The invention relates to a sound absorber (2) for an auxiliary engine of an aircraft comprising an inlet (46), an outlet (48), a housing (4), and a flow channel (6) which has a porous wall material and is arranged in the housing (4). An intermediate space is formed between the housing (4) and the flow channel (6). Said intermediate space is divided into outer cells (10-26) arranged around the flow channel (6) by way of one or more partitions (8). Thus, a very compact sound absorber having very good sound insulation is made possible. By dividing the outer cells (10-26) into outer areas and inner areas, adapting the shape of the sound absorber (2) to a rear section of the aircraft, and attaching a ring-shaped channel to the outlet (48), the sound insulation can be improved further.