The half-roll, when executed in a hard material, is not very compliant. It acts more like a flat annular ring than a roll. The roll is still a flat annular ring at its second eigentone. If this frequency occurs within the operating region of a driver, it becomes a dynamic absorber and rolls off the frequency response most dramatically. Materials having higher modulus-to-weight ratios are available, but their use is costly and sometimes dangerous. Just as an I beam has a higher stiffness-to-weight ratio than does a solid bar, there are special designs that can be embossed with standard tooling into the surround which can obtain useful improvements with low-cost materials. Some aspects of this problem and its evaluation are discussed.
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