Frequency - The speed of vibration of a sound wave, measured in cycles per second, or Hertz. Frequency determines pitch; the faster the frequency, the higher the pitch.

Free field - An environment in which there are no reflective surfaces within the frequency region of interest.

Flutter - A repetitive echo set up by parallel reflecting surfaces.

Flat - The term used to describe an even frequency response in which no frequency is accentuated.

Flanking - The transmission of sound around a perimeter or through holes within partitions (or barriers) that reduces the otherwise obtainable sound transmission loss of a partition.

Flame spread - A measure of the time it takes for fire to spread, when compared to red oak, whose Flame Spread Index (FSI) is 100 in accordance with ASTM E 84.

Far field - Distribution of acoustic energy at a very much greater distance from a source than the linear dimensions of the source itself.

Equalization - The adjustment of timbre, or tone quality, achieved by changing the amplitude of a signal at different frequencies. (Abbreviated: EQ.) Tone controls are simple forms of equalization.

Equal loudness contours - A set of curves of equivalent loudness, which model the ear’s frequency response throughout the audible spectrum. The curves, obtained from actual testing, show how much more sound power is required at one frequency than another to obtain a sound of equal loudness.

Echo - A distinctly discernible reflection, or repetition of a source signal. Note: The term is often used incorrectly to refer to reverberation which consists of densely spaced, indistinguishable reflections.