scholarly journals On the Determination of Acoustic Properties of Membrane Type Structural Skin Elements by Means of Surface Displacements

2021 ◽  
Vol 11 (21) ◽  
pp. 10357
Author(s):  
Daniel Urbán ◽  
N. B. Roozen ◽  
Vojtech Jandák ◽  
Marek Brothánek ◽  
Ondřej Jiříček
Keyword(s):  
Plane Wave ◽  
Sound Absorption ◽  
Sound Pressure ◽  
Transmission Loss ◽  
Laser Doppler Vibrometer ◽  
Sound Transmission ◽  
Acoustic Properties ◽  
Sound Transmission Loss ◽  
Membrane Type

The article focuses on the determination of the acoustic properties (sound transmission loss, sound absorption and transmission coefficient under acoustic plane wave excitation) of membrane-type of specimens by means of a combination of incident plane wave sound pressure and membrane surface displacement information, measuring the sound pressure with a microphone and the membrane displacement by means of a laser Doppler vibrometer. An overview of known measurement methods and the theoretical background of the proposed so-called mobility-based method (MM) is presented. The proposed method was compared with the conventional methods for sound transmission loss and absorption measurement in the impedance tube, both numerically and experimentally. Finite element model (FEM) simulation results of two single layer membrane samples of different shape configurations were compared, amongst which six different variations of the backing wall termination. Four different approaches to determine the sound transmission loss and two methods to determine sound absorption properties of the membranes were compared. Subsequently, the proposed method was tested in a laboratory environment. The proposed MM method can be possibly used to measure the vibro-acoustic properties of building parts in situ.

Incorporation of Nanofiber Layers in Nonwoven Materials for Improving Their Acoustic Properties

2013 ◽  
Vol 8 (4) ◽  
pp. 155892501300800 ◽  
Author(s):  
Amir Rabbi ◽  
Hossein Bahrambeygi ◽  
Ahmad Mousavi Shoushtari ◽  
Komeil Nasouri
Keyword(s):  
Sound Absorption ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Wide Band ◽  
Acoustic Properties ◽  
Sound Insulation ◽  
Sound Transmission Loss ◽  
Factors Affecting ◽  
Nonwoven Materials ◽  
Field Noise

Due to numerous developments in most industries and the increase in the usage of massive and powerful machines in every field, noise has become an unavoidable part of mechanized life and has brought about serious health hazards. The main aim of this work was to investigate the usability of polyurethane and polyacrylonitrile nanofibers for improving sound insulation properties over a wide band of frequencies and reducing weight and thickness of conventional polyester and wool nonwovens. The effect of the number of nanofiber layers and associated surface densities on acoustic properties was investigated. Sound transmission loss and sound absorption analysis using the impedance tube method were carried out as the main factors affecting acoustic behavior of samples. The results show that incorporation of nanofiber layers in nonwoven materials can improve both sound absorption and sound transmission loss simultaneously, especially in mid and lower frequencies, which are difficult to detect by conventional materials.

scholarly journals Non-Wovens as Sound Reducers

2018 ◽  
Vol 55 (2) ◽  
pp. 64-76
Author(s):  
D. Belakova ◽  
A. Seile ◽  
S. Kukle ◽  
T. Plamus
Keyword(s):  
Absorption Coefficient ◽  
Surface Density ◽  
Sound Absorption ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Sound Insulation ◽  
Material Structure ◽  
Sound Transmission Loss ◽  
Sound Waves ◽  
Frequency Range

Abstract Within the present study, the effect of hemp (40 wt%) and polyactide (60 wt%), non-woven surface density, thickness and number of fibre web layers on the sound absorption coefficient and the sound transmission loss in the frequency range from 50 to 5000 Hz is analysed. The sound insulation properties of the experimental samples have been determined, compared to the ones in practical use, and the possible use of material has been defined. Non-woven materials are ideally suited for use in acoustic insulation products because the arrangement of fibres produces a porous material structure, which leads to a greater interaction between sound waves and fibre structure. Of all the tested samples (A, B and D), the non-woven variant B exceeded the surface density of sample A by 1.22 times and 1.15 times that of sample D. By placing non-wovens one above the other in 2 layers, it is possible to increase the absorption coefficient of the material, which depending on the frequency corresponds to C, D, and E sound absorption classes. Sample A demonstrates the best sound absorption of all the three samples in the frequency range from 250 to 2000 Hz. In the test frequency range from 50 to 5000 Hz, the sound transmission loss varies from 0.76 (Sample D at 63 Hz) to 3.90 (Sample B at 5000 Hz).

scholarly journals High sound absorption of polyester composites / fiber hemp / nanocellulose for automotive interior materials

2020 ◽  
Vol 2 (2) ◽  
pp. 170-174
Keyword(s):  
Composite Material ◽  
Composite Materials ◽  
Sound Absorption ◽  
Natural Fiber ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Sound Transmission Loss ◽  
Hemp Fiber ◽  
The Matrix ◽  
Polyester Composite

Human health and environmental comfort are disturbed by the presence of noise, especially in cars, so that effective sound-absorbing materials are currently being developed. To answer the problem of noise in car interiors, polyester composite materials with local hemp fiber and nanocellulose reinforcement were developed. Natural fiber is biodegradable and renewable, and acts as an alternative to the use of synthetic fibers. The method used for the composite material manufacturing process was the casting method. The matrix of the composite material was polyester, while the reinforcement was a combination of local hemp fiber and nanocellulose fiber. Alkalization and non-alkalization processes have been carried out on hemp fiber. The composition of nanocellulose was 0%, 1%, and 3%. The characterization applied in this research were SEM test, FTIR test, sound transmission loss test, and density test. Optimal results were obtained on hemp fiber reinforced polyester composite materials without alkalization and without nanocellulose. Sound transmission loss (STL) was 61.91 dB up to 68.52 dB for the frequency range of 630 Hz to 125 Hz. The standard noise limit on 8-passenger passenger's four-wheeled vehicles is 77-80 dB. Based on the results obtained, the sound absorption is good. The density of this composite material was obtained at 0.989 gram/cm3. This composite material has the potential for developing dashboard material.

scholarly journals Acoustic Properties of 316L Stainless Steel Hollow Sphere Composites Fabricated by Pressure Casting

Metals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1047
Author(s):  
Chunhe Wang ◽  
Fengchun Jiang ◽  
Shuaiqi Shao ◽  
Tianmiao Yu ◽  
Chunhuan Guo
Keyword(s):  
Absorption Coefficient ◽  
Hollow Sphere ◽  
Sound Absorption ◽  
Random Distribution ◽  
Transmission Loss ◽  
Acoustic Properties ◽  
Sound Absorption Coefficient ◽  
Pressure Casting ◽  
Sound Transmission Loss ◽  
At Resonance

In this study, we prepared metal hollow sphere composites (MHSCs) using metal hollow spheres (MHSs) by pressure casting under vacuum conditions, and investigated the acoustic properties. The density of the MHSCs was measured using the mass to volume ratio, the microstructure of the MHSCs was observed using a scanning electron microscope, and the acoustic properties of the MHSCs were tested using an impedance tube. The measured MHSCs showed that the densities of the MHSCs with the random distribution of MHSs with diameter ~3.28 mm (1.74 g/cm3 to 1.77 g/cm3) (MHSC-3.28) were nearly equal to that of the MHSCs with the random distribution of MHSs with diameter ~5.76 mm (1.74 g/cm3 to 1.76 g/cm3) (MHSC-5.76), and lower than that of the MHSCs with the layered structure of MHSs with diameter ~3.28 mm (1.93 g/cm3 to 1.97 g/cm3) (MHSC-LS). Microstructural observations confirmed that the interface region between the MHSs and matrix demonstrated a simple physical combination pattern with pores. The acoustic properties of the MHSCs showed that the sound absorption coefficient of MHSC-LS was lower than that of MHSC-3.28 and higher than that of MHSC-5.76 at off-resonance. The sound absorption coefficient peak value of MHSC-3.28 was higher than that of MHSC-LS, and lower than that of MHSC-5.76 at resonance. The sound transmission loss of MHSC-3.28 was lower than that of MHSC-5.76, which shows the rules are independent from the resonance. The sound transmission loss of MHSC-LS was higher than that of MHSC-5.76 at resonance, but lower than that of MHSC-3.28 at off-resonance. In addition, we discuss the propagation mechanism of the sound waves in the MHSC, which is mainly determined by the distribution of the MHSs in the MHSC.

An improved approach for normal-incidence sound transmission loss measurement using a four-microphone impedance tube

2020 ◽  
pp. 107754632092690
Author(s):  
Zechao Li ◽  
Sizhong Chen ◽  
Zhicheng Wu ◽  
Lin Yang
Keyword(s):  
Transfer Matrix ◽  
Sound Absorption ◽  
Transmission Loss ◽  
Sound Transmission ◽  
Normal Incidence ◽  
Sound Insulation ◽  
Sound Transmission Loss ◽  
The Common ◽  
Wavefield Decomposition ◽  
Insulation Performance

The main aim of this study is to introduce an improved method for determining the sound properties of acoustic materials which is more precise than the common wavefield decomposition method and simpler than the common transfer matrix method. In the first part of the article, a group of formulae for calculating sound transmission loss is represented by combining the wavefield decomposition and transfer matrix methods. Subsequently, a formula for calculating sound absorption coefficients is derived from these formulae by definition. Furthermore, the present formulae are validated by comparing the experimental results achieved with the present formulae and those results obtained by other methods recorded in published articles. Eventually, it is demonstrated that the method can accurately measure the sound insulation performance of materials and the sound absorption properties of limp and lightweight materials.

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