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    Noise Control Engineering Journal

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    Jan 2012

    Volume 60, Issue 1, pp. 1-123


    The effect of time on the contribution of asphalt rubber mixtures to noise abatement

    Elisabete F. Freitas

    Noise Control Eng. J. 60, 1, pp. 1-8 (2012)

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    Road pavement surface layers incorporating rubberized asphalt binders have recently been recommended as a measure to mitigate noise. At first their acoustical performance seems to be superior to that shown by conventional layers. Nevertheless, the knowledge in relation to their behavior throughout their lifetime is limited. This research, carried out over several road sections with open graded and gap-graded mixtures, two of which with rubberized asphalt, by means of controlled pass-by tests, is aimed at observing and studying these type of mixes over a time span of 3 years.
    Show PACS
    43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles

    Low frequency noise absorption by helium-filled duct lining

    Y. S. Choy

    Noise Control Eng. J. 60, 1, pp. 9-21 (2012)

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    Low-frequency noise is hard to tackle by traditional sound absorption material because of its inherent high acoustic impedance and space limitation for installing such material. There is a significant sound reflection at the air-absorber interface due to the high impedance mismatch with ambient air and hence the sound wave does not have a chance to enter the absorber for dissipation. The performance of sound absorption material lining in the duct is even worse due to the grazing incidence on the air-absorber interface. The motivation of this study is twofold: (a) to extend the effective range of sound absorption to lower frequencies by filling helium gas in the porous material lining in the duct, and (b) to tackle low frequency noise with a thin layer of the porous material with near-grazing incidence. The work represents a further extension of our recent investigation of the sound propagation in helium-filled porous material. The acoustic impedance can be reduced by filling a low density gas such as helium in the porous material. This has been validated experimentally. Based on the acoustic properties of the helium-filled material found from the new function established in a recent publication by the authors of this paper, the sound absorption performance of helium-filled duct-lining (HDL) is investigated experimentally and theoretically in the current paper. This helps find out the optimal fibre diameter and the lowest frequency for achieving the 10 dB based on the expansion ratio of an empty expansion chamber of 6.5 which is high enough to assess the performance of silencer. There is good agreement between the theoretical prediction and experimental validation in terms of transmission loss, relative absorption coefficient and reflection coefficient. Helium-filled duct lining performs much better than air-filled duct lining in the thin and long configuration at low frequencies. It is because helium gas contributes large wave refraction that can enhance the sound absorption. This is demonstrated theoretically and experimentally with five different fibre diameter of porous materials.
    Show PACS
    43.50.Fe Noise masking systems
    43.50.Yw Instrumentation and techniques for noise measurement and analysis
    43.25.Jh Reflection, refraction, interference, scattering, and diffraction of intense sound waves

    An experimental study on a cylindrical microperforated panel space sound absorber

    Kimihiro Sakagami, Takayuki Oshitani, Motoki Yairi, Emi Toyoda, and Masayuki Morimoto

    Noise Control Eng. J. 60, 1, pp. 22-28 (2012)

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    A microperforated panel (MPP), which is widely known as one of the most promising alternatives of the next-generation sound absorbers, is typically used with a rigid-back wall with an air-cavity. However, a multiple-leaf MPP space absorber, which does not have any backing structure, double-leaf MPP space absorber (DLMPP) and triple-leaf MPP space absorber (TLMPP) is proposed. However, these are panel-like structure which are limited to where they can be used. In order to develop an MPP space absorber that can be used in more various situations, a trial production of a cylindrical MPP space sound absorber (CMSA) is made with an MPP shaped into a cylindrical. The sound absorption characteristics of a CMSA are measured in a reverberation chamber. As a result, although the absorption coefficient is not very high, a CMSA shows sound absorption characteristics similar to a DLMPP and TLMPP: a resonance peak by a Helmholtz resonator and an additional low frequency absorption by its acoustic permeability appear. The results suggest that a CMSA can be used as a space sound absorber in practical situations.
    Show PACS
    43.25.Gf Standing waves; resonance
    43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
    43.58.-e Acoustical measurements and instrumentation

    The mechanical properties of earmuffs

    W. Williams, M. Seeto, and H. Dillon

    Noise Control Eng. J. 60, 1, pp. 29-35 (2012)

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    The physical properties of circum-aural hearing protectors, such as mass, clamping force and cup volume, have an influence on the attenuation performance of the device. This paper closely examines the physical and acoustic properties 39 of hearing protectors readily available to all users. The results indicate that attenuation increases with clamping force up to a limiting value of around 11 Newtons above which expected increases in attenuation are very small for large increases in clamping force. Likewise increasing the (newly introduced term) bulk of a hearing protector (volume, mass and cup elements) increases the attenuation but, as with clamping force a limit is reached where increased bulk increases discomfort and wearing difficulty.
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    43.66.Vt Hearing protection

    Real-time experiments of ANC systems for infant incubators

    Lichuan Liu, Kaplia Beemanpally, and Sen M. Kuo

    Noise Control Eng. J. 60, 1, pp. 36-41 (2012)

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    This paper presents real-time experiments of applying active noise control (ANC) algorithms for infant incubators to reduce recorded neonatal intensive care unit (NICU) noise. Research shows that 10–15% of newborns spend time in NICU and high noise levels in the infant incubator result in numerous adverse health effects. The ANC system has potential benefits of generating quiet environment for newborns inside the incubators and decreasing the risk of health impairment and disability. Real-time experiments of single-channel and multiple-channel ANC structures were conducted using real recorded NICU noise samples. An average reduction of 13 dB and 17 dB are obtained by using single-channel and multiple-channel ANC systems.
    Show PACS
    43.50.Ki Active noise control
    43.66.-x Psychological acoustics
    87.85.-d Biomedical engineering

    A combined sonic crystal rod of Bragg type with ability of vibration reduction in broad frequency band

    Haisheng Shu, Shaogang Liu, Dan Zhao, Fa Zhang, and Enwu Gao

    Noise Control Eng. J. 60, 1, pp. 42-61 (2012)

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    One dimensional sonic crystal (SC) rod has apparent band gaps in which longitudinal wave and bending wave can be suppressed distinctly. However, each single SC rod’s band gap width is comparatively narrow and the low frequency vibration cannot be reduced generally. For this reason, a combined SC rod is proposed. The combined SC rod consists of three SC rods, each of which has the same periodical structure of typical Bragg type. The transfer matrix of the combined SC rod is deduced and the theoretical results are acquired by means of numerical calculation. Finite element analysis and experiments are carried out. Our results show that: in the combined SC rod, the bending wave can be transformed into the longitudinal wave and therefore the vibration reduction effect can be found in two kinds of band gaps. At the same time the ability of vibration suppression in low frequency range, which is similar to the effect of vibration isolation of traditional “spring-oscillator” system, also can be realized. Additionally, the material arrangement has obvious influence on the performance of the single and combined SC rods. The vibration reduction when the external excitation is loaded on the softer end is obviously stronger than when loaded on another end. The structure and the analysis results of the combined SC rod can be beneficial to the engineering application of SC structures.
    Show PACS
    43.40.Cw Vibrations of strings, rods, and beams
    46.70.Hg Membranes, rods, and strings
    02.10.Yn Matrix theory
    02.70.Dh Finite-element and Galerkin methods
    07.10.Fq Vibration isolation

    A potential role for noise complaints as a predictor of the prevalence of annoyance with aircraft noise

    Sanford Fidell, Vincent Mestre, and Matthew Sneddon

    Noise Control Eng. J. 60, 1, pp. 62-68 (2012)

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    Aircraft noise complaints lodged with airports are regarded for U.S. federal policy purposes as unreliable and uninterpretable indications of noise impacts on airport-area communities. Small numbers of complainants are typically responsible for large numbers of complaints; the bulk of complaints are generally lodged from areas with noise exposure levels which do not meet the federal definition of “incompatible” land use; and federal noise regulatory policy is in any event based on an attitude (annoyance), not on complaint behavior. Recent analyses, however, have demonstrated that predictions of annoyance prevalence rates in airport communities are considerably improved when non-dose related factors, potentially including complaints, are taken into systematic consideration. To the extent that complaints, which are weakly related at best to cumulative noise exposure levels, can be used as an index of non-dose related attitudes toward airport and aircraft noise, they may help to reduce the uncertainty of predictions of annoyance prevalence rates.
    Show PACS
    43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles
    43.50.Nm Aerodynamic and jet noise
    43.50.Sr Community noise, noise zoning, by-laws, and legislation
    43.28.Hr Outdoor sound sources

    Online urban acoustic noise monitoring system

    Andrzej Czyzewski, Jozef Kotus, and Maciej Szczodrak

    Noise Control Eng. J. 60, 1, pp. 69-84 (2012)

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    Concepts and implementation of the Online Urban Noise Monitoring System are presented. Principles of proposed solution used for dynamic acoustical maps creating are discussed. The architecture of the system and the data acquisition scheme are described. The concept of noise mapping, based on noise source model and propagation simulations, was developed and employed in the system. Dynamic estimation of noise source parameters utilized in the system is introduced. The details of implementation of noise map computation and visualization are presented. Advances introduced by the developed solution in the continuous noise monitoring and acoustic maps creation is in focus. The results of measurements and simulations performed by the system prototype are depicted. Noise measurements results gathered by system and created acoustic maps are compared with some other solutions in order to investigate accuracy.
    Show PACS
    43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
    43.50.Vt Topographical and meteorological factors in noise propagation
    43.50.Yw Instrumentation and techniques for noise measurement and analysis

    Acoustic testing facilities at the Office of Mine Safety and Health Research

    J. Shawn Peterson, David Yantek, and Adam K. Smith

    Noise Control Eng. J. 60, 1, pp. 85-96 (2012)

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    The National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) maintains a noise control program as part of its Hearing Loss Prevention Branch (HLPB). This program utilizes two large acoustic laboratories—a reverberation chamber and a hemi-anechoic chamber—to assist OMSHR engineers with the development and evaluation of noise controls. This paper discusses the design, instrumentation, and use of the NIOSH acoustics laboratories and the important role they play in noise control development and evaluation. The NIOSH reverberation chamber meets the absorption, reverberation time, and test room broadband qualification requirements specified in the ISO 3741/ANSI S12.51 acoustics standard for precision method sound power testing. As part of a qualification testing program, NIOSH conducted an uncertainty estimate for sound power level testing in the chamber. For an overall sound power measurement, this uncertainty estimate was 0.4 dB. The NIOSH hemi-anechoic chamber, which uses Eckel Industries SuperSoft Panels on the walls and ceiling, is used primarily for noise source identification to determine significant noise sources on equipment. Testing was completed to ensure that the chamber functions as a free-field. The SuperSoft panels met NIOSH requirements and the chamber was verified as a free-field per the test room qualification criteria set forth in ISO 3745.
    Show PACS
    43.55.Pe Anechoic chamber design, wedges
    43.58.Fm Sound level meters, level recorders, sound pressure, particle velocity, and sound intensity measurements, meters, and controllers

    A hybrid finite element-least square point interpolation method for solving acoustic problems

    L. Y. Yao, D. J. Yu, W. Y. Cui, and J. W. Zhou

    Noise Control Eng. J. 60, 1, pp. 97-112 (2012)

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    This paper presents a finite element-least square point interpolation method (FE-LSPIM) for solving 2D acoustic problem by synthesizing the attractive features of finite element and least-square point interpolation shape functions using the concepts of partition of unity (PU) methods. In the present method, the acoustic domain is discretized using quadrilateral element, and the shape functions of the quadrilateral element are used for PU and the least-square point interpolation method (LSPIM) for local approximation. This enables the proposed method to inherit the compatibility properties of finite element method and the quadratic polynomial completeness properties of meshfree methods, so that the finite element-least-square point interpolation method (FE-LSPIM) will greatly reduce the numerical dispersion error because the numerical dispersion error is essentially caused by the “overly-stiff” nature of the FEM model. Numerical results for benchmark problems show that, the FE-LSPIM achieves more accurate results and higher convergence rates as compared with the corresponding finite elements and Element-free Galerkin method (EFGM), especially for high wave number and irregular meshes.
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    43.20.Bi Mathematical theory of wave propagation
    02.60.Ed Interpolation; curve fitting

    A hybrid acoustic holography technique for moving sound source identification based on wave superposition algorithm

    Diange Yang, Ziteng Wang, Bing Li, and Xiaomin Lian

    Noise Control Eng. J. 60, 1, pp. 113-120 (2012)

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    To solve the ghost sources problem which occurs in the noise source identification, a hybrid acoustic holography technique based on wave superposition method is developed in our current work. This research extended the wave superposition method to the measurement of the moving sound sources and solves the ghost sources problem in moving sound source identification without adding extra microphones. Short-time wave superposition equations for moving sound sources are established employing the Doppler frequency shift, and the equivalent sound sources are calculated according to the pre-estimation results by the beam-forming method. Then the major sound sources are identified through far field acoustic holography based on these equivalent sound sources. Simulation results and validation experiments with known sound pressure generated by loud speakers have proven that our developed method can not only provide better identification results for locating sound sources accurately but also reduce the side lobe significantly and solve the ghost sources problem successfully, suggesting our method’s potential in noise identification work.
    Show PACS
    43.50.Fe Noise masking systems
    43.60.Sx Acoustic holography
    43.50.Yw Instrumentation and techniques for noise measurement and analysis
    43.50.Lj Transportation noise sources: air, road, rail, and marine vehicles

    Uncertainty minimization in LAeqT measurements

    Rufin Makarewicz and Roman Gołębiewski

    Noise Control Eng. J. 60, 1, pp. 121-123 (2012)

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    Usually, the time-term average sound level, L, is not directly measured but calculated from the measured sound exposure levels. Variance of L1,….., Ln quantifies the uncertainty of noise measurements. In any case, a decrease in the variance means an increase in the quality of measurements. This paper shows how to decrease the variance of L1,….., Ln.
    Show PACS
    43.50.Rq Environmental noise, measurement, analysis, statistical characteristics
    43.50.Yw Instrumentation and techniques for noise measurement and analysis
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