Title: Basic Facts about Noise as Related to Aviation
text: NOISE has two aspects: (1) subjectively, it is any unwanted sound; (2) objectively, it is characterized by many variables. The subjective view is important in determining the response of people to aircraft noise and in establishing engineering design objectives for noise control. The engineering of noise control deals with the objective aspect in three parts: 1. The noise source — characterized by its total noise power output and the distribution of this power with respect to frequency and space. 2. The path — propagation in structures, through the air, and over terrain as influenced by properties of materials, geometry, meteorological conditions, and topography. 3. The received noise — its sound level, frequency spectrum, time pattern, and other variables as required to correlate with the subjective response of man in the aircraft, on the line or in the community.