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Car Audio Glossary

Use this glossary for quick explanations of common car-audio terms. Follow the links for more detailed information.

A

AGM Battery — Absorbent Glass Mat battery technology commonly used in automotive electrical systems. AGM batteries can provide useful energy storage, but adding a battery does not increase alternator charging output. Learn about AGM vs. lithium batteries →

Alternator — The engine-driven electrical generator responsible for supplying electrical power and charging the battery while the engine is running. Learn how alternator capacity affects car audio →

Amplifier Current Draw — The electrical current an amplifier requires from the vehicle's electrical system. It can be estimated using RMS output, operating voltage, and amplifier efficiency. Learn how to calculate amplifier current draw →

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B

Big 3 Upgrade — Upgrading important charging and grounding conductors between the alternator, battery, engine, and/or chassis to improve current paths and reduce voltage drop. A Big 3 upgrade does not increase the alternator's actual output capacity. Learn when you need a Big 3 upgrade →

BL — A Thiele/Small parameter representing motor force factor. It relates to the interaction between the magnetic field and voice coil. Learn about T/S parameters →

Bridging — Combining two compatible amplifier channels to drive a single load. Bridged minimum impedance and RMS output must be verified from the exact amplifier specifications rather than inferred from stereo ratings. Learn about amplifier bridging →

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C

Clipping — A condition in which an amplifier is driven beyond its clean output capability and can no longer reproduce the waveform properly. Excessive clipped power can contribute to speaker damage. Learn about amplifier clipping →

Cms — Suspension compliance, a T/S parameter describing how compliant or flexible a driver's suspension is. Learn about T/S parameters →

Crossover — A filter used to control which frequencies are sent to a speaker or subwoofer. Learn about crossover settings →

Crossover Slope — The rate at which frequencies are attenuated beyond a crossover point, commonly expressed in dB per octave. Learn about crossover settings →

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D

DVC (Dual Voice Coil) — A subwoofer with two separate voice coils. DVC designs provide additional wiring possibilities when matching subwoofers to an amplifier. Learn about SVC vs. DVC subwoofers →

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E

EBP (Efficiency Bandwidth Product) — A calculated value based on certain T/S parameters that can provide general information about driver behavior. It should not be used by itself to select an enclosure. Learn about T/S parameters →

Enclosure Displacement — Internal enclosure volume occupied by the subwoofer, port, bracing, and other structures. These displacements may need to be subtracted when calculating net airspace. Learn about gross vs. net enclosure volume →

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F

Final Impedance — The electrical load the amplifier sees after all applicable speakers or subwoofer voice coils are connected. Learn about 1-ohm, 2-ohm and 4-ohm systems →

Fs — Free-air resonant frequency. This T/S parameter identifies the frequency at which the driver's moving system naturally resonates in free air. Learn about Fs and other T/S parameters →

Fuse — A circuit-protection device intended to interrupt excessive current before the protected wiring is damaged. Learn how to choose amplifier fuse size →

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G

Gain — An amplifier input-sensitivity adjustment used to match the amplifier's input stage to the source signal. Gain is not a volume control. Learn how to set amplifier gain correctly →

Gross Box Volume — Internal enclosure volume before applicable displacement from the subwoofer, port, bracing, and other internal structures is subtracted. Learn about gross vs. net airspace →

Ground — The electrical return path for the amplifier. A poor ground connection can contribute to voltage drop and system problems. Learn about car-audio power and ground wiring →

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H

High-Output Alternator — An alternator designed to provide greater electrical output than the vehicle's original charging system, when properly selected for the application. Learn when a high-output alternator may be needed →

HPF (High-Pass Filter) — A crossover filter that allows frequencies above its selected region to pass while attenuating lower frequencies. Learn about crossover filters →

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I

Impedance (Ω) — The AC opposition to current presented by a speaker or subwoofer to an amplifier, commonly represented by a nominal impedance such as 1Ω, 2Ω, 4Ω, or 8Ω. Learn about car-audio impedance →

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L

Le — Voice-coil inductance, typically measured in millihenries (mH). It is one of the electrical parameters used to describe a loudspeaker driver. Learn about T/S parameters →

Lithium Battery — A broad category of battery technology that can provide high current capability and energy storage. Chemistry, BMS, charging voltage, charging limits, alternator behavior, and vehicle compatibility must be evaluated before use. Learn about lithium vs. AGM for car audio →

LPF (Low-Pass Filter) — A crossover filter that allows frequencies below its selected region to pass while attenuating higher frequencies. It is commonly used with subwoofers. Learn how to set subwoofer crossovers →

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M

Mms — The total moving mass of a loudspeaker driver's moving assembly as represented in its T/S parameters. Learn about T/S parameters →

Mounting Depth — The physical depth required behind a speaker or subwoofer mounting surface. Diameter alone does not determine whether a replacement speaker will fit a vehicle. Learn about car-speaker fitment →

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N

Net Box Volume / Net Airspace — The usable internal enclosure volume remaining after applicable internal displacement is subtracted from gross internal volume. Learn how to calculate net airspace →

Nominal Impedance — The standardized impedance rating used to describe a speaker or subwoofer, such as 2Ω or 4Ω. Actual impedance varies with frequency and should not be confused with a simple DC resistance measurement. Learn about speaker impedance →

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O

OFC (Oxygen-Free Copper) — Copper conductor material commonly used for quality car-audio power and ground wiring. Wire selection should also account for current demand and cable length. Learn about car-audio wire sizing →

Ohm (Ω) — The unit used to express electrical resistance and impedance. In car audio, speaker and subwoofer nominal impedance is a critical part of amplifier matching. Learn about 1Ω, 2Ω and 4Ω car audio systems →

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P

Parallel Wiring — A wiring configuration that reduces the resulting impedance when identical speaker or voice-coil loads are connected in parallel. Learn series vs. parallel wiring →

Port Area — The cross-sectional area of a vent in a ported enclosure. Adequate port area is important because a mathematically correct tuning frequency alone does not guarantee adequate airflow capability. Learn about port area and tuning →

Port Length — The effective length of a vent used along with enclosure volume and port area to achieve a target tuning frequency. Learn about port tuning →

Port Tuning / Fb — The resonant tuning frequency of a vented or ported enclosure. Learn how to tune a ported subwoofer box →

Ported Enclosure — A subwoofer enclosure using a tuned vent or port. Ported designs require careful consideration of net volume, port area, port length, and tuning frequency. Compare sealed vs. ported subwoofer boxes →

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Q

Qes — Electrical Q. A T/S parameter describing the electrical damping of a loudspeaker driver around resonance. Learn about T/S parameters →

Qms — Mechanical Q. A T/S parameter describing the mechanical damping of a loudspeaker driver around resonance. Learn about T/S parameters →

Qts — Total Q. A T/S parameter representing the driver's combined electrical and mechanical damping around resonance. Learn about Qts and other T/S parameters →

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R

Re — DC resistance of a loudspeaker's voice coil. Re measured with a meter is normally different from the speaker's nominal impedance rating. Learn about T/S parameters and Re →

RMS Power — A continuous power rating used as the primary basis for properly matching amplifiers with speakers and subwoofers. MAX or Peak ratings should not be substituted for RMS ratings when system matching. Learn how to match amplifier and subwoofer RMS power →

Round Port — A cylindrical vent used in a ported enclosure. Diameter and length must be selected based on enclosure and tuning requirements rather than subwoofer diameter alone. Learn how to calculate round-port diameter and length →

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S

Sd — Effective cone area of a loudspeaker driver. Along with excursion, it contributes to the driver's displacement capability. Learn about Sd, Xmax and T/S parameters →

Sealed Enclosure — An airtight subwoofer enclosure without a port. Sealed and ported designs have different characteristics and neither is automatically best for every application. Compare sealed vs. ported boxes →

Series Wiring — A wiring configuration in which the impedances of the connected loads are added together. Learn series vs. parallel wiring →

Slot Port — A rectangular port commonly constructed as part of a subwoofer enclosure. Its area, length, displacement, and relationship to net enclosure volume must be considered during design. Learn how to design a slot-ported enclosure →

Subsonic / Infrasonic Filter — A high-pass filter used to attenuate very-low-frequency content below a selected frequency. It can be particularly important in some ported subwoofer systems. Learn about subsonic filters →

SVC (Single Voice Coil) — A subwoofer with one voice coil and one corresponding nominal impedance. Learn about SVC vs. DVC subwoofers →

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T

T/S Parameters (Thiele/Small Parameters) — A group of electrical and mechanical parameters used to describe loudspeaker-driver behavior. Common parameters include Fs, Qts, Vas, Xmax, Sd, Re, Le, Mms, Cms, and BL. Learn how to read subwoofer T/S parameters →

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V

Vas — Equivalent compliance volume. A T/S parameter related to the compliance of the driver's suspension. It is not simply a recommended enclosure-volume specification. Learn about Vas and other T/S parameters →

Vd (Volume Displacement) — A measure related to how much air a driver can displace, based on effective cone area and linear excursion. Learn about Vd, Sd and Xmax →

Voice Coil — The electrical coil in a loudspeaker motor assembly. Subwoofers may use single or multiple voice coils, and the number and impedance of those coils affect available wiring configurations. Learn about SVC and DVC subwoofers →

Voltage Drop — A reduction in electrical voltage caused by resistance in wiring, connections, grounds, or other parts of the electrical path, especially as current demand increases. Learn about proper power and ground wiring →

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X

Xmax — Maximum linear excursion of a loudspeaker driver as specified by the manufacturer. Xmax is useful when evaluating a driver's mechanical capabilities and displacement potential. Learn about Xmax and other T/S parameters →

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Plan the Complete System

Car audio components should not be selected in isolation. The vehicle's electrical capacity, amplifier current demand, impedance, speaker and subwoofer RMS capability, enclosure, wiring, fusing, crossovers, and tuning all affect one another.

If you're planning a new system and aren't sure where to begin, start here:

Massive Audio's Complete Car Audio System Planning Guide

Plan the complete system first, then select components that work together!