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1
Moeller, Michael M. Jr. "Noise environment characterization in military treatment facilities." Thesis, Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/48995.
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Hospital sound environments are complex and hard to understand. One of the most important factors in these environments is the effective communication between staff members in regards to patient care and successful communication depends in part on the hospital’s sound environment. In this study, objective sound measurements as well as occupant perceptive data were collected at three hospitals. Sound pressure levels; including maximum, peak, minimum and equivalent levels were recorded in these hospitals, in addition to active impulse response measurements. Acoustic descriptors of the sound environment such as spectral content, level distributions, energy decay and temporal patterns were examined. The perception of the hospital soundscape (sound environment) was evaluated through surveys of the staff, patients and visitors to units. It was found that noise levels in all patient rooms and work areas were significantly higher than guidelines laid out in previous literature and by professional organizations. This work contributes to the field by broadening the metrics used to quantify hospital acoustic environments. In addition, this work added to the field by providing the most rigorous acoustic field measurement set published to date. This was done to create an accurate portrayal of the hospital soundscape environment.
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Jayakumar, Vignesh. "Evaluation and Design of Noise Control Measures for a Pneumatic Nail Gun." University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1428049303.
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Suwit, Pulthasthan Information Technology & Electrical Engineering Australian Defence Force Academy UNSW. "Optimal placement of sensor and actuator for sound-structure interaction system." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Information Technology and Electrical Engineering, 2006. http://handle.unsw.edu.au/1959.4/38741.
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This thesis presents the practical and novel work in the area of optimal placement of actuators and sensors for sound-structure interaction systems. The work has been done by the author during his PhD candidature. The research is concentrated in systems with non-ideal boundary conditions as in the case in practical engineering applications. An experimental acoustic cavity with five walls of timber and a thin aluminium sheet fixed tightly on the cavity mouth is chosen in this thesis as a good representation of general sound-structure interaction systems. The sheet is intentionally so fixed that it does not satisfy ideal boundary conditions. The existing methods for obtaining optimal sensor-actuator location using analytic models with ideal boundary conditions are of limited use for such problem with non-ideal boundary conditions. The method presented in this thesis for optimal placement of actuators and sensors is motivated by energy based approach and model uncertainty inclusion. The optimal placement of actuator and sensor for the experimental acoustic cavity is used to construct a robust feedback controller based on minimax LQG control design method. The controller is aimed to reduce acoustic potential energy in the cavity. This energy is due to the structure-borne sound inside the sound-structure interaction system. Practical aspects of the method for optimal placement of actuator and sensors are highlighted by experimental vibration and acoustic noise attenuation for arbitrary disturbance using feedback controllers with optimal placement of actuator and sensor. The disturbance is experimentally set to enter the system via a spatial location different from the controller input as would be in any practical applications of standard feedback disturbance rejections. Experimental demonstration of the novel methods presented in this thesis attenuate structural vibration up to 13 dB and acoustic noise up to 5 dB for broadband frequency range of interest. This attenuation is achieved without the explicit knowledge of the model of the disturbance.
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Mahapatra, Arun Kiran. "Investigation of noise in hospital emergency departments." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45842.
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The hospital sound environment is complex. Emergency Departments (EDs), in particular, have proven to be hectic work environments populated with diverse sound sources. Medical equipment, alarms, and communication events generate noise that can interfere with staff concentration and communication. In this study, sound measurements and analyses were conducted in six hospitals total: three civilian hospitals in Atlanta, Georgia and Dublin, Ohio, as well as three Washington, DC-area hospitals in the Military Health System (MHS). The equivalent, minimum, and maximum sound pressure levels were recorded over twenty-four hours in several locations in each ED, with shorter 15-30 minute measurements performed in other areas. Acoustic descriptors, such as spectral content, level distributions, and speech intelligibility were examined. The perception of these acoustic qualities by hospital staff was also evaluated through subjective surveys. It was found that noise levels in both work areas and patient rooms were excessive. Additionally, speech intelligibility measurements and survey results show that background noise presents a significant obstacle in effective communication between staff members and patients. Compared to previous studies, this study looks at a wider range of acoustic metrics and the corresponding perceptions of staff in order to form a more precise and accurate depiction of the ED sound environment.
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Nunes, Osmar. "Analise teorica e experimental do campo sonoro irradiado por um compressor hermetico." [s.n.], 2005. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263256.
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Orientador: Jose Roberto de França ArrudaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-08-05T19:37:58Z (GMT). No. of bitstreams: 1 Nunes_Osmar_M.pdf: 3751336 bytes, checksum: 2fc3b9c3cc2af03451617cae482065d1 (MD5) Previous issue date: 2005
Resumo: As características acústicas de compressores herméticos têm se tomado cada vez mais críticas no projeto destes equipamentos e as predições destas características ao longo do projeto, obrigatórias para a adequação deste produto às condições de consumo. Este trabalho apresenta um método de avaliação vibro-acústica de compressores herméticos através de modelos de elementos finitos. Para estas avaliações, forças harmônicas com amplitudes unitárias são aplicadas em pontos específicos da carcaça e os seus campos de pressão sonora resultantes são calculados sob condições anecóicas, sendo que, estas condições foram modeladas através de elementos infinitos acústicos. Através deste método, é possível obter numericamente a potência acústica irradiada por diferentes versões de projeto, compará-las, escolher a versão mais adequada e, se for o caso, obter informações para direcionar modificações em uma versão para a sua adequação aos níveis de potência sonora exigidos. O trabalho mostra as verificações executadas durante o processo de desenvolvimento desta metodologia como análise modal, análises de convergência e comparações de resultados numéricos com analíticos através de modelos de fontes omnidirecionais. Para a verificação de seu funcionamento, são apresentadas as análises vibro-acústicas numéricas de duas versões de compressor. Além disto, dois protótipos com características semelhantes aos modelos analisados foram testados em câmara reverberante para a obtenção de suas potências sonoras e a comparação com os resultados numéricos. Os resultados obtidos desta comparação mostraram boas correlações entre numérico e experimental e fornecem subsídios para avaliar o desempenho entre as diferentes versões de projeto
Abstract: The importance of the acoustic characteristics in design of hermetic compressors has increased along the years. As a consequence, to predict these characteristics in the design phase is mandatory for this product to meet the consumption requirements. This work presents a method for evaluating the vibration and acoustic characteristics of hermetic compressors through finite element models. To perform these evaluations, harmonic forces with unitary amplitudes are applied in specific locations of the compressor housing and their resulting acoustic pressure fields are ca1culated under anechoic conditions obtained through the acoustic infinite elements. By using this method, it is possible to numerically obtain the acoustic power level irradiated by different versions of design in order to compare them and to choose the most adequate version. With the use of this method it is also possible to obtain information to guide modifications in the design and suit it to desired acoustic power levels. This work presents the verifications performed during the development process of this methodology such as modal analysis, convergence analysis and comparisons between analytical and numerical results by using omnidirectional sources. To validate this methodology, the acoustic numerical analysis of two versions of compressor' s housing was presented. Furthermore, two prototypes similar to the models characteristics were submitted to tests in reverberant chamber for obtaining their acoustic power levels and compared with the numerical results. The obtained results of this comparison presented a satisfactory correlation between numerical and experimental results and provided relevant information to evaluate different design versions
Mestrado
Mecanica Computacional
Mestre em Engenharia Mecânica
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Khan, Imran. "Measurements, Analysis Techniques and Experiments in Sound and Vibration : Applied to Operational MRI Scanners and in Remote Laboratories." Doctoral thesis, Blekinge Tekniska Högskola, Institutionen för tillämpad signalbehandling, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-13821.
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High quality noise and vibration measurements outside of a laboratory environment on real life structures and applications are not trivial. True boundary and operating conditions enforce unique challenges on the measurements. Measurements in hazardous situations such as high magnetic fields, and high temperature environments, etc., where ordinary measurement equipment and methods may not be employed, require further precautions. Post measurements objectives such as analysis, design and strategic decisions, e.g., control, rely heavily on the quality and integrity of the measurements (data). The quality of the experimental data is highly correlated with the on-field expertise. Practical or hands-on experience with measurements can be imparted to prospective students, researchers and technicians in the form of laboratory experiments involving real equipment and practical applications. However, achieving expertise in the field of sound and vibration measurements in general and their active control in particular is a time consuming and expensive process. Consequently most institutions can only afford a single setup, resulting in the compromise of the quality of expertise. In this thesis, the challenges in the field of sound and vibration measurements in high magnetic field are addressed. The analysis and measurement of vibration transferred from an operational magnetic resonance imaging (MRI) scanner to adjacent floors is taken as an example. Improvised experimental measurement methods and custom-made frequency analysis techniques are proposed in order to address the challenges and study the vibration transfer. The methods may be extended to other operational industrial machinery and hazardous environments. To encourage and develop expertise in the field of acoustic/vibration measurements and active noise control on practical test beds, remotely controlled laboratory setups are introduced. The developed laboratory setup, which is accessed and controlled via the Internet, is the first of its kind in the active noise control and acoustic measurements area. The laboratory setup can be shared and utilized 24/7 globally, thus reducing the associated costs and eliminating time restrictions.
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Chan, T. M. "Active control of sound in ducts." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390327.
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Chandler-Wilde, S. N. "Ground effects in environmental sound propagation." Thesis, University of Bradford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384241.
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Barlow, G. N. D. "Sound speed measurement and variabilities in the sea." Thesis, Bangor University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.332805.
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Lane, Jeremy David. "Active Control of Noise Through Windows." Thesis, University of Canterbury. Mechanical Engineering dept, 2013. http://hdl.handle.net/10092/10523.
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Windows are a weakness in building facade sound transmission loss (STL). This coupled with the detrimental effects of excessive noise exposure on human health including: annoyance, sleep deprivation, hearing impairment and heart disease, is the motivation for this investigation of the STL improvements active noise control (ANC) of windows can provide.
Window speaker development, ANC window experiments and analytical modelling of ANC windows were investigated. Five different window speaker constructions were characterised then compared with a previously developed window speaker. ANC window testing used three different ANC configurations and was performed in two different
environments, one with a reverberant receiving room, and the other with an anechoic receiving room. Optimisation of ANC systems with particular control source locations was the aim of the modelling. This enabled comparison with the ANC window tests and would aid in further development of ANC windows.
Window speaker constructions were characterised by sound pressure level (SPL) measurements performed in an anechoic room. These measurements were made in a way that enabled comparison with the previously developed window speaker.
Total sound energy reduction calculations were used to determine the relative performance of the tested ANC windows.
An STL model, based on a modal panel vibration model, was initially created and verified against published STL data before it was expanded to include ANC control sources. The model was used to simulate the performed anechoic environment tests and an ideal ANC case.
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Tseng, Wen-Kung. "Sound minimisation for local active control." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.342925.
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Gu, Yi. "Active control of sound radiation from fluid loaded plates." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/39888.
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Active control of sound radiation due to subsonic wave scattering from an infinite or a finite fluid-loaded plate excited below the critical frequency is analytically studied. The disturbance is caused by a flexural wave in an infinite plate, or by a point force on a finite plate at subsonic frequencies. The wave scattering is caused by discontinuities on the plate or by the boundary conditions.
A feed-forward control approach is applied by implementing either point/line forces or piezoelectric actuators on the plate. The amplitude and phase of control forces are determined by the optimal solution of a cost function which minimizes the far-field radiated acoustic power over a prescribed surface in the half space of the fluid field.
The results show that for subsonic excitations, high global reduction in radiated pressure is possible with properly located active control forces. The number and location of control forces employed in order to obtain high control performance are related to the excitation frequency. The far-field sound radiation directivity pattern, the modal amplitudes of the plate vibration, the plate vibration autospectrum in the wave number domain, and the near-field intensity distribution are extensively studied in order to uncover the mechanisms of control.Ph. D.
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Wertel, Scotty John. "Experimental analysis of noise reduction properties of sound absorbing foam." Online version, 2001. http://www.uwstout.edu/lib/thesis/2001/2001wertels.pdf.
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Silcox, Richard J. "Active control of multi-modal sound in waveguides." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339481.
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Joseph, P. F. "Active control of high frequency enclosed sound fields." Thesis, University of Southampton, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280927.
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Nassrallah, Flora G. "Measurement of Occupational Sound Exposure from Communication Headsets." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34577.
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Increased use of communication headsets found in various workplaces raises concerns regarding exposure to potentially hazardous noise levels. Current national and international standards specify a wide range of simple and specialized methods for the measurement of sound exposure under communication headsets. However, to date, quantitative data comparing the degree of agreement between the different measurement methods or their relative performance are lacking, and it is not known if occupational health and safety (OHS) or hearing loss prevention (HLP) stakeholders have the necessary training and equipment to integrate them in their daily practice.
A three-step study addressing several knowledge gaps on this topic is presented in this thesis. First, a questionnaire survey distributed to OHS and HLP stakeholders has revealed that knowledge of specialized measurement techniques and access to the necessary equipment varies significantly depending on the training of the different professionals. There is therefore reason to specify several methods in measurement standards to meet the specific needs and expertise of the different stakeholders involved. Second, a series of experiments conducted with single and multiple expert participants indicated that the Type 1 artificial ear is not suited for sound exposure measurement with communication headsets, while Type 2 and Type 3.3 artificial ears are in good agreement with the acoustic manikin technique specified in the International standard ISO 11904-2. Finally, laboratory experiments were conducted to test the indirect calculation method proposed in the Canadian standard CSA Z107.56. Results revealed that the calculation method is suitable to identify possible situations of exposure over the regulatory limit (e.g. 85 dBA), but refinements are proposed to improve measurement accuracy.
Overall, this thesis provides new knowledge to guide selection of the most suitable methods for the assessment of communication headset exposure taking into account expertise, access to equipment, and field logistic constraints. Results also have direct implications for future revisions of existing measurement standards. Finally, this work could be the basis for detailed guidelines on noise exposure measurements under communication headsets to better inform OHS and HLP professionals and ultimately prevent occupational noise-induced hearing loss.
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Schiller, Noah Harrison. "Decentralized control of sound radiation from periodically stiffened panels." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/30148.
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Active structural acoustic control has previously been used to reduce low-frequency sound radiation from relatively simple laboratory structures. However, significant implementation issues have to be addressed before active control can be used on large, complex structures such as an aircraft fuselage. The purpose of this project is to extend decentralized structural control systems from individual bays to more realistic airframe structures. In addition, to make this investigation more applicable to industry, potential control strategies are evaluated using a realistic aft-cabin disturbance identified from flight test data.
This work focuses on decentralized control, which implies that each control unit is designed and implemented independently. While decentralized control systems are relatively scalable, performance can be limited due to the destabilizing interaction between neighboring controllers. An in-depth study of this problem demonstrates that the modeling error introduced by neighboring controllers can be expressed as the product of the complementary sensitivity function of the neighboring control unit multiplied by a term that quantifies the diagonal dominance of the plant. This understanding can be used to improve existing control strategies. For instance, decentralized performance can often be improved by penalizing control effort at the zeros of the local control model. This stabilizes each control unit and reduces the modeling error induced on neighboring controllers. Additional analyses show that the performance of decentralized model-based control systems can be improved by augmenting the structural damping using robust, low-authority control strategies such as direct velocity feedback and positive position feedback. Increasing the structural damping can supplement the performance of the model-based control strategy and reduce the destabilizing interaction between neighboring control units. Instead of using low-authority controllers to stabilize the decentralized control system, another option is to modify the model-based design. Specifically, an iterative approach is developed and validated using real-time control experiments performed on a structural-acoustic system with poles close to the stability boundary, non-minimum phase zeros, and unmodeled dynamics. Experiments demonstrate that the iterative control strategy, which combines frequency-shaped linear quadratic Gaussian (LQG) control with loop transfer recovery (LTR), is capable of achieving 12dB peak reductions and a 3.6dB integrated reduction in radiated sound power from a rib-stiffened aluminum panel.Ph. D.
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McNicol, Ian David. "Active adaptive cancellation of sound in ducts /." Title page, contents and synopsis only, 1985. http://web4.library.adelaide.edu.au/theses/09ENS/09ensm169.pdf.
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Thomas, Robert Dean. "The active control of the transmission of sound." Thesis, University of Southampton, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316440.
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Tian, Lin 1971. "A superconducting flux QuBit : measurement, noise and control." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8483.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 2002.Includes bibliographical references (p. 197-213).
A superconducting quantum bit can be made with three nano-scale Josephson junctions connected in series. In this thesis, various aspects of this qubit are studied. It is shown numerically that the qubit behaves as a giant magnetic dipole with quantum tunneling between the two qubit states. The natural coupling between qubits plus the manipulation on a single qubit state provides the building blocks for universal quantum computing. The state of the qubit can be determined by measuring its flux with a SQUID. The measurement efficiency and measurement-induced decoherence are investigated. A coherent transition assisted scheme is designed for a projective measurement on the qubit. A general method is developed to study qubit decoherence by environmental noise. The dynamic control approach is applied for preventing off-resonant leakage during gate operations and for de-coupling the qubit from noise.
by Lin Tian.
Ph.D.
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Bull, John Ivan. "Measurement of the airborne sound insulation of traffic noise barriers using impulse response techniques." Thesis, University of Canterbury. Mechanical Engineering, 2014. http://hdl.handle.net/10092/8962.
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This research thesis involves the measurement of the airborne sound insulation of road traffic noise barriers, with the goal of gaining a more in depth understanding of the factors that influence noise barrier performance. A measurement system is developed, based on EN 1793-6:2012, to quantify the airborne sound insulation of a noise barrier in situ. Validation testing is performed to ensure that the system meets the requirements of EN 1793-6:2012. MATLAB code is developed, incorporating all of the signal processing tasks into a single graphical user interface. The measurement system is then used to measure the airborne sound insulation of eight existing traffic noise barriers located around Auckland, New Zealand.
The results from the Auckland field tests show that consistent single number ratings of airborne sound insulation can be achieved on different samples of the same noise barrier. The presence of air gaps and hidden defects will degrade the acoustic performance of a noise barrier, most significantly at the high frequencies. The comparison of single number ratings calculated with differing measurement frequency ranges is discussed, and some comments are made on the measurement standard itself.
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Cazzolato, Ben S. "Sensing systems for active control of sound transmission into cavities." Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phc386.pdf.
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Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1999.Copies of author's previously published articles inserted. One computer disc (CD-ROM) in plastic jacket pasted onto back cover. Bibliography: leaves 319-339. Also available electronically.
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Robert, Rene Jean. "Measuring noise level reduction using an artificial noise source." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54480.
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Buildings located near airports may be subjected to significant noise levels due to aircraft flyovers. Aircraft noise is particularly annoying when compared to other traffic noises due to its intermittent nature. While noise control is typically performed at the source, sound insulation programs are in place to improve the acoustic performance of a residence affected by the flyovers. Noise Level Reduction (NLR) is a common metric used in the United States to determine whether a residence qualifies for such programs. Sound insulation programs are available to houses that have an indoor Day Night Average Sound Level (DNL) greater than 45 dBA. NLR is a single-number metric used to quantify the ability for a building or building element to reduce the transmission of external sound pressure levels generated by aircraft. In addition to determining whether a residence qualifies, NLR can be used to quantify the effectiveness of the modifications performed as a result of the sound insulation program. NLR measurements with a loudspeaker offer an alternative method to those performed with aircraft flyovers, offering flexibility to the consultants that perform these measurements in the field. The purpose of this research was to better understand and improve the loudspeaker test for measuring NLR, providing a resource to the aircraft noise industry. Testing was completed on a "test house" that was constructed on campus with construction methods typical of a mixed-humid climate. The angular dependency, repeatability, and reproducibility of NLR, among other factors, were evaluated with field measurements. Significant NLR variations were observed with changes in lateral and vertical angles of incidence.
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Aldridge, David Charles. "The calibration of microphones and sound level meters for the measurement of impulsive noise." Thesis, Brunel University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.275873.
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Burgemeister, Kym A. "Novel methods of transduction for active control of harmonic sound radiated by vibrating surfaces." Title page, contents and abstract only, 1996. http://hdl.handle.net/2440/37932.
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Large electric transformers such as those used in high voltage substations radiate an annoying low frequency hum into nearby communities. Attempts have been made to actively control the noise by placing a large number of loudspeakers as control sources around noisy transformers to cancel the hum. These cancellation systems require a large number of loudspeakers to be successful due to the imposing size of the transformer structures. Thus such systems are very expensive if global noise reduction is to be achieved. The aim of this thesis is to investigate theoretically and experimentally the use of thin perforated panels closely placed to a heavy structure to reduce the radiation of unwanted harmonic noise. These panels can themselves be vibrated to form a control source radiating over a large surface surrounding the primary source. The problem of the equipment overheating inside the enclosure is alleviated because the holes in the panels still allow natural cooling. An initial study is carried out to determine the resonance frequencies of perforated panels. The use of previously determined effective elastic properties of the panels and Finite Element Analysis to theoretically calculate their resonance frequencies is examined. Secondly the attenuation provided by active noise control using perforated panels as control sources is explored by use of a coupled analysis, where the primary source is assumed to influence the radiation of the perforated control panel. This analysis was found to predict poorly the amount of attenuation that could be achieved, so an uncoupled analysis is undertaken, where both the primary and control sources are assumed to radiate independently of each other. Not only does this greatly simplify the theoretical analysis but it also enables prediction of attenuation levels which are comparable to those determined experimentally. The theoretical model is reformulated to enable comparison of the sound power attenuation provided by perforated panel control sources with that of traditional acoustic and structural control sources. Finally, the use of modal filtering of traditional acoustic error sensor signals to give transformed mode (or power mode) sensors is examined. The independently radiating acoustic transformed modes of the panel are determined by an eigenanalysis and a theoretical analysis is presented for a farfield acoustic power sensor system to provide a direct measurement of the total radiated acoustic power. The frequency dependence of the sensor system, and the amount of global sound power attenuation that can be achieved is examined. Experimental measurements are made to verify the theoretical model and show that a sound power sensor implemented with acoustic sensors can be used in a practical active noise control system to increase the amount of attenuation that can be achieved. Alternatively the sound power sensor can be used to reduce the number of error channels required by a control system to obtain a given level of attenuation when compared to traditional error criteria. The power mode sensor analysis is then applied to the perforated panel control system, with similar results.Thesis (Ph.D.)--Engineering (Department of Mechanical Engineering), 1996.
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Sheffer, Jennifer. "Worker exposure to noise during computer manufacturing measurement and control /." Online version, 2009. http://www.uwstout.edu/lib/thesis/2009/2009shefferj.pdf.
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Sagers, Jason Derek. "Analog Feedback Control of an Active Sound Transmission Control Module." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2461.pdf.
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Ågren, Anders. "On measurement, assessment and control of diesel engine noise." Doctoral thesis, Luleå tekniska universitet, Drift, underhåll och akustik, 1994. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18693.
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The thesis comprises six papers with the overall theme of measurement, assessment and control of diesel engine noise, with an emphasize on control. The radiation of noise is shown to be dominated by the low end of the engine sides and by the engine front. The mode shapes of the crankcase, the oil sump and the timing transmission cover are investigated. The vibrations are measured and analysed through running mode, modal analyses and SEA. The noise radiation is explored in detail with near-field measurements of sound intensity. In the engine front, the noise radiation is shown to have contributions from the timing casing, the oil-sump front and the crankshaft torsion vibration damper. The radiation from the torsion damper is analysed by a regression analysis of measured intensity data and the vibrations of the damper are investigated with a laser-doppler vibrometer. The results show that the damper vibrates in the axial directions with vibration modes that both radiate noise and interfere with the radiation from the engine structure. It is shown that there in the engine front are strong coupled vibration modes between the timing cover and the oil sump front m the frequency range 500 Hz - 1 kHz. The importance of the strong vibration modes in the crankcase and the oil-sump sides is shown. The propagation paths of noise and vibration to the engine front have been examined with an SEA powerflow analysis and by opening the front cover to measure the sound power from the timing gears. The main excitations of the front cover are found to be by engine block vibrations below 1.25 kHz and by tuning gears noise above 2 kHz. Various constructions to control the noise are tested. Two stiffeners are designed and tested to reduce vibrations m the engine low end, one ladder frame introducing stiffness at the crankcase flange and one bearing beam introducing stiffness at the main bearing caps. The stiffeners have hem evaluated by sound intensity measurements and mobility measurements. The ladder frame gave good noise reductions but the bearing beam merely caused frequency shifts of the bearing modes. A decoupling of the oil sump resulted in significant noise and vibration reductions. The timing cover is modified by increasing the damping and by decrease the radiation efficiency. Various interior panels are tested, like plexiglass and aluminium panels of different thicknesses, a rubber damping layer and a combined rubber/steel-sheet damping layer. A thin plastic sheet has low radiation efficiency and may thereby lower the noise emission. A slightly improved model for calculation of radiation efficiency of small irregularly shaped plates is suggested. The traditional SEA prediction model is shown to be ill-conditioned for engine applications. An improved model using geometric averaging is suggested and evaluated. The results show that the new SEA model is working well for frequencies down to 800 Hz for predictions of damping treatments, decoupling of the oil sump and for power-flow determinations. The concept of equivalent mass is found valuable and validations are made according to the consistency and reciprocity theories. A hemi-anechoic engine laboratory is constructed and evaluated. New efficient low-cost diffusing absorbers have been designed, the performance is evaluated with standard deviation analysis of sound pressure measurements. The performance of the absorbers is found to be compeatable with much more expensive commercial designs. Measured sound intensity in three-dimensional vectors is a powerful tool to identify and illustrate sound fields. When used in near-fields to identify complex noise sources large errors may occur. It is shown that the low relative levels of vector components and the reactivity of the sound field give large errors m repeated measurements. Analyses and comparisons are performed on a simple source and on an engine. A two- and a six-microphone probe were used that were hand-held and robot-controlled. It is concluded dig in point-intensity measurements on engineering noise sources, a 4-6 microphone probe and a precision positioner should be used to get reliable measurements.Godkänd; 1994; 20061214 (biem)
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Goldstein, Andre L. "Control of Sound Transmission with Active-Passive Tiles." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/27913.
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Nowadays, numerous applications of active sound transmission control require lightweight partitions with high transmission loss over a broad frequency range and simple control strategies. In this work an active-passive sound transmission control approach is investigated that potentially addresses these requirements. The approach involves the use of lightweight stiff panels, or tiles, attached to a radiating base structure through active-passive soft mounts and covering the structure surface. The resulting double-partition configuration was shown to have good high frequency passive isolation, but poor low frequency transmission loss due to the coupling of the tiles to the base vibration through the air gap. The low frequency transmission loss performance of the partition was increased by using the active mounts to cancel the local volume velocity of the tiles. The use of a decentralized control approach with independent single channel controllers for each tile facilitates the implementation of a multiple tile system in a large scale application.
A coupled structural-acoustic model based on an impedance mobility matrix approach was formulated to investigate the potential performance of active-passive tile approach in controlling sound transmission through plates. The model was initially applied to investigate the sound transmission characteristics of a double-panel partition consisting of a single tile-plate configuration and then extended to model a partition consisting of multiple-tiles mounted on a plate. The system was shown to have significant passive performance above the mass-spring-mass resonance of the double-panel system. Both feedback and feedforward control approaches were simulated and shown to significantly increase the transmission loss of the partition by applying control forces in parallel with the mounts to reduce the tile normal velocity. A correspondent reduction in sound radiated power was obtained over a broad frequency range limited by the tile stiffness.
The experimental implementation of the active-passive tile approach for the control of sound transmission through plates was also performed. Two main experimental setups were utilized in the investigations, the first consisting of a single tile mounted on a clamped plate and the other consisting of four active tiles mounted of a simply supported plate. Tile prototypes were implemented with lightweight stiff panels and integrated active-passive mounts were implemented with piezoelectric Thunder actuators. Both analog feedback and digital feedforward control schemes where designed and implemented with the objective of reducing the normal velocity of the tiles. Experimental results have demonstrated significant broad frequency range reductions in the sound transmission through the partition by active attenuation of the tile velocity. In addition, the experiments have shown that decentralized control can be successfully implemented for multiple tiles systems. The active-passive sound transmission control characteristics of the systems experimentally studied were observed to be in accordance with the analytical results.Ph. D.
30
Garcia, Bonito Juan J. "Local active control in pure tone diffracted diffuse sound fields." Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243146.
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Thomas, Ashwin Paul. "Simulated and laboratory models of aircraft sound transmission." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/52319.
Full textAbstract:
With increased exposure to transportation noise, there have been continued efforts to help insulate homes from aircraft noise. Current aircraft noise guidelines are based primarily on outdoor sound levels. As people spend the majority of their time indoors, however, human perception is evidently more related to indoor sound levels. Investigations are being made to provide further insight into how typical residential constructions affect indoor response. A pilot study has built a single-room "test house", according to typical construction for mixed-humid climate regions, and has directly measured outdoor-to-indoor transmission of sound - with specific focus on continuous commercial aircraft signatures. The results of this study are being used to validate and improve modelling software that simulates a wide range of construction types and configurations for other US climate regions. The improved models will allow for increased flexibility in simulating the impacts of acoustic and energy retrofits. Overall, the project intends to improve the ability to predict acoustic performance for typical US construction types as well as for any possible design alterations for sound insulation.
32
Feng, Tao. "Design and Analysis of Efficient Adaptive Algorithms for Active Control of Vehicle Interior Sound." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1490354549915601.
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Waerder, Maximilian, and Hubertus Murrenhoff. "On the origin and measurement of noise emission in pneumatics." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-200524.
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Noise is a circumstance of ordinary life and mainly originated by continually growing dynamic and the rapid development of society. In the industrial environment there are noise-intensive parts that influence the condition of present operators negatively. Thus, measures of noise abatement have been investigated intensely by industrial companies as well as federal agencies. As a subdomain of fluid power pneumatics is especially known for characteristic noise emission by the use of air as power transmission. The transient decompression of air from pressure levels up to 8 bar and partly high flow rates nearby sonic speed cause the emergence of direct airborne noise at vent ports of pneumatic components. The following paper outlines the mechanisms that induce the emission of high sound pressure levels. In order to achieve reproducible results a test bench for varying pneumatic standard components is introduced. Based on a selection of those components results are compared to standardized measurement procedures whether fulfilling the standardizations’ requirements. In conclusion, two benefits are achieved. Firstly, standardization is derived enabling neutral comparison of standard pneumatic components’ noise emission. Secondly, the measures can be evaluated to determine the most promising way to redesign pneumatic components of lower noise emissions.
34
Farooqui, Maaz. "Innovative noise control in ducts." Doctoral thesis, KTH, Farkost och flyg, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-192927.
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The objective of this doctoral thesis is to study three different innovative noise control techniques in ducts namely: acoustic metamaterials, porous absorbers and microperforates. There has been a lot of research done on all these three topics in the context of duct acoustics. This research will assess the potential of the acoustic metamaterial technique and compare to the use of conventional methods using microperforated plates and/or porous materials. The objective of the metamaterials part is to develop a physical approach to model and synthesize bulk moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. This is achieved using an array of locally resonant metallic patches. In addition to this, a novel thin slow sound material is also proposed in the acoustic metamaterial part of this thesis. This slow sound material is a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound at selective resonance frequencies. A good agreement between theoretical analysis and experimental measurements is demonstrated. The second technique is based on acoustic porous foam and it is about modeling and characterization of a novel porous metallic foam absorber inside ducts. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with robust and less degradable properties. Material characterization of this porous absorber from a simple transfer matrix measurement is proposed.The last part of this research is focused on impedance of perforates with grazing flow on both sides. Modeling of the double sided grazing flow impedance is done using a modified version of an inverse semi-analytical technique. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions.QC 20160923
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Chan, Gary Ka-Yue. "Prediction of low-frequency sound-pressure fields in fitted rooms for active noise control." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/214.
Full textAbstract:
Low-frequency noise is a health concern for workers in industrial workshops; rooms of highly varying size and dimensions, usually containing obstacles (the ‘fittings’). Low-frequency noise can be generated from sources such as reciprocating or rotating machinery, or ventilation systems. As the exposure time to the noise lengthens, workers are increasingly at risk to harmful effects such as hearing loss, communication difficulty, personal discomfort, and even nausea from induced body vibrations. Passive methods of noise control, such as absorption or barriers, generally perform better at high frequencies, but are inadequate at low frequencies. A proposed solution is active noise control, which relies on destructive interference of sound waves to reduce noise levels. However, this depends on phase, and how it is affected when sound waves encounter diffracting obstacles. In addition, the geometrical configuration of the active-control system must be optimized, which can be done using a prediction model. Sound-prediction models can also estimate the decibel level of sound within a given room configuration created by a source and the attenuation provided by the control system. Therefore, it is of interest to develop a model that predicts sound propagation in fitted rooms with phase. In this thesis, sound-pressure fields were investigated in rooms containing parallelepiped obstacles at low frequencies for which the wavelength is comparable to the obstacle dimensions. The geometric theory of diffraction (GTD) was used to model edge diffraction from an obstacle and, thus, the pressure field in shadow regions. A ray-tracing prediction model was improved to consider both the amplitude and phase of sound fields, and also the effects of edge diffraction. To validate the prediction model, experiments were performed in an anechoic chamber where a source and diffracting objects were located. In collaboration with Dr Valeau at the Université de Poitiers in France, a second model based on the finite element method (FEM) was used to compare prediction results. It was found that the phase depends mostly on the direct unblocked source-to-receiver distance. The FEM and experimental results showed that occluding objects cause phase shifts. The implementation of first-order diffraction into the ray-tracing program was successful in predicting shadow zones, thus producing a better prediction of realistic sound fields in rooms with obstacles.
36
Sanguinetti, Mahela. "Measuring hearing protection performance results in a MIRE-compliant reverberatory chamber versus a non-MIRE compliant room." Morgantown, W. Va. : [West Virginia University Libraries], 2008. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5564.
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Thesis (M.S.)--West Virginia University, 2008.Title from document title page. Document formatted into pages; contains iii, 44 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 42-44).
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Balaban, Murat. "Noise Source Identification And Adoption Of Proper Noise Control Strategies On Wheeled Tractors." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12611838/index.pdf.
Full textAbstract:
This thesis is aimed at identifying the noise sources of a wheeled tractor to reduce the noise levels below the legislative limits by controlling noise sources through proper methodologies.
The study focuses firstly on identifying the noise sources of a wheeled tractor by using proper noise source identification techniques. These techniques can be summarized as sound intensity measurements, sound power level determination studies and spectral analysis of the noise data acquired in the
tests. Simple sound intensity mapping techniques are used and the intensity contour maps are generated to identify the noise sources.
Most important and effective noise sources are identified and the critical noise sources are focused to apply appropriate noise control strategies not only at the prototype production stages but also at the early design stages.
Consequently, upon consideration of both structure-borne and flow-induced noise, the pass-by noise level and the operator&rsquos ear noise levels of the tractor are reduced by nearly 3 dB (A) through application of proper noise control strategies.
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Uosukainen, Seppo. "JMC method applied to active control of sound : theoretical extensions and new source configurations /." Espoo [Finland] : Technical Research Centre of Finland, 1999. http://www.vtt.fi/inf/pdf/publications/1999/P386.pdf.
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Homma, Kenji. "Compact Integrated Active-Passive Approach for Axial Fan Noise Control." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29067.
Full textAbstract:
A new active-passive approach for the control of noise radiated from a small axial fan
was investigated. The approach involved the installation of an axial fan into a short duct
with both passive and active noise control functions. First, a systematic methodology for
the analytical modeling of finite-length ducts with multiple discontinuities was
formulated. The procedure involved the modeling of a duct as a collection of simple duct
sections, which were interconnected at multiple junctions.
Analytical studies have shown that a short lined duct provides passive noise
reduction effects through the mass-loading effect of the duct air volume at low
frequencies and the sound absorption by a passive liner at high frequencies. It was also
shown that active control can provide further noise attenuations at low-to-mid
frequencies, thereby enhancing the overall noise control performance. Two alternate
designs of active-passive noise control fan duct were considered. One was a simple non-
segmented duct with a 2x2 active control and the other was an internally segmented duct
with an 8x8 active control. It was indicated that the latter design possesses a significantly
higher global noise control potential than the former with respect to both bandwidth and
attenuation level. This was attributed to the reduction of the unwanted pressure
contributions from the duct cross modes through the high frequency shifting of the
associated cut-on frequencies.
The experimental validation of the noise control approach was also carried out.
An active-passive noise control fan duct incorporating the segmented duct design with
8x8 active control was constructed in conjunction with a hybrid feedforward-feedback
control system. Experimental results have shown significant reductions in the total fan noise power associated with the first four BPF tones by the feedforward control and the
broadband fan noise power by the feedback control. The overall active-passive noise
control characteristics were observed to be in accordance with the analytical results.Ph. D.
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Öqvist, Rikard. "Measurement and perception of sound insulation from 20 Hz between dwellings." Doctoral thesis, Luleå tekniska universitet, Drift, underhåll och akustik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62843.
Full textAbstract:
Population growth and urbanization are projected by the United Nations to add 2,5 billionpeople to the world’s urban population by 2050. We need to construct buildings in anunprecedented scale to meet global housing demand. Sustainable development is critical.Compared to traditional heavy constructions, lightweight wooden constructions are moreenvironmentally friendly and will play a key role in meeting future demands. However, thereare two major problems with lightweight constructions that need to be addressed: 1) Limitedlow frequency sound insulation and 2) Variations in sound insulation.Annoyance from walking sound tend to be higher in lightweight than in heavy constructionseven with the same measured sound insulation. The Swedish research program AkuLiteindicated that the correlation between measured sound insulation and annoyance wassignificantly improved by extending current evaluation methods from 50 Hz down to 20 Hz.Secondly, large variations in sound insulation between nominally identical lightweightconstructions are common, which leads to larger safety margins. By identifying and quantifyingunderlying causes, production costs can be minimized and the performance can be improved.The aim of the thesis is to develop a new evaluation method for impact sound insulation thatbetter correspond to rated annoyance, and to identify and control underlying causes forvariations in sound insulation. The thesis contains six papers.In Paper I and II, sound insulation measurements were carried out in a large number ofnominally identical rooms of two different industrially prefabricated lightweight woodenconstructions. The purpose was to assess and quantify the variations in impact and airbornesound insulation. In Paper I, 30 nominally identical apartments of a volume based system wasevaluated. The apartments on the highest floor achieved significantly better sound insulationdue to the extra weight on lower floors affecting the elastic connections between stories. InPaper II, 18 rooms of a cross-laminated timber system of plate elements were evaluated.Additionally, several potential parameters related to measurement uncertainty wereinvestigated.Paper III deals with measurement uncertainty. An empirical study of reverberation timemeasurements showed that current methods need to be improved, if sound insulationrequirements are to be extended to 20 Hz.Paper IV and V verified that the frequency range 20-50 Hz is important for walking soundannoyance, and that alternative frequency adaptation terms can improve the correlation betweenmeasured impact sound insulation and annoyance ratings. In Paper IV, the methodology was toperform extensive field measurements in apartment buildings of various construction types andto perform questionnaire surveys among the residents. In Paper V, the methodology was toevaluate annoyance based on binaural recordings of walking sound in a two-part listening test.In Paper VI, 70 measurements in a lightweight wooden system were evaluated to quantify thetotal variations in impact and airborne sound insulation from 20 and 50 Hz, respectively. It wasconcluded that the proposed metrics of impact sound insulation were primarily determined bythe impact sound level 20-40 Hz and that the measurement methods must be evaluatedthoroughly to avoid excessive safety margins. A new evaluation method for impact sound insulation from 25 Hz, that correspond to the ratedannoyance for both heavy and lightweight constructions is proposed. By using the proposedmethod and attending the specific causes for variations, the lightweight industry will be able todevelop improved multi-story dwellings with higher perceived acoustic quality.Forskningsfinansiärer:
Sven Tyréns Stiftelse
Formas
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FOUTS, II BRUCE EDWARD. "INVESTIGATION INTO TESTING METHODS AND NOISE CONTROL OF INDUSTRIAL POWER TOOLS." University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1029443901.
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Dungan, Mary Elizabeth. "Development of a compact sound source for the active control of turbofan inlet noise /." This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-03302010-020615/.
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Dungan, Mary E. "Development of a compact sound source for the active control of turbofan inlet noise." Thesis, Virginia Tech, 1992. http://hdl.handle.net/10919/41872.
Full textAbstract:
The concept of a compact sound source driven by piezoactuators is experimentally investigated, and analytical design tools are developed. The sound source, consisting of a thin, cylindrically curved aluminum panel and a pair of collocated, surface-bonded piezoceramic actuators, was developed with the objective of employing it as a secondary sound source in the active control of turbofan bladeinteraction inlet noise.
The sound source was fitted in an experimental duct representative of an aircraft engine inlet, and the interior and exterior sound pressure levels generated by the source were measured. The effects of excitation voltage, excitation frequency, duct length, and downstream termination of the duct were investigated. It was found that the source is capable of generating relatively high acoustic levels at its fundamental frequency (over 130 dB at maximum voltage input).
Techniques for analytically predicting the acoustic levels are investigated. A commercial code for numerical modelling of structural - acoustic radiation was utilized. Results show generally good agreement with experimental measurements for the case of the short duct. It is believed that the model accuracy can be further improved through additional refinements in the modelling techniques.Master of Science
44
Toffin, Eric. "Active control of a coupled plate-cylinder system." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06162009-063337/.
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Sacarcelik, Ozer. "Acoustic Devices for the Active & Passive Control of Sound in a Payload Compartment." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/9950.
Full textAbstract:
The work presented in this thesis can be divided into two main subjects. First, lightweight designs for acoustic devices such as Helmholtz resonators and loudspeakers used for noise control in rocket payload compartments are developed. Second, active control using a hybrid control system (with structural and acoustic actuators) was tested experimentally.
Due to the weight limitations for this application, Helmholtz resonators and loudspeakers are re-designed in order to reduce the device weight as much as possible while maintaining performance. For Helmholtz resonators, this is done by modeling the resonator for different structural shapes, wall materials and wall thicknesses using a finite element analysis software. The final design is then compared to the rigid resonators and is shown to perform effectively. These designs are then successfully applied to the full-scale fairing at Boeing facilities. In order to design a lightweight loudspeaker, a comparative approach was used. A standard 12' loudspeaker is taken as the reference loudspeaker and weight reduction solutions are applied to it while maintaining performance. The loudspeaker is characterized using mechanical, electrical and acoustical theories, and an optimization process is applied in order to minimize a defined cost function, which was taken as the total sound pressure output over a targeted frequency range per mass of the actuator. The results are used to build a lightweight loudspeaker together with a lightweight box, and the new designs are tested for comparison with the reference loudspeaker and shown to increase performance by 1.7 dB over 60-200 Hz band while reducing the mass by 78%.
The second part of this thesis investigates the performance of a hybrid active control treatment featuring distributed vibration absorbers (DAVAs) and loudspeakers applied on a scale payload fairing. Several aspects such as causality, reference signals, and maximum controllable levels of this feedforward control scheme are the subjects of analyses. The results show that this active control approach can achieve significant amount of interior noise attenuation, and the total actuator weight required to control an external level of 138 dB can be reduced to 9.2kg using lightweight loudspeakers. However, it is shown that the attenuation levels can still be improved further by actuator positioning that gives more effective coupling of the actuators with the structural and acoustic modes and by using multiple references for the control system.Master of Science
46
Alsouda, Yasser. "An IoT Solution for Urban Noise Identification in Smart Cities : Noise Measurement and Classification." Thesis, Linnéuniversitetet, Institutionen för fysik och elektroteknik (IFE), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-80858.
Full textAbstract:
Noise is defined as any undesired sound. Urban noise and its effect on citizens area significant environmental problem, and the increasing level of noise has become a critical problem in some cities. Fortunately, noise pollution can be mitigated by better planning of urban areas or controlled by administrative regulations. However, the execution of such actions requires well-established systems for noise monitoring. In this thesis, we present a solution for noise measurement and classification using a low-power and inexpensive IoT unit. To measure the noise level, we implement an algorithm for calculating the sound pressure level in dB. We achieve a measurement error of less than 1 dB. Our machine learning-based method for noise classification uses Mel-frequency cepstral coefficients for audio feature extraction and four supervised classification algorithms (that is, support vector machine, k-nearest neighbors, bootstrap aggregating, and random forest). We evaluate our approach experimentally with a dataset of about 3000 sound samples grouped in eight sound classes (such as car horn, jackhammer, or street music). We explore the parameter space of the four algorithms to estimate the optimal parameter values for the classification of sound samples in the dataset under study. We achieve noise classification accuracy in the range of 88% – 94%.
47
Vissamraju, Krishnasudha. "Measurement of absorption coefficient of road surfaces using impedance tube method." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Summer/master's/VISSAMRAJU_KRISHNASUDHA_59.pdf.
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Esplin, John J. "Active Noise Control of a Centrifugal Fan Mounted in a Mock Laptop Enclosure." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3577.
Full textAbstract:
Noise from information technology (IT) equipment is a significant problem in today's modern society. Active Noise Control (ANC) has shown promise in reducing the effect of IT fan noise on users. Though ANC has been applied to axial fans (such as those found in desktop computers), it has not been applied to centrifugal fans, such as those found in laptop computers. This work applies an ANC method to a centrifugal fan mounted in a mock laptop enclosure. This method is applied in four steps. First, secondary sources are placed in the vicinity of the fan. Second, an accurate model of the radiation from the fan and secondary sources is constructed. Third, the total power radiated from this system is minimized. This creates nodal lines in the vicinity of the fan. Fourth, ANC error sensors are placed on the nodal lines predicted by the model. This creates these nodal lines experimentally, thus creating the minimum power condition. The noise from the exhaust and inlets of the fan will first be controlled individually. Then the method will be applied to the combined system. Global sound power radiation will be measured in all cases.
49
Kestell, Colin D. "Active control of sound in a small single engine aircraft cabin with virtual error sensors." Title page, abstract and contents only, 2000. http://web4.library.adelaide.edu.au/theses/09PH/09phk423.pdf.
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Lam, Siu Tong. "Influence of insertion/donning instruction on frequency-specific sound attenuation achieved with ear canal caps and earmuffs with implications for industrial noise application." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/76037.
Full textAbstract:
A study was conducted to determine the dependency of sound attenuation capabilities of earmuffs and earcaps on various application instruction techniques including: (1) no instruction, (2) no instruction with 70 dBA auditory feedback, (3) manufacturers' package instruction, (4) detailed instruction, and (5) modeled instruction. The hearing protection devices (HPDs) studied were: two earcaps (Willson #20 Sound-Ban, Flents #055 Peace & Quiet Headband), and four earmuffs (E-A-R model 1000, Siebe Norton Industrial model 4540, Peltor H6A/v, and Willson 365A Sound Barrier). HPD comfort and wearer preferences were also assessed. Furthermore, typical excessive industrial machinery noises were sampled and analyzed across the 1/3 octave frequencies. Finally, an example is provided as to how these machinery noise spectra can be matched with HPD attenuation spectra to ascertain the protector which would afford optimal protection for a given noise situation.
Fifty subjects (twenty-five males and twenty-five females) participated in the experiment. Attenuation characteristics of the HPDs were evaluated utilizing the real-ear attenuation at threshold (REAT) method. A three-way mixed factorial design was used for data collection and analysis of attenuation results. Bipolar scales were used to assess individual HPD comfort, and the HPDs examined were ranked to obtain user preferences. In the analysis of attenuation results, analysis of variance CANOVA) and pairwise comparisons were utilized to detect statistical significance. The comfort scales and ranking scores were evaluated using the Friedman one-way block design.
Attenuation results for the earmuffs and earcaps tested showed that they were much less susceptible than earplugs (from a previous study by Epps, 1984) to changes in user insertion/donning instruction technique and also not as dependent on user gender. The main effect of gender was not significant, and in general, any instruction was better than no instruction at all but the effects of those instructions did not differ significantly among each other. As expected, there were main effect differences among the HPDs as to their attenuation capabilities, rated discomfort, and user preference. Because the main objective was on assessing donning instruction effects on HPD attenuation, the comfort/preference assessment was based on only a short (25 minutes) wearing time during the attenuation tests. Therefore, the comfort/preference ratings could likely vary given longer wearing periods and different work environments. All results found are discussed on the basis of the sample data obtained and conclusions drawn from these results should be limited to these experimental conditions and subsequent analyses, as actual attenuation achieved in practice may differ.
The example of HPD-machinery noise matching illustrates that the attenuation/spectral matching procedure may indeed be a feasible way of selecting optimal protection for workers.Master of Science