This research was conducted to analyze the absorption coefficients of sound at several types of materials as well as its combinations. The aim of this research was to find the value of sound absorption coefficients on the materials and its combinations. The materials used in this research were gypsum panel, gypsum-fiber palm, fiber palm-gypsum, and foamed concrete-fiber palm. The test was conducted by using a method of reverberation chamber based on the ISO 354-1985 with the types of the sound source: white noise and pink noise at frequency of 125 Hz – 8000 Hz. Based on the test results of white noise, it was found that the panel of gypsum-fiber palm has α = 0.93 at low frequency; the panel of fiber palm has α = 0.97 at medium frequency; and the panel of foamed concrete-fiber palm has α = 0.89 at high frequency. Further, for the sound source of pink noise, it was found that the panel of gypsum-fiber palm has α = 0.99 at low level; the panel of fiber palm-gypsum has α = 0.86 at medium level; and the panel of fiber palm-gypsum has α = 0.64 at high level. The fiber palm panel could absorb the sounds well since this material has bigger air space (pore) than the foamed concrete and gypsum. Consequently, when the sounds wave enters to this material it will be trapped in the space. The panel of fiber palm affected an increasing of sound absorption coefficient value at the combination materials when the panel of fiber palm was placed under another panel. However, the absorption coefficient values of both fiber palm and fiber palm-gypsum panels are about the same.
Keywords: Coefficient of sound absorption, white noise, pink noise.