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Glossary of Terms

Acoustic Suspension - The support that a calculated amount of trapped air gives to the motion of a driver. Acoustic suspension woofers are designed for use in relatively small sealed enclosures.

Aesthetics - That which deals with the sense of the beautiful. In car audio the finished product needs to look completely stock or like a finished product with all elements matching.

Attenuate - To reduce the level of a signal. Commonly used to match the output of one driver to another.

Baffle - A panel that a driver is mounted to. Either one part of an enclosure or in the case of a Freeair mounting its the panel that separates the front wave from the back wave, eliminating cancellations.

Bandpass - That which results in only a certain band of frequencies being reproduced- either an enclosure or a crossover network.

Bandwidth - Those frequencies that a system or a driver reproduces. Usually measured with some reference to deviation: such as 20 to 20kHz +or-1.0 dB.

Bass Reflex - A subwoofer enclosure design that utilizes a port or vent to augment the woofer output at or about the tuning frequency. From a trademark of the Jensen Co. in the 1930's.

Boomy - In reference to the sound quality of a subwoofer system, boomy refers to an increase in output at upper bass frequencies (80 to 100Hz). The lower bass, if present, is covered up by the undesirable upper bass and lacks good damping.

Butterworth - Used to define the rolloff characteristic of a crossover or a woofer system. Named after the engineer who first mathematically described the response of that shape which has a Q of .707.

Clipping - A situation that occurs when an audio signal is made larger that the power supply that supports it. When this happens the top and bottom portion of the waveform is 'clipped' off, creating a very distorted signal. Clipping can occur at line levels or at the output of an amplifier and will usually damage speakers.

Compliance - A measurement of the main restoring force for a speaker. Generally indicates the springiness of the suspension.

Compound Loading - Mounting two drivers in such a manner that they function like one driver. The resultant enclosure requirement is half as large as for a single driver, which makes it popular for car audio. Also the technology that led to the development of the Solobaric woofers.

Cycles per Second - See Hz.

dB - Decibel. The unit of measure for acoustic intensity level. It is a ratio of two sound intensities in logarithmic form. The smallest change in loudness that a human can detect is defined as one decibel.

Directionality - Determined by the angle into which a speaker radiates its sound. A speaker with a narrow angle of dispersion is very directional, while a wide angle of dispersion is more nondirectional.

Driver - A speaker, an electromechanical transducer that converts electrical energy to mechanical energy.

Efficiency - As it refers to speakers; the ratio of acoustic energy output to the total electric energy input, expressed as a percentage or in dB per watt at a set distance.

Flat Frequency Response - A term used to describe a theoretically perfect speaker which produces a constant output over a specified frequency range. It does not peak or dip at any frequency or band of frequencies.

Flux Density - A measure of magnetic strength in a given area. In car audio it refers to the magnetic field in the gap between the front plate and pole piece of a driver, measured in Teslas.

Halfspace - An environment for measuring a speaker system which simulates the driver flush with a planar surface radiating into a 180° hemispherical field.

Frequency - The speed of change in an electrical signal or of air pressure in an acoustical signal, measured in Hz.

Hz - Hertz. Cycles per second. A unit of measurement for alternating current waveforms or frequency of an audible tone. The standard bandwidth for human hearing is 20 to 20KHz.

High Frequency - In audio, the frequencies from about 5KHz to 20KHz.

Highpass - When information lower in frequency than a given crossover point is attenuated, a highpass filter is in use. Used to reduce intermodulation distortion and increase power handling in a particular driver.

Imaging - The ability to localize the instruments when listening to a stereo recording.

IM Distortion - Intermodulation distortion occurs when a lower frequency affects the faithful reproduction of a higher frequency. The most audible case is when a driver is trying to reproduce an extremely wide range of frequencies.

Impedance - AC resistance. The combined restriction to current flow including DC resistance, inductive reactance, and capacitive reactance. Impedance (Z) is measured in Ohms (£2).

Infinite Baffle - Freeair. Mounting a driver on an infinitely large baffle board that completely separates the sound radiated from the front of the speaker from the sound radiated from its back. For practical purposes the baffle board can be part of the vehicle. An enclosure larger that the Vas of the driver with the front and rear waves isolated from each other would essentially be an infinite baffle application.

Isobaric - See Compound Loading. Refers to the practice of coupling two drivers together to make them act as one.

Lowpass - When information higher in frequency than a given crossover point is attenuated, a lowpass filter is in use. A common application is for woofers.

L-Pad - Attenuation network. Two resistors wired in an L shaped configuration, which converts some of the amplifier power into heat and reduces the amount of power available to the driver.

Masking - Certain types of noise tend to cover up or mask desirable information. A common example is when road noise covers up low bass in a car audio system.

Midbass - Those frequencies from 100Hz up to 350Hz, often overlooked or not reproduced faithfully in a car audio system.

Midrange - A critical band of frequencies from 350 to 5KHz which includes most of the musical information.

Octave - One octave is either a halving or doubling of a frequency. One octave below 1 KHz would be 500Hz. One octave above 1 KHz would be 2KHz.

Ohm - The unit of measure of electrical resistance or impedance.

Order - In crossovers the shape of the rolloff measured in dB per octave is equal to 6 times the order. For example a 12 dB per octave rolloff is called a 2nd order. This also applies to the rolloff of a driver in a given situation. An acoustic suspension enclosure has a 12dB per octave rolloff and is considered a 2nd order box. It is too confusing to use orders on more complex enclosures because it is possible to derive higher orders in different manners and by combining crossover orders with those of the enclosure.

Passive - Any device that has no built in amplification is considered passive. A passive device will always have some insertion loss. Crossovers used after an amplifier are called passive.

Peak - A point in a speaker's response range where a frequency or band of frequencies are produced louder than other frequencies.

Phase - A term used to describe the relative position of two sound waves in relation to one another as it relates to the arrival time to the listener.

Power Handling - In speaker systems, the maximum amount of power that can be safely accommodated without damage to the speaker or distortion of musical reproduction. The limiting factor in a particular driver may be thermal or mechanical depending on the application.

Processors - Any unit in the signal path that is added with the intention of changing the existing signal is called a processor. Equalizers, delays and electronic crossovers are all forms of processors.

Qts - The driver's magnification at resonance. A measure of the driver's ability to dampen its resonance.

Resonant Frequency - Fs. Frequency at which a driver most easily responds to an external force and continues to vibrate after the force is removed. Measured in Hz.

Rolloff frequency - F3. The most common means of measuring the rolloff point of a system is to note the frequency where the energy is 3dB less than that in the passband.

Sealed - An enclosure of finite size that has no exchange of air between the inside volume and the outside world. Commonly used to control cone motion in acoustic suspension woofers.

Sensitivity - The sensitivity of a power amplifier is that input voltage which will result in reaching full rated output. For a speaker it is the acoustic output as measured at one meter away with one watt of input.

Shelving - In equalizers if the response curve is to be boosted or cut through a certain range of frequencies in an equal amount, it is said to be a shelving equalizer. The resulting response curve has a flat area that resembles a shelf.

SPL - Sound pressure level. The measure of sound pressure (loudness) and expressed in dB.

Transducer - Any device that converts one form of energy into another. A microphone converts sound energy into electrical energy and a speaker converts electrical energy into sound.

Transient Response - The ability of an amplifier or speaker to follow sudden changes in audio levels.

Tweeter - A driver used to reproduce the upper range of the musical spectrum, usually from 3.5KHz to 20 KHz.

Vas - The volume of air having the same compliance as that of a driver, measured in cubic feet or litres.

Vented - Ported. When an enclosure has the capability of exchanging air from that inside the enclosure with the outside world through a tuned orifice it is said to be vented or ported.

Woofer - A driver designed to reproduce low frequencies. In car audio it is usually restricted to 100Hz and below. A woofer that is used down below 40Hz can be called a subwoofer.

Z - See impedance.