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• The Search for Nonlinearity in High-Amplitude Noise from Military Jets

  January 18, 2008 (Friday) - 4:00 pm

  Professor Anthony A. Atchley
  Graduate Program in Acoustics, The Pennsylvania State University
  http://www.acs.psu.edu/
  
  The Navy is confronted with complaints about noise from flight operations in the vicinity of military air bases. The proposed relocation of F/A-18 squadrons from Florida to Virginia in 1997 set off a hailstorm of citizen complaints, public relations campaigns and lawsuits. A key problem is accurate assessment of the impact of the noise. Linear propagation theory has been used to predict aviation noise in communities. However, measurements made during static engine run-up tests of the F/A-18 indicate that the sound pressure level 20 m away from a high performance military jet can approach 150 dB (re 20 uPa). Levels this high warn that nonlinear propagation effects may important. In fact, our nonlinear acoustic propagation calculations based on Burgers' equation showed that nonlinear effects produce important changes in the noise spectrum at community distances. Nevertheless, when we began investigating high-amplitude jet noise in 2002, the idea that nonlinearity plays a role was hard to sell to the aeroacoustics community. Today, through the efforts of several research groups, this idea is reasonably well established and the debate has shifted to how nonlinearity changes the impact and perception of the noise. This presentation reviews the search for nonlinearity in high-amplitude jet noise: why earlier field and laboratory measurements of jet noise missed evidence of nonlinearity, the search for simple metrics that unambiguously indicate the presence and relative importance of nonlinear acoustic effects in jet noise propagation, the impact of nonlinearity on perception, and unanswered questions.

• Challenges in Automotive Audio and Infotainment

  January 25, 2008 (Friday) - 4:00 pm

  Paul Shepherd
  Department of Electrical and Computer Engineering, The University of Texas at Austin
  http://www.ece.utexas.edu/
  
  Branded-audio suppliers are regularly challenged by automotive manufacturers to minimize cost. By creating and using intellectual property to overcome problems inherent with commodity audio systems, branded-audio suppliers are able to acquire new business and maintain profitability. The experience of the speaker as a systems engineer for the Bose Automotive Division is reviewed. Challenges of spatial imaging, component packaging, and user experience are discussed, and intellectual-property solutions proposed by multiple companies are presented.

• Case Studies in Architectures for Noise Identification through Low Cost Microphone Arrays

  February 1, 2008 (Friday) - 4:00 pm

  Kurt Veggeberg
  Business Development Manager, Sound and Vibration
  National Instruments, Austin, Texas
  http://www.ni.com/soundandvibration/
  
  Microphone phased arrays have been used for many years. For the most part, phased arrays have been used as a research tool to gain insight into noise sources and into the physical mechanisms causing the noise. Aeroacoustic testing capability in both anechoic and hard-walled facilities has grown tremendously over the last several years, with successful collection of noise source location and directivity data in a variety of experiments.
  
  With the use of high-speed computers and microphone phased arrays, it is now possible to acquire acoustic data in closed-wall wind tunnels, and this has allowed noise measurements to be made early in the product design cycle. This, in turn, has enhanced the ability to incorporate low-noise designs into new products. Recent studies have compared and validated the use of newer and lower cost microphones in arrays. They are already being deployed in a range of applications such as aeroacoustics measurements in wind tunnels, fly-by tests of aircraft, pass-by tests on trains, consumer goods, and a variety of products.
  
  This presentation will be an overview of how flexible modular instrumentation based on PXI (PCI eXtensions for Instrumentation), employing the latest software technology, is being used in making high precision noise measurements. Examples include systems used by NASA and Boeing to test aircraft noise-reducing technologies and the new Aeroacoustics Research Complex. In these applications, higher sampling rates, higher channel counts, increased dynamic range, and distributed architectures were needed in smaller packages.
  
  

• Techniques for Measuring the Acoustical Properties of Musical Instruments

  February 15, 2008 (Friday) - 4:00 pm

  Alex Mayer
  The University of Music and Performing Arts, Vienna, Austria
  http://www.bias.at/welcome_eng.htm
  
  An important area within the diverse field of musical acoustics is the objective evaluation of musical instruments using basic principles of physical acoustics. For example, broadband measurement of the acoustic input impedance can provide valuable information on more subjective instrument parameters such as intonation, sound quality and playability for brass, string and wind instruments.
  
  This seminar will focus on the Brass Instrument Analysis System (BIAS), a tool developed for musical instrument manufacturers at the Institute for Musical Acoustics in Vienna, Austria to measure broadband input admittance of brass instruments. In order to improve the quality of BIAS with respect to reproducibility, accuracy and measurement range, the properties of the BIAS measurement head must be
  investigated and documented. Some preliminary results and challenges facing this investigation are discussed.

• Development of Acoustical Specification for Hard Disk Drive Clicking Noise

  February 22, 2008 (Friday) - 4:00 pm

  Quoc Nguyen
  Client Acoustical Engineering
  Dell, Inc. Austin Design Center
  Round Rock, Texas
  http://www.dell.com/
  
  Recently Dell has seen a rise in noise complaints tied to HDDs, where the customer feedback indicates objection to a "clicking" sound. Dell therefore wished to develop a specification to capture customer objection to this sound. In this presentation, the Dell acoustical engineering team will demonstrate the process to develop and validate a new DD noise sound quality specification.
  

• Micromachined Optical Diffraction-Based Sound and Vibration Sensors

  March 3, 2008 (Monday) - 10:00 am

  Dr. Neal A. Hall
  Micro-Audio, LLC
  Atlanta, Georgia
  
  This presentation will summarize recent developments with micromachined microphones employing diffraction-based optical displacement detection. The approach has the advantage of providing high-displacement detection resolution of the microphone diaphragm, independent of device size and capacitance, creating an unconstrained mechanical and acoustical design space for the mechanical structure itself. Micromachined microphone structures with 1.5-mm-diameter polysilicon diaphragms and monolithically-integrated diffraction grating electrodes are presented in this work. Their architectures deviate substantially from traditional condenser MEMS microphones. These structures have been designed for a 20 kHz broadband frequency response and low levels of Brownian (i.e., thermal mechanical) noise. The rigorous experimental characterization of these structures to be presented indicates a diaphragm displacement detection resolution of 20 fm/sqrt(Hz) and a thermal-mechanical induced diaphragm displacement noise density of 60 fm/sqrt(Hz), corresponding to an A-weighted sound pressure level detection limit of 24 dB(A) for these structures. Modeling and characterization results lead to the projection of 15 dB(A) noise levels from subsequent prototyping efforts, thus approaching the threshold of hearing. For reference, such performance figures are characteristic of only the highest quality traditionally manufactured microphones available today, and which are roughly 100 times larger in size. The potential commercial impact of the technology will be highlighted with reference to design-win opportunities in the areas of hearing aids, acoustic instrumentation, and some medical device applications. Time permitting, possible future directions and applications in medical ultrasound imaging and scanning probe microscopy will be discussed.

• Human Bioresponse to Whole-Body Vibration Underwater

  March 21, 2008 (Friday) - 4:00 pm

  Sarah Gourlie
  Applied Research Laboratories
  The University of Texas at Austin
  http://www.arlut.utexas.edu
  
  Whole-body vibration of humans has been studied extensively since the 1950s, and now a new application for this work is found in an underwater environment. In this seminar, the response of a swimmer or diver to a low frequency sound field is considered. Although the primary concern associated with the underwater sound field is lung injury due to the acoustic pressure, the sound field also has a particle velocity component. Interest has also been expressed in human bioresponse to the particle velocity, which is the main focus of this seminar. With a frequency range of 40 ? 80 Hz, chosen to encompass measured lung resonances, the acoustic wavelength is long enough ? tens of meters ? that the body of a diver can be approximated as a lumped-element system. A diver who is neutrally buoyant will oscillate with the particle velocity of the sound wave and thus experience whole-body vibration.
  
  The seminar focuses on two methods of understanding the effects of this whole-body vibration. The first involves extrapolation from vibration experiments and health standards for vibration exposure in air to the vibration due to the underwater sound field. While information on whole-body vibration below 40 Hz is abundant, it is scarce at the stated frequencies of interest. The second method uses lumped-element mechanical models of the human body to simulate the biomechanical response to the sound field. A model created by Henning von Gierke in 1971 is examined in detail and used to predict the effects of the sound field on the lung and surrounding organs. Preliminary conclusions from the model show that human bioresponse to the acoustic pressure of the sound field dominates the response due to particle velocity.

• Recording Classical Music as an Exercise in Realistically Capturing an Acoustic Event

  April 4, 2008 (Friday) - 4:00 pm

  John Hadden
  CD Producer and Engineer
  London, England
  http://www.johnhadden.com/
  
  The ultimate goal of a classical music engineer is to record a musical performance as realistically as possible, capturing the very subtle details of sound colors, onset transients and dynamics as well as the reverberation, reflections and diffraction of the sounds within an acoustic space. This seminar will focus on elements which contribute to that goal including equipment choice, microphone techniques, choice of venue, positioning of artists and microphones within the venue, and how these various elements can come together to achieve an artistic or aesthetic goal. Some consideration will be given to aspects of digital recording including sampling rates, bit-length, sample rate conversion and pcm versus dsd.
  
  John Hadden has had more than 20 years experience as a freelance classical recording producer and engineer. His recordings appear on many labels, most notably Sony, Teldec, deutsche harmonia mundi, EMI/Virgin Classics and harmonia mundi usa. His recordings have won many international awards, amongst them the Gramophone Award (England), Edison Award (Netherlands), Cannes Classical Award (France), Echo Klassic prize of the German Phono Academy and Premio Internazionale del Disco Vivaldi Antica (Italy). After earning degrees in physics and computer science he undertook graduate studies in music at Washington University. Dissertation research on the history and playing techniques of early valveless horns took him from the U.S. to London, where he began performing professionally on baroque and classical horns. Gradually his interests shifted from performing to recording, an activity which uniquely draws on his technical and musical knowledge.
  

• Three-Dimensional Geoacoustic Inversion of the New Jersey Shelf

  April 11, 2008 (Friday) - 4:00 pm

  Megan S. Ballard
  Applied Research Laboratory
  The Pennsylvania State University
  http://www.arl.psu.edu/
  
  Perturbative inversion, based on a linearized relationship between sound speed in the sediment and modal eigenvalues, is applied to data from the Shallow Water Experiment 2006. Data were collected by towing a low-frequency sound source out and back along radials, spanning a 90 degree angular sector, from a common receiver location. Range-dependent estimates of horizontal wave numbers are obtained along each of the radials using high-resolution signal processing techniques capable of detecting and localizing changes in sub-bottom properties, and that are particularly sensitive to changes in layer structure. Wave number estimates at each range are used in a linearized inversion algorithm to estimate local sediment properties. Locations of the R-reflector and other layering information are used as a priori information in the inversion algorithm. The additional information both constrains the solution of an otherwise ill-posed problem and emphasizes the layered structure of the sediment. These methods have been shown to yield accurate estimates of the sound speed profile deep into the sediment using very few perturbations to the forward model. By combining the local inversion results, a three-dimensional map of sediment sound speed structure is obtained for a 25 km square region of the seafloor.
  

• A Model of the Interaction of Bubbles and Solid Particles under Acoustic Excitation

  April 25, 2008 (Friday) - 3:00 pm

  Todd A. Hay
  Applied Research Laboratories
  The University of Texas at Austin
  http://www.arlut.utexas.edu/
  
  Ph.D. Dissertation Defense
  
  Dynamical equations of motion are presented for the interaction of clustered spherical bubbles and solid particles suspended in liquid. Both the bubbles and particles are free to pulsate and translate, and bubble coalescence is taken into account according to a set of conservation relations. The initial motivation for this research was the need for better understanding of the interaction of bubble clusters which routinely surround kidney stones during shock wave lithotripsy, an extracorporeal kidney stone disease treatment. The bubbles and particles may be of arbitrary size, the particles elastic or rigid, and external acoustic sources are included to an order consistent with the accuracy of the model. Radiation damping due to finite liquid compressibility is also considered, allowing more accurate modeling of situations involving high-amplitude or high-frequency acoustic excitations, e.g., shock wave lithotripsy or high-intensity focused ultrasound.
  
  Analytic time averages of the model equations predict a number of interesting effects due to the presence of the particle. For example, they show that bubbles will be attracted to particles of higher density than the surrounding liquid but repelled from particles of lower density than the liquid. Plots and movie animations obtained from numerical solution of the model equations are presented to demonstrate the effects of key parameters such as particle density and size, liquid compressibility, and particle elasticity on the dynamics of the system. Results will be shown for the free response as well as the response to sinusoidal and shock wave acoustic excitations.
  

• The Size and Shape of Intracochlear Pressure

  May 15, 2008 (Thursday) - 3:30 pm

  Professor Elizabeth S. Olson
  Department of Biomedical Engineering
  and
  Department of Otolaryngology/Head and Neck Surgery
  Columbia University
  http://www.entcolumbia.org/
  
  Upon sound stimulation, the eardrum and ossicles are set in vibration. The stapes vibration pressurizes the cochlear fluids. Due to the cochlea's geometry and its approximately symmetric division by a flexible cochlear partition (which includes the sensory tissue), the intracochlear pressure can be decomposed into two dominant pressure modes. One of these, the compression mode, fills the cochlea nearly uniformly. The other, traveling-wave mode, is anti-symmetric across the partition. The traveling-wave mode creates the cross-partition pressure difference that leads to sensory hair-cell motion and excitation (and damage, with loud sounds). As far as we know, the compression mode serves no physiological function and is simply a by-product of the piston-like drive of the stapes upon the cochlea. Small intracochlear pressure sensors developed a decade ago have been useful in parsing the two intracochlear pressure modes and for probing the traveling-wave mode where it is largest, close to the cochlear partition. The traveling-wave mode shows many of the same interesting features as cochlear partition motion, in particular frequency tuning and nonlinearity that arises from active hair-cell-based mechanical nonlinearity. In this talk these fundamental characteristics of intracochlear pressure will be reviewed.

• Plasmonic and Metamaterial Cloaking: A Route for Acoustic Cloaks?

  June 11, 2008 (Wednesday) - 10:00 am

  Dr. Andrea Alu
  Department of Electrical and Systems Engineering
  University of Pennsylvania
  http://www.seas.upenn.edu/~andreaal/index.html
  
  The quest for miniaturizing and optimizing the performance of electromagnetic devices for numerous applications (wireless and optical communications, imaging, ...) has fostered in recent years a strong interest in artificial materials, metamaterials and plasmonics, whose exciting and anomalous electromagnetic properties may overcome certain limitations of current technology. One of the most striking properties of these materials is the possibility of drastically reducing the visibility of (electromagnetic scattering from) an object. In this sense, in the last couple of years several venues have been suggested to employ metamaterials for electromagnetic cloaking, one of which, based on the use of plasmonic covers, may have arguable advantages over other competing cloaking techniques. In particular, its inherent simplicity in the cloak design and its robustness to variations in the design parameters and frequency of operation make this technique particularly appealing for several applications.
  
  The extension of these concepts to acoustic waves does not seem to be, at least in principle, particularly challenging from the theoretical point of view. However, technological and material limitations need to be seriously taken into account before any attempt to translate and transplant the electromagnetic cloaking concepts to acoustics.
  
  In this talk, I will provide a general overview of the plasmonic cloaking technique to envision thin efficient electromagnetic cloaks and I will explore the possible venues to introduce similar concepts into acoustics. I will compare these concepts with other recently proposed solutions for acoustic cloaks, analyzing and discussing the feasibility and potentials of these different possibilities from a practical point of view. Several potential applications and physical insights of these cloaks, both in electromagnetics and acoustics, will be envisioned.
  

• Human-Based Percussion Detection and Self-Similarity in Electroacoustic Music

  June 12, 2008 (Thursday) - 10:00 am

  John Anderson Mills III
  Department of Electrical and Computer Engineering
  The University of Texas at Austin
  http://www.ece.utexas.edu/
  
  Ph.D. Dissertation Defense
  
  Electroacoustic music is music that uses electronic technology for the compositional manipulation of sound, and analyzing this music requires special measures. A preliminary tool set to analyze percussivity and percussive self-similarity in electroacoustic music has been designed that incorporates models of the human auditory periphery. A collection of human percussion judgments was undertaken to acquire clearly specified sound-event dimensions that humans use as percussive cues. Participants were asked to make judgments about the percussivity of synthesized snare-drum sounds. The grouped results indicate that rise time is the strongest cue for percussivity of the dimensions tested. Gross spectral filtering also has an effect on the judgment of percussivity, but the effect is weaker than rise time and has less effect when the stronger cue of rise time is modified simultaneously.
  
  A percussivity-profile algorithm (PPA) was designed to identify instants in pieces of music that humans would also identify as percussive. The PPA was implemented using a time-domain, channel-based approach and psychoacoustic models. The input parameters were optimized to maximize performance at matching participants' choices in the percussion judgment collection. The PPA was used to analyze pieces of electroacoustic music, which introduced new challenges. A similarity matrix was combined with the PPA in order to find self-similarity in the percussive sounds of electroacoustic music. This percussive similarity matrix was then used to identify structural characteristics of pieces of electroacoustic music.
  

• Models for Acoustically Driven Bubbles in Channels

  August 8, 2008 (Friday) - 3:00 pm

  Jianying Cui Atkisson
  Department of Mechanical Engineering
  The University of Texas at Austin
  http://www.me.utexas.edu/
  
  Ph.D. Dissertation Defense
  
  A model is developed for the dynamics of an acoustically driven bubble in a channel. The bubble is assumed to be smaller than the transverse dimension of the channel and spherical in shape. The channels considered are infinite in length and formed by either parallel planes or tubes with triangular, rectangular, or hexagonal cross sections. For surfaces that are rigid or pressure release, the boundary conditions on the channel walls in each of these geometries can be satisfied using the method of images. Effects due to confinement by the channel walls are thus determined by an analysis of coupled bubble interactions in line and plane arrays. An existing model for the coupled dynamics of spherical bubbles provides the basis for the model. Liquid compressibility is an essential feature of the model, both in terms of radiation damping and the finite propagation speed of acoustic waves radiated by the bubble. Solutions for the frequency response are obtained analytically by perturbation for low drive amplitudes and weak nonlinearity, and by numerical solution for high drive amplitudes and strong nonlinearity. The response of a bubble between rigid parallel planes is found to be mass controlled, whereas for a rigid tube it is found to be damping controlled. The dynamics of a bubble located near the center of a tube are found to depend on the area but not the specific geometry of the cross section. All of the solutions can be extended to tubes with arbitrary wall impedance if the radiation impedance on the bubble is known, for example calculated by normal mode expansion.

• Laboratory Measurements of the Speed of Sound in Water-Saturated Granular Sediments

  September 5, 2008 (Friday) - 4:00 pm

  Theodore F. Argo IV
  Department of Mechanical Engineering
  and
  Applied Research Laboratories
  The University of Texas at Austin
  http://www.me.utexas.edu/
  
  A better understanding of sound propagation in water-saturated granular sediments is required for improved shallow-water sonar performance and mine detection. For example, no existing first-principles model has accurately described both sound speed and attenuation across the range of frequencies of interest in ocean acoustics and across a range of sediment types. This is partly due to the difficulty of obtaining measurements with sufficient control of measurement uncertainty to reveal the true nature of sound propagation in these materials. To address this deficiency, a suite of laboratory measurements is underway. A resonant column is under development for the frequency range 0.4 to 4 kHz and a time-of-flight technique is being employed in the 10 to 700 kHz range. Preliminary resonant-column sound speed measurements with sorted banking sand will be presented, along with a discussion of the challenges in apparatus design and sample preparation. Time-of-flight measurements on an ensemble of monodisperse 250 um glass spheres that utilized a method for controlling the porosity of the sample will also be discussed. With this method, porosity values of 0.37 to 0.43 were achieved. Measurements with both techniques will be compared to existing model predictions and other similar measurements.

• Theory and Estimation of Acoustic Intensity and Energy Density

  September 12, 2008 (Friday) - 4:00 pm

  Derek C. Thomas
  Department of Physics and Astronomy
  Brigham Young University
  http://www.physics.byu.edu/Research/acoustics
  
  In order to facilitate the acquisition and accurate interpretation of intensity and energy density data in high-amplitude pressure fields, the expressions for intensity and energy density are examined to ascertain the impact of nonlinear processes on the standard expressions. Measurement techniques for estimating acoustic particle velocity are presented. The finite-difference method is developed in an alternate manner and presented along with bias and confidence estimates. Additionally, new methods for estimating the local particle velocity are presented. These methods appear to eliminate the errors and bias associated with the finite-difference technique for certain cases.