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Brazilian automotive industry has reached a high level of competition and production, and in this scenario noise radiation is a very important factor in which quality, cost and comfort have to meet consumers' impressions of a vehicle. Engineers face today difficult challenges when it comes to improvement of noise emissions: solutions should be fast, cheap and effective. This work presents a recent study to reduce shell noise radiation from an automated transmission mechanism using two solutions of structural damping: modification in the material of the noise source and attenuation of shell movement by using surface patches of viscoelastic sandwich. Although traditionally applied to whole radiating surfaces, the second solution demonstrates that portions of the material applied in proper selected locations are very effective for reduction of shell noise, therefore enabling the usage of smaller sizes of viscoelastic material instead of complete coverings.

Methods for determining the acoustic absorption coefficient of materials are broadly known in NVH engineering and traditionally rely on measurements performed in specimens carefully prepared such as those used in the Kundt's tube. It is understood that the acoustic behavior of a material slice in a well-controlled test bench provides very different circumstances from those found when the material is used in its application location (in situ condition) mostly because of the structural interactions and the boundary conditions involved. Many questions arise when the goal is to understand which absorbing material will be more effective and, moreover, if its cost is worth enough to solve particular noise issues. To answer those questions, acoustic impedance determination using direct particle velocity measurements were used in this work, in which several absorbing coatings used in specific regions of Brazilian truck cabins were mapped and compared.