Particle Velocity Measurements as a Breakthrough for Determining Acoustic Absorption Coefficient in Brazilian Trucks

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. Results show that the technique is extremely powerful in quantifying the in situ acoustic absorption coefficient, thus providing more realistic results and demonstrating clearly that a more expensive material is not necessarily the most effective solution when dealing with sound absorption problems.