GB887535A - High acoustic-energy transmission-loss panel and the like - Google Patents

Abstract

887,535. Modifying acoustic properties of rooms. BOLT, BERANEK & NEWMAN Inc. Dec.30, 1959 [March 6, 1959], No. 44238/59. Class 13. [Also in Group XL (b)] In a sound-absorbing panel, a fairly level absorption frequency characteristic, due to increased absorption at low frequencies, is obtained by loading the non- porous, resilient, panel with masses, so distributed, that their mean separation is less than the wavelengths corresponding to the frequencies which it is desired to absorb. The panel 1 (Fig. 1), may be made of plastic or metal foil and the masses 3 may be lead weights whose separation is small compared with the relevant wavelengths. The masses act as mass-type impedance _elements effectively connected in parallel with the stiffness (compliance)-type elements of the intervening and supporting panel elements 1<SP>1</SP>, this giving rise to a resonance frequency (maximum absorption) when the net motion of the two elements is effectively zero. The masses may be of unequal weight and distribution (Fig. 2, not shown), they may project on both sides of the panel (Fig. 3, not shown), they may be integral with it (Fig. 6, not shown), or they may be in the form of glass beads on a curtain type of panel (Fig. 4, not shown). The panel may be double-walled, with a honeycomb structure between the walls, masses being placed in some of the compartments (Fig. 7, not shown); it may also have portions of itself of higher density than the rest, these portions acting as the masses.