REACTIVE CHARACTERISTICS OF PARTIAL SCREENS FOR A SOUND SOURCE MOUNTED IN AN INFINITE BAFFLE

Abstract

An analytical method using the assumed acoustic modes at boundaries is constructed to understand the sound radiation from a source mounted in an infinite baffle and blocked by a rigid close fitting shield. Special attention is given to overcome the thin body problem of the screen. An algebraic equation is derived by using the eigenfunction expansion and orthogonality principle in which the acoustic pressures and particle velocities defined on each subdivided surface are expressed by separable coordinates. Change of the radiation impedance of the source due to shielding is evaluated and is verified by experiments. Other acoustical characteristics of the partial screen are investigated in connection with the change of radiation impedance and with geometrical parameters of the system. The results of the parametric study reveal that the close fitting shield may not be a good noise control element for a source radiating broadband noise, especially at low frequencies in the absence of absorbing materials. The analytical results can be useful in the conceptual design stage of partial screens for selectively attenuating the sound radiation from machinery surface in the mid and high frequencies and for designing improved loudspeaker systems at low frequencies. (C) 1995 Acoustical Society of America.