Flexible polyurethane foams are used in targeted applications depending on the specific frequency ranges. In this study, low molecular weight polyol (TF400) and DBTDL gelling catalyst are selected as control parameters to examine their effects on the cellular morphology and acoustic properties. As the contents of the TF400 increase, the cavity and pore sizes get smaller. The cell wall area ratio shows the lowest value at 50% TF400, and it increases drastically after 75% TF400 contents. These morphological results are closely related to the highest acoustic activity at 50% TF400. Air flow resistance also gradually increases with increasing the TF400, and it rapidly increases due to high cell wall area ratio after 75%. Therefore, air flow resistance and cellular morphology are dominant factors to improve acoustic properties at low frequency regions in the polyurethane foams including low molecular polyol.