Term	Definition	Demo
F Connector	A cylindrical, often threaded, connector in which the central wire in a coaxial cable is used as the center pin. Widely used for cable and antenna connections in television.
Fader	In car audio, the front-to-back sound level adjustment.
Far Field	Moving away from a sound source, the far field is the region in which the sound level drops 6 dB for each doubling of distance. The larger the sound source, the farther away the far field begins. When measuring loudspeakers it is necessary to be in the far field, otherwise the frequency response will be different for every measuring distance. Normally, 2 meters or more is required. See Sensitivity.
Farad	The basic unit of capacitance.
Fast Fourier Transform	A computationally very efficient way to calculate a Fourier Transform. See: Fourier Transform
Feedback	In Amplifiers: the practice of connecting (feeding back) a portion of the output signal to the input so that it can be compared to the input signal and errors corrected. The signal must be inverted (negative feedback) to prevent oscillation, or uncontrolled, very loud, howling (positive feedback). Positive feedback is sometimes experienced in public address systems as a ringing or howling when too much of the amplified sound is picked up by the microphones.
FEM (Finite Element Method)	FEM is a form of computer-aided modeling used in engineering. It is used to solve problems in many disciplines. The area or volume to be analyzed is divided into a large number of small elements, and the behavior of each element is modeled by solving the large system of simultaneous equations. FEM is used to predict the behavior of materials and assemblies during the design phase, speeding the process and allowing for experimenting with different alternatives without having to construct prototypes.
FFT	See: Fast Fourier Transform
Fidelity	See: High Fidelity
Field	In a video display of interlaced scan lines there are two fields, presented alternately, one consisting of even-numbered lines, and the other of the odd-numbered lines. See: Interlace.
Fill	Polyfill, glass or mineral fiber or something similar used inside a loudspeaker enclosure. Filling a closed box makes it seem acoustically larger to the woofer, and in all boxes, fill damps standing waves within the box.
Flat Response	Refers to a flat, or linear, frequency response, meaning that an audio component can reproduce all audio frequencies at the same, correct, level. See Frequency Response.
Fletcher and Munson	Scientific pioneers in the investigation of perceived loudness as a function of frequency and sound level. See: Loudness Contours' class='link'>Equal Loudness Contours.
Flush mount	A speaker mounting system that places the front of the speaker on nearly the same plane as the speaker's baffle.
Flutter	Acoustical: a rapid succession of reflected sounds occurring between two parallel surfaces, normally stimulated by a transient sound such as a hand clap. Electronic: in recording media, especially analog tape, a periodic variation in pitch caused by uneven motion of the tape.
FM	see Frequency Modulation
Foley Effects	Sound effects of all kinds, wind, footsteps, door slams, telephones, gunshots, etc. that are added to a movie soundtrack.
Foot-Lambert	A measure of picture brightness. 1 Foot-Lambert is 1 lumen per square foot of screen surface. The SMPTE (Society of Motion Picture and Television Engineers) specification for a film-type movie theater is 16 foot-Lamberts of brightness, a level not always achieved. Direct-view televisions can be as high as 30 foot-Lamberts.
Fourier Transform	Developed by a French mathematician in the early 1800's, the Fourier transform basically separates a waveform into sinusoids (pure tones) of different frequencies, storing the data as amplitude and phase as a function of frequency. These sinusoids can be added together to reconstruct the original waveform. The transformation, therefore, is between the time-domain waveform and the frequency-domain spectrum of a signal or sound. Both are complete descriptions of the signal, and one can be computationally converted into the other. See: Transform, Spectrum, Transfer Function. Impulse Response, FFT, Spectrum Analyzer.
Frame	In video, the portion of a signal that contains all of the scan lines that comprise one image. Interlaced systems have two fields per frame. See: Interlaced, Field.
Free Air Resonance	The natural resonance frequency of a loudspeaker driver when it is suspended in "free space".
Free Field	See Anechoic.
Frequency	The number of vibrations or cycles completed by a signal in one second. Frequency is expressed in cycles, or more commonly, Hertz (Hz).
Frequency Modulation	A method of radio broadcasting in which the radio carrier frequency is frequency modulated by the audio signal. Capable of high sound quality, and relatively immune to interference and static. However, it propagates poorly over long distances and suffers from multipath interference and shadow zone problems in cities and hilly areas.
Frequency Response	A measure of the amplitude vs. frequency performance of an audio component, measured from its input to its output. A perfect electronic device should have a flat, or linear, frequency response over its useful frequency range, indicating that it reproduces all frequencies at the correct level. Loudspeakers are more complicated since the output is sound which is radiated in all directions. It is necessary to measure the frequency response at many locations all around the loudspeaker in order to be able to predict how it may sound in a room. For loudspeakers, there is no single frequency response measurement that is completely descriptive of its performance. See: Transfer Function, Spectrum.
Frequency Weighting	Used in measurement of overall sound levels to take account of the frequency-dependent loudness characteristics of ears at different sound levels. A-weighted measurements attenuate sounds below about 1000 Hz (low sound levels), B-weighting rolls off frequencies below about 200 Hz (middle sound levels), and C-weighting rolls off below about 50 Hz (high sound levels). All three weightings roll off high frequencies above about 7 kHz. Sound levels measured using these weightings are designated dB (A), dB(B), dB(C), as opposed to unweighted (linear) measurements of sound pressure level (SPL).
Front Projector	A projector that delivers an image to the front surface of a reflective screen allowing the audience to view the reflected image. See: Rear Projector, RPTV.
Fundamental	The lowest in a series of harmonically related sounds. In musical sounds, it is the basis for all higher harmonics. In acoustically or mechanically resonant systems, it is the lowest of all resonant modes. See: Missing Fundamental.
Fuse	A device designed to protect other electronic devices by melting and opening the circuit when the system is drawing too much power. If a fuse blows it must be replaced with an identical part, otherwise future protection may be compromised. See: Circuit Breaker.
Fusion Zone	A horribly abused term, evolving from misinterpretations of the Haas effect, implying that all sounds arriving within an interval of time, ranging from about 20 to 50 milliseconds, are perceptually fused or integrated. This is wildly simplistic at best, and totally wrong at worst, because within these time limits there are several levels of clearly distinguishable perceptions including spaciousness, timbre change, image shift, multiple sound images and, at large delays, echoes. See: Haas Effect.