Tunable sound packages consisting of granular aerogels and fibrous media

In this study, two granular aerogel materials, both consisting of particles with sizes on the scale of 1 to 50 mm, were first investigated both theoretically and experimentally to improve our understanding of their acoustical behavior. Specifically, layers of the aerogels were evaluated in terms of their sound absorption coefficients, and loss mechanisms in the frequency region below 2000 Hz were quantified for both aerogels by using a previously-developed modeling tool based on the Biot theory. Further studies were then conducted in order to optimize the acoustical performance of potential sound packages featuring these aerogel particle stacks. For example, one of the aerogel materials was placed in series with a fibrous layer to take advantage of the low and high frequency sound absorption offered by the aerogel and the fibrous layers, respectively. The two types of aerogels were also combined in parallel to show that absorption peaks of one of the materials could be used to compensate for the absorption “dips” of the other material. After experimentally validating the design concepts mentioned above, the aerogel granule stacks' properties were tuned to realize a very low frequency and wideband sound absorption treatment when combined with the fibrous layer.