bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of hearing aids on binaural directional hearing in hearing-impaired individuals
Authors: Gelnett Donna J. , Nilsson Michael J. , Soli Sigfrid D.
Published: October 2005

Binaural directional hearing, the ability of a listener to ‘‘tune out’’ noise from one direction and listen to a signal from another direction, improves speech intelligibility in noise. This ability is present in the hearing-impaired individual, but may be reduced as a result of hearing impairment. The present research examined the relationship between aided and unaided directional hearing, and directional hearing capacity—as measured under headphones with simulated head-related transfer functions and idealized amplification. Reception thresholds for sentences (RTSs) were measured with and without spatial separation of the speech and a spectrally matched noise for 25 hearing-impaired binaural hearing aid users. Directional hearing capacity for these individuals often fell within the normal range. Unaided RTSs were elevated 3–6 dB on average over the capacity measures. Aided RTSs were also elevated 2–3 dB over average scores for directional hearing capacity, suggesting that the interaural cues for binaural directional hearing are either inaudible or absent from the hearing aid output. Detailed analyses will be reported with respect to the type of hearing aid, hearing aid transfer function, and degree of hearing loss.
An introduction to performance enclosure acoustics
Authors: Paoletti Dennis A.
Published: October 2005

This paper will provide an introduction and overview of the acoustical parameters typically established by acoustical consultants in the design of ‘‘enclosures’’ surrounding musicians performing on stage in theaters, concert halls, and multipurpose auditoria. A broad view of enclosure design must include facility design, musical instrument acoustics, engineering, theater consulting, and architectural design. Size, shape, configuration, and materials selection are all important re: the acoustical performance of the enclosure. However, storage for enclosure components, structural considerations (in the engineering design of the enclosure, as well as the engineering of the stage/backstage area that will house the enclosure), and operational and maintenance characteristics must also be considered. As complex as all of these issues are to balance during the design of a performing arts complex, not to mention budget, the success of the enclosure is ultimately in the hands, and ears, of the performing musicians, which leads to further considerations involving psychoacoustics, visual aesthetics, fables, environmental conditions, and even potential conditions surrounding a performance faculty and its performing arts organizations.
Structural intensity of acoustically excited waves in a fluid-loaded elastic plate
Authors: Means Steven L. , Goodman Ralph R.
Published: October 2005

When an acoustic plane wave is incident on a elastic plate, various wave types are excited in the plate for different angles of incidence. The present study determines the structural intensity as a function of incident angle at different depths along the cross section. It is found that for near normal incidence the direction of the intensity parallel to the plane of the plate is opposite the intensity in the fluid and for other angles of incidence. Previously, a similar analysis for a semi-infinite medium by Bunney and Goodman [ 1658–1662 (1973)] did not yield such a result. To gain physical insight into this phenomenon, a study was performed to determine which wave modes are excited at these angles of incidence and to calculate their group velocities.
Ice activities during the AREA 88 experiment. I. A pictorial and video description
Authors: Yang T. C.
Published: October 2005

During the AREA 88 experiment (Spring of 1988), an ice camp was deployed on an ice floe in the general neighborhood of 78 N and 55 W in the central Arctic. The ice floe became active on and off for a period of days. The ice activities were clearly audible in the air (a kind of low-frequency roar). One can unmistakably determine the direction of the noise by stepping outside the tent. Open and refrozen leads were found between the floes. One of them quickly closed up in a matter of minutes swallowing up the geophones just deployed on the refrozen lead. Immediately following this lead closing, the floe next to us started to move laterally at a speed approximately 3 ft/min. During a peak ice activity period, the ice at the edge of our ice floe started to pile up into a form called ice ridges, apparently due to forces between the ice floes which broke the ice and pushed them into a pile of irregular shapes. This ice ridging was recorded on a video tape. Tens to hundreds of blocks of ice of about 5- to 10-ft thickness were also found neatly lying on top of adjacent ice floes, a scene which looked like an act of God.
Acoustic measurements of ice cover variations in the Arctic Ocean
Authors: Artel’nyi Victor V. , Raevsky Mikhail A.
Published: October 2005

Climatic monitoring of the Arctic Ocean implies long-duration observations of the ice cover and water temperature variations by measuring the characteristics of low-frequency acoustical signals traveled along stationary paths. The sensitivity of sounding signal parameters to the variations of the ice cover characteristics is one of the important problems in climatic monitoring. The time structure of the pulse signal in the Arctic waveguide is investigated. The relative influence of the ice cover thickness, density, shear, and compressional sound speeds on the variations of the phase and time delay of the normal modes is studied. It is found that, in the frequency range f≲30 Hz, the variations of the ice cover density and thickness are more efficient than sound-speed variations. Taking the desalination of the subsurface layer into account decreases ice thickness influence. These effects are compared with signal fluctuations in the Arctic Ocean. The fluctuations of the cw signal of the frequency f=20 Hz in the Arctic waveguide are investigated. The internal waves, the submesoscale eddies, and the ice cover drift are considered as signal fluctuations sources. According to the data of numerical simulation, the influence of submesoscale eddies is primary.
Spatial selectivity of differential microphone arrays in rectangular enclosures
Authors: Jan Ea-Ee , Flanagan James L.
Published: October 2005

Omni-directional microphones have been employed in delay-and-sum beamformers to mitigate room reverberation and ambient noise. A one-dimensional beamformer has spatial selectivity in only one dimension. Therefore, higher-dimensional arrays are used to improve spatial selectivity. In comparison, a single differential microphone provides fixed spatial selectivity. This report discusses the performance of arrays of differential microphones. To compute sound behavior in the enclosure, calculation of the incident angle for every arriving signal is required. An image model using the ray-tracing method has been developed to calculate the multipath in an enclosure up to a prescribed order of images. Nonuniform wall reflectivities can be included. For the special case of rectangular enclosures, the algorithm efficiently calculates the incident angle for each arriving signal and all of its associated reflection points. Additionally, it is noted that the number of images for a given order more nearly resembles an arithmetic series instead of a geometric series. [Research supported by NSF Grant No. MIP-9121541 and NSF Subcontract 397-26740.]
An infinite impulse response model for sound travel in a small conference room
Authors: Kovitz Paul S.
Published: October 2005

A new method for predicting an infinite impulse response (IIR) from a source position to a receiver position in a small rectangular room is proposed. The method predicts the IIR for all frequencies below an arbitrary cutoff. The IIR is stated in terms of a z-transform polynomial; the order of the z-transform polynomial follows directly from the room dimensions and the cutoff frequency. The effectiveness of this model is demonstrated from measurements.
An adaptive feedback technique for disturbance rejection: Experimental results
Authors: Miller Daniel H. , Baumann William T.
Published: October 2005

The paper presents experimental results of a hybrid control technique that blends traditional fixed feedback control with adaptive feedback techniques. The objective is to provide damping for transient disturbances via the fixed part of the controller and rejection of steady disturbances via the adaptive part of the controller. This technique differs from the other hybrid techniques in that it does not require a measurement of an external signal coherent with the disturbance, nor does it require knowledge of how the disturbance enters the system. In addition, it provides damping to the system, unlike neutralization-loop techniques. As with all feedback techniques, stability is an issue. The adaptive controller is implemented in such a way as to minimize stability problems and in the case of perfect system identification it is guaranteed to be stable. The experimental results are from a cantilever beam with piezoceramic actuators and sensors. The results for the fixed feedback controller will be compared to those for the adaptive feedback control technique. The comparison will include results from harmonic, narrow-band, and broadband disturbances. [Work supported in part by ONR contract N00014-92-J-1170.]
The impact of sampling location on the minimization of noise in a cavity with flexible walls
Authors: Cunefare Kenneth A. , Biesel Van , Engelstad Steven
Published: October 2005

Many transportation systems, e.g., aircraft and automobiles, have significant interior noise levels. There is substantial interest to reduce such interior noise levels, while minimizing weight penalties. Since the noise field inside such vehicles cannot, in general, be determined analytically, numerical techniques are commonly used to model the structural response of the cavity walls and the accompanying coupling to the interior space. These approaches may then be coupled to an optimization algorithm to determine how the walls should be designed so as to minimize the interior noise. However, a significant feature of such an approach is the need to sample the interior field at a number of points within the volume. This presentation will evaluate how the distribution of the sampling points within a volume may influence the efficiency of an optimization algorithm. The relative merits of sampling points distributed throughout the volume will be compared to points restricted to a layer near the cavity boundaries. The subject cavity will be a simple model of an aircraft fuselage.
Active control of structural intensity in an elastic plate
Authors: Hayek S. I. , Nam M.-Y. , Sommerfeldt S.
Published: October 2005

Active control of structural intensity (SI) in a finite elastic plate coupled to a point damper is achieved through the use of a judiciously located actuator. An algorithm was developed using the magnitude of the structural intensity vector to achieve local or global reduction of SI. The control algorithm showed that controlling each component of the intensity vector (Ix or Iy) generates a parabolic surface, which may or may not intersect the null plane. Under certain conditions based on the locations of the primary mechanical source and the error sensors, as well as the dynamic parameters of the plate, the surface intersects the null plane. If the surface intersects with the null plane, then the intersection generates a circle of possible actuator magnitudes and phases that will make either Ix=0 or Iy=0. If the circles exist for both Ix=0 and Iy=0, then inequalities were derived that will indicate when and if these circles will intersect. The intersection of these circles allows only two possible control solutions that will make the magnitude of the vector SI at the error sensor vanish. When the intersections do not occur, then minimization rather than extinction is achieved. These control strategies are explored and applied to an elastic simply supported plate coupled to a point damper and excited to vibration by a point force. The role of structural damping on control strategies is fully explored.
Correction of errors in Doppler peak velocity measurements made with commercial ultrasound systems
Authors: Winkler Andrew J. , Wu Junru
Published: October 2005

Commercial Duplex ultrasound systems primarily measure peak velocity of blood flow to provide information in diagnosing vascular disease. However, due to errors caused by intrinsic spectral broadening (ISB), the accuracy decreases as Doppler angle increases. In general, vascular technologists keep the Doppler angle under 60°. Since most vessels in the body run almost parallel with the skin surface, any criteria requiring a Doppler angle of say 45° or less would be difficult to achieve. Using the transverse Doppler equation [Newhouse etal., 2091–2098 (1984)] as a correction for ISB, in cojunction with the classical Doppler equation, much more accurate peak velocity measurements were obtained at Doppler angle as high as 80°.
Concentration, fractionation, and separation of small particles in liquid by ultrasound
Authors: Yasuda Kenji , Umemura Shin-ichiro , Takeda Kazuo
Published: October 2005

The efficacy of using an ultrasonic standing plane wave to concentrate small particles in a liquid was theoretically estimated and compared with experimental results. Acoustic energy density was measured by ultrasonic absorption, and particle distribution was observed by darkfield microscopy. The theory predicts that the effect of diffusion is negligible in concentrating polystyrene spheres larger than 5 μm in diameter when they are subjected to 4 J/m3 ultrasound at 500 kHz. The half-width of the steady-state particle distribution in the experiment was of the same order of magnitude as that of the theory. This concentrating technique was applied to the fractionation of polystyrene spheres 10 μm in diameter by using a capillary tube. More than 90% of the particles in a laminar flow were successfully collected. A separation technique based on the competition between the acoustic radiation force and the electrostatic force was also tested. A mixture of polystyrene spheres with two different radii, which lined up on a pressure node of a stationary standing wave, was successfully separated according to their radii by applying a uniform electrostatic force parallel to the acoustic radiation force.
Greenspan acoustic viscometer: Recent results
Authors: Gillis Keith A. , Moldover Michael R. , Mehl James B.
Published: October 2005

Acoustic resonators consisting of a duct coupling two cavities (Greenspan viscometers) have a low-frequency mode whose response is a sensitive function of the viscous diffusivity of the enclosed gas. The response function is determined experimentally by measuring the acoustic pressure in one cavity as a function of the frequency of a source in the other cavity. A theoretical response function, based on a model which includes viscous and thermal boundary layer phenomena in both the duct and the cavities, as well as inertial and resistive duct-end corrections, is fit to the data to determine the viscous diffusivity. Recent measurements in argon, helium, and propane near room temperature span a range of viscous diffusivity from 7×10−7 to 2×10−4 m/s2. Experimental values determined with three different viscometers differ from reference values by average values of 2.7% (viscometer 0), 0.8% (viscometer 1), and 1.8% (viscometer 2). [Work supported by the Office of Naval Research.]
Pitch and pitch strength of iterated rippled noise
Authors: Yost William A. , Guzman Sandra J. , Sheft Stanley
Published: October 2005

A cascade of add, delay (d ms), and attenuate (−1≤g≤1) circuit excited with noise produces iterated rippled noise (IRN) stimuli. The matched pitch and discriminability between pairs of IRN stimuli were studied as a function of g, d, and the number of circuit iterations (n). For g≳0, the pitch of all IRN stimuli equals 1/d. For g<0, pitch depends on n: For small n, there were two pitches in the region of 1/d, while for large n there was a single pitch equal to 1/2d. Peaks in the autocorrelation function of IRN stimuli accounted for all of the results. Peaks in the autocorrelation functions for IRN stimuli indicate the number of intervals in the waveform with durations pd (p=1,2,...,n), and for g<0 intervals related to peaks near 1/md (m=odd integers) caused by assumed auditory filtering. The number of intervals (i.e., the heights of the autocorrelation peaks) determines the discriminability between IRN stimuli, while the reciprocal of the interval duration determines the matched pitch. These results support a temporal rather than a spectral account of the pitch of IRN stimuli. [Work supported by NIH.]
A bridge between place and time. I. The peripheral/central origins of frequency analysis
Authors: Greenberg Steven
Published: October 2005

Auditory theory has traditionally pitted ‘‘place’’ (the tonotopically organized spatial pattern of excitation) versus ‘‘time’’ (the temporal pattern of discharge) with respect to the neural representation underlying specific attributes of acoustic sensation. This long-standing controversy has been of particular significance for models of pitch and frequency analysis, but casts its theoretical shadow over the discipline as a whole. A potential resolution of this historical opposition is proposed, in which place and time are viewed as flip sides of a complex representational matrix of neural activity, bound together through the mechanics of the cochlear traveling wave and its interaction with central loci of coincidence detection and inhibition. Frequency analysis is viewed as possessing two components. One is excitatory, based on spatially circumscribed patterns of temporally coherent peripheral activity and processed by central coincidence-sensitive neural elements. The other involves central inhibitory elements driven by nonsynchronous activity distributed over a broad tonotopic domain. Together, these two components can account for the preservation of frequency selectivity across a wide range of frequencies and sound-pressure levels, despite dramatic changes in the average-rate-based profile of neural activity.
Detection of sinusoidal amplitude modulation having unexpected rates
Authors: Wright Beverly A. , Dai Huanping
Published: October 2005

The detectability of sinusoidal amplitude modulation having unexpected rates was assessed using a probe-signal method. With this method, three listeners were led to expect a target modulation rate (4, 32, or 256 Hz) by presenting the signal most often at that rate, and sensitivity to modulation at six other unexpected rates between 4 and 256 Hz was measured via occasionally presented probe modulation rates. The modulation phase was random on each 2IFC trial and the overall level of the 500-ms wideband carrier was randomly varied between 55 and 75 dB SPL across intervals. The modulation depth at each rate was set so that the modulation was detected on about 90% of the trials when only that rate was presented. Performance at the unexpected rates depended upon the target rate. For the 4-Hz target, modulation at all rates was detected on about 80% of the trials. For the 32- and 256-Hz targets, unexpected modulation rates of 16 Hz and above were detected on 80%–90% of the trials, but modulation rates below 16 Hz were detected nearly at chance. Thus, contrary to the predictions of several popular models, the ability to detect modulation was clearly influenced by expectation of the modulation rate. [Work supported by NIH.]
The effect of temporal placement on gap detectability
Authors: Snell Karen B. , Hu Hue-Lu
Published: October 2005

The detectability of a masked sinusoid increases as its onset approaches the temporal center of a masker. This study was designed to determine whether a similar change in detectability would occur for a silent gap as its onset was parametrically displaced from the onset of a noise burst. Gap thresholds were obtained for four subjects. Signals were 150-ms, 6-kHz low-passed noise bursts presented at an overall level of 75 dB SPL. A 10-ms cosine-squared envelope shaped the onset and offset of the noise burst. Gaps were shaped by a 1-ms cosine-squared envelope. Gaps onsets were displaced by 0, 1, 3, 5, 10, 30, 50, 100, 110, and 120 ms. The displacement was measured from the first point of full amplitude following the 10-ms shaped onset. Gap thresholds were determined in a 3IFC procedure using 75-trial runs. Subjects completed five replications without prior practice. The mean gap threshold was largest for the noise burst closest to signal onset (5.67 ms) and smallest for the gap offset by 60 ms from the signal onset (2.01 ms). For all subjects, gap thresholds decreased as the gap approached the noise burst center.
Shared attention in detection and identification
Authors: Hafter Ervin R. , Bonnel Anne-Marie
Published: October 2005

Brief, incremental [S(+)] or decremental [S(−)] signals were added to an ongoing pedestal. For detection, correct responses were either ‘‘yes’’ to both S(+) and S(−) or ‘‘no’’ to nonsignal trials. For identification, a signal was presented on every trial and responses were either ‘‘S(+)’’ or ‘‘S(−).’’ Subjects monitored either a single channel or, in the ‘‘dual task,’’ two simultaneous channels with independent stimuli. Expanding on previous work with two visual stimuli, here there were one visual stimulus (on a CRT) and one auditory (pure tone). As before, dual-task performance in detection was better than in identification. In addition, detection was as good on each of two channels as on one alone, indicating parallel processing, but identification declined, suggesting shared attention. Testing the idea that pedestal-to-signal transients account for these differences, pedestals were turned off before and after the signal intervals, removing transients as sources of information. This did not affect identification, but detection was now worse than identification and declined in the dual task, suggestive of shared attention.
Auditory detection of changes in mass density and elasticity of a tuning fork
Authors: Lutfi Robert A. , Oh Eunmi
Published: October 2005

The principles of theoretical acoustics were applied to reconstruct the sound-pressure waveform at the ear as would be generated by an idealized tuning fork (struck, clamped bar). The result is an inharmonic sum of damped sinusoids whose individual acoustic parameters (frequency, intensity, and decay modulus) are determined by the mass density and elasticity of the material comprising the bar. In the standard 2IFC procedure, listeners were asked, in effect, to detect changes in the material composition of the bar based on their perception of the acoustic waveform. Listener strategies for detecting such changes were estimated by perturbing slightly the individual acoustic parameters from trial to trial and computing correlations with the listener’s response [cf. R. A. Lutfi and E. Oh, 2963(A) (1994)]. In general, the correlations revealed that listeners fail to make optimal use of the information in the acoustic waveform by tending to give undue weight, for a given material change, on one or more parameters of the acoustic waveform. The results are discussed in terms of their implications for ecological notions regarding the perception of ‘‘higher-order’’ variables in the determination of natural resonant sources. [Research supported by NIDCD.]
Advances in noise control for products other than aircraft
Authors: Lang William W.
Published: October 2005

How much progress has been made in advancing the technology of noise control over the past quarter century? Different techniques of quieting have been applied to the many products that are grouped in the following broad categories: stationary noise sources, moving noise sources (other than aircraft), and specialized industrial machinery and equipment. For all products, the control of noise by engineering design is the goal. To arrive at estimates of progress, two subsidiary questions must be addressed. How is progress to be measured in quantitative terms? Recognizing that trade secrets and patented innovations may be involved, how is it possible to learn what progress has been made for the different classes of products? A key factor is that changes in functional technology may reduce the noise emissions as a desirable by-product; for example, ink-jet and laser printers are much quieter than impact printers. The estimates of progress in product quieting in terms of the reductions of A-weighted sound power levels range from 0 dB for leafblowers up to 50 dB for devices which 25 years ago required cooling fans for their safe and efficient operation, but today require none.
Federal regulations and government activities in noise control
Authors: Miller R. L.
Published: October 2005

Since the demise of the EPA’s Office of Noise Abatement and Control at the hands of former President Reagan, coordinated regulatory action for the control of noise at the Federal level has essentially disappeared. Instead, governmental agencies are left to deal with their noise problems on their own, usually meaning that they respond only to specific legislation, political pressures, or litigation. Agency coordination, when it does occur, is imposed by Executive Order or law. This paper briefly reviews existing Federal regulations controlling the world of transportation noise, but focuses to a greater extent on the on-going efforts of our government that will influence our noise environment into the next century. The paper summarizes the actions of the Federal Aviation Administration, the National Aeronautics and Space Administration, and the Department of Defense as they confront issues of aircraft noise and airspace management; the National Park Service as it struggles to resolve conflicting mandates to preserve natural quiet and solitude while providing access to and public enjoyment of National Parks and Forests; the Federal Railroad Administration and the Federal Transit Administration in their endeavors to control noise from transit, high-speed rail, and mag-lev systems; and the Federal Highway Administration as it develops better tools to assess and control the noise impact of traffic. The paper concludes, speculating on the effects that reduced Federal spending will have on these efforts.
A global vision for the noise control marketplace
Authors: Brooks Bennett M. , DuBois T. James , Hoover Robert M. , Maling George C. , Sutherland Louis C.
Published: October 2005

Much progress has been made over the past 25 years in the United States to define the dangers of excessive noise exposure, and to develop the means to control it. A significant portion of this progress was stimulated by government actions, to regulate the industries which produce noise, establish community and workplace noise standards, and to promote research and development in noise control. Today, the pressures of competition in the global marketplace, which did not exist 25 years ago, are rapidly increasing the motivation for noise control in the private sector. Those industries which seek to sell their products worldwide, particularly in Europe or Japan, find that they must meet stricter standards than now exist in the U.S. Further, foreign companies which already live with stricter standards are producing quiet products that compete for sales in the U.S. These challenges present both a threat and an opportunity to the U.S. economy. Several actions which can be immediately taken to address these issues are suggested.
Toward an overall computational scheme embodying the modern acoustical measures and correlation of the scheme with the categories of acoustical quality of concert halls as determined from the questionnaire and interview method
Authors: Beranek Leo L.
Published: October 2005

An overall computational scheme for estimating from modern acoustical measurements the acoustical quality of concert halls is explored in this study. The method showing promise is based on Ando [ConcertHallAcoustics (Springer-Verlag, Berlin, 1985)]. Identified are the most important acoustical attributes to the rating scheme: RT, G, ITDG, IACC(E), and BR. Preferred values for each of these acoustical attributes is estimated from the results presented in a companion paper [Beranek, ‘‘Correlations between categories of acoustical quality and modern physical quantities’’]. Formulas are borrowed from the Ando study and constants are chosen that express the relative importance, and the degree of falloff in contribution to quality with deviations from optimum, of each of these acoustical attributes. By process of adjustment of the constants, the best fit between the measured physical quantities and the subjective determination of acoustical quality of concert halls is determined. Excellent correlation between the final result and the rank-orderings is obtained. It must be emphasized, however, that other factors are important in concert hall design which are not included in this rating scheme, for example, the degree to which musicians can hear each other and hear themselves on stage and balance among the sections of an orchestra. There may be other unknown acoustical factors that contribute to acoustical quality.
Audibility of individual reflections in a complete sound field. II
Authors: Bech So/ren
Published: October 2005

This is a continuation of paper I, presented at the Wallace Clement Sabine Centennial Symposium in Boston 1994. The threshold of detection (TD) and just noticeable difference (jnd) for an increase in level was measured for six individual reflections in a complete sound field. The subjects were instructed to use changes in timbre as the criteria for detection. The sound produced by a single loudspeaker in a normal size listening room was simulated using an electroacoustic setup. The simulated loudspeaker had directivity characteristics according to the measured characteristics of a real loudspeaker and the room surfaces had frequency-dependent absorption characteristics according to measurements. Values of TD and jnd were measured using four subjects for noise and speech. The results confirmed that the first-order floor reflection contributes individually to the timbre of the sound field. The results have further shown that energy in the frequency range 500–2 kHz is important for the TD level. The noise and speech stimuli have been found to result in significantly different TD and jnd values for all reflections, and is contrary to the previous reported results. [Work financed by Eureka project EU105.]
A preliminary analysis of image shifting in concert halls
Authors: Soulodre Gilbert A.
Published: October 2005

Under typical conditions, the early reflections in a concert hall are attenuated relative to the direct sound and are thus integrated with the direct sound. However, there are instances where, due to focusing effects, the level of a reflection can be greater than or equal to the level of the direct sound. This can result in an apparent shifting of the image away from the true source and toward the source of the reflection. This paper reports on a series of subjective tests designed to provide an initial look at the parameters of the reflected sound which influence image shifting. Tests were conducted using two methods: binaural simulation and multiple loudspeakers in an anechoic chamber. Image shifting was examined as a function of the level, delay, angle of arrival, and spectral content of the reflected sound relative to the direct sound. The results were examined in the context of the Orpheum Theatre in Vancouver where pronounced image shifting occurs at certain locations in the hall due to several large concave surfaces in the ceiling.
Electromagnetic compatibility standards for acoustical instruments
Authors: Kuemmel Ted
Published: October 2005

There is an increasing awareness of the problems caused by interference from electromagnetic fields on electronic devices. The rapid expansion of the use of personal radio communication devices suggests a growing problem. The sophisticated electronic technology now commonly used in acoustical instruments is more susceptible to electromagnetic interference than previous technologies. In 1991, the ANSI Committee S1, Acoustics, formed working group 21 to develop a new standard to address the radio frequency electromagnetic susceptibility of acoustical instrumentation. Now in its eighth draft, the standard provides general specifications for the characteristics of acoustical instruments when used in the presence of radiated electromagnetic fields. The standard provides limits on allowable deviation from specified acoustical performance based on the accuracy class of the instrument. The standard also presents minimum testing requirements and sample test methods to demonstrate conformance to the specifications. Internationally, the IEC Technical Committee 29, Electroacoustics, is also working on this problem. The current status of these efforts and the issues driving them are presented and compared.
Electromagnetic susceptibility of sound level meters
Authors: Finke Hans-O.
Published: October 2005

Tests of electromagnetic susceptibility (EMS) are part of the type of approval procedure for sound level meters in the field of legal metrology. Starting in January 1996 every electronic device on the European market has to have a label that indicates a certification of the device, which also includes requirements on electromagnetic susceptibility. The EMS test of sound level meters at the Physikalisch-Technische Bundesanstalt (PTB) are performed in a radio frequency anechoic chamber. The electric field strength is 6 V/m, the frequency range is 26–1000 MHz. The frequency is varied in steps of 4% and the signal is modulated with 1000 Hz (m=80%). An acoustical signal is applied to the sound level meter and the difference of the displayed levels with and without the electromagnetic field has to be within specified tolerances (0.5 to 2 dB). At the moment not all types of sound level meters comply with these tolerances; with instruments under test deviations up to 18 dB had been observed. The present test procedure will be improved for future regulations and standards (higher strength of field, wider frequency range, influence of accessories). Methods and results will be reported.
Electromagnetic susceptibility of audiometers
Authors: Richter Utz
Published: October 2005

As early as 1991 the Physikalisch-Technische Bundesanstalt (PTB) in Germany decided that tests of electromagnetic susceptibility have to be performed, in general, with all measuring instruments submitted to PTB for pattern evaluation, among them also pure-tone and speech audiometers. A large shielded room is available where electromagnetic fields (10 V/m, 10–935 MHz, 1-kHz tone AM modulation) can be generated. No suitable test method and no limits were found in any known standard for audiometers including IEC 645-1, and no available acoustic measuring equipment did pass the EMC test by itself. So a new test method had to be developed based on loudness balance tests between the 1-kHz-interference tone caused by the electromagnetic field and the ordinary 1-kHz test tone of the audiometer. The tests are performed in the shielded room at fixed carrier frequencies. Taking into account the uncertainty of this subjective test method, an upper limit of 60 dB HL for the interference level was established. Of the first 25 types tested, 92% audiometers did fail the EM susceptibility test in the first run. All of them passed the test after reconstruction.
New requirement for electromagnetic compatibility of acoustical instrumentation
Authors: Schonthal Ernst , Larsen Helge
Published: October 2005

Most electronic equipment is sensitive to electromagnetic signals. Often electronic equipment also radiates electromagnetic signals causing in- terference to other electronic equipment. To insure that the electrical equipment can work without influence from the electromagnetic environment and also can operate without disturbing the environment, all electric equipment including acoustical measuring instruments sold within the European Community must fulfill the requirements per EU50082-1 and -2, starting 1 January 1996. To achieve this goal a new special test laboratory has been established at Bruel & Kjaer in Denmark. Here, all existing and new measuring instrumentation are tested for conformance to EU50082-1 and -2. The results have shown that a number of the existent instrumentation will have to be modified or redesigned. The new Bruel & Kjaer FalconTM range of measuring microphones, preamplifiers, and power supplies has been designed in accordance with the new requirements of EU50082-1 and -2. This paper will describe measurement results and give examples of experience gained through this work.
Noise environments outdoors and the effects of community exposure
Authors: Shaw Edgar A. G.
Published: October 2005

Man-made noise, especially transportation noise, creates acoustical environments that are vastly different from those associated with pristine habitats. During the past 25 years, the day–night average sound level, Ldn, has gained substantial acceptance as a valid measure of the magnitude of any given pattern of community noise, taking into account its complex temporal and spectral characteristics. During the same period, the effects of various levels of noise exposure on human activities and well-being have been widely studied. Data from many social surveys have been brought together and analyzed to clarify the relationship between noise level and the prevalence of annoyance which provides a broad indication of the impact of intrusive noise on human communities. Criteria based on such studies are now widely used in urban planning. In recent years, there have been impressive reductions in the noise emissions from commercial aircraft and notable improvements in the control of airport noise, while highway barriers now provide some relief from motor vehicle noise. Finally, the potential effects of noise on wildlife, especially endangered species, now come under close scrutiny when major projects are planned in remote areas.
The effect of roughness on acoustic penetration of the seafloor as given by a fluid–fluid perturbation model and comparison with recent sediment penetration experiments
Authors: Moe John E. , Thorsos Eric I. , Jackson Darrell R. , Williams Kevin L.
Published: October 2005

Recent experimental results [F. E. Boyle and N. P. Chotiros, 2615–2619 (1992)] reveal acoustic penetration from water into sandy sediments at grazing angles below the compressional critical angle in relation to the mean surface. These authors interpret the results to indicate the excitation of a biot slow wave in the sediment. An additional mechanism for subcritical penetration will be discussed, based on assuming a small level of roughness at the water–sediment interface. Computer simulations of these experiments using theoretical calculations based on Rayleigh–Rice perturbation theory for 2-D surfaces reproduce experimental results, indicating that the acoustic penetration of the surface may be due to scattering (diffraction) from low levels of roughness. The accuracy of perturbation theory for the level of roughness being considered is verified using comparisons with exact calculations in the special case of 1-D surfaces. [Work supported by ONR.]
Marching wave-number-integration approach to range-dependent, two-way seismoacoustic propagation modeling
Authors: Schmidt Henrik
Published: October 2005

An approximate solution to two-way seismoacoustic propagation problems can be obtained by recursive use of wave-number-integration in a stepwise range-dependent environment. The approach is conceptually simple and straightforward. In the range-independent sector containing the source, an ‘‘exact’’ integral representation of the field can be obtained versus range and depth using, e.g., the SAFARI/OASES code [H. Schmidt and F. B. Jensen, 813–825 (1985)]. At the vertical boundary of the next sector we then solve the reflection-transmission problem locally for each plane-wave component, assuming vertical homogeneity of the field. The resulting particle motions now act as virtual sources, the wave-number representation of which can be stated explicitly using the seismic source representation theorem. The resulting transmitted and reflected fields can then be computed at any depth and range within the range-dependent sectors. The procedure is repeated at any vertical cut in a marching scheme. A single-scatter approximation to the backscattered field is subsequently obtained by a backward marching scheme, similarly to the approach used in the two-way elastic PE [M. D. Collins, 1815–1824 (1993)]. A special version of OASES incorporating this approach has been developed, and its performance is demonstrated by solutions to canonical problems such as the ASA benchmark, and seismic problems previously solved using the two-way elastic PE.
Multiple ocean layering models and mode trapping in sublayers for high frequency propagation
Authors: Sidorovskaia N. A. , Werby M. F.
Published: October 2005

It is possible for sublayers in a layered ocean to have pronounced effects on the propagating modes in the water column. For example, atypical effects occur for sound speeds less than the overlaying water column or some overlying sublayers. In some cases one predicts the concentration of a large energy flux in that layer even at model eigenvalues that prohibit propagation in the water column while supporting propagating modes in the sublayer. Since some data suggest the possibility of underlying gaseous regions that support low sound speeds, this is a practical problem. This allows for the possibility that for a layer thick enough to absorb energy before arriving in a higher speed sublayer, the number of propagation modes in the water column can be reduced with increasing frequency. Since this is a frequency-dependent effect [effective (absorbing) thickness of layers is inversely proportional to wavelength or directly proportional to frequency], absorption into the overlying sublayers becomes more pronounced with increased frequency thus reducing the possibility of ‘‘tunnelling’’ which leads to a reduction in propagating modes in the water column. This effect is the converse of the usual case for ocean bottom layering and can be directly measured. Some interesting effects are studied and compared with available data using the high frequency mode model SWAMP. [Work sponsored by the Office of Naval Research.]
Scholte–Stoneley waves on a solid layered ocean floor
Authors: Hargenrader Louis , Überall Herbert
Published: October 2005

The existence of a Scholte–Stoneley interface wave has been pointed out for the two-layer propagation model of Pekeris, as generalized to a shear-supporting ocean bottom. Further, the occurrence of apparent resonances in a solid sediment covering the ocean floor has been noted [S. J. Hughes etal., 1283 (1990)]. By finding the poles in the complex frequency plane corresponding to the various interface-wave (Scholte–Stoneley) and trapped-wave modes (including Love waves), a detailed study is carried out of the various wave modes that exist in the elastic layered problem taking note of their identities and of transitions between mode types, and the resonance behavior associated with them is investigated.
Noise isolation and reduction using spline wavelets
Authors: Ainsleigh Phillip L. , Chui Charles K.
Published: October 2005

A technique is introduced for removing unwanted components from data using B-spline-based multiresolution (B-wavelet) analysis. The time and frequency localization capabilities of wavelets allow two advantages over standard filtering methods: (1) better noise detection arising from the ability to isolate noisy components in wavelet bands where the signal energy is small relative to the noise energy, and (2) less signal loss by selectively filtering only those segments within wavelet bands containing unwanted noise. The procedure is used to remove impulsive noise from time series, and to eliminate multipath interference from frequency domain data.
Frequency normalized leakage correction technique
Authors: Winkel Casey R. , Shipley Kenton A. , Vaidya P. G. , Doughty Tim A.
Published: October 2005

Leakage is a problem in nearly all aspects of signal processing, especially when the FFT is involved. Leakage takes the form of wide frequency spikes due to a ‘‘spilling over’’ of information across frequency bins and occurs most often when the sampling frequency is not an integer multiple of the base frequency. The leakage correction method presented here substantially reduces this problem. The method resamples the original time domain data within specified limits. A frequency error measurement is taken for each sampling rate within the defined limits. The minimum frequency error is recorded along with the fundamental frequency of the record. This method resamples the entire signal one record at a time with a linear interpolator. Nyquist criteria must be satisfied at all times to validate the use of the linear interpolation. Nyquist criteria is satisfied if the sampling rate is at least twice as large as the highest frequency in the signal. The resampled data must satisfy three conditions to eliminate leakage. (1) 2n points per period. (2) Integer number of periods per record. (3) Satisfy Nyquist criteria. The method here satisfies these conditions and results in enhanced time domain data. a)Now at Martin Marietta, Knolls Atomic Power Labs, Schenectady, NY. b)Now at Dept. of Mech. Eng., Purdue Univ., West Lafayette, IN.
The status of Naval underwater acoustic modeling
Authors: Etter Paul C.
Published: October 2005

Results from a survey of recent developments in Naval underwater acoustic modeling are compared with those of two previous surveys conducted at 8-year intervals [P. C. Etter and R. S. Flum, Sr., J. Acoust. Soc. Am. Suppl. 1 65, S42 (1979); P. C. Etter, J. Acoust. Soc. Am. Suppl. 1 82, S102 (1987)]. All surveys cover basic acoustic models and sonar performance models. Basic acoustic models include propagation, noise, and reverberation models. Sonar performance models integrate basic acoustic models, signal processing models and supporting databases into cohesive operating systems organized to solve the active or passive sonar equations [P. C. Etter, UnderwaterAcousticModeling (Elsevier, Amsterdam, 1991); 2nd ed. (Chapman & Hall, 1995)]. Summary tables identify and highlight noteworthy characteristics of 83 propagation models, 15 noise models, 14 reverberation models, and 14 sonar performance models. These surveys provide a retrospective view of modeling developments over the past two decades and document a 160% increase in the number of models that are now available for applications in sonar technology. This updated baseline also suggests future directions for Naval modeling in an era of defense conversion including new applications in oceanographic research.
Accuracy of parabolic approximations for travel time
Authors: Tappert F. D. , Brown M. G.
Published: October 2005

Many different full-wave parabolic approximations are analyzed with regard to the accuracy of their travel time predictions by considering the geometrical acoustic (ray tracing) limit. The two small parameters are ε=(1−n2)/2 and μ=p2/2, where n is the depth and range-dependent index of refraction and p is a scaled ray grazing angle. By expanding the exact and approximate Hamiltonian and Langrangian functions in powers of ε and μ, which tend to have the same order of magnitude, it is found that among the class of parabolic approximations that can be implemented with the efficient ‘‘split-step Fourier’’ algorithm only the recently developed c0-insensitive approximation [Tappert etal., J. Acoust. Soc. Am., to be published] has full second-order accuracy. The highly touted ‘‘modified log’’ parabolic approximation of Berman etal. [ 228–233 (1989)] has only first-order accuracy, the same as the ‘‘standard’’ parabolic approximation, and furthermore it has a second-order bias toward times that are too early. Numerical calculations confirm and quantify these results. [Work supported by ONR.]