Recently much research has focused on the control of enclosed sound fields, particularly in automobiles. Both Active Noise Control (ANC) and Active Structural Acoustic Control (ASAC) techniques are being applied to problems stemming from power train noise and road noise (noise due to the interaction of the tires with the surface of the road). Due to the low frequency characteristics of these noise problems, large acoustic sources are required to obtain efficient control of the sound field. This creates demand in the automobile industry for compact lightweight sources. This work is concerned with the application of active control to power train noise, as well as road noise in the interior cabin of a sport utility vehicle using advanced, compact lightweight piezoelectric acoustic sources. First, a test structure approximately the same size as the automobile was built to study the principles of active noise control in a cavity. A finite element model of the cavity was created in order to optimize the positions of the error sensors and the control sources. Experimental work was performed with the optimized actuator and sensor locations in order to validate the model, and draw conclusions regarding the conditions to obtain global control of the sound field. Second, a broad-band feedforward filtered-X LMS algorithm was used to control power train noise. Preliminary power train noise tests were conducted using arrangements of four microphones and up to four commercially available speakers for control. Attenuation of seven decibel (dB) at the error sensors was measured in the 40-500 Hz frequency band. The dimensions of the zone of quiet generated by the control were measured, and show that noise reductions were obtained for a large volume surrounding the error sensors. Next, advanced speakers were implemented for active control of power train noise. The results obtained with different arrangements of these speakers were very similar to those obtained with the commercially-available speakers. These advanced speakers use piezoelectric devices to induce the displacement of a speaker membrane, which radiates sound. Their lighter weight and compact dimensions are a significant advantage over conventional speakers, for their application in automobile. Third, preliminary results were obtained for active control of road noise. The controller used an optimized set of four reference signals to control the noise at one error sensor using one control source. Two sets of tests were conducted. The first set of tests was performed on a dynamometer, which simulates the effects of the road on the tires. The second set of tests was performed on a rough road. Reduction of two to four decibel of the sound pressure level at the error sensor was obtained between 100 and 200 Hz. / Master of Science

This dissertation considers the effects of long-term amplitude compression used in narrow-band frequency modulated (FM) assistive listening devices on the auditory discrimination of severely and profoundly hearing-impaired individuals. Compression has been used in narrow-band FM transmitters for hearing-impaired children in educational programs for over twenty years. It restricts the peak deviation of the FM signal to within allowable limits. Narrow-band FM equipment can vary in peak limitation approaches via compression, i.e., using a form of compression limiting or using long-term compression (automatic volume control). Numerous investigations have studied the benefits of FM system use, but none have tested the benefits or deleterious effects of these compression forms on the auditory discrimination of hearing-impaired individuals. Despite the marked limitations associated with severe or profound sensorineural hearing impairment in children, spoken language development is possible. Research and experience have suggested that the auditory system represents the best sensory input channel for these children. With appropriate amplification and educational intervention they can achieve dramatic improvements in speech perception, speech production, language development, and educational achievement (Boothroyd, 1985; Hudgins, 1953, 1954; Ling & Milne, 1981; Wedenberg, 1954). Most hearing-impaired children in educational programs across the United States receive the amplified teacher's speech signal via narrow-band frequency modulated (FM) transmission, yet a controlled investigation of the input compression used in these systems has never been conducted. This dissertation reviews and discusses narrow-band frequency modulated (FM) radio wave systems and the use of audio compression. The experiment tested 32 students with severe to profound sensorineural hearing loss under two narrow-band FM transmitter conditions. The FM transmitter conditions were varied on the basis of long-term compression activation points, i.e., 75 dB versus 90 dB. The students' perception of one supra-segmental and eight segmental contrasts were examined using a three-interval, forced-choice paradigm. This procedure measured the students' access to phonologically significant cues. Analyses of the speech perception scores across the two conditions suggested that the use of long-term amplitude compression is advantageous for this population.

To help resolve certain practical issues with acoustical methods for landmine detection, experiments were performed using a pulsed, standoff source consisting of sixteen speakers mounted on a circular arc. This source, as well as a pair of 18-inch subwoofers, were used separately for acoustical excitation of the buried mine, and the response of the target site was examined as a function of source frequency, sound pressure level, and excitation signal type, with a particular focus on multitone signals. In addition, modeling was undertaken to investigate the effects of nonlinearity, including bimodular nonlinearity, on frequency generation. A numerical, time-domain solution based on a lumped-element model proposed by Donskoy et al. [J. Acoust. Soc. Am. 117, 690 (2005)] was developed and used to simulate pulsed excitation and the effects of bimodular nonlinearity, which allowed experimentally observed spectra to be compared with modeled results. / text

Dans un milieu granulaire, la géométrie du contact entre grains induit une dépendance en pression non-linéaire des modules élastiques. Dans un milieu granulaire sous gravité avec une surface libre, la pression augmente avec profondeur. Il en résulte que seules des ondes de surface peuvent se propager. Nous montrons théoriquement que ce système est un guide d'onde à gradient d'indice dans lequel se propagent des ondes transverses et sagittales. Elles se décomposent selon une série discrète mais infinie de modes dont nous avons calculé la relation de dispersion. Leur vitesse augmente faiblement avec leur indice comme n1/6 et rend difficile l'interprétation des mesures. En profondeur finie, un guide d'onde géométrique se superpose au précédent. Les modes modifiés présentent une fréquence de coupure. Expérimentalement, l'émission de paquets d'ondes gaussiens dans un canal (guide d'onde géométrique) a permis d'isoler le mode de surface fondamental et de tracer sa relation dispersion. L'exposant de sa loi d'échelle valide le point de vue du de la théorie de champ moyen et contredit l'hypothèse d'une situation isostatique au voisinage de la surface libre. Cependant, le module de cisaillement est anormalement faible. Un écoulement granulaire gravitaire entraîné dans un silo lisse génère une émission sonore spontanée. Nous montrons expérimentalement et théoriquement qu'elle résulte d'une instabilité convective pour laquelle la friction amplifie et sélectionne la fréquence. Son développement aboutit à la formation d'ondes de choc. Nous pensons que cette instabilité pourrait expliquer le chant des dunes ou le déclenchement dynamique des séismes.

The U.S. Navy is developing through-water acoustic communications capability for undersea, distributed systems. These wireless communication links form a wide-area network of fixed nodes consistent with future autonomous sensors on the seafloor. Mobile nodes may operate in the domain of the grid using the fixed nodes as both navigation reference points and communication access points. This thesis evaluates the experimental performance of such networked communications between an undersea vehicle and a ship. Physical-layer considerations include refraction, wind-induced ambient noise, and vehicle aspect angle.

Approved for public release, distribution is unlimited / This thesis is an analysis of the link-layer and network-layer performance of an experimental Seaweb undersea acoustic network. The objective is to statistically determine RTS/CTS handshaking and ARQ retransmission performance during the Fleet Battle Experiment-India, executed in June 2001. Many factors constrain or impair undersea acoustic communications. Analysis of a sample portion of the data reveals insights about the overall throughput, latency, and reliability of the Seaweb network. / Lieutenant, United States Navy

A well-made flute is always a compromise and the job of flute makers is to achieve a musically and aesthetically satisfying compromise; a task that involves much trial and-error. The practical aim of this thesis is to develop a mathematical model of the flute and a computer program that assists in the flute design process. Many musical qualities of a woodwind instrument may be calculated from the acoustic impedance spectrum of the instrument. A technique for fast and accurate measurement of this quantity is developed. The technique is based on the multiple-microphone technique, and uses resonance-free impedance loads to calibrate the system and spectral shaping to improve the precision at impedance extrema. The impedance spectra of the flute and clarinet are measured over a wide range of fingerings, yielding a comprehensive and accurate database. The impedance properties of single finger holes are measured using a related technique, and fitformulae are derived for the length corrections of closed finger holes for a typical range of hole sizes and lengths. The bore surface of wooden instruments can change over time with playing and this can affect the acoustic impedance, and therefore the playing quality. Such changes in acoustic impedance are explored using wooden test pipes. To account for the effect of a typical player on flute tuning, an empirical correction is determined from the measured tuning of both modern and classical flutes as played by several professional and semi-professional players. By combining the measured impedance database with the player effects and various results in the literature a mathematical model of the input impedance of flutes is developed and implemented in command-line programs written in the software language C. A user-friendly graphical interface is created using the flute impedance model for the purposes of flute acoustical design and analysis. The program calculates the tuning and other acoustical properties for any given geometry. The program is applied to a modern flute and a classical flute. The capabilities and limitations of the software are thereby illustrated and possible contributions of the program to contemporary flute design are explored.

Il existe aujourd'hui un enjeu sociétal majeur à s'intéresser à la propagation du son en milieu extérieur et notamment, dans notre contexte, à diminuer l'incertitude sur l'estimation des niveaux sonores et améliorer ainsi la précision des diverses analyses, du bureau d'étude à l'institut de recherche. Dans le cadre de l'acoustique environnementale, l'influence des conditions météorologiques sur la propagation acoustique en milieu extérieur peut être importante. Il est donc nécessaire d'appréhender et de quantifier les phénomènes météorologiques de micro-échelles que l'on observe dans la couche limite atmosphérique. Dans ce but, le modèle météorologique de recherche de Météo-France (Meso-NH) a été utilisé. Après avoir comparé les résultats de ce modèle à très fine résolution (de l'ordre du mètre) à l'aide des bases de données de deux campagnes expérimentales (Lannemezan 2005 et la Station de Long Terme), il s'est avéré nécessaire de développer cet outil en intégrant la prise en compte de la force de traînée des arbres. Dès lors, les résultats issus de Meso-NH sur les champs de vent, de température et d'énergie cinétique turbulente aparraissent satisfaisants. Ces informations sont par la suite utilisées en données d'entrée du modèle de propagation acoustique. Le modèle acoustique temporel utilisé est basé sur la méthode Transmission Line Matrix (TLM). Son développement a été effectué dans le but d'être appliqué à la propagation acoustique en milieu extérieur : prise en compte du relief, de différents types de sol, des conditions atmosphériques, etc. La validation numérique de la méthode TLM, par comparaison avec d'autres modèles (analytique et numérique de type Equation Parabolique), a permis de montrer la pertinence de son utilisation dans le cadre de l'acoustique environnementale. Enfin, à l'aide de ces modèles, des niveaux sonores simulés sous différentes conditions de propagation (favorables, défavorables, homogènes) ont été comparés aux mesures in-situ réalisées lors de la campagne expérimentale de Lannemezan 2005. Les résultats se sont avérés très satisfaisants au regard de la variabilité des phénomènes observés. Cependant, l'utilisation des champs issus d'un modèle micrométéorologique de type Meso-NH reste délicate du fait de la forte sensibilité du niveau sonore aux profils verticaux de célérité du son. L'étude de faisabilité sur une expérience plus complexe (la Station de Long Terme) est encourageante et, à condition de disposer d'importants moyens de calculs, elle permet de considérer la TLM comme une nouvelle méthode de référence et ainsi, d'envisager d'élargir son domaine d'utilisation à d'autres applications.

This thesis acts as a first step in connecting the sub jective description of piano tone with quantitative measurements of changes in the vibrational and acoustical properties of a piano. Voicing techniques used by piano technicians are applied to a fully strung test piano and a series of tests are undertaken to measure the effect they have on piano tone. The addition of weights and riblets to a piano soundboard, two commonly practiced methods used to change the tone of a piano and even out the transition between the low tenor and high bass bridges, are examined in detail in this thesis. Modal analysis is the first test method applied and is used to determine the mode shapes and the modal properties of the test soundboard. The addition of small masses and riblets is shown to have the ability to change modal properties to varying degrees and connections are made between the output sound, attachment locations, modification locations, and mode shapes of the soundboard. A new technique, piano tone mapping, is introduced as a visualization method that displays the harmonic structure of the entire piano in one image. Using the technique creates a unique fingerprint of a piano that can be compared in various ways to other pianos. The piano tone maps reveal that initial magnitude and decay rate of the output sound are both decreased for notes with attachment points close to modification locations where weights and riblets are added. Impedance testing is also conducted for a number of different modifications. These tests reveal that riblets and weights each have their own frequency bands of influence, with the weights creating impedance changes primarily below 800 Hz and riblets creating impedance changes above 500 Hz, with a region of overlap between 500 Hz and 800 Hz. Tests also revealed that changes in impedance created by these voicing techniques were local in effect, with a region of influence less than 10 cm in radius extending from the location where the weight or riblet is attached.

This thesis acts as a first step in connecting the sub jective description of piano tone with quantitative measurements of changes in the vibrational and acoustical properties of a piano. Voicing techniques used by piano technicians are applied to a fully strung test piano and a series of tests are undertaken to measure the effect they have on piano tone. The addition of weights and riblets to a piano soundboard, two commonly practiced methods used to change the tone of a piano and even out the transition between the low tenor and high bass bridges, are examined in detail in this thesis. Modal analysis is the first test method applied and is used to determine the mode shapes and the modal properties of the test soundboard. The addition of small masses and riblets is shown to have the ability to change modal properties to varying degrees and connections are made between the output sound, attachment locations, modification locations, and mode shapes of the soundboard. A new technique, piano tone mapping, is introduced as a visualization method that displays the harmonic structure of the entire piano in one image. Using the technique creates a unique fingerprint of a piano that can be compared in various ways to other pianos. The piano tone maps reveal that initial magnitude and decay rate of the output sound are both decreased for notes with attachment points close to modification locations where weights and riblets are added. Impedance testing is also conducted for a number of different modifications. These tests reveal that riblets and weights each have their own frequency bands of influence, with the weights creating impedance changes primarily below 800 Hz and riblets creating impedance changes above 500 Hz, with a region of overlap between 500 Hz and 800 Hz. Tests also revealed that changes in impedance created by these voicing techniques were local in effect, with a region of influence less than 10 cm in radius extending from the location where the weight or riblet is attached.