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To satisfy the increased expectations of customers, engineers are challenged to increase fuel economy while also improving noise, vibration, and harshness (NVH) performance. In order to improve fuel economy, engine compartment designs have become more compact with reduced air flow. Elevated temperatures caused by these designs can degrade the durability and acoustic performance of the fibrous acoustic insulator material. A typical method for protecting insulators from elevated temperatures is to apply an aluminum foil patch to the surface. However, foil patches can restrict the insulator's ability to absorb sound and can be difficult to apply to complex part shapes. Foil patches can be perforated to allow the insulator to absorb sound, but there is a cost penalty as well as potential for long term performance degradation due to blocked perforations. Since NVH targets are also increasing, it's important to maximize the benefit of each part.

One measure of perceived quality in a new car is how easily the passengers can communicate. This includes communication between the passengers and also communication to the vehicle itself, as features such as Bluetooth and voice activated controls become increasingly common. Articulation Index (AI) has long been the standard in the automotive industry for evaluating the ease of communication. Previous studies have explained that AI, however, only evaluates the background noise that surrounds the listener; and does not capture changes in modulation of sound before reaching the listener. The telecommunication and construction industries have used Speech Transmission Index (STI) as a measure of communication. This method incorporates the masking effect of background noise, and modulation of the speech signal along the transmission path. This study focused to understand STI, cascade to component characteristics and modify characteristics to improve speech transmission inside vehicles.