Measuring and evaluating the sound absorption of nonwoven materials used in architectural design by using impedance tube

Over the years, sound is getting more important as a design parameter for indoor and outdoor spaces. Particularly, architectural finishing materials which can be reflective, absorber or diffuser are the leading elements that describes the the spaces. Despite the fact that the acoustical comfort perception of the spaces vary according to the subjective values, undesirable reflections and reverberation problems are the main issues that one can encounter for the spaces that must have good acoustcal conditions. With respect to this, the most common solution method is to cover the surfaces with the absorptive materials for the needed places. In addition to this, shaping arregements can be applied for the wall and the ceiling elements that restrict the space. Also, the elements can be applied as diffuser panels in some cases. When sound is taken into considiration as a parameter in designing spaces, the most common approach is using absorptive materials as much as possible is the best way to reach to the perfect acoustical conditions. However it is not the only truth for all cases. Making the space to reach optimum levels should be the main objective. Design datas should depend on the function of the space and the volume of the space. With respect to this, for the purpose of obtaining optimum reverberation time values that are stated with the term of seconds, absorptive materials should be applied that how much the space needs. When sound is taken into considiration as a parameter in designing spaces, the most common approach is using absorptive materials as much as possible is the best way to reach to the perfect acoustical conditions. However, it is not the only truth for all cases. Making the space to reach optimum levels should be the main objective. Design datas should depend on the function of the space and the volume of the space. With respect to this, for the purpose of obtaining optimum reverberation time values that are stated with the term of seconds, absorptive materials should be applied as needed. Applying absorptive materials in spaces has became widespread with the technological developments and rising needs. With respect to this, they can contain different types within itself. Within the scope of the thesis, the classification of these types of materials are clarified in a widespread manner. At this point, the importance of the natural, sustainable, harmless for human health, recycling, with low emission of carbon materials are emphasized. These materials can provide the requisite acoustical properties as much as other materials with the appropriate system details. Thus, one can achieve an integrative solution long lasting, harmless for the nature and human health and usually low-cost system details along with acoustical comfort conditions. In the first part of the thesis, the purpose of the study, the scope of the study and the method that was chosen are explained shortly. Then, the evaluation of the materials (absorber, diffuser and reflective) according to room acoustic discipline. In the second part of the thesis, the evaluation of the materials according to the sound absorbing principle is discussed. With respect to this, materials are not the only one in a space as an absorber but also people and the air. The prerequisite of the material as an absorber is explained. The absorbing principle of the sound is revealed in detail with encouragingly figures. After that, the factors that affects by the absorbing material is discussed with the subtitles. First of all, the primary title of this principle named frequency factor is clarified. In some cases, the need of a specific frequency absorbing will be an issue according to the function of the spaces. It is so important to understand how the frequency factor affects for the need of the specific frequency absorption. Apart from these, there are some secondary factors that affects the absorbing principle like thickness of the material, density of the material, air flow resistance etc. They are also explained in detail with the scope of the thesis. In the third part of the thesis, the classification of the absorbing materials is the main issue. The most common materials that are included in literature datas are discussed. Day by day, new materials are released to the market with the technological developments. From this point of view, porous materials are the most preferred materials with their ease of applying and high performance of absorbing. Within the scope of the thesis, a great deal of absorbing materials are included like variable absorbing panel, panel type and helmholtz resonators. In addition to this, sustainable and recycling materials that can be applied in spaces as an acoustic absorber are emphasized. In the forth part of the thesis, the main field of the study, the acoustical properties of nonwoven materials, is introduced. After explaining the manufacturing technology of nonwovens and the key features, it is explained how the facors affects nonwovens in relation to acoustic absorbing principle. At this point, with the difference of general parameters that affects absorbing principle for materials, there are some other specific factors that affects absorbing principle of nonwovens like fiber diameter, fiber blend and surface effect. In the fifth part of the thesis, the standards that explains measuring methods are introduced in detail. The commonly used measuring methods are reverberation chamber method and impedance tube method. Reverberation chamber method is more certain than the other method. However it is not as practical as impedance tube method. In developing materials, impedance tube method is chosen for a lot of reason. The main reason for that is to reach the sound absorption values very fast. In the sixth part of the thesis, with the result of all of these researches and evaluations are presented. Industrial nonwovens are measured according to "ISO 10534-2: Determination of sound absorption coefficient and impedance in impedance tubes -- Part 2: Transfer-function method". Initially, measuring method, samples and technical equipments are introduced. Industrial nonwoven, recycled wool and wool felt are the main materials that are used in measurements. In scope of this thesis, thirteen different system detail was measured with the impedance tube using transfer function method. Measurements are confirmed with the second same system detail for minimizing the measurement uncertainty. The results of these thirteen different measurements are evaluated singularly with their single number quantities; αw and NRC (Noise Reduction Coefficient). The result of these measurements are stated with figures and graphics comparatively in detail. They are compared depending on four different parameters: thickness, additional materials, perforation ratios and additional materials with perforation ratios. As a result of that, how measurement results are affected from the point of these parameters is evaluated in detail with the figures and graphics. In the seventh and the last part of the thesis, the overall evaluations are presented having regard to the measurements of nonwoven materials. Overall evaluations are summarized and αw and NRC (Noise Reduction Coefficient) values for each measurements are compared. As a result of this work, one can achieve that it is possible to obtain acoustical comfort conditions with recycled sound absorbing materials. It is clearly emphasized that along with the sustainability it is also a low-cost solution for interior designing.