sixth Order Bandpass Enclosure: The most common type of sixth order enclosure where both vents or ports fire outside the enclosure.

Polarity: Being electrically positive or negative.

Pole Piece: The metal pole attached to the magnet structure in a speaker's motor assembly that is surrounded by the voice coil, forming the inside wall of the gap.

Poly-tex: Textured polypropylene speaker cones, proprietary to JBL's GTO line of mobile audio speakers. The textured surface helps to break up harmonic resonances that travel along the cone surface, improving midrange response.

Port: A vent or tube tuned to extend the usable response of a woofer in an enclosure.

Potentiometer: A variable resistor used to attenuate a signal.

Power: The amount of energy in Joules that a device uses or delivers divided by the time the energy was used or delivered.

Power Line Noise: Varying AC noise in a car that is heard as a whining that increases or decreases with engine speed.

Power PMP Cones: Injection-molded PolyMethlyPentene woofer cones used on JBL's Competition Series GTX Multi-element speakers. PMP is much lighter and stiffer than either polypropylene or paper, resulting in excellent transient and bass response. PMP's superior damping characteristics also dramatically improve midrange clarity.

Pre-Amp Outputs: Facilities on an amplifier, signal processor, or source unit that pass a low level signal to an amplifier for further amplification.

Pure Titanium Dome Tweeters: JBL uses pure titanium domes in high-end speakers. Titanium is extremely light and stiff, making it an excellent choice for making tweeters.

Push-Pull Configuration: See Clamshell.


Q: System losses or relevant damping in an enclosure. Defined as the ratio of stored to dissipated energy.

Qec: The Q of a speaker in a sealed box considering only electrical resistance.

Qes: The Q of a speaker at Fs considering only electrical resistance.

QL: The Q of a vented box resulting from box losses.

Q't: The total Q of a speaker's suspension when considering the load of the sealed chamber of a 4th order enclosure.

Qmc: The Q of a speaker in a sealed box considering only mechanical resistance.

Qms: The Q of a speaker at Fs considering only mechanical resistance.

Qtc: The Q of a speaker in a closed box considering both electrical and mechanical resistance.

Qts: The Q of a speaker at Fs in free air considering both electrical and mechanical resistance.

Quiescent Current: Amount of current a device consumes when not doing work.


Re: The DC resistance of a speaker voice coil.

Rms: The mechanical resistance of a speaker's suspension losses.

Remote Out: A "turn on signal" source for amplifiers and signal processors.

Resistance: The property of some materials to restrict the flow of electricity. Measured in ohms.

Resonance: The tendency of an object to vibrate at a certain frequency.

Ripple: Any deviation from flat response in a passband.

Rip Stop Spiders: Spiders made of high strength synthetic (often aramid based) materials that are resistant to tearing.

RMS: Root Mean Square. Method used to calculate continuous average power output of an amplifier.

Roll-off: The attenuation of frequencies above or below a certain point.


Sd: Piston area of a speaker.

Sens: Sensitivity

Sensitivity: A measurement of the sound output of a speaker or speaker system's output relative to the power put in. Typically measured in dB at 1 watt of input, 1 meter away.

Series Wiring: A circuit where components are wired sequentially, dividing the voltage between them.

Series-Parallel: A circuit where there are components wired in series and in parallel to get the desired result. This is often used in multi-woofer systems to optimize the impedance seen by an amplifier.

Series Sixth Order Enclosure: An enclosure consisting of a vented box with its port firing into another vented box.

Short Circuit: The situation that occurs when there is an alternate path created between the positive and negative portions of a circuit, bypassing some or all of the components of the circuit and preventing operation.

Simultaneous Stereo/Mono: The ability of an amplifier to drive three speakers from two channels, deriving either a subwoofer or center channel signal from the two other channels.

Small, R.H.: A pioneer in the study of the relationships of speakers and enclosures. Along with A.N. Theile, Small spelled out what is still the basis for speaker enclosure design.

Sound: Acoustical energy in waves generally accepted to be between 20 and 20,000 cycles per second.

Sound Pressure Level: Acoustic measurement for sound output. Measured in dB, the readings are often "weighted" to reflect how human ears work.

Spider: The part of the speaker attached to the junction of the cone and voice coil that keeps the voice coil aligned in the gap and helps suspend the cone.

SPL: Sound Pressure Level

Stray Field Containment Geometry: A speaker motor assembly designed to reduce stray magnetic fields around the speaker and focus the energy in the voice coil gap. Proprietary to JBL, this method is used in high-end products such as the GTi competition series.

Subwoofer: A speaker or speaker/enclosure system designed to reproduce only bass frequencies. Generally used only below 80Hz.

Symmetrical Field Geometry: A speaker motor assembly design that maintains equal magnetic force throughout the travel of the voice coil. This improves bass response and substantially reduces distortion.


Theile-Small Parameters: A series of driver measurements developed by A.N. Thiele and R.H. Small that models how a speaker will work with an enclosure.

Textured Polypropylene Cones: See Poly-Tex.

Thiele, A.N.: A pioneer in studying speaker/enclosure relationships. Along with R.H. Small, defined what is currently accepted as the basis for enclosure design.

Titanium: A strong, lightweight metal, often used in high-stress situations, e.g., in the manufacture of space vehicles, race cars, airplanes, and medical replacements. JBL has long been a proponent of using titanium for speaker and compression horn diaphragms.

Titanium Composite: Combination of titanium and a special polymer. This material benefits from the strength and lightness of titanium as well as the damping qualities of a polymer to make tweeter diaphragms and speaker cones that are strong, lightweight, and capable of extremely accurate reproduction.

Titanium Composite Injection Molded Curvilinear Cones: Speaker cones made from a titanium/polymer composite that are molded into a curvilinear shape and result in a strong lightweight cone that is capable of excellent bass and transient response, as well as a clear uncolored midrange.


Universal Interface: A JBL innovation that allows amplifiers and other outboard electronics to operate from any type of input from a factory car stereo. The Universal Interface will create a pre-amp quality signal from high power, standard power, or balanced outputs.


Vap: Volume of air having the same compliance as the suspension of a passive radiator.

Vas: Volume of air having the same compliance as the suspension of a speaker.

Vb: Internal volume of a box with a vent or passive radiator.

Vc: Internal volume of a sealed box.

Virtual Center Image Enhancement: The ability of the JBL GTP4 processor to simulate a center channel signal, creating a three-dimensional center image without actually using a center channel speaker.

Voice Coil: A coil of wire attached to the rear of the speaker cone that works with the magnet to provide a motor to drive the speaker. The hookup wires for a speaker connect the head unit or amplifier output to the voice coil.

Voltage: Electrical pressure that can do work.

Voltage Drop: The amount of energy used by a device that has resistance in a circuit.

Volt: The basic measurement of electrical pressure in a circuit.

Volume: Number of cubic feet, cubic inches, or liters of space in a speaker enclosure.

VOM: Volt-Ohm Meter. An analog meter that reads Voltage, Ohms, and Milliamperes.


Watt: The basic measuring unit for electrical or acoustical power.

Wattage: Electrical power.

Waveform: The shape of a sound or electrical wave.

Woofer: A speaker that is designed to reproduce bass frequencies. Generally refers to a large dynamic driver.


Xm: Xmax.

Xmax: The amount of linear travel a cone can make while still being controlled by the voice coil.



Z: The nominal impedance of a driver.