Hexahedron Reverberation Box for Measurement of Frequency Dependent Reverberant Noise Absorption Coefficient and Experimental Verification

- A hexahedron reverberation box has been developed through reverse engineering to study the reverberation time of fibrous felts in diffuse acoustic field condition. The study reinstated the frequency as a prime factor to understand the relation between noise control performance of a sample in transfer matrix method and diffused acoustic field condition. A new non-linear, bi-variant frequency dependent model was formulated through synchronization of impedance tube data and noise absorption coefficient calculated from reverberation time of the felts tested in the hexahedron box. The empirical model was validated for particle board based perforated absorber which yielded a comparable noise absorption value with a mean absolute error as low as 0.02. The reverberation box substantially reduces the size of samples for trial in nondestructive mode. The frequency dependent model for different absorber predicted the noise absorption property from calculated reverberation time (RT60), which would help in engineering specified samples for noise control. The novelty of the work lies in the fabrication of the reverberation box to work with frequency levels as low as 250 Hz i.e., above Schroeder frequency.