Effect of Absorber Placement and Sound Source Type on Room-Acoustic Parameters in a Small Listening Room

The acoustic effect produced by a sound-absorbing material in a small room is not determined by laboratory material characterization and installed area alone; it also depends on spatial deployment and on how the room is excited. This study investigates the combined effects of absorbing-material placement and excitation-source characteristics in a full-scale small listening room. Twelve fixed-amount treatment configurations, each using 12 identical polyurethane-foam absorbers with a total nominal area of 6m2, were compared with an untreated reference. Measurements were performed using a quasi-omnidirectional Brüel & Kjær OmniPower 4292-L source and two directional loudspeakers, Genelec 8020D and AudioSolutions O302B Overture, in a fixed stereo-like source–listener geometry. Room impulse responses were evaluated in one-third-octave bands from 63 to 5000 Hz using T20 and C80. The frequency-resolved results show substantial placement-dependent changes, with the strongest differences occurring mainly in the low and low-mid frequency ranges. As secondary descriptive summaries, the full-band mean T20 reduction reached approximately 0.33 s and the mean C80 increase approximately 5.9 dB, depending on source and configuration. The relative ordering of treatment configurations was itself source dependent. A representative time-domain comparison further showed source-dependent modification of early reflected energy, whereas later energy was reduced more consistently. The results demonstrate that laboratory material characterization, spatial deployment, source–listener geometry, and excitation conditions should be considered jointly when evaluating acoustic treatment in small listening rooms.