Increase of size and bending of glazings, and general improvements concerning NVH, has made of glazings one of the weak points to be treated. No specific acoustic solutions existed.
First question was to determine exactly concerning which problems glazings were involved, and then what and how solutions could be found. Main problems were found concerning booming noise, transmission of airborne external noise and aerodynamic noise. To dispose of good specifications concerning products, simulations had to be done and validated: finite elements code for low frequency behavior (booming and airborne), SEA and modal superposition concerning medium and high frequency (aerodynamic and airborne). This was done for monolithic and laminated glass with their shape, free-free and taking into account boundary conditions: glues, extrusion, encapsulation. The way it has been done is presented: measurements of the characteristics of components (interlayers, glues), use of FEM and FEM-BEM methods from CAD shapes, use of SEA. Validations are also presented. Problems to solve were mostly coupling between windshield eigenmodes and internal modes of the cavity excited by the engine (low frequency), and whistling due to coincidence frequency of glass concerning mostly aerodynamic noise. Solutions are found by using specific interlayer instead of standard PVB within the laminated glass, or by improving boundary conditions by using specific shapes and/or material of the joint, first defined by a specific software. Psychoacoustic criteria are used to optimize the solutions. Shape influence is also studied. Some specific studies concerning both problems are presented.
Some glass solutions now exist to reduce NVH problems within cars, and/or to compensate reduction of weight, which is one main topic of car industry.