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Interior quietness has been improved over the years until it has now become an important fundamental performance requirement of vehicles. Simple approaches to assuring quietness include the addition of sound isolation materials or the provision of sound-deadening space. These approaches, however, have the undesirable effects of increasing the vehicle weight or sacrificing interior space. Previously, we investigated the effect of the fiber composition on sound isolation performance, focusing on polyester fiber material (nonwoven fabric), and researched sound-isolating materials that would not involve a weight increase. That work led to the development of a polyester fiber material with an optimized fiber composition. The material has been applied to a dash silencer that simultaneously achieves improved sound isolation performance and a lighter weight compared with previous materials. That technology provided the basis for developing a polyester fiber carpet pad.

Interior quietness has been improved year by year until it has now become one of the basic performance requirements of vehicles. Traditional approaches to assuring quietness have been to increase the weight of sound insulation barriers or to enlarge sound insulation space. Such methods run counter to the aims of reducing vehicle weight and providing a more spacious interior. In this research, an attempt was made to overcome this trade-off by adopting a new material for the sound-absorbing material used in vehicles. The newly developed-sound absorbing material consists mainly of modified cross-section polyester fabric. It provides noticeably higher sound-absorbing performance than traditional material like shoddy or formed urethane. This is attributed to increased friction between the fibers and air, owing to the greater surface aria of the modified cross-section polyester fiber compare with that of the circular cross-section of ordinary fibers at an identical weight.