Thesis (M.S. in Engineering Acoustics)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Thomas J. Hofler, Andres Larraza. Includes bibliographical references (p. 45). Also available online.

<p> The purpose of this thesis is to share the process behind the development of an approach to composing for central Javanese gamelans that utilizes vertical harmony. This paper will include my history with Javanese gamelan, work on the development of a piano tuning that would work with a gamelan, compositional works that led to the development of the system, a study of existing Javanese gamelan tunings, and a presentation of intervallic relationships and cadences that can be utilized with any gamelan. All of this is done with hope that others who may take interest in writing for central Javanese gamelan will have a new tool at their disposal, and to pique the interest of others in the rich world of possibilities that exist within the instruments. </p><p> There is also an explanation of the process of developing a piano tuning to be used with a traditional gamelan to perform the Concerto for PIano And Javanese Gamelan by Lou Harrison. </p><p> There is some brief discussion on the cognition of interval, and how the brain simplifies complex intervals, and begins to hear them as more simple intervals.</p>

Firefighters wear a plethora of personal protective equipment (PPE) in- cluding a Personal Alert Safety System (PASS) device. This device produces an audible alarm signal when it senses a lack of movement to help rescue teams detect and find firefighters who have become incapacitated on the fireground. Although this alarm works the majority of the time, there are instances where it has failed to be detected or found. Using a passive sonar approach, this study begins to provide a scientific background to improve the signal. The construct of the passive sonar equation helps to define a signal-to-noise ra- tio with information about the environment, source and receiver. This work presents studies of the noise level of the environment (NL), source level (SL) of the PASS device, and detection threshold of the receiver (DT) on the fire scene. To study NL and SL, equipment used by firefighters was recorded and analyzed for the sound pressure level, frequency content, and directionality compared to the PASS alarm. The NL on a fire scene has been found to be broadband, high intensity noise. The loudest piece of equipment was found to be a chainsaw and the quietest to be a pumper truck. The DT involves the ability of firefighters to detect and classify the PASS signal. Physical acous- tic experiments, using an acoustic manikin, show that PPE gear affects the sound reaching the ear by reducing the average received level and introducing peaks and nulls in head related transfer functions. In audiological tests on normal-hearing human subjects, this manifested itself by increasing the sound pressure level required to detect the PASS alarm while wearing PPE gear. Recommendations based on these findings are provided / text

Piezoelectric transducers with cylindrical geometry are often designed to operate in a radial “breathing” mode. In order to tune their performance in a cost effective way, cylinders can be constructed of alternating active (piezoelectric) and inactive (non-piezoelectric) staves. Existing lumped parameter models for such a ring are based on effective piezoelectric properties of the composite ring which reduce the system to a single degree of freedom corresponding to the breathing motion. Unfortunately, if the length of the staves is a sufficiently large percentage of the circumference, the transducer may demonstrate a detrimental higher frequency resonance within the desired bandwidth of operation even when all staves are uniformly excited by an electrical field. This parasitic resonance results from bending motion of the staves associated with stiffness and mass discontinuities of the constituent material properties and can significantly decrease the radiated acoustic pressure and generate distortion of the radiated acoustic waveform. This work presents a multiple-degree-of-freedom lumped parameter model that captures both the breathing and bending resonances of the transducer and provides a more accurate prediction of its effective coupling coefficient. Results are compared with a one-degree-of-freedom model, finite element models, and experimental data. Modifications to account for internal volumes, nonlinearities, and other effects are also presented and discussed. / text

The scattering and attenuation caused by fish schools has been extensively studied for applications in fisheries management and naval sonar. The literature contains extensive in situ measurements of scattering by fish schools, however significant uncertainties exist with respect to characterizing the size, quantity, and distribution of fish within the schools, that confounds accurate measurement-model comparison. Hence there is a need for application of measurement techniques that can more precisely characterize the acoustic properties of fish schools and the variations intrinsic to live subjects in continual motion. To begin to address this deficiency, measurements of the sound speed through collections of live fish were conducted in a laboratory setting. The species chosen for measurement were zebrafish (Danio rerio). The sound speed was investigated using a resonator technique which yielded inferences of the phase speed within the fish school though measurements of the resonances of a one-dimensional waveguide. The waveguide was calibrated to compensate for finite wall impedance and for finite reflections from the ends of the waveguide. Fish densities were investigated ranging from 8.6 to 1.7 fish lengths per mean free path. Measurements agree well with a predictive model that is based on shell-free spherical bubbles, which indicates that the phase speed is not significantly affected by the fish flesh or swimbladder morphology for the species studied. The variation in phase speed due to individual fish motion within the model school was measured to be up to ± 5.6 %. This indicates that precise knowledge of the fish position is required to achieve greater model accuracy. To compliment the phase speed measurements, the attenuation through a cloud of encapsulated bubbles was evaluated through insertion loss measurements. Multiple arrangements of balloons of radius 4.68 cm were used to surround a projector. The insertion loss measurements indicated an amplification of around 10 dB at frequencies below the individual balloon resonance frequency and an insertion loss of around 40 dB above the individual balloon resonance frequency. Analytical modeling of the bubble collection predicted both the amplification and loss effect, but failed to accurately predict the level of amplification and insertion loss. Effective medium models and full scattering models (requiring knowledge of bubble size and position) were evaluated for a model fish school. The two models agree for forward scattering for all frequencies except those immediately around the individual bubble resonance frequency. Back scattered results agree at low frequencies, however as soon as the wavelength becomes smaller than four mean free paths between fish the models diverge. Ramifications of these findings and potential future research directions are discussed. / text

This work presents the fabrication, modeling, and characterization of two first-generation acoustic in-plane pressure gradient sensors. The first is a micromachined piezoelectric microphone. The microphone structure consists of a semi-rigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The rotation of the beam structure is transduced by piezoelectric cantilevers, which deflect when the beam structure rotates. Sensors with both 10 and 20-μm-thick beam structures are presented. An analytical model and multi-mode, multi-port network model utilizing finite-element analysis for parameter extraction are presented and compared to acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multi-mode model. A noise model for the sensor and readout electronics is presented and compared to measurements. The second sensor is a capacitive sensor which is comprised of two vacuum-sealed, pistons coupled to each other by a pivoting beam. The use of a pivoting beam can, in principle, enable high rotational compliance to in-plane small-signal acoustic pressure gradients, while resisting piston collapse against large background atmospheric pressure. A design path towards vacuum-sealed, surface micromachined broadband microphones is a motivation to explore the sensor concept. Fabrication of surface micromachined prototypes is presented, followed by finite element modeling and experimental confirmation of successful vacuum-sealing. Dynamic frequency response measurements are obtained using broadband electrostatic actuation and confirm a first fundamental rocking mode near 250 kHz. Successful reception of airborne ultrasound in air at 130 kHz is also demonstrated, and followed by a discussion of design paths toward improve signal-to-noise ratio beyond that of the initial prototypes presented. A method of localizing sound sources is demonstrated using the piezoelectric sensor. The localization method utilizes the multiple-port nature of the sensor to simultaneously extract the pressure gradient and pressure magnitude components of the incoming acoustic signal. An algorithm for calculating the sound source location from the pressure gradient and pressure magnitude measurement is developed. The method is verified by acoustic measurements performed at 2 kHz. / text

The Salt Silo in Tvøroyri, The Faroe Islands, is set to be turned the largest concert hall in The Faroe Islands. The Salt Silo is a large old silo with wood and concrete walls, and currently acoustics which are not suitable for musical reproduction. The project leaders require the concert hall to be suitable for both classical and rock music, which poses an interesting acoustical challenge. In this paper I will go through which variables should be known and controlled to be able to acoustically analyze and design a concert hall such as The Salt Silo. To not become too large of a project, the paper will focus on the hall's lateral energy fraction and reverberation time. The paper will also look at the Clarity Index parameter (C80) and note how it is affected by the change of reverberation time. The concert hall will be simulated with Odeon auralization software by Brüel &amp; Kjær, and the paper will present the author's suggestion of how the concert hall should be acoustically designed to optimize the values of the reverberation time and lateral energy fraction. The design objective is to create a hall which is suitable for classical music, but where the acoustics can be varied to be able to house modern rock concerts as well. The paper will present a suggestion as to how The Salt Silo should be transformed from an old silo to a modern concert hall which fulfills the criteria which the project leaders have set on reverberation time and lateral energy fraction.

Not available / text

A high conversion efficiency in acousto-optical (AO) modulation can be obtained through careful design of an acousto-optic modulator (AOM), as well as careful selection of the following: the AO crystal material, the orientation in the AO crystal with respect to direction of propagation of the acoustic wave, the piezoelectric transducer material, the orientation of the transducer material, and the AOM fabrication method. A class of AOM's has been introduced wherein the diffraction efficiency of the AOM is improved by augmenting the design of the AOM so as to produce two or more passes of the optical beams through the acoustic beam wherein the Bragg diffraction conditions are satisfied. The effects of changes in acoustic beam direction and optical beam directions of propagation for the multiple-pass configuration are described in this dissertation. An AOM is fabricated in order to test the predicted properties of the class of AOM's incorporating the multiple-pass of optical beams for improving the conversion efficiency in AO modulation. Certain ones of the predicted properties of the multiple pass class of AOM's are confirmed by double pass experimental results for the fabricated AOM.

Noise generated at the trailing edges of airfoils can be an important contributor to the sound levels of aircraft and turbomachinery. Previous work on trailing edge noise has largely neglected the role of the mean boundary-layer profile in the sound generation process. In the present work, a trailing edge scattering problem is formulated using a piecewise-linear symmetric mean flow with a non-zero slip velocity at the centerline, providing a representation that is intermediate between the boundary layer and wake flows. The airfoil is modeled as a zero-thickness, semi-infinite flat plate, appropriate for noise generation by sharp trailing edges in the presence of a high Reynolds number flow. The mean boundary-layer profile adjacent to the airfoil surface supports naturally-occurring vortical disturbances that have a non-trivial pressure field and convect at speeds between the slip and free stream velocities. Using these pressure disturbances to represent the turbulent field that is incident on the trailing edge, a mixed boundary value problem is formulated and solved using the Wiener-Hopf technique. This scattering problem is solved for both low Mach number and O(1) Mach number flows. The results show that the presence of the mean flow profile can significantly increase the amplitude of the sound radiated to the far field. In the O(1) Mach number case, the directivity of the scattered field is also appreciably altered. The results of the scattering problem are used along with a simplified model of the wall pressure wavenumber-frequency spectrum to generate a prediction for the power spectrum of the scattered sound field.