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

An analytical method using the assumed acoustic modes at boundaries is constructed to understand the sound radiation from a source mounted i n an infinite baffle and blocked by a rigid close fitting shield. Spec ial attention is given to overcome the thin body problem of the screen . An algebraic equation is derived by using the eigenfunction expansio n and orthogonality principle in which the acoustic pressures and part icle velocities defined on each subdivided surface are expressed by se parable coordinates. Change of the radiation impedance of the source d ue to shielding is evaluated and is verified by experiments. Other aco ustical characteristics of the partial screen are investigated in conn ection with the change of radiation impedance and with geometrical par ameters 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 t he absence of absorbing materials. The analytical results can be usefu l in the conceptual design stage of partial screens for selectively at tenuating the sound radiation from machinery surface in the mid and hi gh frequencies and for designing improved loudspeaker systems at low f requencies. (C) 1995 Acoustical Society of America.