This article proposes noise isolation index to assess the acoustical comfort level in the interior vehicle cabin. The noise isolation index is developed, validated, and compared for three local compact cars, namely, Axia, Myvi, and Viva which are most widely used vehicles in Malaysia and have not been yet studied. Toward this end, the interior and exterior sound signals are recorded on both stationary and non-stationary (highway, pavement, and urban) conditions and the trends of sound quality loudness (sone) and sharpness (acum) with respect to sound pressure level (Pa) are observed. The findings of this study indicate that the noise isolation index results are literally influenced by factors including type of road surface, engine transmissions, and vehicle design characteristics. The proposed index can be successfully extended by automotive researchers to assess the interior vehicle noise and can be significant factor in vehicle manufacturing process.
