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Mobile Electronics Glossary of Terms and Definitions - A

Mobile Electronics Glossary - A
  ABX Comparator - A device that randomly selects between two components being tested. The listener doesn't know which device is being auditioned.
  Accessory (position) - Refers to the position of the key in the ignition switch; A wire showing 12 Volts (+) when in this position.
  Acoustic Absorption - The sound deadening properties of any substance, measured in sabine units. One sabine is equal to the absorption of 1 square foot of surface which will absorb all incident energy.
  Acoustic Feedback - A squealing sound when the output of an audio circuit is fed back in phase into the circuit's input.
  Acoustic Suspension - A sealed or closed box speaker enclosure.
  Acoustical Energy - Energy consisting of fluctuation waves of pressure called sound waves.
  Acoustics - 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.
  Active Arming - A method for arming a security system that requires some action such as pressing a button on a remote transmitter or entering a code on a keypad
  Active Display - A step-up display feature that generates animated patterns for both segment and dot matrix LCDs that proceed the sequential display of information such as clock, Custom File titles and radio station frequencies.
  Air Gap - The space between the top plate and the pole piece. This is where the voice coil sits.
  Aliasing Noise - The result of the sampling frequency not being at least double the highest analog frequency during the digital encoding of an analog signal.
  Alignment - A class of enclosure parameters that provides optimum performance for a woofer with a given value of Q.
  Alternate-Channel Selectivity - A measurement of a tuner's ability to select one radio station's signal and reject the signal of another radio station two channels (0.4 Mhz) away. Measured in decibels, the higher the number the better.
  Alternating Current (AC) - An electric current that reverses direction at regular intervals. Measured in Volts AC at Hertz, example: 110 volts AC 60 Hz.
  Alternator - 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.
  Alternator Whine - A whining that is heard when the RPMs of an engine increase. The noise is usually the result of a voltage differential created by more than one ground path or a poor ground path (ground loop).
  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.
  Ammeter - An instrument that measures the magnitude of an electric current in amperes.
  Ampere (amp) - A unit that defines the rate of flow of electricity (current) in a circuit.
  Amplification - The increase in signal level, amplitude or magnitude.
  Amplifier - 1 A device which increases the level of a signal by increasing the current or voltage. 2 May also be used to isolate or control a signal and even decrease the level as in a line output converter.
  Amplifier Classes - Audio power amplifiers are classified primarily by the design of the output stage. Classification is based on the amount of time the output devices operate during each cycle of signal swing. Also defined in terms of output bias current, (the amount of current flowing in the output devices with no signal).

Class A operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers are single-ended designs with only one type polarity output devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power.The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion.

Class B operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is due to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio.

Class AB operation allows both devices to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demands. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design.

Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.

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. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.

Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.

Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. The efficiency of class H is comparable to class G designs.
  Amplifier, Power - An amplifier designed for driving loudspeakers and having a higher power output than a line amplifier or preamplifier.
  Amplitude - The maximum value of a periodically varying quantity.
  Amplitude Modulation (AM) - The encoding of a carrier wave by variation of it's amplitude in accordance with an input signal. AM Stereo
  Analog - A way to represent data by means of continuously variable quantities. A control or circuit which continuously changes the level of a signal in direct relationship to the control setting. An electrical signal whose frequency and level vary continuously in direct relationship to the original acoustical sound waves. (something that is analogous)
  Analog to Digital Convertor (ADC) - A circuit that converts an analog signal into a digital signal. With a continuous input signal the ADC will check the signal several time per second (sampling), assign values to the samples and represent it as a binary number (quantization and encoding).
  Analogous - Alike in certain ways. Similar in function but not in origin or structure.
  Anode - The electrically positive pole of an electronic device such as a semiconductor. A diode, for instance, has a positive and a negative pole; these are known as the anode and the cathode
  Antenna - An apparatus used for sending and receiving radio waves, usually constructed of metal.
  Antenna Trimmer - An adjustment found on analog radios used to maximize AM reception. Turning this trimmer to the point where the sound is the loudest increases the sets signal to noise ratio optimizing performance.
  Aperiodic - Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but lower the Q of the system and reduce the impedance peak at resonance. Most restrictive ports are heavily stuffed with fiberglass, dacron or foam.
  Attenuator - A device to decrease or increase the strength of a signal.
  Auto Eject - Feature of a cassette player that ejects the tape when it has finished playing one side.
  Auto Loud - Automatically provides low frequency boost for listening at low levels.
  Auto Memory - A tuner feature that automatically finds the strongest stations in the local area, and places them in preset memories.
  Auto Replay - Feature of a cassette player that automatically rewinds a tape when it has reached the end of one side, then begins to replay.
  Auto Reverse - Feature of a cassette player that automatically plays the reverse side of a tape when one side has reached the end.
  Auto Stop - Feature of a cassette player that automatically shuts off power when a tape has reached the end of either side in any mode.
  Automatic Gain Control (AGC) - A circuit that continuously adjust the recording amplifier gain to maintain a relatively constant recording level.
  Azimuth - The perpendicular alignment of the tape to the head of a tape player / recorder.
Mobile Electronics Basics:
Glossary of Terms and Definitions
Ohm's Law
Recommended Wire Sizes
Tools and Equipment

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