Utilizing Hollow-Structured Bamboo as Natural Sound Absorber

2015 ◽  
Vol 40 (4) ◽  
pp. 601-608 ◽  
Author(s):  
Azma Putra ◽  
Fazlin Abd Khair ◽  
Mohd Jailani Mohd Nor
Keyword(s):  
Absorption Coefficient ◽  
Hollow Structure ◽  
Front Surface ◽  
Normal Incidence ◽  
Frequency Range ◽  
Peak Absorption ◽  
Natural Sound ◽  
Average Absorption Coefficient ◽  
Lower Frequency Range ◽  
Bamboo Structure

AbstractStudies to find alternative low environmental-impact materials for acoustic absorbers are still progressing, particularly those originated from natural materials. However, most of the established works are mainly focused on the fibrous-type absorbers. Discussion on the non-fibrous-type absorbers is still lacking and this therefore becomes the objective of this paper. Use of bamboo by utilizing its hollow structure to absorb sound energy is discussed here. The normal incidence absorption coefficient was measured based on the length and diameter of the bamboo, as well as different arrangement of the bamboo structure subjected to the incidence sound, namely, axial, transverse, and crossed-transverse arrangements. The trend of absorption coefficient appears in peaks and dips at equally spacing frequencies. For all arrangements the peak of absorption can reach above 0.8. Introducing an air gap behind the bamboo shifts the peak absorption to lower frequency. Covering the front surface of the absorber improves the sound absorption coefficient for axial arrangement by widening the frequency range of absorption also towards lower frequency range. The transverse arrangement is found to have average absorption coefficient peaks of 0.7 above 1.5 kHz. By arranging the bamboo structure with crossed-transverse arrangement, the suppressed absorption peaks in normal transverse arrangement can be recovered.

Material Parameter Determination in Glass Wool Mat for Sound Absorption

2011 ◽  
Vol 148-149 ◽  
pp. 1271-1275 ◽  
Author(s):  
Cheng Dong Li ◽  
Zhao Feng Chen ◽  
Jie Ming Zhou ◽  
Bin Bin Li ◽  
Wang Ping Wu ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Prediction Error ◽  
Fiber Length ◽  
Normal Incidence ◽  
Glass Wool ◽  
Parameter Determination ◽  
Frequency Range ◽  
Material Parameters ◽  
Refrigeration Equipment ◽  
Building Engineering

Glass wool mat is widely used in the fields of building engineering, transport facilities and refrigeration equipment. In this paper, the effect of material parameters such as density, thickness, porosity, and flow resistivity on the normal incidence absorption coefficient has been studied. In addition, fiber length is also investigated to achieve appropriate strength. The prediction error of normal incidence absorption coefficient by modified Johnson–Allard model is less than 5% in the frequency range between 800 Hz and 5 kHz. We could use the modified Johnson–Allard model to determine the parameter of glass wool mat for better development.

Preliminary Study on Bamboo as Sound Absorber

2014 ◽  
Vol 554 ◽  
pp. 76-80 ◽  
Author(s):  
Fazlin A. Khair ◽  
Azma Putra ◽  
Mohd Jailani Mohd Nor ◽  
Nurul Atiqah ◽  
M.Z. Selamat
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Hollow Structure ◽  
Chemical Substance ◽  
The Body ◽  
Natural Material ◽  
Sound Absorber ◽  
Tube Test ◽  
Average Absorption Coefficient ◽  
Preliminary Study

Synthetic acoustic materials are known for their poisonous chemical substance to the environment and also the particles which are harmful to human health. Research is now directed towards finding an alternative acoustic absorber made from natural materials. This paper presents the utilization of bamboo, a natural material having hollow structure to act as sound absorber. In an impedance tube test, the hollow path is arranged to face the sound incidence. The result reveals that bamboo having length of 2 cm has average absorption coefficient of 0.95 at frequency above 3 kHz. Performance at lower frequencies can be controlled by adding the air gap behind the system. Introduction of microholes along the body shows no significant effect to increase the sound absorption.

scholarly journals Acoustic Panels Made of Paper Sludge and Clay Composites

2021 ◽  
Vol 13 (2) ◽  
pp. 637
Author(s):  
Tomas Astrauskas ◽  
Tomas Januševičius ◽  
Raimondas Grubliauskas
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
Composite Panel ◽  
Sound Absorption Coefficient ◽  
Core Material ◽  
Paper Sludge ◽  
Frequency Range ◽  
Absorption Properties ◽  
Air Gaps ◽  
The Core

Studies on recycled materials emerged during recent years. This paper investigates samples’ sound absorption properties for panels fabricated of a mixture of paper sludge (PS) and clay mixture. PS was the core material. The sound absorption was measured. We also consider the influence of an air gap between panels and rigid backing. Different air gaps (50, 100, 150, 200 mm) simulate existing acoustic panel systems. Finally, the PS and clay composite panel sound absorption coefficients are compared to those for a typical commercial absorptive ceiling panel. The average sound absorption coefficient of PS-clay composite panels (αavg. in the frequency range from 250 to 1600 Hz) was up to 0.55. The resulting average sound absorption coefficient of panels made of recycled (but unfinished) materials is even somewhat higher than for the finished commercial (finished) acoustic panel (αavg. = 0.51).

Realizing high-efficiency low frequency sound absorption of underwater meta-structures by acoustic siphon effect

2021 ◽  
pp. 2150319
Author(s):  
Li Bo Wang ◽  
Cheng Zhi Ma ◽  
Jiu Hui Wu ◽  
Chong Rui Liu
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
High Efficiency ◽  
Physical Mechanism ◽  
Low Frequency ◽  
Area Ratio ◽  
Underwater Acoustic ◽  
Element Simulation ◽  
Average Absorption Coefficient ◽  
New Perspective

The underwater acoustic siphon effect is proposed in this work, which aims to reveal the basic physical mechanism of high-efficiency sound absorption in meta-structures composed of multiple detuned units. Furthermore, the influence of the area ratio on the underwater acoustic siphon effect is then investigated by finite element simulation (FES) and theoretical calculation. On this basis, a meta-structure with the maximum absorption coefficient of almost 100% and average absorption coefficient of 80% at 600–1400 Hz is achieved. The underwater acoustic siphon effect could provide a better understanding of high-efficiency sound absorption and offer a new perspective in controlling underwater noises.

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).

Emissivity Calculations for Diatomic Gases

1951 ◽  
Vol 18 (1) ◽  
pp. 53-58
Author(s):  
S. S. Penner
Keyword(s):  
Absorption Coefficient ◽  
Atmospheric Pressure ◽  
Radiant Heat ◽  
Published Data ◽  
Radiant Heat Transfer ◽  
Effective Width ◽  
Combustion Chambers ◽  
Average Absorption Coefficient ◽  
Vibration Rotation ◽  
Simplified Procedure

Abstract An approximate method for estimating radiant-heat transfer from gaseous emitters has been developed. An average absorption coefficient is used for an effective width of an entire vibration-rotation band. The procedure for determining an average absorption coefficient in terms of integrated absorption can be justified, approximately, for very large total pressures where the spectral half-width is no longer small compared with the rotational spacing. Because of this limitation, it is to be expected that the procedure proposed here will be particularly useful only in estimating gaseous emissivities for emitters in high-pressure combustion chambers. Nevertheless, it appears that the simplified procedure yields reasonable results even at relatively low total pressures. Thus a comparison of calculated and observed emissivities for CO at atmospheric pressure shows satisfactory agreement, especially at large optical densities. Representative emissivity calculations over a wide temperature range are described. Emissivity calculations on CO, NO, HF, HCl, HBr, and HI can be carried out very rapidly by the use of recently published data on these gases.

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