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Hearing, Sound, Noise, and Vibration
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
Sound-absorbing materials are usually porous and lightweight. As the sound waves travel back and forth within the tiny interstices of the material, their energy is converted to heat by friction. The sound-absorbing characteristics of a material are described by its absorption coefficient—the ratio of the energy absorbed to the energy striking the material. A perfect absorber has a coefficient of 1, whereas a perfect reflector has a coefficient of 0. The absorption coefficient of a material varies with frequency; therefore, frequency analysis of the problem noise is needed if an optimal choice of material is to be made.
Room Acoustics
Published in Randall F. Barron, Industrial Noise Control and Acoustics, 2002
Sound-absorbing materials are used to reduce the sound levels in a room or to reduce the reverberation, if either of these quantities are excessive. As will be discussed in Sec. 7.3, surface absorption materials do not change the sound coming directly from the source to the receiver. Instead, the surface treatment affects sound that has been reflected at least one time from the surfaces of the room. This sound is associated with the reverberant sound field.
Silencers, Mufflers, and Active Noise Control
Published in Lewis H. Bell, Douglas H. Bell, Industrial Noise Control, 2017
Lewis H. Bell, Douglas H. Bell
The simplest form of absorptive or dissipative silencers is the parallel baffle, as illustrated in Fig. 8.1. Basically, these baffles consist of an aerodynamically streamlined entrance and exit with perforated walls backed by highly absorbent acoustical material. The absorbing material is usually fibrous in texture, either glass or mineral wools.
A study of the dielectric properties and resistance of polypyrrole/nylon composites
Published in The Journal of The Textile Institute, 2023
Yuanjun Liu, Yongtao Yu, Xiang Wu, Xiaoming Zhao
In accordance with the loss mechanism, the absorbing agents can be divided into the resistance type, the dielectric type, and the magnetic medium type. The resistance type absorbs electromagnetic waves mainly through their interaction with the electric field, and its main characteristic is absorbance of the waves in a way dependent on electronic polarization or interfacial polarization decay (Liu, Liu & Zhao, 2018). The absorbing efficiency depends on the conductivity and dielectric constant of the material. The absorbing agents mainly include carbon black, metal powders, silicon, graphite, carbon fiber, and conductive polymers (polypyrrole, polyaniline, etc.) (Maity et al., 2014; Zhao et al., 2012; Zhao et al., 2018). Conductive polymers are an important absorbing agent; among them is polypyrrole, which is known for its low density, ease of synthesis, controllable conductivity, and varied morphology (Balint et al., 2014; Yu et al., 2014). Polypyrrole was chosen as the absorbing agent in this investigation; it is a conductive polymer with many potential applications, such as polymer wires, electronic and optical devices, chemical sensors, electrical color displays, anticorrosive materials, and other functional materials and devices.
Mechanical and acoustic absorption characteristics of UHMWPE weft-knitted structures of flexible porous laminated composites
Published in The Journal of The Textile Institute, 2022
Ruosi Yan, Xingteng Zhang, Mengjin Wu, Zhengkun Zhang, Tuo Liu, Lixia Jia
Acoustic absorbing materials can be used in noise reduction to achieve a satisfactory noise reduction effect. Previous research on acoustic absorbing structures have revealed that the different structures of acoustic absorbing materials, such as perforated orifice, fiber hybrid composites, and organic foam exhibited superior acoustic absorption performance (Choe et al., 2018; Hassani et al., 2021; Yang et al., 2019). Porous acoustic absorbing materials with low density and high porosity are the most widely used types of acoustic absorbing materials. Porous acoustic absorbing materials convert the energy of incident sound waves into heat to absorb incident sound waves (Ayub et al., 2018). Fiber hybrid composite structures are categorized as porous acoustic absorbing structures. Presently, plant and chemical fibers (Berardi & Iannace, 2015; Dieckmann et al., 2018) have broad applications in the field of acoustic absorption and noise reduction. Therefore, it is essential to explore the different fibers applied in the field of acoustic absorption and noise reduction.
Acoustic behaviour of textile structures
Published in Textile Progress, 2021
Parikshit Paul, Rajesh Mishra, B. K. Behera
Absorption: The sound wave is absorbed by the material it interacts with and is converted into heat energy inside the absorbing material. The amount of energy that gets absorbed or is transmitted depends on the thickness and nature of the material. Too little absorption causes the sound to reflect. Various sound-absorption materials are available. The sound absorbers may be of pervious or reverberant class. Fibrous materials and open-celled foams are porous absorbents. The ability of sound energy to be absorbed by the material is expressed as the material’s sound-absorption coefficient (α). The sound-absorption coefficient α ranges between 0 and 1, where 0 means 100% reflection, and 1 indicates the highest absorption (Corredor-Bedoya, Acuña, Serpa, & Masiero, 2021; Halliday, Resnick, Halliday, & Walker, 2018; Wilson, 2003).