Acoustic model for shoddy-based fibre absorbers

John Manning, Raymond Panneton


The acoustic behavior of shoddies is not well understood when compared to more ubiquitous porous materials such as fiberglass and certain polymeric foams. Designers must therefore rely on predictive models that are either highly complex or simpler models developed for different materials. The effect can be mitigated by using a larger test sample, however, these tests are more expensive and labor intensive. The second pronounced effect is a microscopic one. Raw shoddy contains a haphazard mix of different fiber types and sizes and characterizing the microstructure for use in predictive models is difficult. The model exchanges a minor loss in precision for this simplification. Charts of the characteristic lengths and static thermal permeability have been omitted for brevity. The behavior of the characteristic lengths is such that individual expressions relating the characteristic lengths to bulk density for each material type are chosen in favor of general expressions.


Porous materials; Acoustic behavior; Acoustic model; Bulk density; Characteristic length; Fiber types; General expression; Labor intensive; Model exchange; Polymeric foams; Predictive models; Test samples

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