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A sound absorbing block of molded structural material has a sequence of internal cavities that communicate with a region containing the sound to be suppressed through a first elongated slot located in an exterior wall of the block. The internal cavities are defined by interior walls, at least one of

A sound absorbing block of molded structural material has a sequence of internal cavities that communicate with a region containing the sound to be suppressed through a first elongated slot located in an exterior wall of the block. The internal cavities are defined by interior walls, at least one of which also contains an elongated, sound-communicating slot. Each slot and its associated cavity define an acoustical Helmholtz resonator that dissipates sound energy incident upon the slot with an absorption peak at a natural frequency fn. The value of fn for each resonator is inversely proportional the square root of the volume of the cavity. The internal cavities are arranged to cascade in order of decreasing stiffness beginning at the first slot. In one form, two sequences of cavities in a block use a common final cavity. Also, the exterior slots can be formed in more than one wall to absorb sound produced in multiple regions.

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In a sound-absorptive block of molded structural material having a front wall, a rear wall, two end walls, a top wall and an opening opposite said top wall where at least the exterior surface of said front wall receives the sound energy to be absorbed, said walls formed integrally with one another t

In a sound-absorptive block of molded structural material having a front wall, a rear wall, two end walls, a top wall and an opening opposite said top wall where at least the exterior surface of said front wall receives the sound energy to be absorbed, said walls formed integrally with one another to provide a load bearing capability and defining an interior space, the improvement comprising at least one interior wall that divides said interior space into sequenced cavities including at least a first cavity adjacent said sound receiving wall and a second cavity separated from said first cavity by said interior wall, a first orifice formed in said sound receiving wall, said first orifice and said first cavity forming a first acoustical resonator that dissipates sound energy at a natural frequency f1, and a second orifice formed in said at least one interior wall to couple acoustically said sequenced cavities, wherein said second cavity is coupled to said sound receiving wall only through said first cavity, said second orifice and said second cavity forming a second acoustical resonator that dissipates sound energy at a natural frequency f2, where f1>f2.