A study of the influence of incidence angle on sound reduction index using NAH-Phonoscopy

摘要

The sound reduction index is generally measured or computed for an incident diffuse field, without considering the influence of the direction of incoming waves. However, when an element is excited by a well directive incident field, due to various situations with incident outdoor noise, its acoustical transparency varies significantly according to the position of the sound source. This paper presents a new technique implemented for measuring the reduction index as a function of the incidence angle. It is based on the use of a Nearfield Acoustical Holography (NAH) system called NAH-Phonoscopy. This equipment is used to express the radiated intensity in the wavenumber space, which gives a wave by wave decomposition of the transmitted field. Therefore, the angular behavior of the acoustical transparency of the partition can be analyzed. In a first section, the physical principles of the NAH-Phonoscopy are detailed. In a second section, it is explained how the NAH-Phonoscopy measurements are used to assess the sound reduction index R(theta). Then, a numerical validation of this method is presented. In the last section, experimental evaluations of R(theta) are discussed.