Efficiency Rating - the loudspeaker parameter that shows the level of sound output when measured at a prescribed distance with a standard level of electrical energy fed into the speaker. Usually recorded as XdB @ 2.83V input signal from 1 meter of distance. However, a driver with a high efficiency rating needs a larger box to play a lower frequency than a driver with a lower efficiency rating.
Electronic Crossover - uses active circuitry in addition to passive to filter unwanted signals for each driver. Usually active filters are employed as LPF (Low Pass Filters) for subwoofers or for the sub out of a preamp / receiver.
Enclosure - a box that contains the driver(s).
Equalizer - electronic device that acts as active filters used to boost or attenuate certain frequencies. Farad - 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.
Filter - any electrical circuit or mechanical device that removes or attenuates energy at certain frequencies.
Flat Response - the faithful reproduction of an audio signal; specifically, the variations in output level of less than ±1 dB which is the threshold of human hearing sensitivity.
Free Air Resonance - the natural resonant frequency of a driver when operating outside an enclosure.
Frequency - the number of waves (or cycles) arriving at or passing a point in one second, expressed in hertz (Hz).
Frequency Response - the frequency range to which a system, or any part of it, can respond.
Fundamental Tone - the tone produced by the lowest frequency component of an audio signal.
Full-range - a speaker designed to reproduce all or most of the sound spectrum within human hearing (20Hz - 20KHz).