bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise characteristics of hot mix asphalt and Portland cement concrete pavements in United States
Authors: Hanson Douglas I.
Published: October 2013

In today’s society, traffic noise is a serious problem that generally is considered an environmental pollution because it lowers the standard of living. Research in Europe and in the United States has indicated that it is possible to build pavement surfaces that will reduce the level of noise generated on roadways. In January of 2002 the National Center for Asphalt Technology initiated a research study with the objective to develop safe, quiet and durable asphalt pavement surfaces. As a part of that study over 300 pavement surfaces [both Portland Cement Concrete (PCCP) and Hot Mix Asphalt (HMA)] throughout the United States have been tested using a close-proximity noise trailer. The study has shown that in general PCCP surfaces have a higher noise level than HMA surfaces. But, it has also shown that by properly choosing the surface texture of the PCCP surface significant reductions in the noise level of a PCCP surface can be achieved. The study has shown that it is possible to construct low-noise HMA mixes and that in general the smaller the nominal maximum size for those mixes (regards whether they are dense graded, SMA or OFGC mixes) the lower the noise level.
Variability of pavement noise benefit by vehicle type
Authors: Rochat Judith L. , Read David R.
Published: October 2013

The Volpe Center Acoustics Facility, in support of the California Department of Transportation (Caltrans), is participating in a long-term study to assess several types of pavement for the purpose of noise abatement. On a four-mile stretch of a two-lane highway in Southern California, several asphalt pavement overlays are being examined. Acoustical, meteorological, and traffic data are collected in each pavement overlay section, where microphones are deployed at multiple distances and heights. Single vehicle pass-by events are recorded primarily for three vehicle types: automobiles, medium trucks, and heavy trucks. Data are analyzed to determine the noise benefit of each pavement as compared to the reference dense-graded asphaltic concrete (DGAC); this includes a modified Statistical Pass-By Index as well as average Lmax values for each vehicle type. In addition, 1/3-octave band data are examined. Automobiles and heavy trucks are the focus of this paper, where benefits due to pavement will be presented for three pavement types: open-graded asphaltic concrete (OGAC) of 75 mm thickness, open-graded asphaltic concrete (OGAC) of 30 mm thickness, and rubberized asphaltic concrete, Type O (open) (RAC) of 30 mm thickness. Average Lmax values and spectral data show that noise benefits due to pavement can vary by vehicle type.
A means to see noise sources
Authors: Kim Yang-Hann , Choi Joung-Woo
Published: October 2013

There are many candidates to visualize noise/sound sources. For example, acoustic holography is one of them. However, to get acoustic holography, we need many microphones and associated data acquisition and processing unit. Especially, when noise is impulsive, the holography system requires two-dimensional microphone array. Depending on the type of noise sources, we have to select the best means that can provide us what we want to have, which can be noise sources’ locations or entire sound distribution in space. This paper addresses various methods that can predict where noise sources are, or how noise is distributed in space. This includes beam forming methods to determine steady or impulsive noise sources, conventional acoustic holography, time domain acoustic holography and moving frame method that can show moving noise sources. We compare these methods and show a guideline that can lead us to select the best means to see noise sources. Various industrial examples are introduced. Time domain acoustic holography of plasma display panel that shows very interesting vibration pattern, beam forming method that depicts short and small noise generated by thermal expansion of a TV set, and moving frame method that shows tire noise are some of the examples.
Beamforming-based partial field decomposition in nearfield acoustical holography
Authors: Hwang Eui Seok , Sun Jong Cheon , Kang Yeon June
Published: October 2013

In this paper, a methodology for partial field decomposition is presented that is based on the beamforming algorithm for the application of acoustical holography to the composite sound field generated by multiple incoherent sound sources. The unique aspect of the method is the use of the estimated sources identified via beamforming as the reference sources in the decomposition procedure. Numerical simulations are performed with particular emphasis on the robustness of the proposed technique under various situations. The experimental results show that the method identifies the sources very effectively regardless of the distance from source to reference and also has potential to be used for application to distributed sources.
Identification of weak spots in the sound insulation of walls using a spherical microphone array
Authors: Gover Bradford N. , Bradley John S.
Published: October 2013

A beamforming microphone array can be useful for the identification of directions of arrival of stronger components of the sound field. When these directions can be traced back to locations in the room containing the array, they can indicate the source of the detected sound. A previously developed spherical array [J. Acoust. Soc. Am. 112, 1980–1991 (2002)] has been used for the identification of localized weak spots in otherwise highly insulating walls. A sound source and the array were placed on opposite sides of a wall sample constructed between two reverberation rooms. The omnidirectional impulse response was measured to each of the 32 array microphones, and subsequent beamforming resulted in 60 directional impulse responses at the array position, distributed over all directions. This set of responses was analyzed to identify directions of peak sound transmission through the wall. The walls tested had STC ratings greater than 50, intentionally modified to contain weak spots or defects, most not severe enough to affect the STC. The results obtained with the array approach were compared to a brute force scan with a microphone located 0.25 m from the wall. The array approach was capable of detecting even minor defects in walls.
Automotive engine air intake system with variable noise control
Authors: Moenssen David J. , Hellie Mark D. , Koston John D. , Shaw Christopher E.
Published: October 2013

Engine air intake systems are routinely tasked with delivering a specific target sound which involves meeting an overall noise level and, in many cases, desired frequency content over the entire engine speed range. In order to meet these targets, it is generally necessary to incorporate one or more reactive tuning devices, such as Helmholtz resonators, into the intake system. Traditional devices provide deep attenuation at their designed frequency, but they also introduce undesirable sideband resonances at a higher and a lower frequency. Even after the addition of several devices, it may still not be possible to match the desired intake noise targets due to their deep attenuation and sideband amplification. The subject of this work is to introduce an electronically controlled variable noise control (VNC) device for engine air intake systems which is capable of adjusting the air intake system’s frequency response as commanded by the engine operating conditions. The VNC device permits the desired amount of attenuation of peaks in the air intake noise without introducing undesirable sideband resonances. In addition, because the tuning is controlled electronically, the VNC device can deliver a target-specific response using the same hardware across multiple vehicle programs.
Application of system engineering processes to analyze and predict engine cooling fan system noise for off-highway machines
Authors: Masini Christopher P. , Mann J. Adin
Published: October 2013

System Engineering processes were applied to create a Cooling Fan System Noise Analysis Tool for a back-hoe loader machine. The Cooling Fan System Noise Analysis Tool combined elements of aeroacoustic theory, Fan Law, sound power measurements and particle image velocimetry into a single computer analysis tool. The cooling fan system consisted of a cooling fan, multiple radiators in front of the cooling fan, a shroud, a mock engine behind the cooling fan, and a simulated engine compartment. A vortex flow structure was measured in front of the cooling fan. The cooling fan system sound power spectrum was measured. The radiated sound power spectrum for the vortex interaction with the fan blades was calculated. Measured and predicted cooling fan system sound power results were compared. The overall structure and approach will be presented along with an overview of the theory and initial results.
Air flow measurement techniques applied to noise reduction of a centrifugal blower
Authors: Laage John W. , Armstrong Ashli J. , Eilers Daniel J. , Olsen Michael G. , Mann J. Adin
Published: October 2013

The air flow in a centrifugal blower was studied using a variety of flow and sound measurement techniques. The flow measurement techniques employed included Particle Image Velocimetry (PIV), pitot tubes, and a five hole spherical probe. PIV was used to measure instantaneous and ensemble-averaged velocity fields over large area of the outlet duct as a function of fan position, allowing for the visualization of the flow as it leave the fan blades and progressed downstream. The results from the flow measurements were reviewed along side the results of the sound measurements with the goal of identifying sources of noise and inefficiencies in flow performance. The radiated sound power was divided into broadband and tone noise and measures of the flow. The changes in the tone and broadband sound were compared to changes in flow quantities such as the turbulent kinetic energy and Reynolds stress. Results for each method will be presented to demonstrate the strengths of each flow measurement technique as well as their limitations. Finally, the role that each played in identifying noise sources is described.
Noise reduction techniques in the design of a pneumatic-driven hand held power tool
Authors: Skinner Christian M.
Published: October 2013

Pneumatic-driven hand-held power tools generate noise in the workplace. Current legislation in Europe and the USA aims at protecting workers against noise exposure. In the United States, the Occupational Safety and Health Administration (OSHA) requires that employers create a hearing conservation program if the noise exposure exceeds 85 dB(A). In the European Community under the Directive 2003/10/EC, employers are required to provide hearing protection if the noise exposure within the working environment exceeds 80 dB(A) and must require hearing protection to be worn if the noise exposure exceeds 85 dB(A). This paper examines the sources of noise which contribute to the overall noise from a hand-held power tool. A test plan was developed to identify these individual sources of noise and to determine if structure-borne noise or airborne noise is the dominant source relative to the overall noise level. The measurements were performed per International Standards Organization (ISO) 15744. This paper will describe the methodology used to identify the noise sources and reduce the overall noise of a hand-held power tool.
Acoustic characterization of pneumatic percussion tools
Authors: Muract Jorge , Kadam Rahul , Burdisso Ricardo , Johnson Marty
Published: October 2013

Pneumatic powered percussion tools are extensively used in construction industry. They are one of the noisiest machines in the construction industry generating noise levels well above 110 dBA which are well beyond the permissible exposure limit (PEL) of 85 dBA. The paper presents comprehensive analysis of the noise generated from these percussion tools. Noise tests were carried out on different percussion tools ranging from small chipping hammers to rock drills from two major construction equipment manufacturing companies. These tests were carried out in an anechoic room as well as in simulated operating conditions to determine the overall sound power levels. A spherical array of microphones was used to obtain an accurate estimate of the overall sound power levels and the directivity. The overall sound power radiation was found to be in the range of 105–115 dBA. An advanced 63 microphone phased array was used to successfully locate and identify the major sources of noise from these tools. The outcome of the tests is illustrated in detail in the paper. Further the paper will suggest noise control methods to reduce overall sound power radiation and discuss potential performance levels.
Sound source identification technique using the inverse boundary element method
Authors: Shi Jiaohua , Martinus Ferdy
Published: October 2013

Numerical acoustic prediction requires the knowledge of the sound source, in most cases in terms of surface vibration data. Traditional approaches to obtain this information are by performing a structural finite-element analysis or by direct measurements. Both of these approaches are time consuming and may not be feasible, particularly when the source dimension is large, the excitation cannot be identified accurately or when due to safety and time concerns, direct measurements are not preferred. In this paper, an advanced source identification technique using the inverse boundary element method is presented. This approach is advantageous since only a small number of sound-pressure measurements are needed and only a boundary element model is required, therefore eliminating the necessity of building a finite-element model. As an example, the reconstruction of surface vibration on a diesel engine is presented. The reconstructed surface vibration was then used to predict the acoustic responses in the field in term of sound-pressure and radiated sound power. It will be shown that the predicted sound-pressure and radiated sound power agrees well with the measured values. The reconstructed surface vibration was also compared to several direct vibration measurements obtained using accelerometers.
Piping noise transmission loss calculations using finite element analysis
Authors: Eberhart Richard , Catron Fred W. , Fagerlund Allen C. , Karczub Denis G. , Mann J. Adin
Published: October 2013

The prediction of noise radiated by piping downstream of a control valve is subject to various uncertainties. One of the significant sources of uncertainty is the pipe-wall transmission loss. Due to the difficulties in experimentally measuring pipe-wall transmission loss accurately, and practical difficulties of taking into account pipe length and boundary conditions, an analytical approach for the calculation of transmission loss is required. The feasibility of uncoupled structural-acoustic finite element based calculations of transmission loss is being investigated for this purpose. By developing the use of finite element based calculations of transmission loss, it is hoped to provide a simple analysis procedure to quantify the effects of pipe length and boundary conditions on the noise level downstream of control valves in practical piping systems. It should also assist in the refinement of analytical/statistical calculations of transmission loss and noise radiation.
Whistler edition
Authors: Gleason Steve
Published: October 2013

In 1995 a sound-reduced version of a large transport refrigeration unit was introduced as one of the quietest options for delivering temperature-sensitive goods to stores and restaurants. It became known as the Whisper Edition. After a couple of years the service department received a few calls about these units whistling. Lab tests found a 5-kHz tone that overwhelmed the 30-hp diesel engine noise. The noise was related to the blower inlet displacement, and a simple modification seemed to resolve the problem. Sporadic reports of whistles resurfaced after a couple more years, and an investigation showed a dimension on the blower inlet needed tighter control. Once those changes were made, recommendations for positioning the blowers in the factory and field solved most problems, and replacing blower inlets addressed the few remaining problems in the field. By now the unit was known in the service department as the Whistler Edition. The problem resurfaced yet again in the factory after a couple more years, and it was there where they recognized a slight tooling ridge on the inlet ring played a role. Subsequent tests showed the ‘‘whistle’’ was actually noise from vibrations in the ring induced by airflow.
Case study of modifications to a wood ‘‘I’’ beam framed floor-ceiling assembly which did not meet minimum International Building Code (IBC) impact insulation class (IIC) or sound transmission class (STC)
Authors: Gernhart Elzo F.
Published: October 2013

A direct comparison, using three identical floor-ceiling assemblies, which did not meet minimum building codes standards for impact insulation class as built. Each floor-ceiling assembly received different corrective measures in an effort to correct the deficiency. All corrective measures were limited to the bottom side of the assembly, since hardwood flooring was installed as the finished floor. All the floor-ceiling assemblies consisted of light weight 16-in. deep ‘‘I’’ beam structural framing members (joist) spaced at 24 in. center to center supporting 3/4 in.-t & g plywood with 1-1/2 in. light weight gypsum concrete covered with 1/2-in. plywood and finished with hardwood flooring. Using tired old industry standard methods, products, and systems the best impact insulation class increase was twelve points which still did not meet minimum building code standards. By installing the state of the art products, using the proper methods available today under the floor-ceiling assembly the field impact insulation class was increased 28 points to a field impact insulation class of 60 without acoustical mat on the top side of the assembly. By design the field sound transmission class was also improved (40 to 55 STC) due to product selection, installations procedures, and design.
Case history: The use of narrow-band frequency analysis to accurately identify multiple, stationary environmental noise sources
Authors: Depies Chris R.
Published: October 2013

The sound quality near an industrial facility is very important in determining community reaction. Often, the sound environment near these facilities is negatively impacted by the presence of low- and mid-frequency tones related to rotating equipment. Complainants often describe the noise as a ‘‘hum’’ or ‘‘whine.’’ A case history will be presented involving a large industrial facility located in the Midwest. The facility reacted to a noise complaint registered by a resident located approximately 0.5 miles from the facility by contracting for an environmental survey to identify the facilities noise emission points and establish a mitigation plan. The use of a FFT Narrowband Sound Analyzer allows the noise control engineer to obtain a detailed sound signature of each potential industrial noise source. The spectrum is then compared with the sound signature measured at the complainant’s location and/or throughout the impacted community to determine the individual noise sources that significantly contribute to the community noise level and quality. The source identification procedure, survey challenges, and related mitigation techniques will be discussed in the paper.
The development of a noise annoyance scale for rating residential noises
Authors: Ryu Jong Kwan , Jeon Jin Yong
Published: October 2013

In this study, 5-point and 7-point verbal noise annoyance scales were developed. The 5-point annoyance scale for outside environmental noise was developed from a survey conducted in four Korean cities. An auditory experiment using residential noises such as airborne, bathroom drainage, and traffic noises was conducted to compare the effectiveness of the 5-point and 7-point scales for rating residential indoor noise. Result showed that the 7-point scale yielded more detailed responses to indoor residential noise. In addition, auditory experiments were conducted to develop a noise annoyance scale for the classification of common residential noises. The modifiers used in the scales were selected according to the method proposed by ICBEN (International Commission on the Biological 12Effect of Noise) Team 6. As a result, the difference between the intensity of 21 modifiers investigated in the survey and the auditory experiment was very small. It was also found that the intensity of the selected modifiers in the 7-point noise annoyance scale was highly correlated with noise levels, and that the intensity difference between each pair of successive levels in the 7-point annoyance scale was almost identical.
Structural-acoustic measurements of pipes with ninety-degree elbows, under water loading
Authors: Doty Benjamin J. , Hambric Stephen A. , Conlon Stephen C. , Fahnline John B.
Published: October 2013

The complicating effects of an elbow, along with internal and external fluid loading on a thick-walled pipe were experimentally examined. The important vibroacoustic behavior of a test structure consisting of a Schedule 40 pipe with a ninety-degree elbow was measured in ARL/Penn State’s reverberant water tank. To characterize coupling between the vibrating structure and the surrounding acoustic fluid, several transfer functions between structural vibration and acoustic radiation were measured using force hammer impulse excitation of the structure as well excitation by an acoustic source. A reciprocal measurement method was validated and used to quantify the sound power radiated by an acoustic source inside the pipe. Results provide a rigorous characterization of the vibroacoustic behavior a test structure with simple geometry and are suitable for validation of analytical and numerical models.
Measuring high frequency valve noise to evaluate interference with ultrasonic flow meters
Authors: Mann J. Adin , Fagerlund Allen , Depenning Charles , Catron Fred
Published: October 2013

Ultrasonic flow meters are installed in lines with particular concern on the location of flow noise sources, such as valves and other geometry changes and restrictions in a piping system. The ultrasonic flow meter operates with a tone burst, typically in the range of 100 to 300 kHz. While this frequency range is far above the typical range for noise control in piping systems, there is good evidence that the flow noise sources generate sound in the operating frequency range of the ultrasonic flow meter. The goal of the work was to establish a procedure to measure the noise generated by piping elements in the frequency range of the ultrasonic flow meter operation. The flow disturbance is placed upstream of the ultrasonic flow meter. The internal noise spectrum are measured at three locations: one upstream of the flow disturbance, one between the flow disturbance and the flow meter, and one downstream of the flow meter. Some available results in the literature will be reviewed along with presenting the experimental setup and preliminary results. The results will show the capabilities of the measurements in this frequency range.
Compact test method for the evaluation of acoustical transmission loss and insertion loss of new helmet material samples
Authors: Maher Matthew G. , Collier Robert D. , Ray Laura E.
Published: October 2013

There is a need to establish a simple and accurate measurement technique for determining the transmission loss of sample materials for helmets over a frequency range of 300–3 kHz. Standard methods, e.g., ASTM E 90-02, for measuring transmission loss of building materials and structures, based on adjacent reverberation chambers, are too costly and impractical. A 1.22-m-long double-wall tube, packed with Owens Corning R13 insulation, has been fabricated using QUIK-TUBETM cardboard concrete forms of 200 and 300 mm diameters. A circular sample of material, also 300 mm in diameter, is placed on the end of the tube and subjected to an external sound field. Transmission loss is established by external and internal microphones. This paper describes the measurement and analysis procedures and examines the associated variables and error terms. Results are presented for 16 material samples with surface weights covering a range from 0.3 to 14.7 kg/m2 and compared with analytical predictions including mass law models. The acoustical characteristics of commercial helmet materials and liners are evaluated in the context of hearing protection systems. The transmission loss measurement procedure has the potential for meeting standardization objectives.
Tone prominence ratio, error sources, and proposed solutions
Authors: Stanley G. (Randy) , DeMoss Jeffrey , Damani Anil
Published: October 2013

Tone prominence ratio is finding increasing use as a tool for product sound design. ECMA-74 Annex D offers a procedure for calculating tone prominence ratio and qualifying tone audibility. However, there are significant potential sources of error when utilizing the ECMA-74 procedure. These include possible misidentification of tone frequency, and ambiguities about what constitutes tone audibility. Misidentification of tone frequency can occur when closely spaced tones exist in the spectrum; whereas, other errors may result from individual subjective assessment of tone audibility. The existing ECMA method does not specify how to identify the primary tone frequency when such ambiguities exist. Real-world examples of potential error sources are presented along with proposed solutions. An unambiguous peak prominence ratio value reporting system is presented along with data to support its improved relevance in terms of hearing perception and subjective annoyance.
Accuracy of the International Space Station acoustical modeling
Authors: Pilkinton Gregory D. , Denham Samuel A.
Published: October 2013

The Space Station Program uses numerous algorithms to simulate on-orbit conditions to define the internal (i.e., habitable) environment of the International Space Station (ISS). Since acoustics has become one of the top ten habitability concerns for the ISS, accurately predicting the acoustic environment that the crewmembers will be exposed to is important. Before each new stage of the ISS, the acoustic predictions are updated. The acoustic environment changes depending on whether hardware is delivered or returned at each stage. If the predictions show that the noise levels are above safety requirements, recommendations are made to the crewmembers to wear hearing protection. For this reason, the predictions of the USL acoustic environment need to be as accurate as possible. This paper details the uncertainty in the predictions of the on-orbit acoustic environment in one module of the ISS, namely, the United States Laboratory (USL).
Uncertainty calculation for noise attenuation measurements of hearing protectors
Authors: Lima Fabiano R. , Gerges Samir N.Y. , Zmijevski Thiago R.L.
Published: October 2013

The objective of this paper is to present a metrology study necessary for accreditation of the Industrial Noise Laboratory (LARI) at The Federal University of Santa Catarina-Brazil for hearing protector noise attenuation procedures using the Real Ear Attenuation at Threshold (REAT) method of the Brazilian National Institute of Metrology Standardization and Industrial Quality-INMETRO. A model for the calculation of measurement uncertainty was developed. The uncertainty calculation was based on the document, ‘‘Guide to expression of uncertainty in measurement,’’ by the International Organization for Standardization, first edition, corrected and reprinted in 1995, Geneva, Switzerland. The uncertainty of each source of error was estimated. The overall uncertainty of the noise attenuation measurement of hearing protectors was calculated for each 1/1 octave band frequency test and the results applied in the single number (NRRSF—noise reduction rating for subject fit) uncertainty calculation. It was concluded that the largest uncertainty is due to the determination of the subject’s hearing thresholds.
De-mystifying the calibration of sound measuring instruments
Authors: Buzduga Mariana
Published: October 2013

Sometimes the users of measuring instruments express expectations for the periodic calibrations that are beyond the purpose of these services. The relationship between measurement uncertainties and traceability is not clearly understood. In addition, some confusion persists about interpreting the calibration results relative to how the instruments meet specifications and the applicable standards. This presentation explains some metrology terms, the extent and limitations of the different types of calibrations of instruments, the relations between uncertainty, tolerances and compliance with standards, and how the calibration data should be used and interpreted. The traceability of the measurements performed with a calibrated instrument will be further discussed. Finally, some aspects about choosing the calibration intervals based on the experience acquired by Scantek, Inc. Calibration Laboratory will be presented.
Opportunities and challenges for novel heat engines in passenger automobiles
Authors: Mozurkewich George
Published: October 2013

Modern automobiles provide several opportunities for potential application of novel heat engines, including air conditioning, waste-heat recovery, auxiliary power units, and motive power. The driving force behind these potential applications is the prospect of reducing the vehicle’s environmental impact by increasing its overall thermal efficiency, decreasing its emissions of greenhouse gases, or both. However, because the automotive sector is mature and highly competitive, any attempt to displace existing technology faces daunting hurdles. Weight and packaging impose tight constraints. Compatibility with existing systems is essential. Reliability must be ensured, often for 150000 miles. Last but not least, cost is paramount in an industry where pennies matter. Some implications of these factors for implementation of thermoacoustic heat engines on passenger vehicles will be surveyed.
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E for thermoacoustic modeling
Authors: Kotsubo Vincent
Published: October 2013

Two of the most extensively used modeling tools in the thermoacoustics community are Sage and DeltaE. These codes are fundamentally different from each other, with Sage using finite differencing and DeltaE using integration of the wave equation. Generally, there is very good agreement between the two codes, with the exceptions being conventional thermoacoustics stacks, where Sage loses accuracy, and low temperatures, where DeltaE does not include real gas properties. The difference between these codes from the user’s perspective comes down to physical viewpoint and features. DeltaE presents an acoustic picture of the system displaying first-order pressure amplitudes and volume flows, whereas Sage presents physical components, mass flows, and pressures. Both codes model mechanical components such as transducers, mass, and springs. Sage has a click-and-drag graphical user interface, which is advantageous in presenting a picture of the system. DeltaE uses a DOS-based interface, which can be cumbersome to a casual user. A particularly powerful feature of Sage is the optimizer, which does a multivariable search to optimize a user-selected parameter. Both codes converge very rapidly.
Development of a thermoacoustic organ
Authors: Stodola Nathan , Tillotson Ben , Bruno Bradford
Published: October 2013

A new musical instrument based on the principles of thermoacoustics has been designed and a prototype has been constructed. The instrument, referred to as the Union Thermoacoustic Organ (UTO), is unique among instruments in several aspects. The UTO creates sound by imposing a temperature difference across a stack of closely spaced channels housed between two heat exchangers in a resonant tube (this arrangement creates a thermoacoustic heat engine). The hot and cold heat exchangers are maintained at temperature by propane flames and liquid nitrogen, respectively. The primary energy source used to create the sound is a flame, so the UTO falls into the broad classification of experimental instruments known as pyrophones. However, unlike previous pyrophones the sound produced by the UTO is easily controlled, so it can play recognizable melodies and even be integrated into ensembles with conventional instruments. The prototype UTO has 14 notes (and hence 14 tubes) which are actuated by means of a mechanical keyboard. The instrument was designed by two senior mechanical engineering students as a capstone design project. The paper describes the principles of operation of this unique instrument, discusses the design and development of the instrument, and gives examples of its musical capabilities.
Harmonic prime movers
Authors: Rice Ian , Smith Gordon
Published: October 2013

Western Kentucky University is undertaking the development of a thermoacoustically powered acoustic agglomerator as a means of pretreating exhaust from coal generators before entering standard industrial electrostatic precipitators. In order to fulfill the design requirement of maintaining a clean, isolated environment for the thermoacoustic components, it will be necessary to operate a thermoacoustic prime mover in a harmonic mode, which normally is not a desirable feature in typical devices. Details of a harmonic-mode prime mover will be presented. [Work supported by KY EPSCoR and the Western Kentucky Office of Sponsored Programs.]
Ultrasonic thermoacoustic cooler
Authors: Kwon Young S. , El-Gendy H. , Symko O. G.
Published: October 2013

The development of a thermoacoustic cooler in the ultrasonic range is presented. This cooler was designed to operate at a drive frequency of 24 kHz using air as the working fluid; the resonator is 7.1 mm long and it contains a cotton wool stack with copper heat exchangers at each end. Since the ultrasonic driver is a key element in this device, a major effort was made to optimize its performance and coupling to the resonator. It is a resonant piezoelectric monomorph loaded with a metallic cone for impedance matching to the resonator. By its design it is capable of intense sound levels, of order 140 dB and higher. The attained cooling power scales with the sound power levels and a COP larger than one is achieved. Studies of heat losses consist of PIV imaging of acoustic streaming (such as Eckart) in this device and back heat flow along the stack. The developed device shows much promise for rapid cooling of small samples. [Work supported by the Office of Naval Research.]
Thermophysical properties, as functions of pressure and temperature, for over 300 fluids, in vapor or liquid phase
Authors: Maynard J. D. , Hilt Matthew G. , Marcus Logan
Published: October 2013

An important undertaking for thermoacoustics, particularly for new concepts involving liquids, multiphases, etc., is the collection of thermophysical properties of fluids. Recently, a computer program was developed which calculates, with a typical accuracy of a few percent, all basic properties of pure fluids and binary mixtures over a full range of temperature, pressure, and concentration (for mixtures). The properties include mass density, specific heat at constant pressure, specific heat ratio, speed of sound, thermal expansion coefficient, viscosity, thermal conductivity, and the liquid–vapor equilibrium pressure. Currently, the program contains the necessary parameters for over 300 fluids, including simple, complex, and polar fluids. A number of parameters are used to calculate properties from reduced PVT surfaces for the various types of fluids; other parameters are used to obtain the liquid–vapor equilibrium line, accurate values on the liquid side of the line, and transport properties. The program is accessed with a web browser interface, so that it may be operated similarly on any computer platform.
The role of modal analysis in stringed instrument design
Authors: French Mark
Published: October 2013

The modal response of stringed instruments clearly contributes to sound quality. Modal analysis was applied to stringed instruments shortly after commercial data acquisition system became available. Even now, the most sophisticated equipment has been used on instruments. In spite of this effort, there is no consensus on the relationship between modal behavior of an instrument and sound quality. Useful guidelines have been developed for the lower modes of guitars and violins, but these are necessary, not sufficient conditions for superior sound quality. It now appears that superior sound quality is based on more subtle interactions of the dynamic response of the acoustically coupled structure and its material properties. Understanding the modal response of the instrument is still extremely useful. The acoustic-structure interaction of the first two or three modes of the instrument clearly demonstrates the basic physics and forms the basis of discrete models that are very helpful in considering the first-order effects of instrument modifications. The modal response of an instrument can also be critical in placing sensors to be used as pickups. Accelerometers are being used to augment piezoelectric bridge pickups and more traditional inductance pickups and their placement greatly affects the resulting sound quality.
A review of multishaker excitation modal testing methods
Authors: Menon Arun , Zhao Weijie
Published: October 2013

Common modal tests employ either impact excitation with a modally tuned hammer or random excitation with a single shaker. While these methods of testing are usually adequate for simple structures, analysis of complex and in many cases nonlinear structures requires more sophisticated test methods. This paper provides a comprehensive overview of test methods less commonly used, but essential for characterizing the dynamic behavior of complex systems and structures made of composite materials. Among the methods discussed are stepped sine, MIMO, MIMO stepped sine, and normal-mode analysis. The paper discusses the suitability of each test method for various circumstances and offers guidance on the application of each method.
A multi-input–multioutput (MIMO) version of the algorithm of mode isolation (AMI) and comparisons with other algorithms
Authors: Allen Matthew S.
Published: October 2013

Experimental modal analysis (EMA) plays an important role in structural acoustic model validation, system diagnosis, and in the design of structural modifications and noise control measures. Recently, EMA has also been used to detect damage in structures and to characterize the elastic properties of complex materials. A multitude of algorithms has been proposed for extracting a system’s modal natural frequencies, damping ratios, and mode shapes from experimentally measured frequency response functions. The overwhelming majority of these algorithms attempts to extract all of the modes simultaneously. The algorithm of mode isolation (AMI) offers a different perspective, sequentially extracting modes in the order of their dominance in the data and then refining the extracted modal parameters through an iterative procedure. This presentation will compare these two approaches using two multi-input–multioutput (MIMO) data sets, typical of many EMA applications. The first data set consists of synthetically generated, noise-contaminated data for a near-square plate, while the second consists of experimentally measured data from the Z24 highway bridge in Switzerland. In each case, the performance of AMI is compared with that of other popular algorithms.
Experimental modal analysis for structural dynamics and vibro-acoustics design engineering
Authors: Van der Auweraer Herman , Peeters Bart
Published: October 2013

System identification plays a crucial role in structural dynamics and vibro-acoustic system optimization. A number of industrially- as well as socially relevant applications will be discussed. The most popular modeling approach is based on the modal analysis concept, leading to an interpretation in terms of visualized eigenmodes. Using the modal models, design improvements can be predicted and the structure optimized. The main modal testing procedures and modal parameter identification methods are reviewed, including both input/output and output-only approaches. The current critical elements in system identification for these applications are outlined and discussed in the broader context of the changing role of testing in the product engineering process. New trends in modal analysis that specifically address these problems are reviewed and illustrated with case studies. This includes the issues of instrumentation, test definition, measurement principles, and parameter estimation.
The influence of modeling assumptions on the modal analysis of vocal fold structures
Authors: Cook Douglas D. , Mongeau Luc
Published: October 2013

Finite-element modal analysis studies of several vocal fold structural models were performed in vacuo under a variety of assumptions. The sensitivity of the vocal folds to changes in geometry and tissue properties was investigated. The Ritz method and the finite-element code adina were used to perform linear modal analysis of two-dimensional and three-dimensional models of the human vocal folds. The results allow for comparison and evaluation of various modeling approaches. In particular, the influence of geometrical constraints was shown to introduce errors of varying magnitude depending on the degree of anisotropy of the vocal fold tissue. [Research supported by the National Institute for Deafness and Other Communication Disorders.]
Thresholds for vowel formant discrimination using a sentence classification task
Authors: Kewley-Port Diane , Oglesbee Eric , Lee Jae Hee
Published: October 2013

Accurate classification of vowels in sentences is challenging because American English has many acoustically similar vowels. Using a 2AFC paradigm, our previous research estimated thresholds for vowel formant discrimination in sentences that were two times smaller than the measured formant distance between close vowels. A new paradigm has been developed to estimate the ability to detect formant differences in a sentence classification task. A seven-token continuum of changes in either F1 or F2 was generated from natural productions of ‘‘bid’’ and ‘‘bed’’ using the synthesizer STRAIGHT. These tokens were spliced into a nine-word sentence at different positions that also contained two other test words, one each from pairs ‘‘cot/cut’’ and ‘‘hack/hawk.’’ Listeners were asked to identify the three words they heard in the sentence. Listeners also identified whether ‘‘bid’’ or ‘‘bed’’ was heard when only the isolated tokens were presented. Thresholds to detect a change from ‘‘bid’’ were obtained from psychometric functions fit to the data. Thresholds were similar for the sentence and word-only tasks. Overall, thresholds in both classification tasks were worse than those from the 2AFC tasks. Results will be discussed in terms of the relation between these discrimination thresholds, vowel identification, and vowel spaces. [Work supported by NIHDCD-02229.]
Speech enhancement based on modified phase-opponency detectors
Authors: Deshmukh Om D. , Espy-Wilson Carol Y.
Published: October 2013

A speech enhancement algorithm based on a neural model was presented by Deshmukh et al., [149th meeting of the Acoustical Society America, 2005]. The algorithm consists of a bank of Modified Phase Opponency (MPO) filter pairs tuned to different center frequencies. This algorithm is able to enhance salient spectral features in speech signals even at low signal-to-noise ratios. However, the algorithm introduces musical noise and sometimes misses a spectral peak that is close in frequency to a stronger spectral peak. Refinement in the design of the MPO filters was recently made that takes advantage of the falling spectrum of the speech signal in sonorant regions. The modified set of filters leads to better separation of the noise and speech signals, and more accurate enhancement of spectral peaks. The improvements also lead to a significant reduction in musical noise. Continuity algorithms based on the properties of speech signals are used to further reduce the musical noise effect. The efficiency of the proposed method in enhancing the speech signal when the level of the background noise is fluctuating will be demonstrated. The performance of the improved speech enhancement method will be compared with various spectral subtraction-based methods. [Work supported by NSF BCS0236707.]
Investigating an optimum suppression rate of steady-state portions of speech that improves intelligibility the most as a pre-processing approach in reverberant environments
Authors: Hodoshima Nao , Arai Takayuki
Published: October 2013

Steady-state suppression has been proposed as a pre-processing approach to improve speech intelligibility in reverberant environments [Arai et al., Acoust. Sci. Technol. 23, 229–232 (2002)]. The goal of this work is to find the suppression rate that improves intelligibility the most. This is done by exploring the relationship between the suppression rates of steady-state portions of speech signals in a reverberant environment and syllable identification. This needs to be investigated because the optimum suppression rate might depend on the amount of overlap-masking, which in turn is determined by the reverberation. A syllable identification test was conducted with 21 normal-hearing listeners in two reverberant environments and six suppression rates. Results show a significant improvement in intelligibility for a 40% and a 50% suppression rate for a reverberation time of 1.1 s and a 60% suppression rate for a reverberation time of 1.3 s. Findings confirm that intelligibility is affected by both suppression rate and reverberation time. Results also show that an optimal suppression rate might not be derived from reverberation time alone. The spectral balance of the room response should also be taken into consideration. [Research supported by JSPS (16203041 and 176911).]
Speech intelligibility criteria for PA system qualification in large aircraft
Authors: Mathur Gopal , Tsangarakis Manolis , Lotts David , Barry Kenneth , Agarwal Naval
Published: October 2013

The military aircraft test and evaluation community uses the Modified Rhyme Test (MRT) test for evaluating speech intelligibility of a communication system in an aircraft. An MRT test is conducted for the flight member/mission areas specified in the MIL/ANSI/ISO specifications. These standards specify that the MRT shall be conducted in a noise field that simulates the actual aircraft noise at the member’s position. Since the method is based on the perception of words by listeners, there are no limitations in respect of the characteristics of the sound system or those of the environment. Modern communication systems, however, incorporate several new electronic designs, e.g., automatic gain control, analog-to-digital (ADC) conversions which can introduce non-linearity in the system. This paper will present results of investigations conducted in a large military aircraft where such features in conjunction with high background noise levels and moving speaker were considered and evaluated. Investigations were focused on ‘‘relative’’ measurements between different system configurations. The MRT was found to be the most reliable method for final verification of PA systems if performed as specified in the ANSI S3.2-1989. Use of an alternative analytical method to measure speech intelligibility as a replacement for MRT will also be discussed.