A class of enclosure parameters that provides optimum performance for a woofer with a given value of Q

In sealed enclosure designs, the ratio of Vas to Vb, where Vb is the volume of the box you will build. See sealed enclosure

The unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. See Ohms Law

An electrical circuit designed to increase the current, voltage, or power of an applied signal.    Class D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle.  Theoretically since the output devices are either completely on or completely off they do not dissipate any power. If a device is on there is a large amount of current flowing through it, but all the voltage is across the load, so the power dissipated by the device is zero (found by multiplying the voltage across the device [zero] times the current flowing through the device [big], so 0 x big = 0); and when the device is off, the voltage is large, but the current is zero so you get the same answer. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching.

A specially designed room, used for testing microphones and speakers, rendered acoustically "dead" by sound absorbing material.

An otherwise sealed enclosure design, but with a vent that is stuffed with damping material, which flattens out the impedance curve of the design. The area of this resistive vent should be about 10 sq. in. per cubic ft. of enclosure volume. This design might take some experimentation with the vent stuffing, testing the impedance curve several times with different amounts of damping material until the flattest impedance curve is found. The aperiodic resistive vent damps the driver in much the same way as fully stuffing a sealed enclosure with damping material (100% fill). In this way, an optimum design may be made up to 20% (or more) smaller due to the extra damping of the resistive vent. Enthusiasts of this design often compare the performance with transmission line enclosures, advocating that the design avoids the "ringing" effects of ported enclosures while alleviating the "pressure effect" of the sealed box.

The reduction, typically by some controlled amount, of an electrical signal.                       

The acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.

An auxiliary input allows you to select an external source and play it through the cd player's amplifier. It's often used for iPods and MP-3 players. Typically you just need an inexpensive patch cable that connects the headphone output from your portable player to the input on the CD player. After that you can select "AUX" as another source like CD or Tuner, and whatever's playing on the portable unit will be heard through the speakers.  Auxiliary inputs can be on the front or the rear of the CD player   Aux inputs are typically 3.5mm stereo plugs, similar to a small headphone jack.

A board or other plane surface used to mount a loudspeaker.

An electric circuit designed to pass only middle frequencies. See also High-pass and Low-pass filters.

First order high pass crossovers (non-polarized capacitors), generally used on midbass or dash speakers to keep them from trying to reproduce deep bass.

A ported enclosure.  Loudspeaker enclosure with a tuned outlet permitting sound from the rear of the speaker cone to be radiated to the front.

The tendency of a loudspeaker to concentrate the sound in a narrow path instead of spreading it.

The use of two amplifiers for high and low frequency ranges in an audio circuit, usually within the same speaker enclosure.

Bluetooth is an open wireless technology standard for exchanging data over short distances (using short wavelength radio transmissions)  The code name given a wireless network protocol, after a 10th century Danish king, Harald Bluetooth, who unified Denmark. The code name was adopted in April, 1998

Combining both left and right stereo channels on an automotive amplifier into one higher powered mono channel. When an amplifier is bridged, the impedance that the amplifier actually "sees" is calculated based upon the output of both stereo channels. Here is a simple formula to help define this:

Bridged Mono Impedance = (Y / X)/2

Y = impedance of driver(s) (both drivers should be identical)

X = # of drivers in circuit

So, hooking up one 4 ohm sub bridged mono would be equal to hooking up two 2 ohm subs in stereo, one to each channel.

A device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an ac current. In automotive applications, special "Power Line Caps" can be connected inline to the amplifier to aid the alternator in supplying current demands of amps. Non-polarized capacitors can be used as first order passive high pass crossovers, or as components in more complex high pass, bandpass and lowpass crossovers. See power line caps.

In home theater, sound decoded from the stereo signal sent to a speaker mounted in front of the listener, specially designed to enhance voices and sound effects from a movie soundtrack. Used in car audio to help offset skewed stereo imaging due to seating positions in the automotive environment.

Degree to which left and right channel signals are separated in a stereo pickup, FM stereo tuner, amplifier, etc

Mechanical suspension compliance of a driver, consisting of the spider and surround.

The part of a dynamic loudspeaker attached to the voice coil that moves and produces the sound. It usually has the shape of a cone or dome.

The spreading of sound waves as it leaves a speaker.

A loudspeaker unit, consisting of the electromagnetic components of a speaker, typically a magnet and voice coil.

Efficiency Bandwidth Product. A rating that helps a builder determine whether a driver is suitable for a sealed or ported enclosure. EBP of less than 50 indicates the driver should be used in a sealed, 50 - 90 indicates flexible design options, over 90 indicates best for a ported enclosure.

EBP = Fs / Qes

Electronic device used to boost or attenuate certain frequencies.

The roll-off frequency at which the driver's response is down -3dB from the level of it's midband response, sometimes called the cutoff frequency.

The basic unit of capacitance. A capacitor has a value of one farad when it can store one coulomb of charge with one volt across it.

The faithful reproduction of an audio signal; specifically, the variations in output level of less than 1 dB above or below a median level over the audio spectrum.

The natural resonant frequency of a driver when operating outside an enclosure.

The tone produced by the lowest frequency component of an audio signal.

A speaker designed to reproduce all or most of the sound spectrum.

The ratio of the depth, width, and height of a speaker enclosure, based on the Greek Golden Rectangle. Usually recommended for home speakers, difficult to use in car audio applications. The Ratio: W = 1.0, Depth = 0.618W, Height = 1.618W.

Refers to a point of (usually) zero voltage, and can pertain to a power circuit or a signal circuit. In car audio, the single most important factor to avoid unwanted noise is finding and setting a good ground.

Harmonics artificially added by an electrical circuit or speaker, and are generally undesirable. It is expressed as a percentage of the original signal. See THD.

An audio system designed to reproduce the theater sound experience while viewing movies in the home. Minimally consisting of a Dolby Pro Logic® surround sound receiver, left and right front speakers, a center channel speaker, and at least (1) surround sound speaker. These plus optional subwoofer(s), surround speaker(s), and digital formats such as Dolby Digital® can enhance the viewing experience by drastically improving the sound quality of movie soundtracks.

The opposition of a circuit or speaker to ac current; the combined effect of a speaker's resistance, inductance, and capacitance that opposes the current fed to it. It is measured in ohms and varies with the frequency of the signal.

The capability of a coil to store energy in a magnetic field surrounding it. It produces an impedance to an ac current. Inductors are commonly used in audio as low pass crossovers. See Le.

A filter designed to remove extremely low frequency (25Hz or lower) noise from the audio signal. Useful for Ported box designs.

The inductance of a driver's voice coil, typically measured at 1 kHz in millihenries (mH).

An electric circuit designed to pass only low frequencies. See Band-pass and High-pass filters.

The tendency of a speaker system that consists of more than one driver to produce a lobed frequency response in space with in-phase reinforcement (lobes) from the various drivers occurring at some elevations and out-of-phase opposition (nulls) at points between the lobes.

A loudspeaker has its magnetic field contained so that it can’t discolor or damage a CRT type TV monitor..

The frequency range above bass but below treble that carries most of the identifying tones of music or speech. It is usually from 300 - 400 Hz to 3kHz or so.

A unit of electrical resistance or impedance                                                             

The relationship and timing of sounds that come from different drivers (subs, mids, tweets) mounted in different locations in the vehicle

A type of audible distortion caused by time delay between various parts of the signal; can be caused by equalizers

The orientation of magnetic or electric fields. The polarity of the incoming audio signal determines the direction of movement of the speaker cone. Must be observed when wiring speakers, so that they are "in phase". See Out of Phase

A type of speaker enclosure that uses a duct or port to improve efficiency at low frequencies. Excellent design for lower power systems, as the port often adds up to +3 dB to low frequency efficiency. F3 can be set considerably lower with proper design, although low frequency roll-off is generally -24 dB/octave. Good transient response with proper tuning, although the driver loses damping below the tuning frequency. Excellent power handling about Fb, but source material or frequencies below Fb cause the driver to progressively perform as if it were not enclosed at all. Due to this, ported enclosures without a low frequency filter may have lower power handling compared to other designs. More difficult to properly build and tune than a sealed enclosure, with several "optimum" alignments available depending upon the Qts of the driver. Though it can be dated to the 1930's, the ported alignments were thoroughly researched and standardized by A.N. Thiele in the 60's and R. Small in the 70's. This work was further expanded by D.B. Keele and others.

P = Volts^2 / Impedance

The magnification of resonance factor of any resonant device or circuit. A driver with a high Q is more resonant than one with a low Q

In autosound, the ambience created by a pair of rear speakers that helps complete the soundstage. A set of high quality components for the front powered by an external amp and a set of coax mounted on the rear deck powered by the head unit or small amp is a good example of a rear fill application. Rear fill speakers should be faded so that they create a richer ambience, but you should not be able to isolate any sounds coming from them.

In electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons. Speakers have resistance that opposes current.

In electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons. Speakers have resistance that opposes current.

An acronym for "root mean square." Used in audio to help rate the continuous power output of an amplifier or input capability of speakers. This is the preferred method for comparing anything in audio applications.

The attenuation that occurs at the lower or upper frequency range of a driver, network, or system. The roll-off frequency is usually defined as the frequency where response is reduced by -3 dB.

The overall damping of a 4th order bandpass enclosure. i.e., if you were to figure a 4th order bandpass enclosure with a Qtc of 0.70 for Vr (the sealed chamber), then you would also figure Vf (ported chamber) with an S of 0.70.

Air tight enclosure that completely isolates the back wave of the driver from the front. Very tight, defined sound (with Qtc = 0.707) with very good transient response and power handling. Low frequency roll-off is at -12 dB/octave. Less efficient than other designs, and higher distortion levels at resonance.

The ratio, expressed in dB, between the signal and noise.  Ratio of desired signal voltage to unwanted noise and hum voltage. Expressed in decibels (dB)

The waveform of a pure alternating current or voltage. It deviates about a zero point to a positive value and a negative value. Audio signals are sine waves or combinations of sine waves.

A buildup of sound level at a particular frequency that is dependent upon the dimensions of a resonant room, car interior, or enclosure. It occurs when the rate of energy loss equals the rate of energy input into the system. This is what you hear when you listen into a sea shell.

A loudspeaker designed to reproduce sub-bass frequencies.

he outer suspension of a speaker cone; holds the diaphragm in place but allows it to move when activated. Usually made of foam or rubber.

Usually representative of the monophonic sound extracted from the stereo signal sent to smaller rear or side speakers used in a home theater.

The percentage, in relation to a pure input signal, of harmonically derived frequencies introduced in the sound reproducing circuitry and hi-fi equipment (including speakers).

The upper end of the audio spectrum reproduced by tweeters, usually 3 - 4 kHz and up.

A speaker that is composed of three individual voice coils and cones; used for the reproduction of sounds in three segments of the sound spectrum.

When a special passive crossover is used with an automotive amplifier to safely power a subwoofer in bridged mono (low pass circuit) as well as a pair of stereo speakers (high pass circuit). Normal inductors and capacitors can be used for Tri-way output.

Type of speaker system composed of two ranges of speakers, usually a woofer and tweeter.

The equivalent volume of compliance, which specifies a volume of air having the same compliance as the suspension system of a driver.

Total box volume, usually in cubic feet or liters. Used specifically in sealed and ported designs.

A unit of measurement used to measure how much "pressure" is used to force electricity through a circuit.

A small supplementary cone attached to the center of the speaker's main cone for the purpose of increasing high frequency response.

Maximum linear cone excursion of a driver, measured in inches or millimeters.