An acoustic device having a housing and an acoustic transducer is disclosed. The housing has a transducer space for the acoustic transducer, and a back volume space. The back volume is filled with a sound adsorber material. The sound adsorber material in the back volume space is configured to virtually increase the size of the back volume space, and shift the resonant frequency of the back volume space. The acoustic chamber for the acoustic transducer and the sound adsorber material is integral to the split-shell housing of the acoustic device. The sound adsorber material is retained in a portion of the acoustic chamber by an acoustically permeable material that facilitates gas exchange within the back volume space, and between the sound adsorber material and the transducer space. The acoustically permeable material is configured in different arrangements to facilitate the gas exchange.