Comparative study of the sound absorption coefficient of two absorbent materials with two empirical methods for low frequency

2018 ◽  
Vol 144 (3) ◽  
pp. 1848-1848
Author(s):  
Nelson L. Legat ◽  
Claudia C. Silva ◽  
Nilson Barbieri ◽  
Key F. Lima
Keyword(s):  
Absorption Coefficient ◽  
Comparative Study ◽  
Sound Absorption ◽  
Low Frequency ◽  
Sound Absorption Coefficient ◽  
Empirical Methods

scholarly journals Study on the sound absorption behavior of multi-component polyester nonwovens: experimental and numerical methods

2018 ◽  
Vol 89 (16) ◽  
pp. 3342-3361 ◽  
Author(s):  
Tao Yang ◽  
Ferina Saati ◽  
Kirill V Horoshenkov ◽  
Xiaoman Xiong ◽  
Kai Yang ◽  
...  
Keyword(s):  
Numerical Methods ◽  
Absorption Coefficient ◽  
Empirical Model ◽  
Surface Impedance ◽  
Sound Absorption ◽  
Low Frequency ◽  
Accurate Method ◽  
Small Error ◽  
Sound Absorption Coefficient ◽  
Acoustical Properties

This study presents an investigation of the acoustical properties of multi-component polyester nonwovens with experimental and numerical methods. Fifteen types of nonwoven samples made with staple, hollow and bi-component polyester fibers were chosen to carry out this study. The AFD300 AcoustiFlow device was employed to measure airflow resistivity. Several models were grouped in theoretical and empirical model categories and used to predict the airflow resistivity. A simple empirical model based on fiber diameter and fabric bulk density was obtained through the power-fitting method. The difference between measured and predicted airflow resistivity was analyzed. The surface impedance and sound absorption coefficient were determined by using a 45 mm Materiacustica impedance tube. Some widely used impedance models were used to predict the acoustical properties. A comparison between measured and predicted values was carried out to determine the most accurate model for multi-component polyester nonwovens. The results show that one of the Tarnow model provides the closest prediction to the measured value, with an error of 12%. The proposed power-fitted empirical model exhibits a very small error of 6.8%. It is shown that the Delany–Bazley and Miki models can accurately predict surface impedance of multi-component polyester nonwovens, but the Komatsu model is less accurate, especially at the low-frequency range. The results indicate that the Miki model is the most accurate method to predict the sound absorption coefficient, with a mean error of 8.39%.

Broadening of the Sound Absorption Bandwidth of the Perforated Panel Using a Membrane-Type Resonator

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Xuezhi Zhu ◽  
Zhaobo Chen ◽  
Yinghou Jiao ◽  
Yanpeng Wang
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Degrees Of Freedom ◽  
Low Frequency ◽  
Absorption Capacity ◽  
Sound Absorption Coefficient ◽  
Sound Waves ◽  
Frequency Range ◽  
Absorption Bandwidth ◽  
Membrane Type

In order to broaden the sound absorption bandwidth of a perforated panel in the low frequency range, a lightweight membrane-type resonator is installed in the back cavity of the perforated panel to combine into a compound sound absorber (CSA). Because of the great flexibility, the membrane-type resonator can be vibrated easily by the incident sound waves passing through the holes of the perforated panel. In the low frequency range, the membrane-type resonator and the perforated panel constitute a two degrees-of-freedom (DOF)-resonant type sound absorption system, which generates two sound absorption peaks. By tuning the parameters of the membrane type resonator, a wide frequency band having a large sound absorption coefficient can be obtained. In this paper, the sound absorption coefficient of CSA is derived analytically by combining the vibration equation of the membrane-type resonator with the acoustic impedance equation of the perforated panel. The influences of the parameters of the membrane-type resonator on the sound absorption performance of the CSA are numerically analyzed. Finally, the wide band sound absorption capacity of the CSA is validated by the experimental test.

scholarly journals Sound absorption properties of multi-layer structural composite materials based on waste corn husk fibers

2020 ◽  
Vol 15 ◽  
pp. 155892502091086
Author(s):  
Lihua Lyu ◽  
Jing Lu ◽  
Jing Guo ◽  
Yongfang Qian ◽  
Hong Li ◽  
...  
Keyword(s):  
Composite Materials ◽  
Absorption Coefficient ◽  
Sound Absorption ◽  
Low Frequency ◽  
Sound Absorption Coefficient ◽  
Absorption Properties ◽  
Cavity Depth ◽  
Air Cavity ◽  
Corn Husk ◽  
Structural Composite

In order to find a reasonable way to use the waste corn husk, waste degummed corn husk fibers were used as reinforcing material in one type of composite material. And polylactic acid particles were used as matrix material. The composite materials were prepared by mixing and hot-pressing process, and they were processed into the micro-slit panel. Then, the multi-layer structural sound absorption composite materials were prepared sequentially by micro-slit panel, air cavity, and flax felt. Finally, the sound absorption properties of the multi-layer structural composite materials were studied by changing flax felt thickness, air cavity depth, slit rate, and thickness of micro-slit panel. As the flax felt thickness varied from 0 to 10 mm in 5 mm increments, the peak of sound absorption coefficient shifted to low frequency. The sound absorption coefficient in the low frequency was improved with the air cavity depth varied from 0 to 10 mm in 5 mm increments. With the slit rate increased from 3% to 7% in 2% increments, the peak of sound absorption coefficient shifted to high frequency. With the thickness of micro-slit panel increased from 2 to 6 mm in 2 mm increments, the sound absorption bandwidth was broaden, and the peak of sound absorption coefficient was increased and shifted to low frequency. Results showed that the highest sound absorption coefficient of the multi-layer structural composite materials was about 1 under the optimal process conditions.

Preparation and Sound Absorption Coefficient Test of Aluminum Foam with CaO Granules Infiltrating Agent

2018 ◽  
Vol 933 ◽  
pp. 55-60
Author(s):  
Yong Zhang ◽  
Zong Min Chen ◽  
Zhao Jun Wang ◽  
Jing Hui Liu
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Aluminum Foam ◽  
Low Frequency ◽  
Processing Parameters ◽  
Sound Absorption Coefficient ◽  
Pressure Infiltration ◽  
Pure Alcohol ◽  
Infiltration Pressure ◽  
High Sound

Three kinds of aluminum foam of different pore sizes were prepared with a tailor-made low-pressure infiltration device. CaO granules in three sizes (0.45~0.71mm,0.71~090mm and 1.25~1.60mm) were selected as infiltrating agents. The processing parameters were as follows: granules preheat temperature of 700 °C,infiltration pressure of 0.04 MPa and aluminum liquid temperature of 720 °C. In order to improve the removal performance and porosity, mixture of CaO powder of finer than 300 mesh and pure alcohol was mixed uniformly with granules, which made the slurry-coating granules conformal contacts rather than point contacts as in the traditional infiltration method. The testing results show that among all aluminum foam specimens tested with transfer function methods, two kinds have high sound absorption coefficient in low frequency (250~1600Hz).

Nanomaterials in PU Foam for Enhanced Sound Absorption at Low Frequency Region

2014 ◽  
Vol 938 ◽  
pp. 170-175 ◽  
Author(s):  
R. Gayathri ◽  
R. Vasanthakumari
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Foam Cell ◽  
Research Work ◽  
Low Frequency ◽  
Absorption Capacity ◽  
Polyurethane Foams ◽  
Sound Absorption Coefficient ◽  
Enhanced Absorption ◽  
Pu Foam

Lot of research is going on to develop materials suitable for absorbing sound and reducing noise. By virtue of their superior vibration damping capability and attractive characteristics such as visco elasticity, simple processing and commercial availability, polyurethane foams are extensively applied not only in automotive seats but also in various acoustical parts. However, the sound absorption coefficient of polyurethane foams is high (0.8 1.0) in high frequencies in the range 300 to 10000Hz while it is found to be low (0 to 0.5) at low frequencies (10 to 200 Hz). In this study new polyurethane based porous composites were synthesized by in situ foam rising polymerization of polyol and diisocyanate in the presence of fillers such as nanosilica (NS) and nanoclay (NC). The effect of these fillers at various concentrations up to 2% was studied for sound absorption characteristics in the frequency range 100-200Hz. Sound absorption coefficient was determined using standing wave impedance tube method. The sound absorption coefficient of filled PU foams increases from 0.5 to 0.8 with frequency increase from 100 to 200 Hz at higher content of the nanofillers employed. This research work is further extended to study the sound absorption capacity of unfilled PU foam with varying thickness and also hybrid foams with woven glass (GFC) and polyester cloth (PEC). The unfilled foam with 60mm of thickness gives sound absorption value same as that of 15mm of filled foam. Further enhanced absorption value is achieved with PU/NS-GFC hybrid. The results obtained are explained based on the porosity of composite structure and foam cell size.Key words Polyurethane foam, sound absorption coefficient, nanosilica, nanoclay, low frequency sound.

scholarly journals Synthesis and Evaluation of Polyurethane Foam Composites for Enhanced Sound Absorption at Low Frequency

2019 ◽  
Vol 8 (3) ◽  
pp. 6815-6818
Keyword(s):  
Absorption Coefficient ◽  
Polyurethane Foam ◽  
Sound Absorption ◽  
Low Frequency ◽  
Weight Fraction ◽  
Crumb Rubber ◽  
Polyurethane Foams ◽  
Sound Absorption Coefficient ◽  
Filler Materials ◽  
Frequency Range

Polyurethane foams are extensively used as sound absorbing materials in various automobile parts. However, the sound absorption capability of polyurethane foam ispoorin low frequency range. The advancement of technologies to develop newerpolymer composites, provide scope to develop composite polyurethane foam with better sound absorption coefficient in low frequency range. Composite foams are made with two different filler materials as crumb rubber and coconut fiber, in varying weight fraction of up to 2.0%. Density, Sound absorption coefficient, and Noise reduction, measurements were done on all polyurethane foams. The effect offiller additionsto polyurethane foams ondensity and sound absorption coefficient at low frequency are discussed.The 1.4 % crumb rubber polyurethane foam offers the best combination of low density, improved sound absorption coefficient value and noise absorption at low frequency.

scholarly journals Effect of Porous Materials Combination in Layers on Sound Absorption Characteristics

2015 ◽  
Vol 773-774 ◽  
pp. 210-215
Author(s):  
Muhd Hafeez Zainulabidin ◽  
M.H.M. Yusuff ◽  
Al Emran Ismail ◽  
M.Z. Kasron ◽  
A.S.M. Kassim
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Low Frequency ◽  
Sound Absorption Coefficient ◽  
Frequency Range ◽  
Sound Absorber ◽  
Number Of Layers ◽  
Combination Number ◽  
Impedance Tubes ◽  
Absorption Characteristics

This paper describes the investigation and analysis on two materials in which one material is a relatively good sound absorber at low frequency range and another is a relatively good sound absorber at high frequency range, combined together in layers to form a better sound absorber for a wider range of frequencies. The layer combinations of the materials are varied and the values of Sound Absorption Coefficient, α are measured experimentally by using impedance tubes with two microphones transfer function method according to ISO 10534-2 standard. The results obtained are compared in terms of the order of material and the number of layer combinations of materials for each sample. The orders of combinations and number of layers of combinations have significant influence on the sound absorption characteristics. The order of materials has reversed effect on Sound Absorption Coefficient, α as the number of layer combination is increased. Increase in the combination number will make the specimen performed relatively better at a wider frequency range.

scholarly journals Improved Sound Absorption Properties in Polyurethane Foams by the Inclusion of Al2O3 Nanoparticles

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Binxia Yuan ◽  
Xinyi Fang ◽  
Jianben Liu ◽  
Yan Liu ◽  
Rui Zhu
Keyword(s):  
Energy Dissipation ◽  
Absorption Coefficient ◽  
Sound Absorption ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Sound Absorption Coefficient ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Dissipation Process ◽  
Single Hole

At present, the scale of China’s power grid is becoming larger and larger, and the control of low-frequency noise in substations (especially for transformers) is very important. The sound-absorbing materials have become one of the important ways to control low-frequency noise. The single polyurethane material cannot satisfy the requirements for reducing low-frequency noise, so it is very necessary to study its composite with other materials. In the paper, the flexible polyurethane foam and Al2O3 nanoparticle composites were obtained by the impregnation method. The method was simple, safe, and easy to control. The morphology and sound absorption coefficient of the foam materials before and after filling were analyzed. Single-hole acoustic cavity models of PU and Al2O3-PU composite were established through the finite element. The absorption and dissipation process of sound pressure for single hole was studied to understand the energy dissipation process. Meanwhile, through studying acoustic energy storage and acoustic energy dissipation, the loss factor of a single hole was obtained, which can predict the change rule of the sound absorption coefficient for PU foam and Al2O3-PU.

scholarly journals Optimization of Low Frequency Acoustic Absorption Characteristics of Underwater Acoustic Cover Based on Nelder-Mead Simplex Method

2021 ◽  
Vol 2095 (1) ◽  
pp. 012082
Author(s):  
Jiabei Wang ◽  
Hao Zhou
Keyword(s):  
Absorption Coefficient ◽  
Composite Structure ◽  
Sound Absorption ◽  
Resonant Cavity ◽  
Low Frequency ◽  
Optimization Method ◽  
Geometric Parameters ◽  
Sound Absorption Coefficient ◽  
Material Parameters ◽  
Covering Layer

Abstract In order to solve the low frequency sound absorption problem of acoustic covering layer, the local resonant cavity covering layer is established. The geometric parameters and material parameters of the composite structure are taken as optimization variables, the maximum sound absorption coefficient in the frequency band of 10-2000Hz is taken as optimization objective, and the Nelder-Mead simplicated method was used as optimization method to optimize the established model. The optimization results show that the sound absorption coefficient of the composite structure is increased by 13% and 24% respectively after the optimization of geometric parameters and material parameters. The sound pressure level of the sound wave emitted into the water area is reduced by about 3dB after the optimization, and the power loss is equivalent to increasing by half. Therefore, the sound absorption performance is improved. The research results can provide a theoretical basis for the design of acoustic coating.

scholarly journals Enhanced Low-Frequency Sound Absorption of a Porous Layer Mosaicked with Perforated Resonator

Polymers ◽  
2022 ◽  
Vol 14 (2) ◽  
pp. 223
Author(s):  
Xin Li ◽  
Bilong Liu ◽  
Qianqian Wu
Keyword(s):  
Porous Material ◽  
Absorption Coefficient ◽  
Porous Layer ◽  
Acoustic Impedance ◽  
Sound Absorption ◽  
Perforated Plate ◽  
Low Frequency ◽  
Sound Absorption Coefficient ◽  
Frequency Sound ◽  
Two Samples

A composite structure composed of a porous-material layer mosaicked with a perforated resonator is proposed to improve the low-frequency sound absorption of the porous layer. This structure is investigated in the form of a porous-material matrix (PM) and a perforated resonator (PR), and the PR is a thin perforated plate filled with porous material in its back cavity. Theoretical and numerical models are established to predict the acoustic impedance and sound absorption coefficient of the proposed structure, and two samples made of polyurethane and melamine, respectively, are tested in an impedance tube. The predicted results are consistent with that of the measured. Compared with a single porous layer with the same thickness, the results show that the designed structure provides an additional sound absorption peak at low frequencies. The proposed structure is compact and has an effective absorption bandwidth of more than two octaves especially below the frequency corresponding to 1/4 wavelength. A comparison is also made between the sound absorption coefficients of the proposed structure and a classical micro-perforated plate (MPP), and the results reveal equivalent acoustic performance, suggesting that it can be used as an alternative to the MPP for low–mid frequency sound absorption. Moreover, the influences of the main parameters on the sound absorption coefficient of PPCS are also analyzed, such as the hole diameter, area ratio, flow resistance, and porous-material thickness in the PR. The mechanism of sound absorption is discussed through the surface acoustic impedance and the distributions of particle velocity and sound pressure at several specific frequencies. This work provides a new idea for the applications of the thin porous layer in low- and medium-frequency sound absorption.

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