High acoustic transmission loss panel

Claim 1

AN ACOUSTIC PANEL FOR PROVIDING HIGH ACOUSTIC TRANSMISSION LOSS OVER A WIDE BAND OF ACOUSTIC FREQUENCIES, COMPRISING A SANDWICH OF AT LEAST THREE LAYERS OF STIFF LIGHT-TRANSMITTING SHEET MATERIAL TWO OF WHICH FORM THE OUTER SURFACES OF THE PANEL, EACH LAYER BEING SEPARATED FROM BUT CONNECTED TO THE ADJACENT LAYER BY AN INTERMEDIATE LAYER OF SHEARABLE BUT SUBSTANTIALLY INCOMPRESSIBLE LIGHT-TRANSMITTING ELASTIC MATERIAL, THE LAYERS BEING SUBSTANTIALLY COEXTENSIVE, THE EFFECTIVE LONGITUDINAL STIFFNESS OF THE LAYERS OF ELASTIC MATERIAL BEING SUBSTANTIALLY LESS THAN THE LONGITUDINAL STIFFNESS OF THE LAYERS OF STIFF MATERIAL, THE EFFECTIVE SHEAR MODULUS U AND DENSTIY P OF THE CONNECTED LAYERS INTERMEDIATE THE SAID OUTER SURFACES BEING RELATED TO THE VELOCITY CS OF SHEAR WAVES IN THE SAID PANEL SUBSTANTIALLY BY THE EQUATION CS=$U/P, WHERE CS IS NO GREATER THAN SUBSTANTIALLY SEVEN-TENTHS THE VELOCITY C0 OF ACOUSTIC WAVES IN THE MEDIUM SURROUNDING SAID PANEL, AND THE THICKNESS OF SAID LAYERS OF STIFF MATERIAL AND SAID LAYERS OF ELASTIC MATERIAL BEING OF THE ORDER OF TENTHS OF AN INCH AND HUNDREDTHS OF AN INCH, RESPECTIVELY.