Physical Acoustics Research Articles

Physical acoustics homework problems written by students: Undisciplined, irreverent, and original

“Study hard what interests you the most in the most undisciplined, irreverent and original manner possible” [Perfectly Reasonable Deviations from the Beaten Track, Richard P. Feynman, Basic Books, 2005]. Writing original homework problems is a powerful way students of physical acoustics can practice Feynman’s advice. Three problems that involve a broad range of concepts covered in introductory graduate-level physical acoustics courses illustrate how the student-author unleashed his creativity in an undisciplined manner, injected his problems with an irreverent sense of humor, and derived a great sense of originality and ownership over physical acoustics. The problems synthesize David T. Blackstock’s problems 1D-2, 1E-3, 1G-1, 1G-3, 7-6, 10-10, and 10-11 [Fundamentals of Physical Acoustics, David T. Blackstock, Wiley, 2000], addressing concepts including acoustic intensity, impedance, horns, enclosures, and radiation. [CAG was supported by the ARL:UT Chester M. McKinney Graduate Fellowship in Acoustics.]

Graduate study in physical acoustics at the University of Mississippi

The University of Mississippi is a PhD granting institution with an R1 Carnegie designation placing it among schools with the highest level of research activity. The Department of Physics and Astronomy at the university has a diverse range of research opportunities which includes Physical Acoustics. Our acoustics program is affiliated with the National Center for Physical Acoustics (NCPA). NCPA is an 85,000 square foot standalone facility on the campus of the University of Mississippi solely dedicated to the physics and engineering applications of acoustics. It has research groups dedicated to ultrasound, infrasound, aeroacoustics, atmospheric propagation, porous media, and ocean acoustics. Graduate students in both physics and engineering are pursuing PhD and MS degrees at NCPA, and four faculty members from the physics department have their research laboratories in the facility. In addition to acoustics, our department provides a broad range of research opportunities in other subfields. We have two groups associated with recent Nobel Prizes in Gravitation and High Energy Physics and offer additional programs in Computational Physics and Atmospheric Physics. Our faculty are involved with national and international collaborations including the Laser Interferometer Gravitational Wave Observatory (LIGO), The European Center for Particle Physics (CERN) and Fermilab.

Graduate programs in physical, engineering, and underwater acoustics at the Naval Postgraduate School

The Departments of Physics and of Electrical and Computer Engineering at the Naval Postgraduate School offer graduate programs in acoustics leading to MS and PhD degrees in applied physics and engineering acoustics. Engineering acoustics degrees can be completed in either traditional or distance learning modes. The departments also offer stand-alone academic certificate programs in fundamentals of engineering acoustics, underwater acoustics, and sonar system applications, with a set of three certificates leading to a MS degree in engineering acoustics. MS and PhD programs are interdisciplinary, with courses and laboratory work drawn principally from the fields of physics and electrical engineering. Subjects covered include waves and oscillations; fundamentals of physical and structural acoustics; the generation, propagation, and reception of sound in the ocean; civilian and military applications of sonar systems; and acoustic signal processing. Topics of recent theses and dissertations include development and field testing of novel sensors for atmospheric and ocean acoustics, modeling and measurements of ambient noise and sound propagation in the ocean, sound scattering in underwater waveguides, acoustic vector sensors and vector field properties, acoustic communications, noise interferometry, time reversal in acoustics, geo-acoustic inversion, acoustic remote sensing of the ocean, and acoustics of autonomous underwater and aerial vehicles.

Graduate studies in acoustics and wave physics at Institut d’Acoustique - Graduate School, Le Mans, France

This poster presents the graduate studies in Acoustics at Le Mans (France) offered at the “Institut d’Acoustique - Graduate School”. Graduate studies in Acoustics at Le Mans University have been awarded in 2018 the excellence label “École Universitaire de Recherche” among 28 other reference centers for all fields of Science, through a highly selective national call. Our master and engineering school programs range from physical acoustics, environmental acoustics, acoustics and vibrations to international masters on electro-acoustics and on wave physics. The education through research is carried out at the LAUM, UMR CNRS, one of the largest acoustics laboratory in the world. Several details, objectives, student feedbacks and contact informations on the graduates studies will be given on the poster.

The New Rady Shell at Jacobs Park in San Diego

Located along the waterfront at Jacobs Park, the Rady Shell is the summer home for the San Diego Symphony. The shell opened in summer 2021 as a unique outdoor venue in downtown San Diego. When not used for performances, the lawn is open to the public. Salter provided input on the physical acoustics and technology components within the shell. This presentation focuses on the interior acoustics of the shell. The shell utilizes the first Meyer Sound Constellation system designed for stage acoustics in an outdoor venue. To enhance the experience for the symphony on stage, a mixture of reflective and diffusive panels were used to provide some natural early reflections. During design, the ODEON Room Acoustics software was used to predict the acoustical response on the stage. Above the stage, the shell features a checkerboard pattern of absorptive and reflective panels. At the lawn, Salter worked with L'Acoustics to design a sound system that focused sound on the audience to reduce impact to the neighboring properties.

Graduate acoustics education in the Cockrell School of Engineering at The University of Texas at Austin

While graduate study in acoustics takes place in several colleges and schools at The University of Texas at Austin (UT Austin), including Communication, Fine Arts, Geosciences, and Natural Sciences, this poster focuses on the acoustics program in Engineering. The core of this program resides in the Departments of Mechanical Engineering (ME) and Electrical and Computer Engineering (ECE). Acoustics faculty in each department supervise graduate students in both departments. One undergraduate and nine graduate acoustics courses are taught in ME and ECE. Instructors for these courses include staff at Applied Research Laboratories at UT Austin, where many of the graduate students have research assistantships. The undergraduate course, taught every fall, begins with basic physical acoustics and proceeds to draw examples from different areas of engineering acoustics. Three of the graduate courses are taught every year: a two course sequence on physical acoustics, and a transducers course. The remaining six graduate acoustics courses, taught in alternate years, are on nonlinear acoustics, underwater acoustics, ultrasonics, architectural acoustics, wave phenomena, and acoustic metamaterials. An acoustics seminar is held most Fridays during the long semesters, averaging over ten per semester since 1984. The ME and ECE departments both offer Ph.D. qualifying exams in acoustics.

Broadband core and resonance logger measurements of sound speed and attenuation in the New England mud patch

Extensive measurements of sound speed and attenuation have been performed on sandy sediments over the last few decades, which have motivated a variety of physical sediment acoustics models. Recently, the seabed characterization experiment (SBCEX) was performed in 2015–2017, in part, to quantify the geoacoustic properties of a clayey-silt accumulation, known as the New England Mud Patch (NEMP). Due to the variability and frequency range reported by the various direct measurements and geoacoustic inversions, the sound speed measured in the NEMP lacked any noticeable frequency dependence. In 2022, an additional coring cruise was completed in the NEMP area and included shipboard core and resonance logger (CARL) measurements, expanding upper limit of the band to 1 MHz. CARL measured sound speed and attenuation as a function of depth from 100 kHz to 1 MHz using a time-of-flight technique, and sound speed along the entire core length from 12 kHz to 16 kHz using a resonance technique. Positive dispersion and depth dependance was observed in the 200 kHz to 1 MHz band. The frequency and depth dependence of the CARL measurements will be presented and compared with previously published model fits to the 2015–2017 SBCEX dataset. [Work sponsored by ONR.]

When is a Pepsi® can more than just a beverage container? When it is the inspiration for an acoustics homework problem!

When teaching acoustics to graduate students, some of most effective homework problems require students to compare multiples approaches, combine concepts from related topics, and evaluate numerical answers using experimental data. A problem from David T. Blackstock’s Fundamentals of Physical Acoustics textbook asks students to model an empty beverage can as a Helmholtz resonator, first using the simple formula and the measured dimensions of a real can. Then, students are asked to evaluate whether the simple formula is valid and to provide a more accurate solution if it is not. Most students find an improved impedance approach solution which changes the calculated frequency by approximately 9%. However, most students fail to realize that this problem is exactly analogous to the problem of elastic longitudinal waves in a fixed, mass-loaded bar, with the related first approximation of a simple mass-spring system in which 1/3 of the spring’s mass must be included. Further challenges arise when students attempt to measure the resonance of the empty can and obtain a measured frequency (with damping) that does not match calculated values. The pop-can resonator problem, its analogues, and some experimental challenges will be discussed in detail.

Safety in Cities and Transport through Sound Monitoring

This paper deals with the use of modern technology for security purposes, focusing on the situation in cities (urban noise and shooting) and in transport (passenger rail). The authors aimed to highlight the possibilities and capabilities of installation of technology in the field of applied physical acoustics (sensors, evaluation system with the possibility of setting sensitive sensing filters, end output) and the possibilities of monitoring, including the response of security forces or security measures to the detected danger. In the paper, the authors also include graphical representations of the energy-normalized spectra of the different sound backgrounds and classification classes of acoustic events and types of acoustic events to clarify the differences of the selected monitored events.

Field testing a High-Frequency acoustic attenuation system for measuring fine suspended sediments and algal movements

Acoustic measurements of suspended sediment have the potential to allow remote, autonomous monitoring of sediment movements at much higher temporal resolution than traditional manual sampling methods. Although suspended sands present a challenging measurement problem due to their logarithmic distribution with depth, fine clay sediments are distributed evenly throughout a stream cross section, making them amenable to point measurements. In order to improve measurement capabilities for fine sediments in stream channels, The National Center for Physical Acoustics at The University of Mississippi has developed a remote, autonomous acoustic system to monitor fine sediments transported in streams. The system was tested on the Middle Rio Grande near San Acacia, New Mexico, and in Goodwin Creek in Panola County, Mississippi. The acoustic instruments were compared to sediment concentrations from physical samples in both deployments. Diurnal patterns were found in the acoustic signals from the Middle Rio Grande, and a follow up experiment at The University of Mississippi Biological Field Station was used to investigate the potential effects of algal biomass on acoustic attenuation measurements. The results showed diurnal patterns in attenuation were associated with patterns in light, temperature, and dissolved oxygen. These results combined with information from the literature indicate diel movement of algal colonies in the water column of some water bodies may interfere with high-frequency acoustic measurements in natural environments and that acoustic methods have the potential to allow ecological researchers to evaluate mass algal movements in the field. Results from Goodwin Creek demonstrate that the acoustic system is able to provide measurements of sediment concentration with high temporal resolution that track well with expected sediment transport patterns in response to discharge hydrographs.

Using heat maps in teaching acoustics: Interaction of incident plane wave or incident beam with a solid plane structure.

Using heat maps provides frame and relevance to topics covered in physical acoustics courses as students can more easily visualize complex ideas and situations. Students can also form a much better understanding of the physical phenomena involved and build more advanced critical thinking when heat maps are used. It is the aim of the paper to provide ways for students to interact with heat maps by using two examples: first, the interaction of a plane wave (not only monochromatic) with an interface separating a fluid and a solid medium and, second, the interaction of an acoustic beam with such an interface (including a solid layer). These heat maps permit both to describe non-specular effects for the reflected acoustic beam due to the generation of a modal wave and, in the case of anisotropic media, highlight the difference between the direction predicted by Snell-Descartes law and that predicted by energy flux.

Pitch discrimination is better for synthetic timbre than natural musical instrument timbres despite familiarity.

Pitch discrimination is better for complex tones than pure tones, but how pitch discrimination differs between natural and artificial sounds is not fully understood. This study compared pitch discrimination thresholds for flat-spectrum harmonic complex tones with those for natural sounds played by musical instruments of three different timbres (violin, trumpet, and flute). To investigate whether natural familiarity with sounds of particular timbres affects pitch discrimination thresholds, this study recruited non-musicians and musicians who were trained on one of the three instruments. We found that flautists and trumpeters could discriminate smaller differences in pitch for artificial flat-spectrum tones, despite their unfamiliar timbre, than for sounds played by musical instruments, which are regularly heard in everyday life (particularly by musicians who play those instruments). Furthermore, thresholds were no better for the instrument a musician was trained to play than for other instruments, suggesting that even extensive experience listening to and producing sounds of particular timbres does not reliably improve pitch discrimination thresholds for those timbres. The results show that timbre familiarity provides minimal improvements to auditory acuity, and physical acoustics (e.g., the presence of equal-amplitude harmonics) determine pitch discrimination thresholds more than does experience with natural sounds and timbre-specific training.

Inharmonicity in plucked guitar strings

We have considered the vibration of various types of pinned guitar strings and have investigated the deviation of the partials from integer multiples of the string's fundamental vibration frequency. We measured the inharmonicity parameter B and compared it to a direct calculation based on a model equation. We generally found very good agreement between the two determinations of B for monofilament strings, but perhaps not surprisingly, we find rather poor agreement for wound strings. Furthermore, we show that the methodology used to carry out this experiment can easily serve as the basis for an upper division physics laboratory on physical acoustics including a more thorough investigation of the classical wave equation in a real-world application.

The Soundscapes of the Lower Chuya River Area, Russian Altai: Ethnographic Sources, Indigenous Ontologies and the Archaeoacoustics of Rock Art Sites

The acoustics of the Lower Chuya River area rock art landscape are analyzed through both the exploration of its acoustic properties and the ethnographic information gathered about the region. The results obtained in the acoustics tests undertaken in the area, in particular at the rock art sites of Kalbak-Tash I, Kalbak-Tash II, and Adyr-Kan, are examined. They indicate that the perceived loudness resulting from a natural amplification of sound (strength parameter) and music and speech clarity may have been some of the reasons behind the selection of these locations for rock art production. The ethnographic sources related to the Altai and other Siberian areas are then reviewed as a way of providing an ontological framework for the study of Altaian sonic concepts and behaviors in nature. As the sources indicate, at least for the historical period and presumably earlier, in the prehistoric period, all existing beings are entangled by sound, and they mimic each other in endless ways. We argue that these sites were selected in a non-linear relational ontological framework. It is suggested that the multidisciplinary perspective combining archaeology, physical acoustics, and ethnography has considerable potential for providing a new, richer understanding of rock art landscapes.

Oh, snap! A within-wing sonation in black-tailed trainbearers.

Vertebrates communicate through a wide variety of sounds, but few mechanisms of sound production, besides vocalization, are well understood. During high-speed dives, male trainbearer hummingbirds (Lesbia spp.) produce a repeated series of loud snaps. Hypotheses for these peculiar sounds include the birds employing their elongated tails and/or striking their wings against each other. Each snap to human ears seems like a single acoustic event, but sound recordings revealed that each snap is actually a couplet of impulsive, atonal sounds produced ∼13 ms apart. Analysis of high-speed videos refutes these previous hypotheses, and furthermore suggests that this sonation is produced by a within-wing mechanism - each instance of a sound coincided with a distinctive pair of deep wingbeats (with greater stroke amplitude, measured for one display sequence). Across many displays, we found a tight alignment between a pair of stereotyped deep wingbeats (in contrast to shallower flaps across the rest of the dive) and patterns of snap production, evidencing a 1:1 match between these sonations and stereotyped kinematics. Other birds including owls and poorwills are reported to produce similar sounds, suggesting that this mechanism of sound production could be somewhat common within birds, yet its physical acoustics remain poorly understood.

A Review of Research on the Neurocognition for Timbre Perception

As one of the basic elements in acoustic events, timbre influences the brain collectively with other factors such as pitch and loudness. Research on timbre perception involve interdisciplinary fields, including physical acoustics, auditory psychology, neurocognitive science and music theory, etc. From the perspectives of psychology and physiology, this article summarizes the features and functions of timbre perception as well as their correlation, among which the multi-dimensional scaling modeling methods to define timbre are the focus; the neurocognition and perception of timbre (including sensitivity, adaptability, memory capability, etc.) are outlined; related experiment findings (by using EEG/ERP, fMRI, etc.) on the deeper level of timbre perception in terms of neural cognition are summarized. In the meantime, potential problems in the process of experiments on timbre perception and future possibilities are also discussed. Thought sorting out the existing research contents, methods and findings of timbre perception, this article aims to provide heuristic guidance for researchers in related fields of timbre perception psychology, physiology and neural mechanism. It is believed that the study of timbre perception will be essential in various fields in the future, including neuroaesthetics, psychological intervention, artistic creation, rehabilitation, etc.

МЕТОД СВЧ АКУСТИЧЕСКОГО ИССЛЕДОВАНИЯ МАТЕРИАЛОВ ПОД ВЫСОКИМ ДАВЛЕНИЕМ

The arrangement of a new integrated measuring system (IMS) "HBAR + DAC" and its application to study changes in the acoustic properties of a paper and polycrystalline molybdenum samples under the influence of high pressure are discussed. When creating an IMS for the synthesis of piezoelectric films of aluminum-scandium nitride, the magnetron deposition method was used. The quality and thickness of the films were controlled by X-ray diffraction analysis and atomic force microscopy. For the first time, it is shown that the HBAR in the IMS content has good operational characteristics in the microwave band up to 8.8 GHz under the high-pressure impact on the samples. A decrease in the Q-factor of an HBAR as a sensitive element occurred to values of ~2500 – 3000 at the upper pressure limit, which is quite sufficient for accurate measurements of the resonant frequencies of acoustic overtones. The possibilities of IMS for studying the features in the behavior of solids under the high-pressure impact and the registration of plastic deformations in metals are demonstrated. It is found that the pressure dependence of the relative frequency shift of overtones during compression of a paper sample has a linear character. Thanks to this, the calibration of the high-pressure chamber on diamond anvils was performed using the RAMAN method. It is found that the frequency shift of overtones allows more accurately determining the stresses in the diamond anvil up to 5 GPa. When compressing a sample of polycrystalline molybdenum, the phenomena of plastic deformation and creep, as well as the transit flight of an acoustic wave through the sample, starting from a pressure of 3 GPa, were detected. The results obtained will be useful for researchers, students and postgraduates in the fields of high pressure physics and physical acoustics.

Analysis of GNSS, Hydroacoustic and Optoelectronic Data Integration Methods Used in Hydrography.

The integration of geospatial data in hydrography, performed using different measurement systems, involves combining several study results to provide a comprehensive analysis. Each of the hydroacoustic and optoelectronic systems is characterised by a different spatial reference system and the method for technical implementation of the measurement. Therefore, the integration of hydrographic data requires that problems in selected fields of electronics, geodesy and physics (acoustics and optics) be solved. The aim of this review is to present selected fusion methods applying the data derived from Global Navigation Satellite System (GNSS), Real Time Kinematic (RTK) measurements, hydrographic surveys, a photogrammetric pass using unmanned vehicles and Terrestrial Laser Scanning (TLS) and compare their accuracy. An additional goal is the evalution of data integration methods according to the International Hydrographic Organization (IHO) S-44 standard. The publication is supplemented by implementation examples of the integration of geospatial data in the Geographic Information System (GIS). The methods described indicate the lack of a uniform methodology for data fusion due to differences in both the spatial reference systems and the techniques used. However, the integration of hydroacoustic and optoelectronic data allows for high accuracy geospatial data to be obtained. This is confirmed by the methods cited, in which the accuracy of integrated geospatial data was in the order of several centimetres.

The critical role of Logan Hargrove in establishing the physical acoustics summer school

First established in 1988, the Physical Acoustics Summer School (PASS) was patterned off of a long tradition in European scientific communities of carving out a week or more for established scientists and graduate students to come together in a remote location in order to focus on the state of the science and build community between existing and emerging generations of thought leaders. PASS has convened every two years from that time until a global pandemic disrupted that in 2020. During those early years, Logan Hargrove was an enthusiastic and energetic supporter of physical acoustics research, but had a vision to build a program to support the field beyond funding individual research projects through ONR—he wanted to support a vibrant and long-term physical acoustics community. Logan’s vision is now a well-established reality and still guides the planning and organization of PASS today. In this talk, I will present some of the history of PASS and its evolution over the years with a focus on Logan’s critical role all along the way.

Logan Hargrove’s greatest contribution to the University of Mississippi

We believe that Logan always felt that the people and community of Physical Acoustics were the most important product of his ONR research program. In particular, the PhD students who were able to receive degrees and continue to work in Physical Acoustics after graduation were dear to him. A characteristic of his funding was that he always provided sufficient funds for tuition, salary for the student, summer salary for the PI, and travel to ASA meetings to present the work and to interact with others PI’s and students in Physical Acoustics. We are very thankful for his support and will talk about the students supported by Logan at the University of Mississippi over the last four decades.