Glossary of electronics terms used in our articles

AC
An abbreviation for alternating current .
Alternating Current
Abbreviated as AC. A current which periodically reverses it's direction of flow. The power from a standard US wall outlet is a (roughly) sinusoidal AC waveform which alternates between polarities at a frequency of 60 cycles per second.
Ampere
Abbreviated Amp. A measurement of the amount of electric current flowing in a circuit. An ampere is the equivalent of the unvarying current which, when passed through a reference solution of Silver Nitrate in water, deposits silver at the rate of 0.0011118 grams per second.
Audio Frequencies
The audio frequencies are considered to be from 20 to 20,000 cycles per second.
Bass Response
Bass refers to the low components of sound. As used here this phrase describes frequency response from about 800 Hz to 20 Hz, although the exact range considered bass will depend on the source of the information.
Cable Rating- CL2X, CL3X, CL2, CL3
The CL stands for class, I:E: CL2 cable is "class 2 rated". Speaker wire falls under article 640 of the National Electrical Code. There can be additional local regulations for installations. According to the current code (2008) CL2 and CL3 cable are always permitted for single family residential use. An X (as in CL2X) is a residential suffix that signifies a lower grade than CL2 or CL3. CL2X or CL3X may be installed in raceways. In addition, if the X rated cable is under 1/4 inch in diameter it may be installed in a one or two family residential dwelling without a raceway. If it is not concealed it may also be installed in multifamily dwellings. Higher rated cables such as CL3P (Plenum) are acceptable. For other than residential use, or if you have any doubts please refer to the National Electrical Code and any local regulations.
Capacitance
An electrical phenomenon whereby an electric charge is stored.
Cone
As used here refers to the part of a speaker driver that pushes air by moving in and out with the application of electrical current. Most commonly made of paper for woofers, the cone may be plastic, Kevlar or another material. In the case of tweeters the material may be paper, silk, mylar or another material. Tweeter cone movement may be so small as to not be visible. In addition, many tweeters do not use a standard cone, but may use a soft dome or other appropriate technology.
Crossover
As used here refers to a network of components that separate various audio frequencies out to send them to the proper driver in a speaker system. A tweeter needs the high frequencies and wants the low frequencies blocked. A crossover may perform other functions such as driver impedance compensation and driver level matching.
Current
As used in these articles, current is defined as the flow of electrons through an electrical wire. Current is measured in amperes. An analogy likens current to the amount of water flowing in a pipe (wire).
Cycles Per Second
As used on this website, one cycle refers to the time taken for a sinusoidal waveform to go from 0 to maximum positive voltage, return to 0, go to maximun negative voltage and return to zero again. Measured in Hertz (Hz). 10 Hz=10 cycles per second.
Direct Current
A current which does not reverse polarity Abbreviated DC.
Driver
As used here refers to a component of a speaker system that produces sound by moving the air. Example: a tweeter is the driver for the high frequencies in a speaker system and is usually enclosed in the speaker box with other drivers and components.
Dynamics
As used here, this is a loosely defined term indicating the difference between loud and soft sounds that a speaker produces. This translates into a speaker that provides bass "punch" and "impact". A very dynamic speaker also makes hard sounds hard, instead of mushy sounding. This aspect would probably technically relate to impulse and transient response, but is part of what makes a speaker sound dynamic and alive.
Efficiency
Referred to a speaker system efficiency is the amount of sound produced using a standard measurement reference, which is usually 1 watt input measured at one meter away. The measurement is usually in Decibels (Db). A common efficiency is 88 Db at 1 watt, one meter referenced to 8 Ohms impedance. A 3 Db difference in sensitivity is equivalent to doubling your amplifier power. In other words, an 87 Db efficient speaker driven with 100 watts will reach the same volume level as a 90 Db efficient speaker driven with 50 watts of power. Make sure when comparing that all models compared are using the same measurements, including the speaker impedance.
Frequency
As used in these articles, frequency is defined as the number of occurrences of a complete waveform within a given time period. For our purposes (Audio electronics) this is usually specifed in cycles per second, or Hertz, abbreviated Hz.
Gauge(Ga)
As used here, a measure of wire size. A smaller number for gauge indicates larger wire. 24 gauge wire is smaller than 16 gauge wire.
Hz
Abbreviation for Hertz, a measurement of frequency, or cycles per second.
Hertz
The hertz is a measure of frequency, informally defined as the number of events occurring per second (symbol: Hz).The hertz is named after the german physicist Heinrich Hertz, who made important scientific contributions to electromagnetism.
Impedance
As used in these articles the term refers to electrical impedance. Impedance describes a measure of opposition to a sinusoidal Alternating Current. In practical terms electronic devices such as speakers resist current flow to a certain extent, and this resistance to AC is called impedance and measured in Ohms (such as an 8 Ohm speaker). Resistance to a direct current is simply called resistance, and is also measured in Ohms.
Impedance Matching
In the context of this web site this refers to a device that protects an amplifier or receiver from the perils of low impedance. Devices do this by switching resistors or an autoformer to present a standard 8 or 4 Ohm load to the amplifier regardless of the impedance of the speakers connected. Speakers connected in parallel present a lowered impedance to electrical current. For our purposes we do not have to deal with the fact that measured impedance varies with frequency as this measurement is standardised for speaker drivers. The parallel impedance formula is: Z=1/ (1/z1+1/Z2+1/Z3+1/Z4.......)
Inductance
The property of an electric circuit (or conductor) by which an electromotive force is induced in it by a variation of a current. The unit of inductance is the henry.
Kevlar
Kevlar is a material sometimes used for making speaker cones because it's strength and light weight make for a superior product.. In many cases it has the appearance of woven fabric. Kevlar is an aramid fiber made by DuPont.
Khz
An abbreviation for Kilohertz
Kilohertz (Abbreviated Khz)
A frequency measurement. Kilo means 1000 and is thus a shortened form of writing 1000 Hertz (Hz.) 12 Khz=12,000 Hz.
Midrange Driver
The part of a speaker system that produces the middle audio frequencies. Not all speakers have or need a midrange driver. If they do it is commonly larger than the tweeter and smaller than the woofer.
Midrange Response
The frequency response range considered as the midrange will depend on who is defining it. We consider the frequency range from about 800 Hz to 5 Khz as the midrange.
National Electrical Code-NEC
Also known as NFPA 70 the code is a United States standard for the safe installation of electrical wiring and equipment. It is part of the National Fire Codes published by the National Fire Protection Association (NFPA). It is important to note that while the NEC must be adhered to, there may also be additional state, county and city codes that must be followed.
Ohm
The measurement of electrical resistance. An Ohm is defined as the amount of resistance that will produce a current of one Ampere with the application of one Volt. Named for the German electrician, G.S. Ohm. This term is also used as a measurement of impedance. With regards to home speakers the standard impedance is 8 ohms, although you may see variations from 2 to 32 ohms.
Oscillate
Refers to a back and forth movement. As used here refers to a back and forth movement of an electrical current or voltage. The practical result of amplifier oscillation is the creation of a tone that sustains itself, as in the screeching microphone feedback everyone has heard. An amplifier may oscillate at a frequency above hearing range. In that case the amplifier may overheat, have reduced audio power output and increased distortion. It may not be obvious that the amplifier is oscillating without viewing the signal on an oscilloscope. Some finicky high end amplifiers and improperly designed amplifiers may oscillate if used with high capacitance or inductance cables.
Oscilloscope
An electronic measuring instrument that provides a visual representation of the time variation of electrical quantities,such as voltage or current. In other words, it shows waveforms.
Plenum
As used here refers to a ventilation airspace in which cable may be run. Cable that runs directly through air that you will breath needs a better fire rating and is substantially more expensive.
Resistance
A hinderance or opposition to the passage of electrical current offered by conducting bodies (wire, etc.). The unit of resistance is the Ohm.
Resistor
An electrical device that resists the flow of electrical current. Resistors are measured in Ohms, and color coded to represent the resistance value.
RMS
An abbreviation for Root Mean Square, which amounts to a method of averaging an Alternating Current waveform which allows a valid comparison to Direct Current or other means of measuring energy. The rms value is 0.707 times the peak value, and the peak value is 1.41 times the RMS value. This applies to sinusoidal waveforms. Consider this value an average value.
RMS Watts
In the context of our articles, consider this phrase to mean the long term (continuous) power output available from a receiver or amplifier. This is in contrast to the so called "Peak Power Output" which is usually the output power available for a fraction of a second.
Speaker System
A speaker system is usually composed of one or several wooden boxes with multiple drivers mounted on the outside and containing crossover components and sound damping material inside. Speaker systems may be simple or incredibly complicated with various port systems, passive radiators and other innovations.
Sinusoidal Waveform
A waveform that can be expressed mathematically by using the sine function. On an oscilloscope screen it will look more or less like this:

The waveform labeled AC is a sinusoidal waveform, as contrasted with a DC voltage.
Transformer
A transformer consists of two coils of wire are wound on opposite sides of a metal core. When an electric current is passed into one coil, a transient electric current is induced in the other. By varying the number of windings of the coils, the voltage and current can be increased or decreased. The number of turns in the windings also affect the impedance of a transformer allowing it to be used for impedance matching. The windings may also be tapped at several places allowing a choice of different voltages selectable with a switch. This is how transformer style impedance matching volume controls function.
Treble Response
Treble refers to the high components of sound. The frequency range that is considered the treble range will vary among different sources. We consider the range from about 5 Khz to 20 Khz to be the treble range.
Tweeter
The part of a speaker system that reproduces the high audio frequencies. The tweeter is normally smaller than the other parts of a speaker system which may consist of midrange drivers, woofers, and other components.
Twisted Pair
Refers to a method of cable construction where 2 conductors, one for positive polarity and one for negative polarity are twisted around each other. It is measured in twists per inch. Proper twisted pair construction has some unique and interesting properties. It is inherently self shielding, although not as RF proof as coaxial cable. If properly constructed it has advantages of very good high frequency response, self shielding, reduced inductance and increased capacitance. It can be less lossy than coaxial style cable. This is the construction used in Cat 5 and Cat 6 computer cable.
Voltage
The diffence in electrical charge between two points in a circuit. An analogy likens voltage to the pressure of water in a pipe.
Watt
A measure of the amount of work done by a certain amount or amperage of electric current at a certain pressure or voltage. In the context of our use relates to the ouput power of an amplifier or speaker. Wattage is also used as a measurement of the maximum power handling of certain components such as speakers or volume controls. Power (P)=Current (I) times Voltage(E). Just remember it as the PIE formula. P=IxE
Waveform
The shape of a wave illustrated graphically by plotting the values of the period quantity against time.
Woofer
The part of a speaker system that produces the low audio frequencies. Has a larger cone than the other parts of a speaker system which may consist of a tweeter for high frequencies and a midrange driver for the center frequencies.