Articles and methods of making and using the articles are provided. The articles include inorganic agglomerates having an average dimension in a range from about 50 microns to about 2 mm. The porous agglomerates each include a network of carbon or silica, and metal oxide particles embedded in the network. Some agglomerates are capable of lowering a resonant frequency of an acoustic device when the resonant frequency is in a range from about 50 Hz to about 1500 Hz.