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Vocal recognition of individuals versus relative dominance rank among breeding male northern elephant seals (Mirounga angustirostris)

Stephen J. Insley, Marla M. Holt, Brandon Southall, and Elizabeth C. Atwood

POMA Volume 12, pp. 010001 (August 2011); (5 pages)

Online Publication Date: August 03, 2011

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Whether an animal truly recognizes an individual or a simple rule-based category (e.g. neighbor or offspring) has important behavioral and evolutionary implications such as the accuracy of social reciprocity. Many tests of individual recognition have focused on neighboring territorial males ("dear enemy" or "neighbour-stranger" recognition). Unfortunately the static territorial context of these tests, mostly with male songbirds, opens them to the criticism of being merely associative habituation. More dynamic mating assemblages, such as leks where vocally advertising animals encounter numerous others, are a potentially rich and largely untested alternative. The female defense polygyny practiced by male northern elephant seals during terrestrial breeding is such a dynamic system. To examine whether elephant seals were recognizing individuals or dominance categories we conducted a total of 53 playback experiments to 18 males at Año Nuevo State Reserve. Each playback was a series of threat calls assigned to four dominance conditions relative to the subject. Dominance was based on the outcomes of interactions among contesting male dyads. Responses were measured using three assays in situ and from video records of each experiment. Results indicate that males do recognize familiar individuals although responses are primarily based on relative dominance rank.

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43.80.Ka	Sound production by animals: mechanisms, characteristics, populations, biosonar
43.80.Lb	Sound reception by animals: anatomy, physiology, auditory capacities, processing

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Mid-basin deep-water low-frequency ambient noise estimation

William M. Carey and Richard B. Evans

POMA Volume 12, pp. 010002 (January 2012); (25 pages)

Online Publication Date: January 26, 2012

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Estimating the increase in noise due to commercial shipping is of interest because of naval operations and it's environmental consequences to marine life. Recent low-frequency noise calculations (Evans and Carey, Proc. 9 th ICTCA, Univ. Bundeswehr, De) for the mid-Philippine sea illustrate the major uncertainties due to the basin's slope reflectivity, the number density and the source level radiation characteristics of commercial ships. Canonical source level characteristics are based on Naval studies on measurements some three decades ago. In the early seventies, Ross (J.O.E. 30(2), 2005) estimated the rate of increase of noise levels based on an empirical relationship between the radiated source level and tonnage to be order 0.5 dB /year based on the commercial ships of that era. Currently there are as many as seven classes of ships with an order of magnitude increase in tonnage, hull size, drafts and propeller size. A plausible consequence is a radiation characteristic with a different directionality and effective efficiency. Deep ocean calculations are presented illustrating the uncertainties of slope enhancement and shipping noise levels. The current commercial ships are reviewed, qualitative estimates of the radiation characteristics are presented, and ambient noise implications discussed.

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43.30.Bp	Normal mode propagation of sound in water
43.30.Jx	Radiation from objects vibrating under water, acoustic and mechanical impedance
43.30.Nb	Noise in water; generation mechanisms and characteristics of the field
43.30.Qd	Global scale acoustics; ocean basin thermometry, transbasin acoustics

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Speciation and Sounds of Fishes: Dividing up the Bandwidth

Joseph Luczkovich and Mark Sprague

POMA Volume 12, pp. 010003 (May 2012); (11 pages)

Online Publication Date: May 03, 2012

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Fishes in the drum family (Sciaenidae) make sounds to communicate, but they do not make the same sounds. The species-specific calls have different dominant frequencies, are produced in spawning aggregations at different times of the day and season, and there is spatial segregation among the spawning fish populations. We predicted that the pattern of bandwidth use by these species would show low overlap in space, time, and sound frequency. We monitored the seasonal pattern of sound production of Sciaenidae in Pamlico Sound (NC) using autonomous sound recorders that recorded 10 s of sound every 15 min during May-Nov. The observed bandwidth ranges and spawning season for species are weakfish 300-400 Hz in May-Aug, silver perch 800-1500 Hz May-Aug, spotted seatrout 200-400 Hz June-Sep, red drum 100-200 Hz in Sep-Oct. Overlapping calls in these species were rare temporally and spatially, as evidenced by long-term passive acoustic monitoring. Two other species of fishes (oyster toadfish and striped cusk eels), in unrelated families, also compete for acoustic bandwidth in Pamlico Sound, but overlap temporally with the sciaenids. There is low probabilty of signaling confusion for these species but higher probability for Sciaenids. It appears that bandwidth partitioning has evolved in the Sciaenidae.

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43.30.Sf	Acoustical detection of marine life; passive and active
43.80.Ka	Sound production by animals: mechanisms, characteristics, populations, biosonar

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Customized Room Acoustics Simulations Using Scripting Interfaces

Arthur Van der Harten

POMA Volume 12, pp. 015001 (June 2011); (15 pages)

Online Publication Date: June 05, 2011

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Geometrical computer modeling is commonly used in consulting practice to make predictions of room acoustical quality. A large number of new parameters have been created by academicians and acousticians in recent years-so much that it has been difficult for room acoustics simulation providers to include them all. This presentation will demonstrate how customized scripted simulations in Rhinoceros (a CAD program), using Pachyderm (an open source geometrical acoustics simulation engine), can allow the use of new parameters, or parameter simulation types, without reliance on software vendors to release software versions explicitly implementing new code.

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43.55.Br	Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Cs	Stationary response of rooms to noise; spatial statistics of room response; random testing
43.55.Fw	Auditorium and enclosure design
43.55.Ka	Computer simulation of acoustics in enclosures, modeling

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Understanding the perceptual effects of diffuser application in rooms.

Philip Robinson, Ning Xiang, and Jonas Braasch

POMA Volume 12, pp. 015002 (June 2011); (9 pages)

Online Publication Date: June 17, 2011

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Acoustic diffusers have been applied in rooms for echo elimination and reduction of spatial variation, but perceptual effects are not fully understood. At worst, diffusive surfaces have been blamed for tonal distortion and coloration, while other studies have found high correlation between preferred concert halls and diffusive interior surfaces. Evaluating perceptual effects of diffusive surfaces presents several unique challenges. While many geometric acoustic modeling programs incorporate spatial scattering algorithms which produce perceivable differences in auralization results, and may accurately reproduce acoustic parameters of real halls, these differences are not necessarily representative of the perceptual effects of diffuser application in rooms. Accurate investigations of diffusion can be conducted using real or scale model room measurements, but equalization must be performed to isolate the independent effects of scattering and absorption. This paper presents experimental methods to objectively gauge the perceptual effect of scattering surfaces.

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43.55.Br	Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Hy	Subjective effects in room acoustics, speech in rooms
43.55.Ka	Computer simulation of acoustics in enclosures, modeling

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From Portugal to Florida, and the Newman award

Antonio P. Carvalho

POMA Volume 12, pp. 015003 (July 2011); (15 pages)

Online Publication Date: July 10, 2011

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I was 31 years-old when, in 1991, I left the University of Porto to study architectural acoustics at the University of Florida with Professor Gary W. Siebein. In 1994, I finished my Ph.D., I got the Robert Bradford Newman Award, and my career changed. In fact, that 1994 would be the BIG BANG of my future life. Personally, academically, and scientifically, my Universe blew up and began expanding. What I learned and what I taught in the 17 years after that (and what the architectural acoustics changed in Portugal and Southern Europe) is the subject of this paper.

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43.10.Gi	Editorials, Forum
43.55.Fw	Auditorium and enclosure design
43.55.Gx	Studies of existing auditoria and enclosures

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Rating of the loudest college basketball arenas for ESPN magazine

Micah Shepherd, Stephen A. Hambric, Neal D. Evans, Daniel J. Domme, Andrew W. Christian, Bryan P. Cranage, Kieran Poulain, Andrew J. Orr, Andrew R. Barnard, and Michael D. Gardner

POMA Volume 12, pp. 015004 (October 2011); (7 pages)

Online Publication Date: October 07, 2011

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A recent ESPN magazine article ("These go to 11," ESPN Magazine 15 Nov 2010) ranked the top collegiate basketball arenas according to "noise potential." The rankings were established by a team of Penn State Acoustics students using the theory for sound build up in large rooms, since actual measurements were infeasible. Both diffuse field and direct field contributions of the sound pressure were estimated at center court for octave band frequencies from 125 Hz to 4 kHz. Seating geometries, materials and other relevant information were collected for each arena and used with estimated absorption coefficients to determine the room constant. The diffuse field contributions were then combined with approximate sources terms based on the seating capacity of the arena, the proximity of the fans to the court and whether they were students. The sound pressures were then combined into a total A-weighted sound pressure level and used to determine the ranking. The direct and reverberant contributions of each arena were then compared to establish the positive and negative aspects of each arena in terms of noise potential. This comparison reveals how Kansas and Duke reached the top of the ranking, despite having drastically different arena geometry and capacity.

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43.55.Gx

Studies of existing auditoria and enclosures

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Effects of surface scattering and room shape on the correspondence between statistical- and geometrical-acoustics model predictions.

Jason Summers

POMA Volume 12, pp. 015005 (August 2011); (16 pages)

Online Publication Date: August 03, 2011

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Much of room acoustics relies on approximate models of sound. The high-frequency approximation of geometrical acoustics, in which sound is modeled by ensembles of classical phonons, is the basis for many computational modeling techniques. The earliest mathematical model of sound in rooms, given by Sabine's decay equation, is a statistical approximation that assumes homogenous and isotropic (diffuse) sound fields and continuous absorption processes. Sabine's statistical-acoustics model is related to geometrical acoustics as a limiting case for rooms that are ergodic, sufficiently mixing, and weakly absorbing. Various semi-empirical corrections are possible (e.g., Eyring), though a true first-order correction requires additional information. Surface scattering (as characterized by scattering and diffusion coefficients) and room shape are critical in determining the relationship between statistical- and geometrical-acoustics predictions, as these physical attributes determine key statistical properties of phonon trajectories. Here, this relationship is examined theoretically. Limiting conditions are described under which various statistical-acoustics models are valid. Underlying assumptions of Sabine's and Eyring's decay models are detailed. For more general conditions, a series of heuristics are outlined. Based on this discussion, it is shown that statistical acoustics cannot yield an internally consistent formula for relating surface scattering to sound-field diffusivity.

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43.55.Br	Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Cs	Stationary response of rooms to noise; spatial statistics of room response; random testing
43.55.Dt	Sound absorption in enclosures: theory and measurement; use of absorption in offices, commercial and domestic spaces
43.55.Ka	Computer simulation of acoustics in enclosures, modeling

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A Multi-faceted Study of Sound Diffusing Elements in an Auditorium

Arthur Van der Harten, Timothy Gulsrud, Larry Kirkegaard, and Andy Kiel

POMA Volume 12, pp. 015006 (August 2011); (13 pages)

Online Publication Date: August 16, 2011

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Sound diffusing elements are often provided in auditoria as a means of providing diffuse sound reflections intended to improve listening conditions. Some recent consulting experience, however, has revealed that sound diffusing elements can sometimes have unintended consequences that detract from, rather than improve, listening conditions in an auditorium. This paper discusses a specific example from Hamer Hall at the Arts Centre, Melbourne, Australia. The influence of large scale sound diffusing elements along the upper sidewalls and ceiling of this hall has been studied subjectively and objectively through critical listening, in situ measurements, computer modeling, and scale model measurements. We review the results of this multifaceted study, and discuss the delicate balance between positive and negative impacts of sound diffusion in auditoria.

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43.55.Br	Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Gx	Studies of existing auditoria and enclosures

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Efficient acoustic radiance transfer method with time-dependent reflections

Samuel Siltanen, Tapio Lokki, and Lauri Savioja

POMA Volume 12, pp. 015007 (August 2011); (16 pages)

Online Publication Date: August 30, 2011

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Modern desktop computers are equipped with graphics cards that provide massive parallel computation power that was previously available only in supercomputers. On the other hand, there are several room acoustics modeling methods, but only some of them scale well to hundreds or thousands of parallel processors. The scalability of the acoustic radiance transfer method is examined. It is shown that it can almost fully utilize the available computing power. In simple cases, this technique achieves real-time performance. While taking into account the limitations of the energy-based acoustic modeling approach, the presented system can model arbitrary reflections. The directionally-dependent reflections are presented as bi-directional reflectance distribution functions which depend on the incoming and outgoing directions of acoustic energy. It is also possible to add time-dimension to such a reflection model. Some measurements are presented to show that spreading in time dimension occurs at reflections. Most of the previous room acoustic modeling techniques have ignored that phenomenon, but the acoustic radiance transfer technique can be easily modified to take it into account.

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43.20.Dk	Ray acoustics
43.55.Br	Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Ka	Computer simulation of acoustics in enclosures, modeling

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The state of the art in the measurement of acoustical coefficients

Peter D'Antonio and Brian Rife

POMA Volume 12, pp. 015008 (August 2011); (18 pages)

Online Publication Date: August 30, 2011

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For over 100 years, the acoustical industry has measured and characterized sound absorption. And yet, standard measurements of the random incidence absorption coefficient, according to ISO 354 and ASTM C423-09, are still inaccurate and lack reproducibility among labs. Research is underway to improve accuracy by replacing traditional hanging diffusors with boundary mounted diffusors, to allow proper determination of the rev room's surface area and volume, evaluating edge diffraction, replacing Sabine with Eyring, etc. Calibration methods using an absorptive or reflective reference are also being evaluated to improve reproducibility. The field of measuring and characterizing scattered sound is in its infancy by comparison, yet in the past three decades much progress has been made. Two standards have emerged for measuring scattering (ISO 17497-1) and diffusion (ISO-17497-2) and the current state of the art for both will be reviewed. This paper is intended to be a tutorial on the evolution and current state of the art.

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43.55.Br	Room acoustics: theory and experiment; reverberation, normal modes, diffusion, transient and steady-state response
43.55.Ev	Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance
43.55.Nd	Reverberation room design: theory, applications to measurements of sound absorption, transmission loss, sound power

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A homemade Edison tinfoil phonograph

Andrew McNeese, Jason D. Sagers, Richard D. Lenhart, and Preston S. Wilson

POMA Volume 12, pp. 025001 (September 2011); (31 pages)

Online Publication Date: September 15, 2011

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In 1877 Thomas Edison invented the phonograph, a device capable of recording and reproducing sound. The original design used the sound induced vibrations of a stylus to etch a time-locked copy of the acoustic wave onto a rotating, foil-covered cylinder. Playback was made possible by reading the etched signal with a second stylus attached to a transmitting diaphragm. The transparency of Edison's original design makes the phonograph a useful tool to demonstrate and discuss the concepts of acoustic waves and sound-structure interaction. A short history of the invention is given, a homemade version of Edison's original phonograph is presented, and the essence of the sound-structure interaction is explained.

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43.38.Ar

Transducing principles, materials, and structures: general

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Graduate and undergraduate laboratory courses in acoustics and vibration

Aldo A. Glean, John Judge, Joseph F. Vignola, Patrick F. O'Malley, and Teresa J. Ryan

POMA Volume 12, pp. 025002 (March 2012); (9 pages)

Online Publication Date: March 19, 2012

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Two laboratory courses covering acoustics and vibration measurements have recently been developed in the Mechanical Engineering department at the Catholic University of America. The first course, a junior-level dynamics lab, is the first mechanical engineering laboratory course taken by undergraduates. We use acoustics and vibration experiments to illustrate measurement principles broadly applicable to a variety of engineering disciplines. The second course, aimed at first year graduate students, gives a more in-depth coverage of similar topics with an emphasis on automated collection and processing of large data sets. The latter course is intended for students interested in pursuing graduate research in vibration and acoustics, but neither course assumes previous acoustics and vibration background. We describe several of the experiments conducted in these courses and relate them to specific learning objectives.

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43.10.Sv

Education in acoustics, tutorial papers of interest to acoustics educators

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Modeling of frequency responses for arbitrary earphone designs

Yu Du and Weidong Li

POMA Volume 12, pp. 030001 (August 2011); (14 pages)

Online Publication Date: August 16, 2011

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Earphone design process often involves selecting receivers, style and dimensions of sound tubes, and damping used in the tubes. Currently, this is largely a trial-and-error process in the field, especially when multiple drivers are used. The response characteristics of current earphone designs thus heavily rely on designers' experiences. This study is concerned with the development of a modeling approach to aid the earphone design process. During the model development, it is assumed that the earphone response is measured inside an earcoupler (e.g., IEC 60711). Furthermore, it is also assumed that the dynamic characteristics of the selected receiver(s) and the impedance of the terminal earcoupler are known. As a modular approach, each element is modeled as a four-pole network (FPN) using the electrical transmission line theory. All elements are then connected, in series or parallel depending on the actual structure, to form the whole earphone model. With this model, it is convenient to change parameters and predict the response based on the selected structural features, including the sound tubes and damping values, between the receiver(s) and the earcoupler. A design case is provided to illustrate the model application.

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43.38.Si

Telephones, earphones, sound power telephones, and intercommunication systems

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Wood for Guitars

Trevor Gore

POMA Volume 12, pp. 035001 (June 2011); (22 pages)

Online Publication Date: June 24, 2011

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Numerous famous luthiers have used low grade salvaged timber and non-wood products to demonstrate that how a guitar is designed to exploit available materials is more important than using prime tonewoods. The material properties of timber are highly variable and are not the single figures frequently quoted in reference books. Within-species material properties can vary by a factor of two. Consequently, there is significant overlap of the material properties of one species with others, implying that wood species substitution is possible with little acoustical impact if the component is designed and built to acoustical tolerances rather than dimensional tolerances. However, species selection remains a significant factor in designing guitar components, primarily for structural rather than acoustical reasons. The woods chosen have to survive long-term loading without excessive distortion over time whilst still allowing the radiating surfaces to vibrate freely. Important parameters include Young's modulus, density, stability with humidity variation, heat bendability, and hardness. The author considers wood for soundboards, braces, backs, sides, necks, fretboards, and bridges. Guitars designed to acoustical criteria (rather than dimensional criteria) where the effects of different stiffnesses and densities of species are minimised, sound very similar.

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43.75.Gh	Plucked string instruments
43.75.Yy	Instrumentation and measurement methods for musical acoustics

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Evolution of Music Wire and its Impact on the Development of the Piano

N Giordano

POMA Volume 12, pp. 035002 (July 2011); (10 pages)

Online Publication Date: July 05, 2011

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The earliest pianos were strung with brass and iron strings, and the material properties of these strings placed limitations on the design of those instruments. Over time, improvements in technology produced wire with improved tensile strength, which allowed important changes in piano design. This work culminated in the mid-to-late 1800s with the availability of steel music wire, and piano design has changed remarkably little since that time. This paper reviews how improvements in music wire influenced the development of the piano and speculates on how further improvements might (or might not) impact piano design. Our analysis includes spectral data from instruments from several different eras.

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43.75.Bc	Scales, intonation, vibrato, composition
43.75.Cd	Music perception and cognition
43.75.Mn	Pianos and other struck string instruments

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Designing soundboards with flexural disk models

Evan B. Davis

POMA Volume 12, pp. 035003 (January 2012); (13 pages)

Online Publication Date: January 13, 2012

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A flexural disk soundboard and ported box system is developed to explore various structural acoustic design strategies for musical instruments. The flexural disk is used to link structural and acoustic properties of the soundboard. Musical instrument are designed to reproduce a range of frequencies defined by the playing range of their strings. The lowest frequency of the playing range is the note of the lowest open string. The highest commonly played note frequency is taken to be octave above the frequency of the highest open string. The fundamental frequency of the main wood mode of many string musical instruments is tuned to the geometric mean of the playing range. The main air mode is commonly tuned an octave below the main wood mode. The simple flexural disk models with their linked structural acoustic properties demonstrate a solid structural acoustic logic to the empirically developed instruments and why these designs have been so resistant to change by inventive and creative contemporary instrument makers.

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43.40.Dx	Vibrations of membranes and plates
43.75.Gh	Plucked string instruments

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Spectral filtering characteristics of a motorcycle helmet

John Kennedy, Nigel Holt, Michael Carley, and Ian Walker

POMA Volume 12, pp. 040001 (May 2011); (11 pages)

Online Publication Date: May 19, 2011

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Noise transmission characteristics of a motorcycle helmet have been analysed using a combination of insertion loss measurements and loudness matching in a behavioural study. Results demonstrate the action of the motorcycle helmet as a spectral filter. The insertion loss measurements confirm previously published data showing attenuation in the frequency range above 500Hz. A further feature, the significance of which is addressed and highlighted here for the first time, is an amplification of noise below 500Hz. In short, the helmet acts as a frequency dependent filter on the input to the human auditory system. Data from the matching task were used to generate equiloudness curves which show the effect of the helmet on riders' perceptions of loudness. The generated curves were compared to the international standards (ISO226). The character of the equal loudness curves was strongly influenced by the helmet. This difference is discussed in the framework of the filtering characteristics of the helmet.

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43.50.Qp	Effects of noise on man and society
43.66.Cb	Loudness, absolute threshold
43.66.Vt	Hearing protection

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The experimental measurement of motorcycle noise

Michael Carley, John Kennedy, Ian Walker, and Nigel Holt

POMA Volume 12, pp. 040002 (June 2011); (13 pages) | Cited 1 time

Online Publication Date: June 05, 2011

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The noise source mechanisms involved in motorcycling include various aerodynamic sources and engine noise. The problem of noise source identification requires extensive data acquisition of a type and level that have not previously been applied. Data acquisition on track and on road are problematic due to rider safety constraints and the portability of appropriate instrumentation. One way to address this problem is the use of data from wind tunnel tests. The validity of these measurements for noise source identification must first be demonstrated. In order to achieve this extensive wind tunnel tests have been conducted and compared with the results from on-track measurements. Sound pressure levels as a function of speed were compared between on track and wind tunnel tests and were found to be comparable. Spectral conditioning techniques were applied to separate engine and wind tunnel noise from aerodynamic noise and showed that the aerodynamic components were equivalent in both cases. The spectral conditioning of on-track data showed that the contribution of engine noise to the overall noise is a function of speed and is more significant than had previously been thought. These procedures form a basis for accurate experimental measurements of motorcycle noise.

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43.28.Ra	Generation of sound by fluid flow, aerodynamic sound and turbulence
43.50.Lj	Transportation noise sources: air, road, rail, and marine vehicles
43.50.Nm	Aerodynamic and jet noise

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Collecting data on wind turbine sound to identify causes of identified concerns

William Palmer

POMA Volume 12, pp. 040003 (July 2011); (21 pages)

Online Publication Date: July 22, 2011

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Regulations for wind turbines are generally based on A-weighted sound levels, and typical sound spectrums in the community from a localized source. Regulatory limits are based on levels believed to cause little annoyance. Large industrial wind turbines are a sound emitter that present a spatially distributed source principally arising close to the blade tips, rotating 50 to 150 metres overhead so that sound arises from a wide area. They pose a relatively new source of sound to communities, particularly the quiet rural communities where they are mostly located. Community experience shows that the same A-weighted sound limits that are acceptable for typical sound spectrums and localized sources give rise to a considerable level of annoyance from wind turbines. This paper sets out to identify the differences in the sound found at locations considered acceptable by regulators 500-600 m from wind turbines (about one-third of a mile), in spectrum, intensity, duration, and special characteristics, such as tonality or amplitude modulation compared to the sound levels at control sites distant by at least 5000 m (about 3 miles) from wind turbines. An explanation of the data collection method is given, as well as an analysis of extensive sound samples gathered.

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43.50.Qp	Effects of noise on man and society
43.66.Lj	Perceptual effects of sound

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Sound fields inside street canyons with inclined flanking building façades

SK Tang and K. E. Piippo

POMA Volume 12, pp. 040004 (July 2011); (7 pages)

Online Publication Date: July 22, 2011

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Street canyons are common in modern cities. It is well known that the multiple sound reflections within the canyons tend to increase the noise levels inside the canyons. An scaled down model experiment was conducted in the present investigation to study the effect of the inclination of building façade on the sound field. A line source consisted of 100 2-inch aperture loudspeakers were used to simulate the road traffic source. The whole experiment was carried out inside an anechoic chamber. The canyon was 4m long, 2m high and 1m wide (1:4 scale down ratio). The case of a single façade was used acted as the reference. The reverberation inside the model canyon was strong when the two model façades are vertical (inclination 90 deg) and parallel to each other. However, it was found that such reverberation deteriorated very rapidly as the inclination of one of the model façade was reduced to 80 deg. The sound strength inside the model canyon was also reduced. The sound levels at the top region of the canyon decreased more rapidly. It was also found that the effect of the opposite façade was basically unchanged once its inclination was less than 60 deg.

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43.50.Gf	Noise control at source: redesign, application of absorptive materials and reactive elements, mufflers, noise silencers, noise barriers, and attenuators, etc.
43.50.Rq	Environmental noise, measurement, analysis, statistical characteristics

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The effects of windscreen flow on noise in motorcycle helmets

John Kennedy, Michael Carley, Nigel Holt, and Ian Walker

POMA Volume 12, pp. 040005 (September 2011); (13 pages)

Online Publication Date: September 15, 2011

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Vortex shedding from a motorcycle windscreen results in three flow regions in which the rider's helmet may be immersed. First, the helmet may be completely in the free stream. Second, it may be in the path of vortex shedding from the windscreen. Third it may be underneath the shed vortices and shielded from the free stream by the windscreen. On-track noise tests were conducted and showed a difference in sound pressure level of more than 10dB and a change in spectra content, due to changes in riding position and helmet angle. Similar tests carried out in a wind tunnel, using simultaneous microphone and flow visualization measurements, allowed the identification of the flow regions. The potential contribution of vortex shedding to the noise was assessed using wavelet analysis to identify intermittent flow structures.

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43.28.Ra	Generation of sound by fluid flow, aerodynamic sound and turbulence
43.50.Lj	Transportation noise sources: air, road, rail, and marine vehicles
43.50.Nm	Aerodynamic and jet noise

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Separating Anthropogenic and Natural Sounds in a Park Setting

Jack Gillette and Paul Schomer

POMA Volume 12, pp. 040006 (December 2011); (7 pages)

Online Publication Date: December 19, 2011

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The National Park Service needs the ability to determine the extent of both man-made and natural sounds in national parks. To do this, they need to separate anthropogenic noises from natural ones. To be accurate, the measurement of the sound in a park requires hundreds of hours of data spread out over various times of day, days of the week, and seasons, and must be spatially sufficient. With this quantity of data to analyze, manual listening to determine the presence of audible tones and noises can be an almost impossible task. Our assumption is that nearly all anthropogenic noises except for jet aircraft will include tones below 1000 Hz because nearly all have motors, and that nearly all natural sound tones are at frequencies greater than 1000 Hz. Because anthropogenic and natural sounds are uncorrelated, we intend to create software to detect virtually all anthropogenic sounds at the expense of falsely detecting some natural sounds. Furthermore, we can accurately estimate the natural sound's LEQ based on a much smaller sample, and then subtract the LEQ of the natural sound from the total to find the LEQ for the anthropogenic sound. This paper discusses the development and testing of this process.

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43.50.Lj	Transportation noise sources: air, road, rail, and marine vehicles
43.50.Rq	Environmental noise, measurement, analysis, statistical characteristics
43.50.Yw	Instrumentation and techniques for noise measurement and analysis

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Laboratory measurements on gas hydrates and bubbly liquids using active and passive low-frequency acoustic techniques

Chad Greene, Preston S. Wilson, and Richard B. Coffin

POMA Volume 12, pp. 045001 (June 2011); (8 pages) | Cited 1 time

Online Publication Date: June 21, 2011

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The unique molecular structures of gas hydrates result in curious acoustic properties, which have yet to be adequately described. Understanding the acoustic behavior of stable and dissociating gas hydrates in liquids is vital for their localization and quantification using seismic or echosounding techniques. Further, with improved characterization of the acoustic properties of gas hydrates and bubbly liquids containing methane gas, acoustic methods may become an invaluable tool for monitoring hydrate dissociation and determining the magnitude of its effects on climate change. Acoustic properties of gassy substances are known to have a strong dependence on excitation frequency; however, tabulated values of hydrate material properties are most often measured in the frequency range of hundreds of kilohertz, while natural hydrate deposits and gas seeps are typically surveyed at seismic frequencies several orders of magnitude below laboratory measurement frequencies. This presentation details laboratory experiments in which a low-frequency (10 Hz to 10 kHz) acoustic resonator apparatus was used to measure (a) sound speeds of bubbly liquids containing ideal and real gases and (b) bulk moduli and dissociation pressures of natural structure I and structure II gas hydrate samples. [Work supported by the Office of Naval Research.]

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43.58.Dj

Sound velocity

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Experimental investigation of a characteristic shock formation distance in finite-amplitude noise propagation

Michael Muhlestein and Kent Gee

POMA Volume 12, pp. 045002 (June 2011); (8 pages)

Online Publication Date: June 22, 2011

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Unlike initially sinusoidal waveforms, the definition of the "shock formation distance" for noise is complicated by the fact that not all shocks form at the same rate. Examination of the concept of a "characteristic" shock formation distance for noise raises some questions: Is there some generalization of the shock formation distance for sinusoidal signals that can be applied to noise? If so, is it inversely proportional to amplitude and frequency, as the pure tone distance is? In this study, initially sinusoidal, narrowband, and broadband noise data have been acquired using 3.18 mm microphones flush mounted along the walls of an anechoically terminated plane-wave tube. The behavior of the time derivative statistics for the sine-wave tests has been used to guide formulation of a statistical definition of a characteristic shock formation distance for initially Gaussian noise.

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Show PACS

43.25.Cb

Macrosonic propagation, finite amplitude sound; shock waves