The specification and drawings present a new method and apparatus for reducing loudspeaker size by partitioning the back cavity of the loudspeaker using a sound sponge block. The sound sponge block is an array of narrow ducts (e.g., parallel ducts, or parallel round cylinders of a small diameter) made of a pre-selected material with predetermined dimensions (e.g., the diameter and length) formed within a single block which is placed behind a loudspeaker diaphragm but not in a direct contact with it. The sound sponge block, comprising the multiple very narrow ducts (e.g., with duct diameters on the order of microns) substantially absorbs the sound waves radiated from a rear side of the diaphragm in the backward direction due to significant drop in the impedance for very narrow tube diameters.