MIL-HDBK-1908B
Attenuating helmets or headsets snv. Hearing protectors that provide the wearer with electronic communications.
Aural nondetectability distance snv. The distance at which, for given conditions, the one-third octave-band pressure levels of a noise source at a listener's location are below both the sound level of a quiet environment and average hearing in all one-third octave bands. For a more detailed explanation and examples, see MIL-STD-1474.
Auxiliary system acq. A system mechanism or structure other than the airframe, power plant, or armament, e.g., heating and ventilation, pressurization, defrost and defog, inverters, pumps, auxiliary power unit (APU).
Average hearing snv. The binaural free-field hearing threshold of normal ears for steady-state noise, given in ISO 226.
B-duration (pressure envelope duration) snv. The duration of the primary portion of an impulse noise plus the duration of significant subsequent fluctuations. These durations are considered to be the time interval during which the envelope of pressure fluctuations [positive and negative] is within 20 dB of the peak pressure level. Significant subsequent pressure fluctuations are those whose summed duration is greater than 10% of the duration of the primary portion. The primary portion of an impulse noise is the period of time followed by a level that remains 20 dB below the peak pressure level for a significant duration. For a more detailed explanation and
examples, see MIL-STD-1474.
Backup uci. A capability that returns a user to the last previous display, field, or character in a defined transaction sequence. Also refers to preserving a second copy of files for data protection purposes.
Band snv. A continuous range of frequencies. In communications, the frequency spectrum between two defined limits.
Band level snv. The level of the sound or vibration contained within a particular band.
Band-center frequency (fc) (geometric) snv. The mid-band frequency is the geometric mean between the band edge frequencies of a band. The geometric mean is the square root of the product of the band edge frequencies (see "band-edge frequencies, filter"), fc = (f1 x f2)1/2.
Band-edge frequencies, filter snv. The upper (f2) and lower (f1) frequencies, above and below the frequency of maximum response of a filter, at which the response to a sinusoidal signal is 3 dB below the maximum response.
Bandwidth, filter snv. The difference between f1 and f2 (see "band-edge frequencies, filter"). This difference may be expressed in Hz, as a percentage of the mid-band frequency, or as the interval between the band-edge frequencies, in terms of octaves or parts thereof, such as one-third or one- fifteenth.
Basic item acq. A term used to distinguish an end item of equipment from individual components, assemblies, subassemblies, and parts; e.g., overhaul of the basic item weapon system (AH-64 helicopter air frame including components repaired while on the air frame) versus overhaul of engines, accessories and components, and assemblies which have been removed from the basic item and overhauled to meet established supply requirements for the AH-64 helicopter.
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