Automotive floor carpet serves the purpose of insulating airborne noises like road-tire noise, transmission noise, fuel pump noise etc. Most commonly used automotive floor carpet structure is- molded sound barrier (PE, vinyl etc.) decoupled from the floor pan with an absorber such as felt. With increasing customer expectations and fuel efficiency requirements, the NVH requirements are increasing as well. The only possible way of increasing acoustic performance (Specifically, Sound Transmission Loss, STL) in the mentioned carpet structure is to increase the barrier material. This solution, however, comes at a great weight penalty. Theoretically, increasing the number of decoupled barrier layers greatly enhances the STL performance of an acoustic packaging for same weight. In practice, however, this solution presents problems like- ineffectiveness at lower frequencies, sudden dip in performance at modal frequencies. Also, practical constraints in achieving ideal decoupling limit the advantages of the technique. This paper aims at exploring the effects of multi-layering of barrier material on STL performance of automotive carpets. Another focus area of this paper is the optimization of several multi-layered structures to make it effective for automotive floor carpet application in frequency band of 500Hz to 8000 Hz. Also, methods of improving decoupling in automotive carpet to improve STL performance have been studied. An approximate mathematical model has been developed in the paper to explain the STL behavior of automotive carpets. The model has been validated by comparing results with actual test results at ARAI. Based on the model, effect of changes in parameters of backing material, absorber/decoupler, type of bonding between backing and absorber has been discussed. In addition, guidelines for a part designer have been developed to decide the kind of carpet structure to be used for given NVH requirements.
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