1-Ohm Stable
Refers to an amplifier’s ability to operate when wired to a speaker load that offers a 1 ohm impedance.
2-Ohm Stable
The amplifier can operate safely when connected to a 2-ohm load (two 4-ohm speakers wired in parallel to one channel of the amplifier), producing up to 100% more power than if connected to a 4-ohm load
The study of sound. The science of production, effects, and transmission of sound waves through various mediums and the effects of absorption, diffraction, interference, reflection, and refraction.
A device that is turned by a motor to produce AC voltage, which is then rectified (turned into DC) and used to supply voltage to the vehicle’s electrical system.
(a) A device which increases the level of a signal by increasing the current or voltage. (b) May also be used to isolate or control a signal and even decrease the level as in a line output converter.
American Wire Gauge (AWG)
A standard of the dimensional characteristics of wire used to conduct electrical current or signals. AWG is identical to the Brown and Sharpe (B & S) wire gauge.
Amplifier, Power
An amplifier designed for driving loudspeakers and having a higher power output than a line amplifier or preamplifier.
Auxiliary Input
An input on the face or rear of the receiver that enables you to connect a plug-and-play satellite radio tuner or portable music player (CD, MP3, or cassette) to the receiver. The input jack can be either Mini or RCA.
A two-part filter that cuts both high and low frequencies allowing the band of frequencies between these two points to pass.
The range of frequency response between lower and upper frequencies points which audio signals pass through an electrical device or conductor where the signal has rolled off by three decibels.
The rigid frame of a speaker that supports all of it’s components.
The low audio frequency range typically below 500 Hz (hertz).
An electrically connected group of cells, wired in series, that stores an electrical charge and supplies a direct current (DC).
Combining two outputs of an amplifier to use as one, usually to a woofer. The provides an increase in power output (wattage) necessary to reproduce lower frequencies at higher volume levels.
Butyl Rubber Surround 
Butyl rubber has greater internal loss than standard urethane, preventing harmonic distortion at higher frequencies. It more efficiently absorbs edge reflections that can cause audible distortion, resulting in clearer bass performance
The ability of a conductor or dielectric to store electric charge.
Power stabilizing capacitors store the necessary power amplifiers need to punch larger bass notes while limiting clipping. They store energy during intervals when it is not required, which is most of the time, and release it when demand exceeds what is available from the car’s power system
Cast Basket 
A type of speaker basket or frame that is cast as a single piece of relatively thick, rigid metal. This contrasts with a Stamped frame that is shaped by pressure, much like a car body fender. Cast metal is heavier and more rigid, and thus less likely to “ring” at certain frequencies, and will hold its shape somewhat longer against the pull of gravity. This is mainly advantageous in the larger woofers of 12″ or greater. Smaller drivers will likely not benefit perceptibly from being cast.
CEA-2006 Compliant
On May 28, 2003, the Consumer Electronics Association published standard CEA-2006, “Testing & Measurement Methods for Mobile Audio Amplifiers.” This “voluntary” standard advocates a uniform method for determining an amplifier’s RMS power and signal-to-noise ratio. Using 14.4 volts, RMS watts are measured into a 4-ohm impedance load at 1 percent Total Harmonic Distortion (THD) plus noise, at a frequency range (for general purpose amplifiers) of 20 Hz to 20,000 Hz. Signal-to-Noise ratio is measured in weighted absolute decibels (dBA) at a reference of 1 watt into 4 ohms. This applies to both external amplifiers and the amplifiers within in-dash receivers.
The metal frame of the vehicle.
1 Any closed path followed by electrical current. 2 A configuration of electrically or electromagnetically connected components or devices.
A speaker composed of larger cone for low range frequencies and a smaller cone or tweeter for higher frequencies aligned on the same axis. A crossover network is necessary to route the proper signals to each driver. These may be passive (usually included). If the speakers are bi-amplified, an active crossover will be used to route the proper range of frequencies to the respective amplifier channels.
The most common shape for the radiating surface of a loudspeaker referred to as the part that moves the air.
A selective filter, which splits signals into different frequency bands that can be fed independently to separate speakers. A passive crossover filters signals after they have been amplified. An active crossover (more effective and flexible) filters signals before amplification, sending different signals to different amps.
Crossover (High-Pass Filter)
A built-in high-pass filter allows only frequencies above the crossover point to pass through. This filter may work with the speaker outputs, preamp outputs, or both.
Crossover (Low-Pass Filter)
A built-in low-pass filter allows only low frequencies to pass through. This filter may work with the speaker outputs (very rare), preamp outputs, or both.
Separate speakers, usually a tweeter and mid-range with appropriate crossover.
The rate of flow of electricity, measured in amperes (amps).
Decible – dB
One-Tenth of a Bel. This is a measurement of the comparative strength of two powers, and can be applied when measuring any signal in the audio, video, and electromagnetic spectrum. If two powers differ by one Bel, there is a difference of 10 times the power. If comparing amplifiers, where one is rated at 10 watts while the other is 100 watts, then we have a difference of 10 decibels, or one Bel. Decibels should be understood as ratios, not fixed quantities.
Digital Filter
Circuit that removes unwanted digital artifacts from the signal while it is still in the digital domain, allowing the use of more gently-sloped, better-sounding analog filters.
An electrical circuit element that allows current to flow in one direction.
Direct Current (DC)
In a capacitor, the release of stored energy to a load. In a battery, the conversion of chemical energy to electrical energy.
Sound that is modified or changed in some way. Measured as a percentage of the whole signal.
Digital Signal Processing (or Processor). A type of processing accomplished by a microcomputer chip specifically designed for signal manipulation, or a component using such processing. The term is often misused as a synonym for ambience synthesizer; however, DSP can do much more than sound field creation.
The ratio of energy output to total energy input, expressed as a percentage. With speakers, this refers to the ratio of total acoustic watts radiated to total electrical watts input.
A box housing a speaker to separate the front sound waves from the rear sound waves.
A built-in EQ lets you tailor the sound to your listening tastes and to your vehicle’s acoustics. Receivers with built-in EQs will have one or more equalizer “bands” in addition to standard bass and treble controls. These equalizer “bands” usually have fixed center frequencies and bandwidths (although some may be adjustable).
Equalizer Presets
Preset EQ curves are stored tone settings — boosting and cutting different frequencies can make big changes in the way your music sounds. Preset EQ curves are stored in memory, and are easily activated. If you listen to a wide variety of music, these presets are useful for making dramatic tonal changes instantly. (For example, you could use one EQ preset with heavy bass boost for rap or reggae, and a second preset with flat bass and a slight midrange/treble boost for jazz. This saves you from constant readjustment of the tone controls.)
-3 dB cutoff frequency, in Hz
Enclosure resonance (usually for bass reflex systems), in Hz
Driver free air resonance, in Hz. This is the point at which driver impedance is maximum. “This parameter is the free-air resonant frequency of a speaker. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you’ve ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from ‘ringing’. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well.”
A device that protects electric circuits by interrupting power in a circuit when an overload occurs. Rated in amperes (amps).
The basic unit of capacitance. A capacitor has a capacitance of 1F when a charge of 1 Volt across the capacitor produces a current of 1 Ampere through it. Named after Michael Faraday.
The cylindrical portion of a speaker’s voice coil section. A wire is wound around this cylinder to form a coil such that when current interacts with the magnetic field it produces a pumping motion that alternatively compresses and rarifies air, and creates the velocity for such air masses to reach our ears as sound.
The amount of amplification used in an electrical circuit. Ground: The electrical neutral line having the same potential as the surrounding earth; the negative side of a direct current power system; the reference point for an electrical system.
Ground Loop
A ground loop occurs when any piece of equipment or any incoming wire is connected to a different ground or grounds. If your in-dash receiver and amplifier are grounded to different locations, for example, a ground loop may occur. In this situation, the multiple ground paths can, in effect, act as an antenna for interference. The interference is turned into noise, and you hear it in your system.
Hertz (Hz)
The unit of measurement for frequency. 1 Hz is equal to 1 cycle per second.
High Pass Filter
A network of elements used to attenuate all frequencies below a predetermined frequency. Frequencies above the cutoff point pass without any effect.
Term which refers to a set of speaker components used to reproduce frequencies above 500 Hz as in a set of separates. May also refer to tweeters which are used to reproduce frequencies usually above 2.5 kHz. Not bass.
International Auto Sound Challenge Association
The opposition to the flow of alternating current (AC) in a circuit. Measured in ohms.
Low Pass Filter
A network of elements used to attenuate all frequencies above a predetermined frequency. Frequencies below the cutoff point pass without any effect.
A device which has the ability to attract or repel pieces of iron or other magnetic material. Speaker magnets provide a stationary magnetic field so that when the coil produces magnetic energy, it is either repelled or attracted by the stationary magnet.
Mobile Electronics Certification Program.
Amplifier power supply switching device designed for optimum performance.
1. an art of sound in time that expresses ideas and emotions in significant forms through the elements of rhythm, melody, harmony, and color.
A measurement used of how much the flow of electricity is restricted or impeded. The higher the measurement the higher the resistance.
Parametric Equalizer
A multi-band equalizer enabling control of at least three essential “parameters” of the internal bandpass filter sections. These parameters being: amplitude, center frequency and bandwidth. This allows the user to not only control the amplitude of each band, but also to shift the center frequency and to widen or narrow the width or coverage of the affected section of the aural spectrum. Regulation is done by either rotary and slide controls. Other types of parametric equalizers exist which allow control of center frequency, but not bandwidth. For rotary control units, the most common term is quasi-parametric. For units with slide controls the popular term is paragraphic. The frequency control may be continuously variable or switch selectable in steps. Cut-only parametric equalizers (with adjustable bandwidth or not) are called notch equalizers, or band-reject equalizers
Peak Power 
Peak power is measured during a brief musical burst, such as a sudden drum accent. Some manufacturers display peak power ratings on the face of their products. The RMS power rating is more significant, and we recommend using it for comparison purposes.
Pink Noise
Sound with all frequencies perceptible to the human ear reduced to an equal energy level.
Preamp Outputs
Jacks on the rear of a CD receiver that allow you to use a standard RCA patch cable to add an external amp. Some receivers have two sets, which help if you plan to add a 4-channel amp or a second amp. Some receivers have three sets, one of which is usually intended to be used for a subwoofer amp.
Pre-amplifier (pre-amp)
The circuit which takes a small signal and amplifies it to be fed into the power amplifier for further amplification. Contains controls for volume, regulating tone, and channel balance.
The electrical quality of having two opposite poles, one positive and one negative. Polarity determines the direction in which a current tends to flow.
If the port length and diameter is correctly matched to the box volume and subwoofer’s characteristics it will greatly increase efficiency and a good-ported box offers lower distortion
Quad Voice Coil
Four voice coils with one driver. This means more power and more flexibility when configuring your speakers.
Relay (SPDT)
(Single Pole Double Throw Relay) an electromagnetic switch, consist of a coil (terminals 85 & 86), 1 common terminal (30), 1 normally closed terminal (87a), and one normally open terminal (87).
The opposition to the flow of AC or DC voltage in an electric current. Measured in ohms.
An electrical device that resist the flow of electrical current. The higher the value of resistance (measured in ohms) the lower the current will be.
Root Mean Square, a realistic measurement of the maximum output of an amplifier. The higher the figure, the more powerful the unit.
Sealed Enclosure
A type of speaker enclosure that does not allow the pressure generated by the back wave of the speaker to leave the enclosure.
Santoprene Surround
A speaker surround material constructed of Santoprene (a manufactured rubber), offering improved resistance to stretching and deterioration over time compared to Butyl rubber.
Signal-to-Noise Ratio
A measure of how well a CD player silences background noise. Higher ratings, in decibels (dB), indicate less noise.
A transducer which converts electrical energy into acoustical energy (sound).
Subwoofer Preamp Outputs 
RCA output jacks (usually coupled with a built-in low-pass filter) for connection to a subwoofer amplifier.
SMT (Surface Mount Technology)
When a component is mounted on the surface of the PCB instead of inside the board. This causes less signal loss making it a more efficient product.
Sound Pressure Level. Monitored using pro kit and measured in decibels – basically the amount of volume produced.
A high frequency driver specifically designed to reproduce only the high frequencies (treble) of the audible spectrum.
Voice Coil
The voice coil is the coil of wire fixed to a cylinder at the apex of the loudspeaker cone that interacts with a magnetic field. With the help of other speaker components, the voice coil is the active transducer that converts electrical signals from the amplifier or receiver into mechanical energy, which we hear as sound. The voice coil cylinder is the part of the speaker around which the voice coil is wound. More advanced speakers offer a heat-resistant voice coil to prolong speaker life.
The unit of measure for electrical potential.
The difference in electrical potential between two points in a circuit. It’s the push or pressure behind current flow through a circuit.
Watt (wattage)
A measurement of real power. The product of voltage and current in a resistive circuit.
A loudspeaker made to reproduce the lower range of the audio spectrum (bass), in a 2-way or more complex speaker system.
A measure of a speaker cone’s maximum Excursion (back and forth motion) in one direction while still maintaining a linear behavior (moving in a straight line with high precision). This factor is measured in inches or millimeters. X max is more precisely defined as the width of the voice coil that extends beyond the front plate plus 15%. This relates to how far the speaker can move in either direction without appreciable distortion.
This parameter represents the speaker’s impedance at resonance.