Comparison of acoustic 3D spacer fabrics with traditional acoustic materials: Limitations and potentialities

Background: Natural waste is one of the materials that has the potential to become acoustic material because it has a porous texture and meets the requirements of suitable sound-absorbing materials. Utilizing natural waste as acoustic material can reduce cassava peel waste, especially in cassava peel processing industries, both from factories and home industries. Methods: This research is conducted to determine the potential of cassava peel waste as a natural material that can be utilized to create acoustic materials made from natural substances. In this study, cassava peel waste was tested as a sound-absorbing acoustic material using the impedance tube method. The sample was made by mixing finely ground cassava peel waste and PVAc (Poly-vinyl-acetate) white glue, then molding the mixture into circular molds with a diameter of 10 cm and thicknesses of 3.5 cm and 4 cm, respectively. Findings: The results indicate that the sample with a thickness of 3.5 cm has an absorption coefficient of 0.45 at a frequency of 500 Hz, while the 4 cm thick sample has an absorption coefficient of 0.32 at 600 Hz. Both samples show that cassava peel waste is a viable soundproofing material with absorption coefficients above 0.3, making it an effective, eco-friendly acoustic panel material. Conclusion: Cassava peel waste demonstrates good potential as an acoustic material, with promising sound absorption properties, making it an environmentally friendly and accessible alternative to conventional soundproofing materials. Novelty/Originality of this Study: This study introduces cassava peel waste as a sustainable and accessible material for acoustic applications, offering an innovative solution to both waste reduction and soundproofing. The research highlights the potential of using locally available natural waste, specifically cassava peel, in the creation of eco-friendly acoustic panels, which is a novel approach not widely explored in the acoustic material industry.

Experimental criteria for sound insulation material recommendation and design have an important share in indoor acoustic control. Among these criteria, laboratories with devices such as impedance tubes, alpha cabins and reverberation rooms used to measure and analyze parameters such as sound transmission loss and sound absorption coefficient have been investigated. In literature, it has been observed that there are studies on acoustic materials and the tests applied to these materials, but the application is more limited. According to research data, an Alpha Cabin model system design that can be used to develop new types of acoustic sound materials has been proposed. In addition to the fact that a large number of experimental measurements can be performed at lower costs using the designed Alpha Cabin model system, many tests can be performed easily for different material designs in a very short time. To perform these tests, the Alpha Cabin system has been designed based on noise and sound insulation. For example, floating flooring, ribbed connection, and so on. Afterward, different insulation materials were used for insulation purposes and standards were achieved. The Alpha Cabin test system, which was designed and developed, overlaps the experimental and theoretical data for 500, 2000, and 4000 Hz when compared with the values of 29.1 dB for 500 Hz, 38.6 dB for 2000 Hz, and 49 dB for 4000 Hz measured in the Acoustic Facade Panel Test Room, and it has been observed that it can be used in the development of new sound insulation materials.

A model comparison of the absorption coefficient of a Microperforated Insertion Unit in the frequency and time domains

The measurement of the absorption coefficient of acoustic materials is usually performed in an impedance tube under normal incidence on a small sample, or in a reverberant room under diffuse field incidence on a large sample of material. Both methods are prone to well-documented experimental limitations and errors. The approach proposed here uses a virtual source antenna (a point source moved at successive positions) over a material sample typically 1 to 4 m2 in size, and a fixed microphone pair directly above the material surface. Several methods have been tested to reconstruct the absorption coefficient under oblique plane wave or diffuse field incidence. Among these, the inversion of the Allard propagation model over an absorbing plane, in order to extract the material properties (complex wavenumber and density) from measured microphone transfer functions, is presented here. Absorption coefficients are shown for various acoustic materials.

Acoustic materials are widely used for improving interior acoustics based on their sound absorptive or sound diffusive properties. However, common acoustic materials only offer limited options for customizable geometrical features, performance, and aesthetics. This paper focuses on the sound absorption performance of highly customizable 3D-printed Hybrid Acoustic Materials (HAMs) by means of parametric stepped thickness, which is used for sound absorption and diffusion. HAMs were parametrically designed and produced using computational design, 3D-printing technology, and feedstock material with adjustable porosity, allowing for the advanced control of acoustic performance through geometry-related sound absorbing/diffusing strategies. The proposed design methodology paves the way to a customizable large-scale cumulative acoustic performance by varying the parametric stepped thickness. The present study explores the challenges posed by the testing of the sound absorption performance of HAMs in an impedance tube. The representativeness of the test samples (i.e., cylindrical sections) with respect to the original (i.e., rectangular) panel samples is contextually limited by the respective impedance tube’s geometrical features (i.e., cylindrical cross-section) and dimensional requirements (i.e., diameter size). To this aim, an interlaboratory comparison was carried out by testing the normal incidence sound absorption of ten samples in two independent laboratories with two different impedance tubes. The results obtained demonstrate a good level of agreement, with HAMs performing better at lower frequencies than expected and behaving like Helmholtz absorbers, as well as demonstrating a frequency shift pattern related to superficial geometric features.

Acoustical materials are usually used for architectural design, ambient noise, and traffic noise to absorb sound. The sound absorption coefficient (SAC) is often used as the performance index of acoustical materials. It is measured using the reverberation room method (RRM) and the impedance tube method (ITM). The sound source of the RRM is a random incidence in various directions, whereas that of the ITM is a normal incident. The SAC measured by the RRM is more extensive, practical, and costly than ITM. Usually, the SAC measured by RRM is used as the commercially available acoustical materials index. However, RRM requires large-area test samples for measurement and a special sound field of reverberation room for test experiments. Therefore, this study aims to use the ITM to measure SAC. The measured SAC, frequency, thickness, and material density were employed as independent variables and substituted in the obtained multiple regression model to predict SAC obtained by RRM. In addition, the measurement characteristics of impedance tubes provide varisized calibers for different frequency ranges to measure a relatively accurate SAC. Based on the abovementioned characteristics, this study proposed a dual-model for estimating the SAC of the reverberation room method to achieve the best-estimated result. After experimental validation, the dual-model estimated result was compared with SAC from the reverberation room method. It was observed that the maximum absolute value of all errors did not exceed 0.16. Most of the absolute errors were below 0.1, proving the accuracy of this method. Therefore, the method proposed in this study can shorten the acoustical material development schedule for manufacturers and save the cost of the development process.

Objective: This study investigates the techniques for measuring the acoustic absorption coefficient that use an impedance tube, to evaluate their use by students of scientific-technical degrees. Theoretical Framework: This topic presents the concept of absorption coefficient and how it is obtained using impedance tubes. Method: The absorption coefficient of an acoustic insulator is measured as a function of frequency, thickness and density, with an experimental system that uses the transfer function method in an impedance tube. Results and Discussion: The results reveal that the absorption coefficient varies with frequency, being lower at low frequencies. An increase in thickness and/or density produces better acoustic absorption performance. The results are compared with others obtained with an experimental system that uses the standing wave method in an impedance tube. The agreement between the two methods is quite good. Research Implications: The advantages and disadvantages of the two methods are discussed, and their use by students of scientific-technical degrees is assessed. It is recommended to use the transfer function method when students work more autonomously, for example, in final degree projects. Originality/Value: This work offers teachers information related to the experimental study of the acoustic absorption coefficient, which allows them to choose the most appropriate method for each student based on their ability to work autonomously and their knowledge.

The porous characteristics of recycled natural fibres make them suitable for use as acoustic materials. Straw and water hyacinth fibres are natural materials that can potentially be used as composites in damping devices. This study evaluated the acoustic performance of two types of reinforced composites containing natural fibers (water hyacinth and rice straw) and gypsum adhesives in reducing stress levels in the textile industry. The evaluation was carried out through laboratory tests using impedance tubes and direct testing in a textile factory to reduce the stress level of production machine workers and operators. Rice straw and water hyacinth fibres were thoroughly mixed in proven mass ratios of 10% and 30% with water and gypsum plaster as a binder. The mixture was pressed into a mould at a pressure of 3 MPa before being heated in an oven at 900ºC for 5 hours. Perforations measuring 4 to 8 mm in diameter were then made at equal distances on the panels. Acoustic panel performance tests were carried out with impedance tubes according to ISO 10534-2 standards at sound frequencies ranging from 0 to 6400 Hz. Field tests were also conducted at a textile factory, with each machine unit generating a sound source of 100 to 110 dB. Heart rate data was collected, and noise measurements were carried out before and after the panels were installed in the area around the operating machines. The results showed that the rice straw-gypsum composite with four perforations performed the best, achieving an α coefficient of 1.0 at a frequency of 1500 Hz and an NRC of 0.50, indicating effective noise reduction. The installation of acoustic panels around the noise source in the textile industry reduced noise levels by up to 9.8 dB and was found to affect workers' heart rates, indicating reduced stress levels. The questionnaire results also showed a significant effect on the stress levels of workers. The use of natural fibers in composite materials has the potential to be an eco-friendly and sustainable solution for soundproofing applications. Doi: 10.28991/CEJ-2023-09-06-02 Full Text: PDF

Acoustic porous materials are extensively used in many engineering applications like building, automobile, aviation, and marine. The health risk factor and environmental claims, associated with traditional materials such as glass wool, mineral fibers, and polymer foams demand for the alternative porous acoustic absorbing materials. Advances in additive manufacturing (AM) allow to manufacture complex structures and give an alternative method to produce porous materials. This study investigates the acoustic properties of porous sound-absorbing material produced by using additive manufacturing (AM) technique and explores the feasibility of AM to manufacture acoustic absorptive materials. For study, three samples with different aperture ratios were fabricated by AM technique, and their sound absorption coefficients were measured experimentally by using the impedance tube. The theoretical formulation for predicting normal sound absorption coefficient of sample with and without air gap was developed and compared with experimental results. The predicted absorption coefficient agrees well with measured results. The measured results indicate that the absorption coefficient of the structures fabricated through AM can be altered by varying aperture ratio and air gap behind the sample. This study reinforces the capability of AM for producing complex acoustic structures with better acoustic properties.

Acoustic cones are often the primary absorption treatment choice for constructing anechoic chambers. Reverberation chamber estimation of room absorption will most accurately represent the actual effect of three-dimensional treatments, such as cones. However, for low frequencies, large reverberation chambers are often required, which may not be available due to space and cost constraints. Impedance tubes measurements are more accurate than reverberation chamber measurements in terms of sound absorption coefficient. Conversely, due to the two-dimensional nature of impedance tubes, room absorption of three-dimensional objects is difficult to estimate. Absorption coefficient of the material is a function of not only surface area but also material thickness. This paper proposes a technique to estimate the room absorption of three-dimensional treatments based on measured absorption coefficient of different thickness treatment specimens by impedance tube. This extrapolation of impedance tube measured absorption coefficient to actual room absorption can be used to evaluate the effectiveness of absorptive acoustic room treatments, including effects of adhesives and air gaps, without the need of constructing the actual treatment prototypes. The validity of this impedance tube room absorption estimation was verified for a tetrahedral cone treatment using a large reverberation chamber room absorption measurement.

Abstract. This study aims to investigate the potential of durian husk fiber (Durio zibethinus) as the base material for environmentally friendly acoustic panels. The samples were prepared as composites with a fixed composition ratio of durian husk fiber and epoxy resin at 2:1, and with varying thicknesses of 1 cm, 2 cm, 3 cm, and 4 cm. The sound absorption coefficient was measured using the impedance tube method based on ISO 10534-2 in the frequency range of 200–1600 Hz. The results showed that all samples demonstrated good acoustic performance. The 3 cm thick sample provided the best performance with the highest absorption coefficient value of 0.98 at a frequency of 1600 Hz. Increasing the thickness to 4 cm reduced the material's acoustic performance, indicating an optimal thickness limit for sound absorption. This study indicates that durian husk fiber has high potential as an alternative acoustic material that is effective and sustainable, especially for absorbing noise in mid to high frequency ranges.

Mask ability in absorbing sound has been proven as it increases in line with thickness adding. Another characteristic that can optimize the absorption is density. This article aims to study the effect of mask density on the sound-absorption capability. This research was conducted by making absorber material models made of masks from two different brands. In the model making, this research uses two types of masks, the folded peach-colored folded face mask black duckbill type which are arranged up to 2.5 cm in thickness. In that thickness, the folded peach mask has 254 kg/m3 density and the black mask has 305 kg/m3 density. The analysis is carried out using the tube method. The research results show that at a frequency of 400 Hz, the folded peach mask has the highest absorption coefficient of 0.70, whereas the black mask has an absorption coefficient of 0.48. There is a significantly reduced absorption coefficient at the 600 Hz frequency that makes the mask not meet the standard. It can be concluded that the mask material can be used as an acoustic material as it meets the acoustic standard on absorption coefficient of at least 0.3. These findings support previous research on the potency of mask waste as an acoustic material. Therefore, the absorber material from used mask could be a solution to reduce non-degradable waste.

Acoustic cones are often the primary absorption treatment choice in the construction of anechoic chambers. The estimation of sound absorption coefficient of three-dimensional treatments, such as cones, is usually accomplished by the reverberation time method. This method requires isolated, large, heavily constructed reverberation chambers which may not be available due to space and cost constraints. Impedance tubes are an alternative to reverberation chamber measurements for estimating sound absorption coefficients. However, due to the two-dimensional nature of samples used in the impedance tubes, sound absorption of three-dimensional objects is difficult to estimate. Absorption coefficient of the material is a function of not only surface area but also material thickness. This paper proposes a technique to estimate the sound absorption of a three-dimensional treatment using the absorption coefficient data from impedance tube tests. This extrapolation of impedance-tube-measured absorption coefficient to actual sound absorption of cones can be used to evaluate the effectiveness of absorptive acoustic room treatments without the need of testing the actual treatment prototypes.

The impedance tube method is widely used for measuring sound absorption (or reflection) coefficients of acoustic materials as a function of frequency. However, the sound absorption coefficients obtained using the impedance tube method may have some variations due to the dimensions (limits) of an impedance tube, sample preparation and sample mounting. This paper assesses the performance of the two-microphone impedance tube method as a function of frequency for different tube dimensions and materials and presents suggestions for increasing the reliability and repeatability of impedance tube measurements. First, after summarizing a systematic way for measuring acoustic transfer functions, sound absorption coefficients of a variety of materials ranging from conventional absorbing acoustic materials to samples with thin films are measured using two tubes with different tube diameter and microphone spacing. Uncertainty of sound absorption coefficients for various materials is discussed, and the frequency limits of impedance tubes are assessed. Then, a method for minimizing uncertainty due to sample mounting is proposed and the main findings are discussed.

Optimization of acoustic porous material absorbers modeled as rigid multiple microducts networks: Metamaterial design using additive manufacturing