Design of multi-layered porous fibrous metals for optimal sound absorption in the low frequency range

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.

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Analysis of Sound Absorption Properties of Three-Leaf Microperforated Panel Absorbers without a Rigid Backing

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.937.465 ◽

2014 ◽

Vol 937 ◽

pp. 465-471

Author(s):

Xiao Ling Gai ◽

Xian Hui Li ◽

Rui Wu ◽

Bin Zhang ◽

Jun Juan Zhao

Keyword(s):

Sound Absorption ◽

Low Frequency ◽

Wide Frequency Range ◽

Structure Design ◽

Frequency Region ◽

Theoretical Development ◽

Frequency Range ◽

Absorption Properties ◽

High Frequency Region ◽

Energy Dissipated

Microperforated panel (MPP) absorbers have been developed rapidly and used in many fields in recent years. First, based on the Maa’s theory, the theoretical development of MPP is reviewed in this paper. Furthermore, structure design and processing technology of MPP are introduced. Finally, the further development of MPP is discussed. Based on the MPP theory and electro-acoustical equivalent circuit principle, sound absorption properties of three-leaf microperforated panel (TMPP) absorbers without a rigid backing are studied to broaden the sound absorption bandwidth of MPP structure. Simulation results show that TMPP absorbers without a rigid backing have two resonance peaks and the energy dissipated coefficient remains constant in the low frequency range. The resonance frequency moves toward low frequency region with the increasing of the distance, thickness and pore diameter of MPP and moves toward high frequency region with the increasing of the perforation when other parameters keep invariant. The energy dissipated coefficient more than 0.5 over 8 octaves by choosing proper parameters. In conclusion, TMPP absorbers without a rigid backing have good sound absorption properties in a wide frequency range.

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Sound-Absorbing Composites Based on Flax and Polymer Fibers

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.806.161 ◽

2015 ◽

Vol 806 ◽

pp. 161-166 ◽

Cited By ~ 3

Author(s):

Nikolay V. Yakimovich ◽

Sergey N. Bukharov ◽

Victor V. Kozhushko ◽

Anastasiya S. Khmara ◽

Vladimir P. Sergienko

Keyword(s):

Composite Materials ◽

Sound Absorption ◽

Low Frequency ◽

Single Layer ◽

Polymer Fibers ◽

Frequency Range ◽

Normal Absorption

The paper considers sound absorption of the composite materials, which are based on the natural flax and polymer fibers. The thickness of a single layer of obtained nonwoven composite is about 10 mm. The analysis of absorption dependences is carried out for different thicknesses of the material. It is shown that in the low frequency range the absorption almost linearly increases depending on the thickness. The coefficient of the normal absorption increases with the frequency in the range from 50 Hz up to 1600 Hz. The hot-pressed material can be used for panel production. The sound absorption increases with the thickness of the pressed material. The measurements show the possibilities of application of the composite for the production of the parts of cabs’ interior.

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

International Journal of Recent Technology and Engineering - 2 ◽

10.35940/ijrte.c5762.098319 ◽

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.

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Modifikasi Permukaan Elemen Peredam Bising Dengan Profil Berbentuk Prisma

INDONESIAN JOURNAL OF APPLIED PHYSICS ◽

10.13057/ijap.v6i01.422 ◽

2016 ◽

Vol 6 (01) ◽

Author(s):

Hanif Azimut

Keyword(s):

High Frequency ◽

Sound Absorption ◽

Coupling Effect ◽

Low Frequency ◽

The Other ◽

Frequency Range ◽

Closed Type ◽

Wave Resonance ◽

Half Wave ◽

Absorption Performance

The influence of surface modification by using prism shaped profile on the sound absorption of absorber element was investigated experimentally. A prime number based configuration of the two types opened and closed type rism shaped profile inclusion was tested by using impedance tube according ASTM E1050 standard. The result shows that sound absorption at low frequency band below 200 Hz increased with the increasing of closed prism number. It is related to the coupling effect between the cavities of the absorber element and the prisms that changes reactance of the coupled structure. In the other side, a half wave resonance like effect occur on the use of opened prisms inclusion, which is increase the sound absorption performance at mid to high frequency range between 800 Hz to 1,25 kHz.

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Effect of Porous Materials Combination in Layers on Sound Absorption Characteristics

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.773-774.210 ◽

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.

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An innovative composite plywood for the acoustic improvement of small closed spaces

Holzforschung ◽

10.1515/hf-2016-0122 ◽

2017 ◽

Vol 71 (6) ◽

pp. 521-526

Author(s):

Francesco Negro ◽

Corrado Cremonini ◽

Marco Fringuellino ◽

Roberto Zanuttini

Keyword(s):

Sound Absorption ◽

Resonance Effect ◽

Low Frequency ◽

Frequency Range ◽

Honeycomb Core ◽

Final Size ◽

Absorption Properties ◽

Reverberation Chamber ◽

The Core ◽

Dining Room

Abstract Poor acoustics is a common problem in many small closed rooms such as offices or dining rooms. Sound absorbing panels used as wall or ceiling coverings can be a remedy. In the present paper, the sound absorption properties of a composite made of two plywood skins bonded to an inner honeycomb core of plywood cells, designed by the authors in a previous study, were improved by drilling the surfaces. The holes communicate with the void cells of the core, activating the Helmholtz resonance effect. The acoustic behavior of small specimens and final-size samples are described, which were also tested in a reverberation chamber and in a real dining room. The developed lightweight composite plywood achieved αmax 0.90 values (maximal sound absorption coefficients) around 400 Hz, i.e. in the low frequency range, resulting in being well suited for various acoustic improvements.

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Modifikasi Permukaan Elemen Peredam Bising dengan Profil Berbentuk Prisma

INDONESIAN JOURNAL OF APPLIED PHYSICS ◽

10.13057/ijap.v6i01.1794 ◽

2016 ◽

Vol 6 (01) ◽

pp. 23

Author(s):

Julius Indra Kusuma ◽

H Harjana ◽

Iwan Yahya

Keyword(s):

High Frequency ◽

Sound Absorption ◽

Coupling Effect ◽

Low Frequency ◽

The Other ◽

Frequency Range ◽

Closed Type ◽

Wave Resonance ◽

Half Wave ◽

Absorption Performance

The influence of surface modification by using prism shaped profile on the sound absorption of absorber element was investigated experimentally. A prime number based configuration of the two types opened and closed type rism shaped profile inclusion was tested by using impedance tube according ASTM E1050 standard. The result shows that sound absorption at low frequency band below 200 Hz increased with the increasing of closed prism number. It is related to the coupling effect between the cavities of the absorber element and the prisms that changes reactance of the coupled structure. In the other side, a half wave resonance like effect occur on the use of opened prisms inclusion, which is increase the sound absorption performance at mid to high frequency range between 800 Hz to 1.25 kHz.

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Influence of Sugar Palm Ash Fraction and Resonator Configuration on Acoustic Absorption Performance of Expose Brick

INDONESIAN JOURNAL OF APPLIED PHYSICS ◽

10.13057/ijap.v4i01.1160 ◽

2016 ◽

Vol 4 (01) ◽

pp. 19

Author(s):

Zulfa Kamila R ◽

Iwan Yahya ◽

Utari U

Keyword(s):

Performance Improvement ◽

Performance Optimization ◽

Sound Absorption ◽

Low Frequency ◽

Helmholtz Resonator ◽

Raw Material ◽

Frequency Range ◽

Helmholtz Resonators ◽

Resonator Structure ◽

Absorption Performance

Sound absorption performance optimization of expose brick has been conducted in associated with the fraction of sugar palm ash in its raw material and configuration of Helmholtz resonators inside the brick structure. The testing was conducted experimentally refer to ASTM E-1050-98 standard procedure. In this case there are three variations sugar palm ash fractions of 0%, 5%, and 10%, as well as two array resonator configurations. The results showed that the brick with fraction of 10% sugar palm ash has the best sound absorption performance. As for the configuration of array identical Helmholtz resonator giving better performance improvement at low frequency span than complex resonator structure with coupled cavity where the best performance occur on(376-488) Hz frequency range with the absorption coefficient α of 0.54.

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Evaluation of Special Hearing Aids for Deaf Children

Journal of Speech and Hearing Disorders ◽

10.1044/jshd.3604.527 ◽

1971 ◽

Vol 36 (4) ◽

pp. 527-537 ◽

Cited By ~ 1

Author(s):

Norman P. Erber

Keyword(s):

Hearing Aids ◽

High Frequency ◽

Hearing Aid ◽

Low Frequency ◽

Acoustic Stimulation ◽

Deaf Children ◽

Frequency Range ◽

Frequency Limit ◽

Unpublished Studies ◽

Published Research

Two types of special hearing aid have been developed recently to improve the reception of speech by profoundly deaf children. In a different way, each special system provides greater low-frequency acoustic stimulation to deaf ears than does a conventional hearing aid. One of the devices extends the low-frequency limit of amplification; the other shifts high-frequency energy to a lower frequency range. In general, previous evaluations of these special hearing aids have obtained inconsistent or inconclusive results. This paper reviews most of the published research on the use of special hearing aids by deaf children, summarizes several unpublished studies, and suggests a set of guidelines for future evaluations of special and conventional amplification systems.

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