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Identical fiber wheel liners were installed on two different mid size vehicles in order to compare the noise reduction for each vehicle. The fiber liners represented material in current production. A baseline noise level was established with the existing plastic wheel liners and then comparisons were made with fiber wheel liners. Noise levels were compared in the wheel well and in the interior for similar vehicle operating conditions. For both vehicles, significant tire noise reduction at the source was measured with fiber liners compared to plastic liners. One of the vehicles also demonstrated noise reduction in the passenger cabin with fiber liners. Insight into potential explanations for these differences was provided by comparing the noise levels at different locations within the vehicles. The results show how fiber liners are an additional tool to reduce the noise in a vehicle and how the NVH design for the balance of the vehicle can leverage the NVH impact of these parts.

In recent years several variants of lightweight multi-layered acoustic treatments have been used successfully in vehicles to replace conventional barrier-decoupler interior dash mats. The principle involved is to utilize increased acoustic absorption to offset the decrease in insertion loss from the reduced mass such that equivalent vehicle level performance can be achieved. Typical dual density fibrous constructions consist of a relatively dense cap layer on top of a lofted layer. The density and flow resistivity of these layers are tuned to optimize a balance of insertion loss and absorption performance. Generally these have been found to be very effective with the exception of dash mats with very high insertion loss requirements. This paper describes an alternative treatment which consists of a micro-perforated film top layer and fibrous decoupler layer.

The typical goal of most sound absorbing materials is to maximize the sound absorption for a given thickness, weight and cost. In this study, tests were conducted on an example polyester fiber sound absorber pad to establish baseline acoustical performance and to extract poro-elastic material properties, which were then used to computer model the acoustical performance of this material. Good agreement was obtained for the measured and predicted sound absorption for the base fiber material. Opportunities to improve the performance of this material were then investigated using computer models of various acoustically-tuned facings in combination with the base pad. The results show how overall sound absorption can be improved and how the frequency dependent performance can be tuned to meet specific requirements.

Flat, constant thickness composites that consisted of a microperforated top layer plus a fibrous decoupler layer were tested for random absorption and transmission loss (TL) performance. The top, microperforated layer consisted of a relatively thick film that contained small, precise micro-perforations. For reference, top layers that consisted of a resistive scrim and an impervious film were also included in this study. Two fibrous materials of constant thickness were used for the decoupler layer between a steel panel and the top microperforated film. The composites' absorption and TL performance were also modeled using the well-known transfer matrix method. This method has been implemented in a commercially available statistical energy analysis (SEA) software package. A comparison of testing and modeling results showed reasonable agreement for absorption results and even better agreement for transmission loss and insertion loss results.

Sound absorption for multiple materials was measured in a small reverberation room using different sample sizes. The largest samples were cut to progressively smaller sizes to study the effect of sample size on sound absorption. The materials tested included three different recycled fibers, two PET fibers with facers, and one open-cell foam. These materials spanned low, medium, and high sound absorption over the range of test frequencies. The results for each material and each sample size are reported and compared. Comments are provided on sample size for labs with small reverberation chambers. These results will be considered in the development of an SAE test method for sound absorption using small reverberation rooms.

The sound absorption coefficient and transmission loss of automotive floor systems with several different fiber decoupler materials are presented. Flooring materials included tufted carpet with and without mass layers and non woven carpet without mass layers. Decouplers included die cut and molded fiber under pads in a range of fiber types and weight. Mass backed floors as well as lightweight dissipative floor systems are compared. The results show a range of performance for sound absorption and transmission loss that allows an NVH engineer to select material combinations to achieve targeted noise reduction in a vehicle.

Tire noise reduction was evaluated with acoustically designed exterior wheel arch liners. The wheel liners were made with a fiber blend selected to meet acoustical requirements, process demands, and durability challenges. Fiber liners were installed in a vehicle and noise level measurements were made under a range of operating conditions. The results show the reduction in tire noise that can be achieved at the source and in the vehicle. A critical part of this evaluation was a rapid analysis technique to select metrics that correlated with subjective assessments. The analysis techniques also helped quantify the improvements over a baseline condition.