Tesi sul tema "Sound – Transmission"

This thesis has been written in an endeavour to review the current available literature on the transmission loss of building facades. Tests were also carried out to compare laboratory results and theory with results obtained in practice, and to get a feeling for the difficulties involved.

The sound transmission loss characteristics of plywood based sandwich panels were investigated. Measurements were made of the sound transmission loss of a range of materials and used as a baseline for comparison while a sound transmission loss optimisation method was developed. A unique test rig was built and calibrated to determine selected mechanical properties of materials of interest. The results of sound transmission loss and material properties measurements were used to select an appropriate prediction model, which was then used in conjunction with a mathematical optimisation model to determine combinations of materials and panel parameters which result in improved sound transmission loss. An effort was made to reproduce these predictions in experimental testing by constructing several prototype panels.

This thesis examines the transmission of sound through lightweight parallel plates, (plasterboard double wall partitions and timber floors). Statistical energy analysis was used to assess the importance of individual transmission paths and to determine the overall performance. Several different theoretical models were developed, the choice depending on the frequency range of interest and method of attachment of the plates, whether point or line, to the structural frame. It was found that for a line connected double wall there was very good agreement between the measured and predicted results, where the dominant transmission path was through the frame and the cavity path was weak. The transition frequency where the coupling changes from a line to a point connection is when the first half wavelength is able to fit between the spacings of the nails. For point connected double walls, where the transmission through the frame was weaker than for line connection, the cavity path was dominant unless there was absorption present. When the cavity was sufficiently deep, such that it behaved more like a room, the agreement between the measured and predicted results was good. As the cavity depth decreases the plates of the double wall are closer together and the agreement between the measured and predicted results were not as good. Detailed experiments were carried out to determine the transmission into the double wall cavities and isolated cavities. It was found that the transmission into an isolated cavity could be predicted well. However, for transmission into double wall cavities the existing theories could not predict transmission accurately when the cavity depth was small. Extensive parametric surveys were undertaken to analyse changes to the sound transmission through these structures when the material or design parameters are altered. The SEA models are able to identify the dominant mechanisms of transmission and will be a useful design tool in the design of lightweight partitions and timber floors.

This thesis examines the sound transmission loss (STL) through composite sandwich panel systems commonly used in the marine industry. Experimental, predictive and optimisation methods are used to evaluate the acoustic performance of these systems and to improve their acoustic performance with noise treatment. The complex nature of the material properties of composite sandwich panels was found to be dependent not only on the physical properties but also the frequency of incident noise. Young’s modulus was found to reduce with increasing frequency as has been predicted in the literature which is due to the shear stiffness dominating over the bending stiffness. Two methods for measuring these properties were investigated; ‘fixed-free’ and ‘free-free’ beam boundary condition modal analyses. The disagreement between these methods was identified as the clamping fixed nature that increased flexibility of the beam. Composite sandwich panels can be modelled as homogeneous isotopic materials when predicting their acoustic performance provided the dilatational resonance is above the frequency range of interest. Two such panels were modelled using this simple sound insulation prediction method, but the agreement between theory and experimental results was poor. A variable Young’s modulus was included in the model but agreement remained relatively poor especially in the coincidence frequency region due to variation of Young’s modulus with frequency. A statistical method of optimisation of the parameter settings by fractional factorial design proved successful at identifying the important parameters that affect the sound transmission class (STC) of a noise treatment material applied to a panel. The decouple foam layer and attachment method were the most significant factors. The same method, with higher resolution was then used to identify the important parameters that affected the noise reduction class (NRC) finding that the outer foam thickness without a face sheet were the most significant factors. The independent optimisation studies performed for each of the STC and NRC produced conflicting results meaning that both could not be achieved simultaneously.

It is difficult to predict the sound radiation from large factory roofs. The existing infinite panel theories of sound insulation are not sufficient when the sound radiates at grazing angles. It has been shown that the reason for the collapse of the theory is the well known result for the radiation efficiency. This research will present a simple analytic strip theory, which agrees reasonably well with numerical calculations for a rectangular panel. Simple analytic strip theory has lead to the conclusion that it is mainly the length of the panel in the direction of radiation, rather than its width that is important in determining its radiation efficiency. The findings of the current research also indicated that apart from the effect due to coincidence, a panel was non-directional compared to an opening.

A new Statistical Energy Analysis (SEA) formulation for double walls isderived. The new formulation uses three elements to describe the double wall,one for each plate and the third for the cavity including the mass-controlledmodes of the plates. This means that the influence of the double wall resonance(mass-air-mass resonance) can be predicted by SEA. Calculations aremade and compared to measurements, showing fair agreement.

In ABB, Soundplan is the usually used software to predict the industrial noise for power transmission plants. However, the sound sources in Soundplan are modeled as point sources between which there are no sound reflections. For the real situation, the sound sources are very big and can be regarded as noise barriers. So it is important to take the reflections between sound sources into consideration.COMSOL Multiphysics is Finite Element Method (FEM) software which can model acoustic object with sound-reflective boundaries. First, the COMSOL model for single component inside the power transmission plant will be discussed. Then the COMSOL model for the whole plant will be calculated at different frequencies. The total sound pressure level at different receivers will be compared between COMSOL and Soundplan results. COMSOL can be used to predict the sound propagation of the power transmission plant and it can give different results when the outline of the plant is changed.

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.

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.

Many engineering structures are built from frameworks of beams, particularly lightweight structures. For the purpose of noise control from airborne and structure-borne sources, it is useful to be able to predict vibration transmission across these frameworks. This thesis investigates the potential use of Advanced Statistical Energy Analysis (ASEA) to predict structure-borne sound transmission when the beams support multiple wave types due to wave conversion at the junction. In contrast to Statistical Energy Analysis (SEA), ASEA is able to account for high propagation losses and indirect coupling through the use of ray tracing. SEA and ASEA were validated through comparison with measurements and numerical experiments with Finite Element Methods (FEM). When each beam supports at least two local modes for each wave type in the frequency band of interest and the modal overlap factor is at least 0.1, FEM and measurement data tend to have average values which form smooth curves such as those predicted by SEA and ASEA. It was shown that SEA and ASEA models could incorporate Euler-Bernoulli and Timoshenko theory by changing over from Euler-Bernoulli to Timoshenko group velocity when calculating the coupling loss factors. However, comparisons with measurements were not conclusive although there were indications that a suitable crossover frequency could be when Timoshenko and Euler-Bernoulli group velocities differ by at least 26%. Agreement between FEM and ASEA indicates that it is appropriate to ignore phase effects in the ray tracing approach used with ASEA. This was particularly noteworthy for the three-bay and five-bay truss beams as these were perfectly periodic for which phase effects could be important. Results for an L-junction, a rectangular beam frame and a five-bay truss with relatively long beams and relatively high internal loss factors demonstrated that ASEA was able to incorporate high propagation losses. This was not possible with SEA. For a three-bay truss beam with relatively short beams ASEA showed close agreement with FEM and measurements confirming that there was significant indirect coupling rather than high propagation losses. There are indications from the five-bay truss beams that ASEA may no longer be accurate in predicting the response on beams that are at least three structural junctions away from the source beam, particularly when ASEA predicts high propagation losses on the receiving beam.

Thesis (Ph. D.) -- University of Maryland, College Park, 2004.
Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

Sound transmission through a fluctuating deep ocean environment is considered. It is assumed that the environment consists of a range-independent background, on which a small-scale perturbation, due for example to internal waves, is superimposed. The modal description of underwater sound propagation is used extensively. The temporal spread of modal group arrivals in weakly range-dependent deep ocean environments is considered. The phrase "modal group arrival" refers to the contribution to a transient wavefield corresponding to a fixed mode number. It is shown that there are three contributions to modal group time spreads which combine approximately in quadrature. These are the reciprocal bandwidth, a deterministic dispersive contribution, and a scattering-induced contribution. The latter two contributions are shown to be proportional to the waveguide invariant beta, a property of the background sound speed profile. The results presented are based mostly on asymptotic theory. Some extensions of the asymptotic modal theory are developed. These theoretical results are shown to agree well with full-wave numerical wavefield simulations and available exact mode theoretical results. Theoretical predictions of modal group time spreads are compared to estimates derived from data that was collected during the 2004 LOAPEX experiment. The effects of deficiencies in the receiving array on estimates of modal group time spreads are discussed. It is shown that in spite of array deficiencies in the LOAPEX measurements it is possible to estimate modal group time spreads for almost all propagating modes and these estimates agree well with results obtained from numerical simulations and the developed theory. The effect of ocean internal waves on sound speed fluctuations is also considered, motivated by the observation that the amount of energy being scattered along the propagation path is sometimes greater in the experimental data than predicted by numerical simulations and theory. It is shown that the usual assumption that the potential sound speed gradient is proportional to the squared buoyancy frequency is often not a good approximation.

Modeling sound transmission is a challenging task. An existing beam-tracing model for empty, parallelepiped rooms with specularly-reflecting surfaces is extended to predict room-to-room sound transmission between a source and receiver rooms separated by a common wall. This wall is modeled as one locally-reacting homogenous partition with frequency-independent transmission loss. Besides, sound transmission is modeled in Ray-Tracing (CATT-TM) and FEM (COMSOL). A reference configuration consists of two identical reverberation rooms is chosen following the recommendations of the literature and most of the prescriptions of the reverberation room standard, ASTM 3423. The capability of various room-to-room predictions models, in particular, the phase and energy-based beam tracing models (PBTM, EBTM) in reproducing the results of the diffuse-field theory is investigated. Both EBTM and CATT-TM are found to be reasonably accurate in reproducing the diffuse sound field for a reverberation room (i.e. for diffuse sound fields). However, the predicted levels deviate considerably from the diffuse-field theory with changes in the acoustical characteristics of the room (room aspect ratio, the magnitude of the surface absorption and surface absorption distribution (i.e. for non-diffuse sound fields). EBTM has been validated in both source and receiver rooms through existing results from ODEON in the literature and by comparing the prediction results with the new CATT-TM for the reference configuration. PBTM has been compared with finite element method (COMSOL) results in the low-frequency region. Both phase-based models match well in source room with a reasonable discrepancy. However, the PBTM has not reproduced the sound field predicted by COMSOL in the receiver room. Moreover, Waterhouse effect is studied by both PBTM and EBTM model in the reverberation rooms which is ignored in the classical diffuse-field concept. However, its significant effect is exhibited near the reflecting boundaries inside the reverberation room only in the PBTM predictions. Hence, based on recommendations of the ASTM standards during measuring sound transmission between rooms, sources and receivers should be placed sufficiently far away from the reflecting surfaces, edges and corners of the rooms to avoid the errors due to the Waterhouse effect.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

This thesis examines sound transmission through framed and unframed single and double panel systems. The most common example of such a system is a plasterboard double wall. Numerical modelling techniques were used to accurately simulate the motion of the system in response to airborne stimulus. The model was first applied to the simple case of a panel, freely suspended in an anechoic environment. The modelled results were compared to a series of very detailed experimental results, in which many relevant system parameters had been measured. A very good level of agreement was found between the modelled and experimental results for all the system parameters. The model was then applied to the case of a traditional sound transmission loss test for a single panel. The diffuse incident sound field was approximated using a collection of plane wave sources, and the transmitted intensity was calculated directly. The model was seen to give sound transmission loss results which compared very well with experiment. Such a model proved very useful in studying aspects of sound transmission loss which past workers have found difficult to investigate using other approaches. The level of sound transmitted through the panel was seen to be largely invariant with angle of incidence, illustrating that the 'mass law' is not valid for finite panels. The non-resonant transmission of a finite panel was also predicted accurately by modelling a panel which could vibrate in the fundamental structural mode only. The model was used to conduct several parametric studies, which illustrated the effect of changes in mass, stiffness and size on the sound transmission loss of a single panel. The model was also applied to framed double panel systems. Several major simplifications were required to enable an expedient solution to be obtained for these systems, nevertheless the predicted results compared well with their experimental counterparts. Parametric studies showed that there were significant advantages in having cladding of unequal mass on each side of a double wall, due to an associated reduction in resonant transmission. It was also found that smaller walls had higher levels of sound insulation, but this effect was not the same as that associated with decreasing the stud spacing in a wall of constant size.

Transfer path analysis (TPA) is an established and valuable tool in the automotive industry, to determine the contributions of structure-borne sound sources to receiver responses at target positions. The classical TPA approach is based on contact forces at the interface between source and receiver to characterise the dynamic loads induced by the source and frequency response functions (FRFs) to quantify the transfer paths of the sound from the interface locations to the target positions. With knowledge of the determined contributions it is then possible to decide whether source loads or FRFs must be improved to optimise the target quantities. Recently a timesaving improvement to classical TPA has been proposed, where the loads are characterised using the in-situ blocked force method, so that dismantling of source and receiver is not necessary. This method is therefore called in-situ TPA. However, if the contributions of internal structure-borne sound sources to the overall vibro-acoustic behaviour of a product are desired it is of benefit if the target quantities are blocked forces. Thus it would be possible to virtually couple the product with the properties of an overall receiver. Therefore this thesis presents a TPA approach called “blocked force transmissibility transfer path analysis” (bfTPA). In this context, the proposed internal-source-path-receiver-model (ISPRM) poses the theoretical basis of bfTPA. The aim of the presented novel TPA is to determine the contribution of internal structure-borne sound sources to an overall target quantity of a product. The presented approach uses the vector of in-situ blocked forces measured externally at the contact interface of the overall product and a corresponding set of “blocked force transmissibility” (BFT) functions relating the external coupling degrees of freedom (DOFs) to the internal source DOFs in order to propagate the external in-situ blocked forces back to multiple internal in-situ blocked forces. To prove the methodology of the presented approach three case studies, which increase in complexity, were carried out experimentally. The case studies concern a beam and an electric power steering system with paraxial servo unit (EPSapa), respectively. EPSapa systems consist of multiple embedded vibrational components which are defined as “internal sources”. The electric motor, the ball nut assembly and the toothed belt are identified as the main internal sources of an EPSapa system. Hence they are characterised by means of experimentally determined blocked forces. For the determination, micro electro mechanical systems (MEMS) accelerometers are embedded at the so called “internal interfaces”. This poses a novel application of the in-situ method in combination with the dealing of continuous and revolving internal interfaces. Concluding a further application of the bfTPA methodology is presented. It allows the external in-situ blocked forces of EPS systems or other products to be predicted based on internal insitu blocked forces and the BFT functions within internal receivers such as housings, for instance. Hence, the proposed approach is called “virtual component assembly”. It offers the advantage to synthesize a virtual EPS system based on the in-situ blocked forces of its components which are determined on test benches.

The focus of this thesis is on the prediction of sound attenuation through a lined duct, based on a mathematical model. Ducts with a single section as well as multi-segmented sections are discussed. The duct of interest has a rectangular cross-section as normally used for ventilation purposes. The mean flow in a ventilation duct is very low and can be neglected. In this thesis, two-dimensional analytical models are developed for sound transmission in a series of different duct configurations. Two models of the lining behaviour are considered, either locally-reacting or bulk-reacting. The models are used first to obtain the transverse and axial wavenumbers of various modes of the duct. The required finite numbers of wavenumbers are tracked using Müller’s method. The wavenumbers are traced from a very low frequency to high frequency using small frequency steps. It is found that, for a duct with a bulk-reacting lining, the number of modes with a transverse wavenumber below a particular value may exceed the corresponding number of modes in a duct with a locally-reacting lining. These additional modes are termed lining modes. The number of lining modes depends on the lining thickness. Dispersion curves are presented for both types of lining. The transmission of sound through the duct is then calculated using the mode-matching technique. The mode-matching model allows analysis of multi-modal wave propagation in the duct. The model is first developed for an infinitely long rigid duct with a finite length of lined insert. The estimation from the locally reacting model, that is widely available in the literature, is compared with the estimation from the newly developed bulk-reacting model. Although the locally reacting model often overestimates the performance of a bulk-reacting lining it is found that this is not always the case, especially for a small lining thickness and at lower frequencies where the locally reacting model may under-estimate the performance. The analytical model is then extended to a multi-segmented lining where the lined section is uniformly segmented with rigid walled sections in a periodic manner. For a bulk-reacting lining, the segmented arrangement renders the lining more similar to the behaviour of a duct with a locally-reacting lining and improves the peak attenuation. Little improvement is found in the case of a multi-segmented locally-reacting lining. The effect of duct height, lining thickness and lining flow resistivity on sound attenuation is studied using the analytical model. Experiments are presented which validate the analytical model.

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.

Sandwich panels with aluminium face sheets and honeycomb core material have certain advantages over panels made of wood. Some of the advantages of these constructions are low weight, good moisture properties, fire resistance and high stiffness to-weight ratio etc. As product development is carried out in a fast pace today, there is a strong need for validated prediction tools to assist during early design stages. In this thesis, tools are developed for predicting the sound transmission through honeycomb panels, typical for inner floors in trains and later through double-walled structures typical for rail-vehicles, aircrafts and ships. The sandwich theory for wave propagation and standard orthotropic plate theory is used to predict the sound transmission loss of honeycomb panels. Honeycomb is an anisotropic material which when used as a core in a sandwich panel, results in a panel with anisotropic properties. In this thesis, honeycomb panels are treated as being orthotropic and the wavenumbers are calculated for the two principal directions. The wavenumbers are then used to calculate the sound transmission using standard orthotropic theory. These predictions are validated with results from sound transmission measurements. The influence of constrained layer damping treatments on the sound transmission loss of these panels is investigated. Results show that, after the damping treatment, the sound transmission loss of an acoustically bad panel and a normal pane lare very similar. Further, sound transmission through a double-leaf partition based on a honeycomb panel with periodic stiffeners is investigated. The structural response of the periodic structure due to a harmonic excitation is expressed in terms of a series of space harmonics and virtual work theory is applied to calculate the sound transmission. The original model is refined to include sound absorption in the cavity and to account for the orthotropic property of the honeycomb panels. Since the solution of the space harmonic analysis is obtained in a series form, a sufficient number of terms has to be included in the calculation to ensure small errors. Computational accuracy needs to be balanced with computational cost as calculation times increases with the number of terms. A new criterion is introduced which reduces the computational time by up to a factor ten for the panels studied. For all the double-leaf systems analysed, the sound transmission loss predictions from the periodic model with the space harmonic expansion method are shown to compare well with laboratory measurements.

QC 20120607

This thesis deals with the constitution of a practice that is characterized as a performative demonstration of a process - the "making of place". This is framed by the presence of a sonic performer who explores the potential of gesture, text, technology and place in constructing a creative relationship with everyday life. This practice-based research consists of a written thesis and 12 original performance works in areas of work that have been designated as walking, field recording and mobile transmission. What does it mean to perform sound? As an artist who began his career creating sound design and improvising with performance artists, choreographers and theatre directors, I came to understand that every aspect of the construction of an event matters: body, text, place and sound. It is this interdisciplinarity - alongside the move from conventional performance spaces to outdoors - that prompts me to propose a post-medium approach, considering everything that happens in and around sound as significant to its ' performance. This approach concentrates on the ethics of constructing a site-specific interaction between place, performer and sonic experience; that focuses on sonic performance as a relational site of encounter instead of reception; explores the intersubjective, multi-sensorial and creative potential of the subject; and considers the 'noise' of thoughts and existence not as a distraction from entering a sonic experience, but ultimately as an essential part of listening. Performing sound thus complicates traditional separations between music and sound art, as a result of medium specificity or context , and becomes a process in which the expression of performance is, at its core, a reflection of how to present sound. This reflection is crucial to very expansion of the notion of performance in everyday life.

The ability to predict sound fields in coupled volumes is important for noise control and acoustic quality with buildings, cars, aircraft and trains. This thesis investigates methods to assess the diffusivity of sound fields in rooms and the prediction of sound transmission between coupled volumes using statistical approaches. Sound fields in a box-shaped room were assessed using ray tracing with the spatial correlation coefficient for instantaneous sound pressure. The results were compared with the theory for a three-dimensional diffuse field and propagating plane waves. Three different options were considered for the measurement lines: (1) pairs of points formed by one fixed point when the other point varies along the same line, (2) pairs of points with fixed spacing and (3) all permutations of points with variable spacing. The general conclusion is that option (1) can lead to conclusions that seem inappropriate. Options (2) and (3) were found to have potential as assessment procedures, but definitively characterising a sound field as diffuse was not possible. Sound transmission between coupled volumes was investigated using an empty cuboid, a cuboid with staggered barriers and a car cabin model based on Statistical Energy Analysis (SEA) and Experimental SEA (ESEA). Experimental work on corridors was used to validate the ray tracing models. For sound transmission along an empty cuboid, the direct field was significant with highly absorptive surfaces such that a propagating two-dimensional model overestimated transmission for low absorption, and underestimated it for high absorption. SEA incorporating coupling loss factors from the general form of ESEA gave improved agreement with ray tracing and showed the importance of indirect coupling between subsystems. For a corridor with staggered barriers, source locations for the Power Injection Method used in ESEA were assessed to ensure accurate predictions of sound transmission along the corridor. For the corridor and car cabin, the general form of ESEA tends to always result in a working SEA model and be more accurate when a source position (point or surface) used for the power injection process is similar to the actual source position. This tends to be more apparent when using a single source rather than multiple sources.

This thesis resumes the work done to study the acoustical performance of several building construction types proper from the south of Europe. It was made special attention to the flanking contribution. Initially, it was performed an exhaustive study of the existent bibliography with the aim of identifying and valuing the several acoustic experimental measurement methods related to the estimation of flanking contribution. Therefore, three possible applying methods were found: (i) Sound pressure method used in combination with elements shielding; (ii) Sound intensity method capable of obtaining the most reliable results without using the shielding process; (iii) Vibration velocity measurement procedure whose foundation lies on the relation between the vibration velocity of each element and the different flanking paths. This method is based on the velocity measures obtained from the transmitted vibrations by these elements, which are converted on acoustic estimation. From these three measurement methods the sound intensity is the only standardized and allows quantifying the contribution of each flanking path separately. For that reason, the intensity method was used as reference. It was also compared with the sound pressure method, respecting the estimation of airborne sound insulation without including the flanking contribution, and with the vibration velocity method when considering the flanking transmission. There were performed several experimental measurements to compare the results in laboratory and field conditions, for both structure and airborne sound transmission, through the three measurement methods. Taking the results obtained in consideration it is intended to establish a vibration velocity method as a measurement procedure on the estimation of airborne sound insulation with flanking contribution evaluation. At the same time it was calculated the sound insulation prediction by means of the methods referred on the EN 12354-1 (2000). Gathering all this information and comparing all the results, it is possible to conclude if the prediction methods are suitable for the south European countries, especially to the Spanish buildings. It must be referred that the vibration velocity method is only capable of producing results through the application of mathematical models which simulate the radiation efficiency estimation. The authors of these models were selected, as the most recent and known, among the bibliography and their models were applied to the specific conditions found for this thesis. These results were expressed by means of graphics representing vibrational velocity levels spatially distributed. The experimental work developed for this thesis implies a profound knowledge of all the measurement methods, and allowing obtaining data capable of concluding on the advantages and disadvantages of each method. Finally, conclusions and specific proposals are presented in order to stimulate the development of new studies. Esta tesis resume el esfuerzo que se ha realizado al estudiar las prestaciones acústicas de diversas topologías constructivas propias del sur de Europa, haciendo especial hincapié en el efecto de las transmisiones indirectas. Inicialmente, se ha estudiado de una forma exhaustiva la bibliografía existente con el objeto de identificar y valorar los diversos métodos de medida experimentales relacionados con la estimación de las transmisiones indirectas. Asimismo, se han encontrado tres posibles métodos para aplicación: (i) El método de presión, utilizado en combinación con el aislamiento de tabiques o apantallamiento; (ii) El método de intensidad acústica, capaz de obtener resultados muy fiables sin recurrir al apantallamiento; (iii) El procedimiento de medida de vibraciones, cuyo fundamento radica en la relación entre la velocidad de vibración de cada uno de los elementos implicados y de los distintos caminos de flanco. Este tiene como base medidas de velocidad, midiendo las vibraciones transmitidas por estos elementos que después se convierten en estimación acústica. De estos tres métodos de medida, el único estandardizado, que proporciona la contribución de cada camino de flanco por separado, es el método de intensidad. Por ello, este método ha sido utilizado como “método de referencia”. Se comparó con el método de presión, en lo que respecta a medida de aislamiento a ruido aéreo sin incluir transmisiones por flanco. Se comparó también con el método de vibraciones por velocidad, cuando se han tenido en cuenta las transmisiones por flanco. Se han realizado diversas tandas de medidas experimentales para comparar los resultados de acuerdo a los tres métodos de medida, tanto en condiciones de laboratorio como en condiciones reales (in situ), así como para medidas de impacto y aéreas. En base a los resultados obtenidos, se plantea establecer el método de vibración como posible procedimiento de medida en la estimación del aislamiento sonoro de edificaciones con la estimación de las transmisiones de flanco. vii En paralelo con estos experimentos, se calculó la predicción de la transmisión acústica incluida en la normativa EN 12354-1 (2000). Con esta información se añade otro conjunto de datos, comparables con los resultados experimentales, permitiendo concluir sobre la aplicabilidad, o no, de este método de predicción en los edificios del sur de Europa, más en concreto en los españoles. Con el método de vibraciones solamente es posible obtener resultados mediante la aplicación de modelos matemáticos de estimación de la eficiencia de radiación acústica. Los autores de estos modelos se han escogido entre la bibliografía como los más conocidos y más novedosos, aplicados a las específicas condiciones de entorno elegidas y posibles para esta tesis. Los resultados de estos datos se expresan mediante gráficas de distribución espacial de niveles de velocidad de vibración. El trabajo desarrollado experimentalmente implica un conocimiento profundo de todos los métodos de medición acústica referidos en esta tesis, permitiendo obtener datos que indiquen las ventajas y inconvenientes de cada uno de los métodos, así como los resultados comparados de las estimaciones obtenidas por cada uno de ellos. Al final, se presentan las conclusiones y propuestas específicas, para el desarrollo de nuevos estudios. Esta tese resume o esforço que foi feito ao estudar as prestações acústicas de diversas topologias construtivas próprias do sul da Europa, com especial atenção no efeito das transmissões marginais de flanco. Inicialmente, foi estudada de uma forma exaustiva a bibliografia existente com o objectivo de identificar e valorizar os diversos métodos de medida experimentais relacionados com a estimação das transmissões marginais, em concreto as de flanco. Com isto, foram encontrados três possíveis métodos para utilizar: (i) O método de pressão, utilizado em combinação com o isolamento independente de paredes; (ii) O método de intensidade acústica, capaz de obter resultados muito fiáveis e sem recorrer ao isolamento de paredes; (iii) O procedimento de medida de vibrações, cujo fundamento reside na relação entre a velocidade de vibração de cada uma das paredes implicadas e dos diferentes caminhos de flanco. Este procedimento tem como base medidas de velocidade, onde são medidas as vibrações transmitidas por estes elementos que posteriormente são convertidas em estimação acústica. De entre estes três métodos de medida, o único normalizado, que proporciona a contribuição de cada caminho de flanco de forma separada, é o método de intensidade. Por isto, este método foi utilizado como “método de referência”. Este método foi comparado com o método de pressão, no que diz respeito a medida de isolamento a ruído aéreo sem incluir as transmissões de flanco. Foram realizadas diversas séries de medidas experimentais para comparar os resultados para os três métodos de medida, quer em condições laboratoriais como em condições reais ou in situ, assim como para medições com excitação por percussão e aérea. Com base nos resultados obtidos pretende-se estabelecer um método de vibrações como possível procedimento de medida na estimação do isolamento sonoro dos elementos de compartimentação dos edifícios com a contabilização das transmissões de flanco. xi Em paralelo com estes ensaios calculou-se a previsão da transmissão acústica através da norma EN 12354-1 (2000). Com esta informação é acrescentado um outro conjunto de dados, comparáveis com os resultados experimentais, permitindo concluir sobre a aplicabilidade, ou não, de este método de previsão aos edifícios do sul da Europa, mais concretamente aos espanhóis. Com o método de vibrações isoladamente é possível obter resultados mediante a aplicação de modelos matemáticos que estimam a eficiência de radiação acústica. Os autores de estes modelos foram escolhidos de entre a bibliografia, como os mais conhecidos e também mais recentes, foram aplicados às condições do meio eleitas e possíveis para esta tese. Os resultados foram expressos mediante gráficos de distribuição espacial de níveis de velocidade de vibração. O trabalho desenvolvido experimentalmente implica um conhecimento profundo de todos os métodos de medição acústica referidos neste tese, permitindo obter dados que indiquem as vantagens e os inconvenientes de cada um dos métodos, assim como os resultados comparados das estimações obtidas por cada um deles. No fim, apresentam-se conclusões e propostas específicas para o desenvolvimento de novos estudos.
PRODEP III

Sound transmission by the hyoid apparatus during echolocation in bats Chelsie C.G. Snipes1 and Richard T. Carter1 1 East Tennessee State University, Johnson City TN, USA The morphology of the stylohyal-tympanic bone articulation found in laryngeally echolocating bats is highly indicative of a function associated with signal production. One untested hypothesis is that this morphology allows the transfer of a sound signal from the larynx to the tympanic bones (auditory bulla) via the hyoid apparatus during signal production by the larynx. To test this hypothesis, we used µCT data, CAD editing software, and finite element analysis (FEA) to model the propagation of sound through the hyoid chain into the tympanic bones. This involved making digital segmentations from the µCT data of the tympanic bones and cartilaginous segments and converting it into a digital mesh body. Since the cartilaginous segments are not visible in CTs, we segmented the air in each gap and subsequently used a Boolean function in CAD software to fit each bony end into their respective cartilaginous segment. Further post-processing of the model included a reduction in the number of facets bodies and smoothing surfaces which allowed us to convert it into a solid body model. The solid body geometry was then uploaded into FEA software and assigned material properties for cortical bone, cartilage, and bulla. Additional biomechanical data, including Young’s Modulus, Poisson’s ratio, and speed of sound through each material were defined in previous literature. We ran two FEA analysis with our model: the first was an acoustic analysis that modelled sound propagation through our material (bone and cartilage), and the second was a coupled modal and structural analysis that modelled resonant behavior and sound pressure wave propagation from the hyoid body to the tympanic bones. Our models support the hypothesis that bats use this physical connection between the larynx and auditory bulla to transfer sound (mechanical excitation). Our models show both pressure waves and vibration due to resonance could be used to transfer this signal and this resonance behavior can be modulated by restraining the hyoid apparatus, perhaps through muscle contraction. We propose that by modulating the resonant behavior of the hyoid apparatus, bats can selectively filter which frequencies of sound are transferred from the larynx to the auditory bulla during echolocation signal production.

Globally, the ever increasing consumer interest in multichannel audio is a major factor driving the research intent in soundfield reconstruction and compression. The popularity of the well commercialized 5.1 surround sound system and its 6-Channel audio has been strongly supported by the advent of powerful storage medium, DVD, as well as the use of efficient telecommunication techniques. However, this popularity has also revealed potential problems in the development of soundfield systems. Firstly, currently available soundfield systems have rather poor compatibility with irregular speaker arrangements. Secondly, bandwidth requirement is dramatically increased for multichannel audio representation with good temporal and spatial fidelity. This master???s thesis addresses these two major issues in soundfield systems. It introduces a new approach to analyze and sysnthesize soundfield, and compares this approach with currently popular systems. To facilitate this comparison, the behavior of soundfield has been reviewed from both physical and psychoacoustic perspectives, along with an extensive study of past and present soundfield systems and multichannel audio compression algorithms. The 1th order High Spatial Resolution (HSR) soundfield recording and reproduction has been implemented in this project, and subjectively evaluated using a series of MUSHRA tests to finalize the comparison.

Sandwich panels are extensively used in constructional, naval and aerospace structures due to their high stiffness and strength-to-weight ratios. In contrast, sound transmission properties of sandwich panels are adversely influenced by their low effective mass. Phase velocity matching of structural waves propagating within the panel and the incident pressure waves from the surrounding fluid medium lead to coincidence effects (often within the audible range) resulting in reduced impedance and high sound transmission. Truss-like lattice cores with porous microarchitecture and \emph{reduced} inter panel connectivity relative to honeycomb cores promise the potential to satisfy the conflicting structural and vibroacoustic response requirements. This study combines Bloch-wave analysis and the Finite Element Method (FEM) to understand wave propagation and hence sound transmission in sandwich panels with a truss lattice core. Three dimensional coupled fluid-structure finite element simulations are conducted to compare the performance of a representative set of lattice core topologies. Potential advantages of sandwich structures with a lattice core over the traditional shear wall panel designs are identified. The significance of partial band gaps is evident in the sound transmission loss characteristics of the panels studied. This work demonstrates that, even without optimization, significant enhancements in STL performance can be achieved in truss lattice core sandwich panels compared to a traditional sandwich panel employing a honeycomb core under constant mass constraint.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

The sound transmission loss of a range of plywood panels was measured to investigate the influence of the orthotropic stiffness of the plywood panels. The plywood panels were tested as single and also double leaf partitions, with a range of stud configurations. A new method was developed for predicting the sound transmission loss of single leaf partitions with both orthotropic and frequency dependent stiffness values. The sound transmission loss was evaluated for two significantly different sample sizes. The observed influence of the sample size on the measured sound transmission loss was profound. The construction of the partition was shown to significantly affect the influence of the sample size on the sound transmission loss. A qualitative analysis based on existing published research of the contributing factors is presented, and methods for adjusting the results for the small sample size for comparison with the large results were developed. The influence of a range of acoustic treatments of lightweight plywood partitions was investigated. The treatments involved internal viscoelastic materials and decoupled mass loaded barriers in various arrangements. The attachment between the treatment and the plywood panel was found to influence the sound transmission loss significantly. A prediction method based on published models was modified to allow the influence of the treatments to be included. Reasonable agreement was achieved between the predicted and measured results for a wide range of samples. A prediction method was developed that accounts for the influence of orthotropic, frequency dependent material parameters. This method utilised an adaptive, numerical integration method to solve an analytical formulation for the sound transmission loss. The influence of the finite sample size was accounted for using an expression for the finite panel radiation impedance. The finite panel radiation impedance was predicted analytically and an approximation was also presented. The presence of a significant source room niche was accounted for by applying an appropriate limit to the integration range of the angle of incidence. The prediction methods developed are compared with the measured transmission loss results from both the small and large test facilities. Good agreement was seen for some of the predicted results. Generally the agreement within the coincidence region was worse than for the rest of the transmission loss curve. The inclusion of orthotropic and frequency dependent stiffness values significantly improved the agreement within the coincidence region.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on February 25, 2008) Vita. Includes bibliographical references.

Lightweight building materials are now commonly employed in many countries in preference to heavyweight materials. This has lead to extensive research into the sound transmission loss of double leaf wall systems. These studies have shown that the wall cavity and sound absorption material placed within the cavity play a crucial role in the sound transmission through these systems. However, the influence of the wall cavity on the sound transmission loss is not fully understood. The purpose of this research is to obtain a comprehensive understanding of the role played by the wall cavity and any associated sound absorption material on the sound transmission loss through double leaf wall systems. The research was justified by the fact that some of the existing prediction models do not agree with some observed experimental trends. Gösele’s theory is expanded and used in the creation of an infinite and finite vibrating strip model in order to acquire the desired understanding. The sound transmission loss, radiated sound pressure and directivity of double leaf systems composed of gypsum boards and glass have been calculated using the developed model. A method for calculating the forced radiation efficiency has also been proposed. Predictions are compared to well established theories and to reported experimental results. This work also provides a physical explanation for the under-prediction of the sound transmission loss in London’s model; explains why Sharp’s model corresponds to Davy’s with a limiting angle of 61° and gives an explanation for Rindel’s directivity and sound transmission loss measurements through double glazed windows. The investigation also revealed that a wide variety of conclusions were obtained by different researchers concerning the role of the cavity and the properties of any associated sound absorption material on the sound transmission loss through double wall systems. Consequently recommendations about the ways in which sound transmission through cavity systems can be improved should always be qualified with regard to the specific frequency range of interest, type of sound absorption material, wall panel and stud characteristics.