Microphone Acoustic Characteristics for Aircraft Flyover Testing
Eric Nesbitt, Justin Lan, Stefan Hunkler
Abstract
This paper discusses ground plane microphones, their characteristics and a method for correcting ground plane measurements to represent what a 1.2 meter pole microphone would measure. Currently the 1.2 meter microphone is the standard method for the measurement of flyover noise levels as defined in ICAO (International Civil Aircraft Organization) Annex 16. This work supports ongoing efforts within CAEP (Committee of Aviation Environmental Protection) and the ICCAIA (International Coordinating Council of Aerospace Industries Associations) to define an improved method for this type of measurement for use in noise certification testing of large civil airplanes. One of the key motivations for this work is to reduce dependence on ground characteristics and define a method which will result in nearly free-field type measurements. In addition, an improved method for simply applying corrections to the free-field type measurements is also presented. In this context, test data has been taken both in the laboratory and from flyover measurements. In addition, both analytical and numerical studies have been carried out and will be summarized in this paper.