Techniques are available today to attenuate the output sound of the trumpet. All of these techniques involve using passive mutes. Due to the limitations in the sound one can obtain with passive mutes, another solution, using active noise control, is proposed to predictably attenuate the output sound of the trumpet. With the new system, it is theorized any desired output sound can be obtained. Within this thesis a model of the trumpet physics is derived and an investigation of the implementation of two analog feedback controllers and two digital LMS controllers is performed. The model of the trumpet mechanics is studied to understand the trumpet system before applying the control systems. Analysis is performed on the type and the location of the acoustic control actuator and the error sensor to be used. With the chosen actuator and sensor, the two types of controllers are designed and realized. The farfield spectrum of the trumpet's response to a single note is analyzed for each controller and the resulting attenuations compared. The model of the trumpet system is then used to demonstrate the coupling of the trumpet and the player and to show the effects of the controllers on the behavior of the player's embouchure. With the inclusion of the controllers in the trumpet system, the farfield spectrum was successfully attenuated at two harmonics of the tone passed through the trumpet. Testing was not performed with an actual trumpet player due to the high sound pressure levels (160 dB SPL) required from the control actuator. From a derived model of the control actuator, specifications for an acoustic driver capable of delivering the high sound pressure level were calculated. Design and fabrication of the proposed actuator will be completed during future work. / Master of Science

The wings of most species of owl have been shown to possess three unique physical attributes which allow them to hunt in effective silence: a comb of evenly-spaced bristles along the wing leading-edge; a compliant and porous fringe of feathers at the trailing-edge; and a velvety down material distributed over the upper wing surface. This investigation focuses on the last of the mechanisms as a means to reduce noise from flow over surface roughness. A microscopic study of several owl feathers revealed the structure of the velvety down to be very similar to that of a forest or a field of crops. Analogous surface treatments (suspended canopies) were designed which simulated the most essential geometric features of the velvety down material. The Virginia Tech Anechoic Wall-Jet Facility was used to perform far-field noise and surface pressure fluctuation measurements in the presence of various combinations of rough surfaces and suspended canopies. All canopies were demonstrated to have a strong influence on the surface pressure spectra, and attenuations of up to 30 dB were observed. In addition, all canopies were shown to have some positive effects on far-field noise, and optimized canopies yielded far-field noise reductions of up to 8 dB across all frequencies at which roughness noise was observed. This development represents a new passive method for roughness noise control with possibility for future optimization and application to engineering structures. / Master of Science

This research is concerned with the minimization of annoyance due to aircraft noise to airport communities. The approach developed is an interactive one which permits interaction with the Decision Maker. The immediate vicinity of an airport is divided into several areas based on population and proximity to the runways. The user can then minimize annoyance over any set of areas subject to the appropriate constraints. After any optimization, the results may be reviewed. The results provided include noise and annoyance in each area as well as the gradient of the objective and slackness associated with each constraint. This would assist the user in making a decision and aid in sensitivity analyses. At each stage of optimization, the problem solved has a nonlinear objective function and linear constraints. This problem is solved by solving successive surrogate linear problems. The method uses a first-order Taylor series expansion about the solution point to set up the surrogate linear problem. The first solution point is obtained by solving an approximate linear problem. The approach suggested is then applied to an example airport. Different scenarios are considered to illustrate the use of the model. Both the formulation of the objective as well as the constraints are illustrated. / Master of Science

A fundamental study of the Herschel-Quincke (HQ) tube concept for the reduction of noise in circular ducts is presented here. Recent testing of the Herschel-Quincke tube concept on the Pratt-Whitney JT15D and AlliedSignal TFE731-60 engines showed the potential for the practical application of this approach. A model of the HQ-system has been developed to aid in the design of the system tested. The model has revealed new noise control mechanisms associated to the implementation of multiple HQ-waveguides in a duct in the presence of higher order modes. However, the practical nature of these engine facilities results in limitations with regard to the fundamental research knowledge that could be gained from testing in a more controlled laboratory environment. A series of experiments was conducted at the NASA Langley Research Center 0.30 m ducted fan test facility where detailed modal measurements were performed. The main goals of this research endeavor were to evaluate the accuracy of the previously developed theoretical model and provide insight into the noise control mechanisms. Experiments were performed with different disturbance mode structures, number of HQ tubes and arrays, and axial positions. The modes in the duct were generated with an array of acoustic drivers (no flow case) and measured with logarithmically spaced circumferential and helical microphone arrays located on the duct wall. The modal amplitudes of the incident, transmitted, and reflected modes in the duct were determined from the microphone measurements. This allowed for the comparison of analytical and experimental modal amplitudes, modal powers, total power, and reductions. The results of this study provide insight into the three noise control mechanisms associated with this approach: reflection, circumferential scattering, and radial scattering. Comparison with the experimental results shows that the model accurately predicts the sound power attenuation except near the cut-off frequency of the modes where it tends to overestimate the attenuation. The effect of the number of tubes in the array and its axial position was also evaluated. Overall, the results of this study validate the general modeling approach for the HQ tube concept. / Master of Science

Active Structural Acoustic Control (ASAC) has been previously demonstrated for systems excited by single and multiple frequency disturbances. This work is an extension of ASAC techniques to the control of sound radiation from structures excited by a disturbance with broadband frequency content. An adaptive, multi-input multi-output (MIMO), feedforward broadband acoustic control system has been developed. The control approach is the least mean squares (LMS) algorithm. The compensators are adaptive finite impulse response (FIR) digital filters. The system identification of the control loop transfer functions were implemented with infinite impulse response (IIR) digital filters. The control inputs were implemented with piezoelectric ceramic actuators (PZT). Both far-field microphones and polyvinylidene fluoride (PVDF) structural sensors designed to optimally control the efficient acoustic radiating modes were used as error sensors. The disturbance was band-limited zero mean white noise and was input with a point force shaker. In the control of harmonically excited systems, satisfactory attenuation is possible with a single-input single-output (SISO) controller. In contrast, for Systems excited with broadband disturbances, a MIMO controller is necessary for significant acoustic attenuation. Experimental results for the control of two simplySupported plates are presented. Aspects addressed include the evaluation of the microphone and PVDF error sensors, optimization of sensors and actuators, FIR compensator size, controller sample rate, and convergence time. Thus this work provides a methodology for controlling broadband acoustic radiation from a structure with regard to the practical aspects of ASAC. / Master of Science

At low frequency where the acoustic wavelength is greater than the size of the vibrating structure, the radiated acoustic power is directly related to the volume velocity of the structure. Thus, minimizing the volume velocity is an effective noise reduction approach for low frequency structurally radiated noise. This thesis analytically investigates a passive volume velocity noise control device for acoustic surface treatment of planar structures. The device is referred to as a weak radiating cell. This device consists of two mechanically coupled surfaces such that, when placed on a vibrating structure, the response of the two surfaces are nearly out-of-phase and of equal strength over a wide frequency range. The response of the two surfaces forms a local acoustic dipole, with minimum volume velocity, that results in noise reduction. Thus, the control of low frequency structurally radiated noise is achieved by covering the structure with an array of these weak radiating cells. Several numerical models are developed to investigate the weak radiating cell noise control mechanisms. The first model consists of a simply supported beam treated with an array of weak radiating cell. In this model, the dynamic interaction effects between the beam and the cells are included. Results from this model predict an overall sound power level reduction of 9.8 dB between 0-1600 Hz and 20 dB between 0-251 Hz. In addition, this model is used to investigate techniques to improve the noise reduction capabilities of the device. A model of weak radiating cells applied to a simply supported plate is next developed as an extension of the beam model. The results from this model are compared to previous experimental data. Good agreement is observed between results, which validates the modeling technique. Lastly, a model of an infinite 2D plate treated with weak radiating cells is developed. The model does not consider any dynamic interaction effect between the structure and the cells. Only the acoustic behavior of the weak radiating cell is included in this model. In addition, both the structural and acoustic responses are obtained in closed form through a wavenumber transform approach. Each of these models and their results offer valuable information that results in a better understanding the weak radiating cell and it potential as a low frequency passive noise control device. / Master of Science

This study was made to find the effects of noise on the human body, to measure sound levels that exist in school power laboratories, and to design and evaluate the effectiveness of two noise control devices. An accurately calibrated testing device was used to measure sound levels in an attempt to determine if excessive noise exists in school power laboratories and to find the extent to which such noise can be reduced by shielding or enclosing the engine test area. It was found that noise has undesirable physical and psychological effects on the human organism. Sixty-two and one-half per cent of the engines tested registered sound levels above 90 dBA; even so, simple, inexpensive noise control devices do control the noise levels generated in the school power laboratories.

<div>Modeling methodologies based on state-of-the-art and classic theories of acoustics have been developed to provide a comprehensive toolbox, which can be used to model multilayer systems that involve acoustical and/or damping treatments, and to optimize these treatments' performance by designing their geometrical structures. The objective of this work was to understand, predict and optimize conventional sound absorbing porous media's near-field damping performance, so that automotive and aerospace industries can take full advantage of layered porous treatments' lightness and multi-functionality: i.e., absorption of airborne sound and reduction of structure-borne vibration, for noise control applications. First, acoustical models that include the Transfer Matrix Method and the Arbitrary Coefficient Method were developed to build connections between the bulk properties and acoustical properties of porous media when coupled into layered systems. Given a specified layered system consisting of a vibrating panel and a porous damping treatment, the acoustics models were then incorporated into the Near-field Damping model to predict the acoustical near-field and spatial response of the panel, based on which the near-field damping performance can be evaluated for a limp or an elastic porous layer when applied on different structures including an infinitely-extended panel, a partially-constrained panel, an aircraft fuselage-like structure and a vehicle floor pan-like structure. Furthermore, the relations between the material's microstructural details and bulk properties were established via an Air-Flow Resistivity model for porous media that are made of fibers, and the optimal fiber size that provides the largest damping for certain vibrating structures was identified. Relatively large fibers were found to be better at reducing lower frequency vibrations; fibers made of polymer were found to have manufacturing benefits over fibers made of glass to achieve equivalent optimal damping performance; and elastic fibers were found to have both manufacturing and damping advantages over limp fibers.</div>

Darbo tikslas – Įvertinti ar Kauno miesto triukšmo valdymo politika ir taikytos priemonės 2006 – 2013 m. buvo įgyvendintos pakankamai efektyviai, kad apsaugotų gyventojus nuo triukšmo. Uždaviniai: 1. Išanalizuoti triukšmo taršos pokytį Kauno mieste 2006 – 2013 m. 2. Įvertinti Kauno miesto savivaldybės triukšmo valdymo politikos veiksmų ir taikytų priemonių efektyvumą 2006 – 2013 m. Darbo metodai. Teisinių ir operatyvinių dokumentų (vykdytų priemonių planai, Kauno miesto gyventojų skundai, valstybinio audito ataskaitos ir kt.) bei Lietuvos Respublikos ir Europos Sąjungos teisės aktų analizė, pusiau struktūruotas interviu. Antrinių duomenų analizės pagalba išanalizuotas triukšmo pokytis Kauno mieste 2006 – 2013 m. ir įgyvendintų triukšmą mažinančių priemonių efektyvumas. Nustačius esmines problemas ir kompetencijas Kauno miesto savivaldybėje, buvo parengtas pusiau struktūruoto ekspertinio interviu klausimynas, kurio pagalba apklausti specifinės srities ekspertai, darbe tiesiogiai susiduriantys su triukšmo valdymo politikos įgyvendinimu, dirbantys Kauno miesto savivaldybės administracijoje. Rezultatai. Pagrindinė Kauno miesto savivaldybės triukšmo valdymo politikos problema – nepakankamas vietos valdžios dėmesys triukšmo taršai, ši sritis nėra prioritetinė savivaldybės politikos sritis, neįtraukta į Kauno miesto savivaldybės strateginį veiklos planą. 2006 – 2013 m. Kauno miesto savivaldybė triukšmo valdymo įgyvendinimo politikai skyrė 112 tūkst. Lt., 100... [toliau žr. visą tekstą] / Aim of this thesis – to evaluate noise control politics implementation and used measures performance in Kaunas city during the year of 2006 – 2013 in order to ensure healthy environment without noise pollution. Main objectives: 1. To analyze the alteration of noise pollution in Kaunas city in 2006 – 2013 2. To evaluate performance of noise control politics and used measures in municipality of Kaunas city in 2006 – 2013 Work methods. This thesis is based on analysis of European Union and Lithuanian legislation acts, operational documents (strategic planning documents, complaints of the citizens, reports of national audit, etc.). Also a qualitative research method of semi structured interview was used in this thesis. The interview was based on communication (certain questionnaire) with experts who are directly working on noise politics implementation in municipality of Kaunas city. Results and conclusions. The goal of this thesis was reached by combining research of science sources what helped to structure and highlight the main problems such as low level supervision of municipality policy from national governance institutions, no strategic approach to the noise control politics in municipality of Kaunas city, ineffectively used (or even unused) donations. The interview with experts empowered to analyze the situation from the inside of the organization and it showed that noise pollution control in not a subject of priority in municipality of Kaunas city. Inability to... [to full text]

Near-field Acoustical Holography is a tool that is conventionally used to visualize sound fields through an inverse process in a three-dimensional space so that either sound field projections or sound source localization can be performed. The visualization is conducted by using sound pressure measurements taken in the near-field region close to the surface of the unknown sound source. Traditional Fourier-based Near-field Acoustical Holography requires a large number of measurement inputs to avoid spatial truncation effects. However, the use of a large number of measurements is usually not feasible since having a large number of microphones is costly, and usually the array is limited in size by the physical environment, thus limiting the practicality of this method. In the present work, because of the desire to reduce the number of microphones required to conduct acoustical holography, a method known as Statistically Optimized Near-field Acoustical Holography initially proposed by Steiner and Hald was analyzed. The main difference between the present work and the concept mentioned by Steiner and Hald is the cylindrical coordinate system employed here for the purpose of experimenting on a bladeless fan, which resembles a cylindrical structure and which could be assumed to be a cylindrical source. The algorithm was first verified <i>via</i> simulations and measurements, and was then applied to experimental data obtained <i>via</i> pressure measurements made with a cylindrical microphone array. Finally, suggestions for noise control strategies for the bladeless fan are described, based on the measurement results.<br>