Field Measurements of Air Raid Warning Devices

Abstract

Total war has created the necessity of warning the civilian population of impending air attack. Acoustic signaling has proved to be an effective method of warning the people. The Office of Civilian Defense, which is charged with the protection of the civilian population, has sponsored a project to determine the characteristics of sound signaling devices for air raid warnings. As a criterion by which the sound output of a signaling device can be judged, sound levels have been taken at 100 feet from the source. Measurements have been made in a large open space with the device mounted about 20 feet above the ground. Frequency analyses of each device have been made. Distribution of energy has been determined both for the individual components and for frequency bands. Measurements have also been made at distances of 700, 1400 and 2800 feet from the source. Varying atmospheric conditions, such as wind, had considerable effect upon the attenuation of sound with distance; in fact, for most of the devices submitted, the effect of the wind seems to be as important or more so than the distribution of energy in the different frequency components. Measurements taken over city terrain show that the attenuation of sound is greater than when taken over open spaces. The results of these measurements can be obtained upon application to the National Bureau of Standdards in Letter Circular LC 685 and Letter Circular LC-685 Supplement.