The acoustical signatures as observed by an auditor on the ground are explored for various radiating bodies. Specifically, a theory that describes the origin of sonic booms of two unsteady point sources and of an airplane is developed. In 1968, Garrick and Maglieri conducted an experiment where a General Dynamics F-106 was subjected to sinusoidal pitch oscillations. At the time, the results of the observed sonic boom were not understood; they had expected a distorted sonic boom. The theory presented in the present study offers an explanation of the results. An essential point needed in order to understand their observations is the source distribution for an acoustically radiating body. This source distribution occupies a region of space many times the length of the airplane. Therefore, any attempts to distort a sonic boom must deal with the grand scale of the source distribution.

<p> This thesis is about the process behind building, tuning, and composing music for a new set of metallophones called the "Lightbulb" instruments. This project began in 2011 and has continued to expand over the past two years: the first piece to be written for the instruments is titled <i> Prana,</i> and this thesis describes how the process of building and tuning the instruments informed the compositional process behind <i><b> Prana.</b></i> The premiere of <i>Prana</i> led to the formation of the Lightbulb Ensemble, which performs on these new instruments. The instruments and the group continue to develop.</p>

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.

<p> This dissertation reports studies of the internal structure of jammed granular materials and how granular sound propagation and vibrational modes are influenced by disorder in particle positions and contact forces. We investigate the role of particle scale forces on sound amplitude and speed, how to characterize the bulk pressure via the density of states, and force network modularity. We perform our experiments on a vertical, 2D, photoelastic granular material. Acoustic waves are excited from the bottom of the system and observed via particle scale sensors and a high speed camera. This novel combination of spatial and temporal measurements allows us to observe the role of force chains in sound propagation. The sound amplitude is largest through particles with strong contact forces, and we see that sound travels fastest along high force paths, giving rise to multiple sound speeds. Combining acoustic excitations with a method from thermal physics, we developed a new method to measure the density of modes, <i>D</i>(<i>f</i>). From <i>D</i>(<i> f</i>), we define a critical frequency, <i>f_c</i>, that scales with the bulk pressure, and comparing <i>D</i>(<i> f</i>) to Debye scaling, we find an excess of low frequency modes. Disorder in the force chain network and particle configurations plays a crucial role in <i>D</i>(<i>f</i>), as Debye scaling is only recovered for high pressure, hexagonally ordered packings. Finally, we characterize the force network by dividing it into modules of highly connected nodes. These communities become progressively more ordered as the pressure on the system is increased and the force chains become more uniform. Together, these studies illustrate the importance of the force chains in understanding static and dynamic granular properties.</p>

<p> Wind turbine noise at low frequencies less than 300Hz is not only annoying to humans but has been proven to cause serious health issues. Additionally, animals are severely affected by wind turbines because a small increase in ambient noise (as is produced by wind turbines) significantly reduces their listening ability. In an attempt to better understand and characterize the aerodynamic noise of wind turbine blades, experimental testing was completed on PowerWorks 100kW and GudCraft WG700 blade specimens in the University of California, Davis Transportation Noise Control Center's anechoic chamber. Experimental testing and data analysis proved approximately 4.0dB to 6.0dB was produced due to the blades' geometric design for both blade specimens at low frequencies. This noise was maximized at the blades' leading edge along the central portion of the blades' radius. Theoretical prediction models have been used to determine that, for typical wind speeds and low frequencies, noise generated due to the tip passing frequency is clearly predominant.</p>

<p> <i>Gran Duo</i> (1999-2000) by Magnus Lindberg (b. 1958) is the result of a commission by Sir Simon Rattle, former conductor of the City of Birmingham (England) Symphony Orchestra, and the Royal Festival Hall to commemorate the third millennium. Composed for twenty-four woodwinds and brass, Lindberg divides the woodwind and brass families into eight characters that serve as participants in an attentive twenty-minute conversation.</p><p> The document includes biographical information about the composition to further understand Lindberg&rsquo;s writing style. The composer&rsquo;s use of computer-assisted composition techniques inspires an alternative structural analysis of <i>Gran Duo.</i> Spectral graphs provide a supplementary tool for score study assisting with the verification of formal structural elements. A tempo chart allows the conductor to easily identify form and tempo relationships between each of the nineteen sections throughout the five-movement composition.</p><p> In order to reveal character areas and their relation to the structure of the work, the analysis of texture, timbre, and rhythm reveal the formal structure of the composition, which reflects a conversation between the brass and woodwinds in this setting for wind instruments.</p>

Most inversion techniques described in the literature rely on the validity of ray tracing, which breaks down in the presence of caustics. The linearized acoustic inverse problem with constant reference velocity is analyzed in order to quantify the effects of a caustic in a probing wavefront on the scattered signal. When the sound velocity is perturbed by a localized, unidirectional, high frequency inhomogeneity, the surprising result obtained is that the energy in the scattered field is spread out if the perturbation is located on the caustic. This spreading of energy allows the construction of an oscillatory integral representation of the scattered field, which has the same form, whether or not an incident caustic is present. On the other hand, a sequence of localized high frequency sound velocity perturbations is constructed such that the size of the scattered signal relative to the size of the inhomogeneity becomes arbitrarily large as the support of the perturbation approaches the caustic. In regions where there are no caustics, a general inverse operator if found for smoothly varying reference velocities. This operator is shown to be equivalent to an inverse operator constructed by Beylkin (1985).

Two current challenges in seismic imaging are to obtain more detailed images of complex structures from reflection data and to constrain the regional structure of the Earth using wide-angle data. These are complex problems for which traditional methods fail because they are based on too many simplifying assumptions. I develop a unified approach which addresses these tasks by starting with a fundamental problem formulation, leading to a practical numerical solution which converges rapidly. It is based on pre-stack depth migration and cell-stripping tomography in heterogeneous media, which allow layer-stripping and retain all the information from the data, incorporates a depth focusing technique for improved image resolution and utilizes user-interaction and geologic input to guide and constrain the imaging process. I first describe a fast and accurate dynamic ray-tracing scheme in heterogeneous media which allows complex model definition and rapid two-point ray tracing. This ray tracing method is then used to compute Green functions in a layer-stripping pre-stack depth migration algorithm. The algorithm itself is based on a Kirchhoff integral in heterogeneous media using exact weighting factors and specialized to 2.5 D migration. I examine the migration results with a depth-focusing technique which analyzes common image panels for horizontal alignment, relating the degree of non alignment, or Migration Moveout (MMO) to corrections in the velocity model along the raypaths. Finally, I develop a cell-stripping tomography (CST) algorithm which distributes velocity residuals only to the relevant cells, allowing resolution of both horizontal and vertical discontinuities and providing starting models for migration. Although computer-intensive, this unified approach is successful both in synthetic tests and for obtaining local and regional images of the edge of the Santa Maria basin in central California. It is more faithful to the velocity and dip information contained in the data, allows more control over the imaging process and with available computing power promises to be routinely applicable.

Dwellings in congested urban areas are confronted with both invigorating and aggravating penetrations of proximic sound and street activity within constricted environments. Typically the physicality of a building is there to serve as SHELTER from weather, intruders, and to create an interior effect. Here building elements, both physical and electronic, are considered to serve as MODULATORS of environmental infiltration. If the DWELLING is a holistic physiological system then it should be an extension of our physiological being and an extension of the urban landscape. Attunement of infiltrating SOUND and VISION (or MOTION) for dwellings in urban areas can provide for more appropriate environments. Contextual sound and motion can be managed into useful energies in urban habitats to provoke different sensory terrains.

A general theory for the dynamics of aspherical droplets useful to interpret frequency spectra more accurately for thermophysical property measurements was developed. The oscillations of a non-spherical droplet oscillating about an oblate spheroid subjected to external forces are considered. The effect of the static deformation and the interaction between the drop oscillation and the external field on the resonance are investigated. The analysis developed can be extended to consider different static shape deformation shapes. In order to validate the analytical predictions and to conduct further investigations, an experimental apparatus and a novel experimental procedure were developed. Experimental data and observations on the frequency splitting and surface tension, and the dynamics of the droplet in the experimental apparatus are presented. Finally, the effect of fullerenes on some dynamic features of levitated droplets is investigated.