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Jet-powered aircraft create intense noise from aerodynamics. Low-flying, high-speed military aircraft produce especially loud aerodynamic noise. The shape of the nose, windshield or canopy of an aircraft affects the sound produced. Much of the noise of a propeller aircraft is of aerodynamic origin due to the flow of air around the blades.
The primary sources of jet noise for a high-speed air jet (meaning when the exhaust velocity exceeds about 100 m/s; 360 km/h; 225 mph) are "jet mixing noise" and, for supersonic flow, shock associated noise. Acoustic sources within the "jet pipe" also contribute to the noise, mainly at lower speeds, which include combustion noise, and sounds ...
Detailed information on measurement of aircraft acoustic signature to meet the requirements of Annex 16 is found in ICAO Document 9501 [6] and IEC 61265. [7] Data acquisition in one-third-octave bands is required, followed by processing to yield a logarithmically-scaled value in decibels relative to a sound pressure of 20 micropascals for each one-third-octave band.
Landing quota count values are based on the certificated approach noise level at maximum landing weight minus 9.0 EPNdB. Aircraft were originally divided into six QC bands from 0.5 to 16, but following a review by the Department for Transport [ 1 ] a seventh category – Quota Count 0.25 – was added in March 2007 [ 2 ] and an eighth category ...
Noise may be measured using a sound level meter at the source of the noise. [23] [24] [25] Alternatively, an organization or company may measure a person's exposure to environmental noise in a workplace via a noise dosimeter. [26] The measurements taken using either of these methods will be evaluated according to the standards below.
A graph of the A-, B-, C- and D-weightings across the frequency range 10 Hz – 20 kHz Video illustrating A-weighting by analyzing a sine sweep (contains audio). A-weighting is a form of frequency weighting and the most commonly used of a family of curves defined in the International standard IEC 61672:2003 and various national standards relating to the measurement of sound pressure level. [1]
Aircraft designers are also using acoustic instrumentation to reduce the noise generated on takeoff and landing. Acoustical measurements and instrumentation range from a handheld sound level meter to a 1000-microphone phased array.
Whether using a sound level meter or a noise dosimeter, the processing is somewhat similar. With a calibrated sound level meter, the incoming sounds are going to be picked up by the microphone and then measured by the internal electronic circuits. [5] The sound measurement that the device outputs can be filtered through an A, B, or C weighting ...
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