bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupling and attenuation of waves in plates by randomly distributed attached impedances
Authors: Turner Joseph A. , Weaver Richard L.
Published: October 2005

The average response of an infinite thin plate with statistically homogeneous attached random impedances is examined. The added impedances, which represent typical heterogeneities that might occur on complex shells, provide light coupling between the extensional, shear, and flexural waves. The mean plate response is formulated in terms of the Dyson equation which is solved within the assumptions of the first-order smoothing approximation, or Keller approximation, valid when the heterogeneities are weak. Scattering attenuations are derived for each propagation mode. It is shown that the attenuation of one wave type due to coupling to another is proportional to the modal density of the other wave type. Thus the attenuation of extensional and shear waves is predominantly due to mode conversion into flexural waves and is proportional to the large modal density of flexural waves. The flexural degrees of freedom serve as a sink for the energy of the membrane modes and constitute for them an effective fuzzy structure. The specific case of delta-correlated springs is considered for purposes of illustration.
Hybrid processing structure for the analysis of scattering from stiffened, fluid-loaded cylindrical shells
Authors: Bondaryk Joseph E. , Schmidt Henrik
Published: October 2005

A hybrid processing structure, which combines classical direct analysis techniques with forward modeling, is used to interpret data from a set of bistatic scattering experiments. Measurements of scatter of plane waves incident on the bow of a finite cylindrical empty shell and a duplicate rib-stiffened shell were made in the frequency range 2<ka<12. First, array processing was used to focus the measurements from the acoustic field to the radiating source strength at the surface of each shell. Then a transmission line model of each shell was matched to this focused data by using a simulated annealing algorithm to adjust model parameters. This hybrid procedure allows estimation of critical parameters of the structural wave propagation on the shell, such as the structural wave speeds, decay rates and reflection coefficients at discontinuities. Results show that small cross-coupling coefficients between flexural and compressional wave types at the slope discontinuities on the empty shell are responsible for most of the radiation later in time. High reflection coefficients at the ring stiffeners on the rib-stiffened shell are shown to cause energy compartmentalization in the bays between ribs and pressure doubling of incident structural waves at the ribs.
A new method of measuring the Young’s modulus in a paper cone
Authors: Tao Qing-Tian , Zhang Zhi-Liang
Published: October 2005

In this paper, a new method of measuring Young’s modulus in a paper cone is presented. The characteristics of this method are as follows. (1) The distribution of Young’s modulus along generatrix of the cone can be measured. (2) The technology of laser modulation is applied in this method. As a consequence, the setup of measurement has no influence on the vibration behavior. This new method has been tested and verified.
The performance of bearing estimation using spatial domain forward–backward predictor with higher-order statistics
Authors: Sung Chih-Yuan , Chern Shiunn-Jang
Published: October 2005

The modified forward–backward linear predictor (MFBLP) methods with higher-order statistics, viz., the second-order statistics and the fourth-order cumulants, together with the broadband array structure are developed in this paper for bearing estimation. Here, the desired source signals of interest are narrow band and the additive Gaussian noise sources in the related sensors are assumed to be spatially correlated or uncorrelated with each other and white/colored processes in the temporal domain. In this paper, the MFBLP method with second-order statistics for bearing estimation will be emphasized. Moreover, to extract the principal eigenvalues of presented MFBLP methods a new search algorithm is also proposed. An analytical study of the MFBLP method with second-order statistics is first developed, under the assumption that the additive noise is white Gaussian process. From the observation of analytic results, a modification of the MFBLP method with second-order statistics is suggested. From simulation results, it is shown that the MFBLP methods with higher-order statistics is superior to the conventional MFBLP method with the linear array data directly, in terms of threshold signal-to-noise ratio (SNR). This is especially true when data length becomes relatively larger. Moreover, the performance improvement of using the new search algorithm together with all the MFBLP methods is discussed thoroughly.
Stimulus-driven, time-varying weights for comodulation masking release
Authors: Buus So/ren , Zhang Leiji , Florentine Mary
Published: October 2005

This study tests the hypothesis that comodulation masking release (CMR) is mediated by ‘‘listening in the valleys’’ [S. Buus, J. Acoust. Soc. Am. 78, 1958–1965 (1985)]. Detectability was measured for signals consisting of six consecutive 25-ms, 1-kHz tone pulses presented in a 50-Hz-wide masker or in maskers consisting of seven 50-Hz-wide noises, one critical band apart, with either correlated or uncorrelated envelopes. The level of each signal pulse varied randomly around masked threshold according to Gaussian distributions with rms perturbations (standard deviations) of 3 or 6 dB. For each listener and condition, the responses from 5000 trials were sorted to construct conditional psychometric functions for d′ as a function of signal-pulse intensity for ten ranges of short-term level of the on-frequency masker band during the pulse. The slopes of these functions for three normal listeners decrease markedly with increasing short-term masker level for the correlated multiband masker, but are largely constant for the other maskers. This indicates that the weight applied to the signal channel is high when the masker level is low and vice versa for the correlated masker, but is approximately constant for single-band and uncorrelated multiband maskers. These findings provide direct evidence that CMR is mediated by ‘‘listening in the valleys,’’ but models based on direct envelope comparison may also account for the results if they are modified to include a compressive nonlinearity before the comparison.
Vowel identification based on amplitude modulation
Authors: Moore Brian C. J. , Alcántara Joseph I.
Published: October 2005

This study investigated the extent to which flat-spectrum harmonic complexes could be identified as one of six vowels when three pairs of successive harmonics, located at the first, second, and third formant frequency values, were amplitude modulated. In experiment 1, the amplitude modulation (AM) rate was at or close to 10 Hz. In condition 1, all components were added in cosine phase, and the 10-Hz AM was in phase for all ‘‘formants.’’ Performance improved monotonically with increasing modulation index, m. In condition 2, m was fixed at 0.5 and the level of each background harmonic was varied randomly (roved) from stimulus to stimulus. Even a rove range of only ±2 dB reduced scores considerably. Condition 3 was like condition 1, but with components added in random phase. Performance was very poor for all modulation indices. This suggests that subjects were unable to use momentary differences in level between formant and background harmonics, and supports the idea that, for cosine-phase stimuli, they were using information from the low-amplitude portions (‘‘valleys’’) of the cochlea-filtered waveforms. In further conditions, the components were added in cosine phase and the AM had a different phase and/or different rate (10, 16, and 24 Hz) on the different formants. Scores were very similar to those obtained when the AM was identical for all formants.

In experiment 2, the AM rate was at or close to 2 Hz. When all formants were modulated in phase at 2 Hz, very good performance was found for components added in cosine phase, and performance was essentially unaffected by making the AM different in rate and/or phase across formants. When the components were added in random phase, performance was well above chance when the formants were modulated in-phase at 2-Hz, but worsened markedly when the modulation differed in rate and/or phase across formants. Randomizing the level of each background harmonic caused performance to deteriorate and to become similar for cosine-phase and random-phase stimuli. Performance deteriorated further when the AM differed in phase across formants. The results suggest that, for a 2-Hz modulation rate, and when information from the valleys is not available, performance depends on momentary increases in level of the formant harmonics relative to the background.
A longitudinal investigation of duration and temporal variability in children’s speech production
Authors: Smith Bruce L. , Kenney Mary Kay , Hussain Sarmad
Published: October 2005

A number of cross-sectional, acoustic studies have found that young children’s speech segments tend to be longer and more variable than those of older children and adults. However, very little longitudinal information of this nature is available that considers changes across time for individual children. The present investigation is a longitudinal analysis of several temporal characteristics of the speech of 12 children of various ages who were each seen twice, approximately 11/2 years apart. For the group, durations decreased on average from the initial to the follow-up recordings by approximately 10%, and temporal variability decreased by about 40%. For the individual children, however, it was found that some of them showed few, if any, changes in some of the temporal measurements made at the two different times, whereas others showed substantial differences. Younger children also did not necessarily show longer durations or greater variability than older children, nor did younger children always show greater changes across time than older children. Thus, although cross-sectional studies indicate that there is a general tendency when comparing groups for increased age to be associated with shorter durations and reduced variability, individual children may not evidence such patterns or changes across time.
Wind-instrument reflection function measurements in the time domain
Authors: Keefe Douglas H.
Published: October 2005

Theoretical and computational analyses of wind-instrument sound production in the time domain have emerged as useful tools for understanding musical instrument acoustics, yet there exist few experimental measurements of the air-column response directly in the time domain. A new experimental, time-domain technique is proposed to measure the reflection function response of woodwind and brass-instrument air columns. This response is defined at the location of sound regeneration in the mouthpiece or double reed. A probe assembly comprised of an acoustic source and microphone is inserted directly into the air column entryway using a foam plug to ensure a leak-free fit. An initial calibration phase involves measurements on a single cylindrical tube of known dimensions. Measurements are presented on an alto saxophone and euphonium. The technique has promise for testing any musical instrument air columns using a single probe assembly and foam plugs over a range of diameters typical of air-column entryways.
Effect of static pressure on acoustic transmittance of Albunex(R) microbubble suspensions
Authors: Brayman Andrew A. , Azadniv Mitra , Miller Morton W. , Meltzer Richard S.
Published: October 2005

Albunex(R) (ALX), an albumin-stabilized microbubble echo contrast agent, is sensitive to pressures similar to those produced by the heart. The tested hypothesis was that the acoustic transmittance of ALX suspensions will increase with increasing hydrostatic pressure (Ps). The test involved an acoustic setup analogous to a spectrophotometer. The acoustic transmittance of microbubble suspensions was strongly Ps dependent. Transmittance at 1 MHz was essentially zero at ambient pressure, increasing to ∼50%, ∼63%, and nearly 100% at Ps of 80, 120, and 400 mm Hg, respectively. The ultrasound pulses used to interrogate samples were without measurable effect on the acoustic transmittance of suspensions maintained at ambient pressure during experimental measurements. The data indicate that many of the microbubbles are destroyed at Ps comparable to those produced by the heart.
Acoustic basis for recognition of aspect-dependent three-dimensional targets by an echolocating bottlenose dolphin
Authors: Helweg David A. , Au Whitlow W. L. , Roitblat Herbert L. , Nachtigall Paul E.
Published: October 2005

The relationships between acoustic features of target echoes and the cognitive representations of the target formed by an echolocating dolphin will influence the ease with which the dolphin can recognize a target. A blindfolded Atlantic bottlenose dolphin (Tursiops truncatus) learned to match aspect-dependent three-dimensional targets (such as a cube) at haphazard orientations, although with some difficulty. This task may have been difficult because aspect-dependent targets produce different echoes at different orientations, which required the dolphin to have some capability for object constancy across changes in echo characteristics. Significant target-related differences in echo amplitude, rms bandwidth, and distributions of interhighlight intervals were observed among echoes collected when the dolphin was performing the task. Targets could be classified using a combination of energy flux density and rms bandwidth by a linear discriminant analysis and a nearest centroid classifier. Neither statistical model could classify targets without amplitude information, but the highest accuracy required spectral information as well. This suggests that the dolphin recognized the targets using a multidimensional representation containing amplitude and spectral information and that dolphins can form stable representations of targets regardless of orientation based on varying sensory properties.
Some acoustical properties of the otic bones of a fin whale
Authors: Lees Sidney , Hanson Douglas B. , Page Elizabeth A.
Published: October 2005

The otic bones in this report are the tympanic bulla, the periotic, and the three ossicles (malleus, incus, and stapes) of an adult fin whale (Balaenoptera physalus). The purpose was to determine if the periotic was denser than the other otic bones. It was found in one male adult fin whale that the density of all the otic bones is approximately the same, 2.50 kg/m3 with a maximum of 2.58. The lowest density was observed in the stapes (2.36). The sonic velocity seems to vary as the density but there also seems to be a structural effect. The maximum sonic velocity was 4.89 km/s in the malleus. The specific acoustic impedance was as high as 12.5 megarayles in the periotic. These values compare with those for human femur of 1.95 for the density, 3.73 for the sonic velocity, and 7.33 for the specific acoustic impedance. The ossicles weigh as much as 200 times as much as human ossicles. The density of whale ossicles are about ten percent greater than human ossicles. The mechanical natural frequency of the whale ossicles must be very low. The approximate uniformity of the properties of this whale’s otic bones may be characteristic of the middle ear. The density of the otic bones of land mammals is less than for whales. The density of the horse petrosal (2.29 g/cc) is essentially the same as the density of adult human ossicles (2.23–2.27 g/cc). The high density of the otic bones for all mammals suggests it may be related to hearing acuity perhaps by increasing the specific acoustic impedance, which increases the acoustic contrast with the other body tissues.
A note on the acoustic penumbra behind a curved surface
Authors: Berthelot Yves H.
Published: October 2005

It appears that a slight modification of the definition of source–receiver distance in the creeping wave series of Berry and Daigle [J. Acoust. Soc. Am. 83, 2047–2058 (1988)] yields consistently better agreement with experimental data at several points in the shadow zone, for several frequencies, and for several impedance surfaces. It is also in better agreement with predictions from matched asymptotic expansions and the data of Berthelot and Zhou [J. Acoust. Soc. Am. 93, 605–608 (1993)].
Permanent removal of the wall porosity in monolithic catalyst support ceramics
Authors: Bernard Miguel , Velea Doru , Sabatier James M.
Published: October 2005

A technique is described that allows for the permanent removal of the wall porosity from monolithic catalyst support ceramic samples in order to have a better characterized porous medium. Specific acoustic impedance measurements for a rigid-backed ceramic sample have confirmed the effects of wall porosity on sound propagation in square-tube, capillary-type porous ceramics previously observed by Arnott and co-workers [J. Acoust. Soc. Am. 90, 3299–3306 (1991)].
Estimating surface orientation from sonar images.
Authors: Makris Nicholas C.
Published: October 2005

Sonar images of remote surfaces are typically corrupted by signal-dependent noise known as speckle. This noise arises when wavelength scale roughness on the surface causes a random interference pattern in the sound field scattered from it by an active system. Relative motion between source, surface, and receiver cause the received field to fluctuate over time with complex Gaussian statistics. Underlying these fluctuations, however, is the expected radiant intensity from the surface, from which its orientation may be inferred. In many cases of practical importance, Lambert’s law is appropriate for such inference because variations in the projected area of a surface patch, as a function of source and receiver orientation, often cause the predominant variations in its radiance. Therefore, maximum likelihood estimators for Lambertian surface orientation are derived. These are asymptotically optimal when a sufficiently large number of independent samples are available, even though the relationship between surface orientation and measured radiance is generally nonlinear. Here, the term optimal means that the estimate is unbiased and its mean square error equals the Cramer–Rao lower bound, which is also derived. The requisite number of independent samples necessary for asymptotic optimality of the maximum likelihood estimate is given for some special cases.
Broadband frequency response modeling for inversion of a shallow-water waveguide with a range-dependent soft clay bottom (Yellow Shark ’95 experiment).
Authors: Soukup Raymond J. , Hermand Jean-Pierre , Michelozzi Enzo
Published: October 2005

During the Yellow Shark ’95 experiment the broadband frequency response (200–800 Hz) of a shallow-water waveguide was measured for the purposes of performing multimodal inversion of its acoustic and geoacoustic properties. Measurements from vertical receiving arrays deployed every 8 km along a 40-km tomography transect showed that the frequency response was mostly flat with high transmission loss at selected frequencies. This differs from often observed frequency dependence in other shallow-water environments where there is some low frequency with minimum loss, suggesting an optimum frequency of propagation. Range-dependent geoacoustic and seismic data along the transect and water sound-speed data measured during the acoustic transmissions permitted the development of a realistic environmental model. Normal-mode modeling results with C-SNAP indicated that the presence of a soft clay top layer with a speed less than the water column was a decisive factor in the observed frequency dependence, since it acted as an alternative waveguide to lower-order modes. The modeled frequency dependence and absolute level of transmission loss closely agreed with the measurements obtained at the different ranges and depths, resulting in a validation of theoretical arguments involving selected frequencies of high transmission loss as a major feature of this type of environment.
Inversion techniques for characterizing a coupled mode acoustic waveguide.
Authors: Rouseff Daniel , Siderius Martin
Published: October 2005

A method for characterizing a range-dependent acoustic waveguide by remote sensing is examined. The approach is to transmit from a limited number of source locations and measure the propagating field along a vertical array. Characterization of the environment is cast as an inverse problem where the goal is to determine the mode coupling coefficients from the acoustical measurements. Ideally, measurements from the source at a single location should suffice to characterize the medium when the propagation is adiabatic. When there is coupling, the problem is underdetermined and unstable if the number of source locations is less than the number of propagating modes. Tikhonov regularization is used to build stability into the inversion algorithm. The number of measurements required is shown to be directly related to the nature and extent of the mode coupling. The method is demonstrated by numerical simulation for two shallow water scenarios: a sloping bottom and a randomly rough bottom. [Work supported by ONR.]
Determination of sub-bottom sediment properties and their spatial distributions from chirp sonar data.
Authors: Turgut Altan
Published: October 2005

Determination of impedance and attenuation coefficients for upper sediment layers from chirp sonar data is performed by using simulated annealing algorithms. Normal incidence reflection seismograms are calculated for layered marine sediments using the Biot theory of acoustic wave propagation in porous media to produce synthetic data. A time-domain inversion algorithm progressively identifies each reflection and applies random perturbations to corresponding model parameters to minimize the quadratic deviation between the data and synthetic seismograms. Numerical simulations indicate that such an inversion scheme can be efficiently used to survey large areas for characterization of sediment properties and their spatial distributions. In addition, impedance and attenuation estimates are used to predict the sediment porosity, density, permeability, and sound speed using the Biot theory. Finally, chirp sonar data (3 to 7 kHz) collected on the New Jersey Shelf as a part of SWARM-95 (Shallow Water Acoustic Random Media) experiment are analyzed. Inversion results confirm previous coring and in situ observations that alternating sand and clay layers are present at the Hudson Apron site.
Radiation impedance of a circular vibrating plate on the surface of viscoelastic media.
Authors: Kimura Masao
Published: October 2005

Radiation impedance of a vibrating plate on the surface of a visco-elastic medium such as marine sediment varies with the viscoelastic properties of the medium. Therefore, it is possible to predict the viscoelastic properties using the characteristics of the radiation impedance. In this paper, the characteristics of radiation impedance of a circular vibrating plate on the surface of viscoelastic media were obtained by numerical analysis. The results showed that the values of ka (k is the wave number, a is the radius of a circular vibrating plate) at which the imaginary part of the radiation impedance becomes zero can be related to the ratio of the shear wave velocity to the longitudinal wave velocity, that is, the Poisson’s ratio. Next, measurements of radiation impedance for three kinds of urethane rubbers and two kinds of dry beach sands were done, and the measured values were compared to the calculated values.

The goal of this informal workshop is to bring together several researchers working on various aspects of voice perception. Historically, the study of voice has been treated as a more-or-less autonomous area quite distinct from other research problems in speech and hearing sciences. In this workshop, some of the traditional problems of voice classification and perception will be discussed and reviewed and then these efforts will be related to recent findings in speech perception and spoken word recognition which have shown important dependencies between traditional voice parameters and perceptual analysis of the speech signal. The contributors to the session include: Jody Kreiman, Diana VanLancker, Keith Johnson, Robert Remez, Peter Jusczyk, and David Pisoni. Please bring your slides and overheads and join in the discussion on some long-standing problems related to the ‘‘indexical’’ and ‘‘linguistic’’ functions of speech. For further information about this informal workshop, please feel free to contact D. B. Pisoni via E-mail: pisoni@indiana.edu. Everyone with an interest in speech perception, production, and spoken language processing is welcome to attend and contribute to the discussion of these problems.
Ambient noise from the surf zone: Surface and acoustic waves.
Authors: Melville W. Kendall
Published: October 2005

Wave breaking is probably the dominant source of ambient noise in the ocean. In deep water, breaking is intermittent in both space and time, but, in the surf zone, every wave of any appreciable size breaks, or shoals, before it reaches the shore. This makes the surf zone and its neighboring region offshore acoustically different from deeper water. In shoaling, surface waves dissipate their energy, generate currents and turbulence that mix the water column, suspend sediments and entrain bubbles, and generate sound. It is the potential relationships between the sound generation and propagation and the other physical processes associated with surface waves, and the shoaling bottom topography, that is the subject of this talk. This is an open field in acoustical oceanography and underwater acoustics, with few measurements available but a great deal of potential. In this lecture the processes associated with the shoaling of surface waves will be reviewed and the resulting implications for sound generation and propagation will be discussed. The potential for the inversion of acoustic data to infer other surf zone processes will be explored.
Recent results in surf zone ambient noise measurements.
Authors: Livingston Ellen S.
Published: October 2005

Over the years only a few measurements have been made of surf zone ambient noise. Recently, however, several sets of data have been taken in and near the surf zone in conjunction with coastal oceanography and seismoacoustic studies. In this talk, an overview is given of past and present surf zone studies and differing approaches are discussed and contrasted. The variety of results now starting to come forward from the new data are outlined. Important issues opened by these recent results and new applications anticipated are discussed as well.
Surf noise and biological sounds in the near-surf-zone environment.
Authors: D’Spain Gerald L. , Hodgkiss William S. , Kuperman William A. , Berger Lewis P.
Published: October 2005

The Marine Physical Lab’s Adaptive Beach Monitoring Experiment was conducted from 24 April to 14 June 1995, in and near the surf zone off the S. California coast. Other participants included NRaD/NCCOSC, NRL, ARL/PSU, and ARL/UT. The focus here is on the underwater acoustic noise field properties. Contributions of breaking surf are studied in the 1- to 400-Hz band using a 35-element subsection of a bottom hydrophone array oriented perpendicular to the coast and located 3.4-km offshore in 20-m water. A 3-week time series of endfire-beamforming results are compared to the ocean surface wave height data collected over the same period. Source tow data quantify the propagation effects of surf noise to the array site and permit inversions for bottom geoacoustic properties. The array data are supplemented by the distance dependence from shore of data from bottom-mounted sonobuoys in the 100-Hz–20-kHz band, and air acoustic data recorded just landward of the shoreline. Biologics are a substantial component of the noise field and must be accounted for in evaluating the contribution from surf. Fish sounds themselves can be used as novel sources in inversion for bottom geoacoustic properties. [Work supported by ONR, Code 32.]
Matched-field inversion in a rapidly fluctuating shallow-water waveguide.
Authors: Makris Nicholas C.
Published: October 2005

A number of useful applications for matched-field inversion have been envisioned for the littoral zone. These include the estimation of environmental parameters, such as the sound-speed structure of the water column and geoacoustic properties of the sediment, as well as the more traditional localization of submerged objects. However, natural disturbances such as passing surface and internal gravity waves often place shallow-water waveguides in such a state of flux that a signal, deterministic when transmitted from a source, becomes fully randomized after propagating only several channel depths away in range to a receiver. When not properly accounted for, such randomization can severely degrade the accuracy of a matched-field inversion, which presumably is for parameters that remained fixed during the measurement process. Therefore, the general performance of a matched-field inversion is examined from the perspective of statistical estimation, under the worst case scenario of a waveguide that may be fluctuating rapidly during a given transmission or set of transmissions. Specific examples for shallow-water matched-field tomography and object localization using ambient noise are then considered.
Inversion of the underwater sound field to quantify the formation of a subsurface bubble layer.
Authors: Nystuen Jeffrey A.
Published: October 2005

The underwater sound field can be used to quantify oceanic processes that actively produce sound, including, for example, wind/wave breaking (wind speed) and rainfall. These ‘‘active’’ sound sources are subsequently modified by the acoustic environment. In the case of wave breaking or rainfall, the sound source is located at the ocean surface. One of the principal features of the near-surface zone in the ocean capable of modifying the sound field is the ambient bubble field. Frequency-dependent modifications of the underwater sound field during heavy rainfall are observed. Using a rainfall generated sound field as an example, the change in the spectral character of the sound field will be used to quantify the formation and decay of an ambient bubble field. Documentation of the formation of a bubble layer has implications for gas and momentum exchange at the ocean surface by rainfall.
Acoustic measurements of breaking waves in the surf zone.
Authors: Deane Grant B.
Published: October 2005

A series of measurements have been made to characterize the sound generated by breaking waves in the surf zone around Scripps Pier. Simultaneous video and acoustic data were made to allow the acoustic energy radiated by individual waves to be correlated with the breaking event at the surface. The acoustic measurements were made directly below breaking waves in 2 m of water and 170 m from the shoreline. Spectral analysis of the data demonstrates the presence of a strong acoustic field below the breaking waves. Overhead waves generate sound for some several seconds, and are clearly distinguishable from nearby surf. The breaking wave spectrum is bimodal, with two peaks in intensity around 30 and 1000 Hz. A preliminary analysis of the data shows an acoustically active region of water propagating with the breaking wave. [Work supported by ONR.]
Preliminary characterization and modeling of ambient noise due to high surf during DUCK94.
Authors: Paquin-Fabre J. , Wilson James H.
Published: October 2005

Broadband noise due to surf that propagates kilometers out to sea with little transmission loss has been observed for many years, but rarely directly measured and characterized. In October of 1994 a coastal research experiment, DUCK94, was conducted off the coast of Duck, North Carolina. Neptune Sciences, Inc., under Naval Research Laboratory sponsorship, participated in that experiment with the objectives of obtaining ambient noise data at offshore positions for investigations of nearshore acoustic noise generated by waves and surf. Measurements were taken, using modified Navy standard sonobuoys, primarily during high surf events (wave heights of 1.7 to 2.4 Hmo,m). Preliminary analysis of the data indicates a broadband noise maxima between 400 and 600 Hz. In order to characterize ambient noise due to surf for modeling purposes, source level densities for heavy surf are currently being developed using the measured AN data and a finite element parabolic equation transmission loss model.
Ambient noise measurements in the acoustic beach monitoring experiment.
Authors: Melville W. K. , Deane G. B. , Shear R. M. , Terrill E. , Epifanio C. L.
Published: October 2005

During the spring of 1994 (April–June) the Marine Physical Laboratory/SIO conducted the acoustic beach monitoring (ABM) pilot experiment at Camp Pendelton, CA. One component of the experiment was concerned with measurement of ambient noise up to 40 kHz, at distances up to several kilometers offshore. An array of three modified SSQ 57B sonobuoys were moored at distances from 1.5 to 3.5 km offshore. The surf zone was instrumented with pressure gauges and a current meter, and a comprehensive meteorological station was set up on the beach. A directional microphone on the beach was used to monitor the surf noise. Supporting oceanographic and meteorological data was available from the SIO coastal data information program. Near-shore acoustic spectra are characterized by two broad peaks in the ranges of 100–500 Hz and 1–7 kHz, respectively. The higher frequency peak rapidly attenuates offshore, while the lower frequency peak is essentially unattenuated over ranges of several kilometers. In contrast to deep water, the correlation of surf zone ambient noise with the local wind is poor since the shoaling waves may be dominated by swell from distant storms. Short term averages of acoustic power correlate very well with the amplitude modulation (groupiness) of the incident waves. [Work supported by ONR.]
Global directivity measurements of near shore ambient noise.
Authors: Glegg Stewart A. L. , Olivieri Marc P. , Coulson Robert K.
Published: October 2005

In the summer of 1995 a shallow-water ambient noise experiment was carried out 1-mile offshore of the Boca Raton Inlet. A volume array was deployed that provided both vertical and horizontal directivity measurements of the ambient noise. This paper will describe the array processing algorithm used to obtain the global directivity measurements with high resolution and present the ambient noise measurements. The results showed that the ambient noise was strongly anisotropic and dominated by biological noise from a local fishing pier located approximately 1 mile to the south. Measurements were also made of local boat traffic and it was found that the vertical arrival structure could be separated into clearly defined beams associated with each bottom bounce along the propagation path. [Work supported by ONR.]
Ambient noise generated by surface wind waves—Numerical and experimental results.
Authors: Liu Jin-Yuan , Chen Chuen-Song
Published: October 2005

Using a previously developed noise-generation model for sources due to surface processes [W. A. Kuperman and F. Ingenito, J. Acoust. Soc. Am. 67, 1988–1996 (1980)], a numerical study of ambient noise, which incorporates realistic wind wave spectrum (e.g., Pierson–Moskowitz), was made for seismoacoustic ocean wave guides. The results demonstrate a close relationship between the noise field and the source field, allowing one to gain insight to the interplay of both fields. Experimental data of ambient noise and wind waves were collected in an experimental site near the central part of Taiwan. The measured data were also used to generate numerical results of ambient noise which are then compared with experimental data. The comparison has shown a reasonable agreement in the frequency range dominated by the surface wind waves for a receiver not too close to bottom. By modeling the marine environment as a shallow- water seismoacoustic wave guide, it was demonstrated that the noise model of the noise field was greatly affected by the sediment properties. [Work supported by National Science Council of Republic of Chian (Taiwan).]
Time-domain and frequency-domain explorations of nonlinearity in musical wind instruments.
Authors: Fletcher Neville H.
Published: October 2005

Nonlinearity is an essential feature of the operation of sustained-tone musical instruments, as well as being an important feature in many impulsively excited instruments. Analysis of the behavior of wind instruments can be approached either through the time domain, in which case the linear resonant parts of the instrument are characterized by their impulse response, or in the frequency domain, in which case the characterization is in terms of mode shapes and frequencies. The generator mechanism in some cases has an embedded linear mode structure as well, but there is an essentially nonlinear coupling between it and the main instrument resonator. This paper examines the different types of information, or the complementary views of the same information, that can be obtained by time-domain and frequency-domain approaches to wind instrument acoustics.
Wind instruments: Some unanswered questions.
Authors: Nederveen Cornelis J.
Published: October 2005

The basics of functioning and tuning of wind instruments is reasonably explained by small-amplitude descriptions. Some details must be cleared up, such as corrections at the hole/bore transition, bends, and radiation at hole ends. In some cases, however, the linear description fails. For example, a clarinet becomes unplayable when its usual holes are replaced by much smaller and shorter ones (of the same impedance) [D. H. Keefe, J. Acoust. Soc. Am. 73, 1804–1820 (1983)]. Since it was noted that this tube could be blown with another (i.e., a saxophone) mouthpiece, it was supposed that the superimposed static flow influences the tube impedance. This assumption was provisionally confirmed by measurements. Understanding this phenomenon may help to improve the ease of playing of the lowest notes on saxophones. The common quantitative description of the flute action does not explain why certain fork fingerings cannot be blown and why the ‘‘reed-flute’’ has a dominating fifth harmonic in its initial transient. To contribute to the discussion on the influence of wall vibrations on tone quality, a mechanism will be proposed which is possibly responsible for a coupling between air and wall vibrations.
Understanding the operation of auxiliary fingerings on conical double-reed instruments.
Authors: Cronin Robert H. , Keefe Douglas H.
Published: October 2005

Players of the modern bassoon are accustomed to using ornate fingerings to stabilize and correct certain notes that are difficult to tune. These ‘‘auxiliary’’ fingerings open or close tone holes far below the first open tone hole. The primary subject of the investigation was a modern German-system bassoon. Calculations of impedance versus frequency were made using a program based on the Plitnik–Strong model of 1979, with several extensions. The model, in turn, was validated by comparison with measurements taken with a system developed by Keefe et al. The authors also investigated the behavior of auxiliary fingerings on a replica baroque bassoon, and sorted out a puzzling ‘‘feature’’ of a replica Renaissance alto shawm. Based on this work, criteria for ‘‘good’’ note behavior are postulated. [Work supported by the International Double Reed Society.]
A linearized model of bassoon sound production: The role of auxiliary fingerings.
Authors: Keefe Douglas H. , Cronin Robert H.
Published: October 2005

A quantitative theory of sound regeneration in the bassoon helps explain differences in the playing frequency and mouthpiece spectra associated with the use of auxiliary fingerings. The linearized condition for steady-state oscillations at a frequency f is 0=Y(f)+YG(f); the air-column input admittance is Y(f) and the double-reed generator admittance is YG(f), whose real part is negative (Fletcher, 1979; Thompson, 1979). The generator admittance is based upon a simple Bernoulli-type flow model, and the cane reed is modeled as a damped oscillator. Model parameter values are empirically determined and combined with measured input admittances, allowing direct comparison of Y(f) and −YG(f) at frequencies below and above the open tone-hole lattice cutoff frequency (Benade, 1960). Auxiliary fingerings produce significant differences in input admittance magnitude and phase above cutoff, and sound production is stabilized for a fingering such that the linearized condition is satisfied near a harmonic multiple of the playing frequency. The model accounts for intonation shifts associated with changes in auxiliary fingerings. While sound production in the bassoon is highly nonlinear, the fine structure of the linear air-column response at frequencies above cutoff is an essential contributor. [Work partially supported by the International Double Reed Society.]
Time-domain simulation of an organ flue pipe.
Authors: Adachi Seiji
Published: October 2005

Due to the difficulty in treating jet behavior, a general agreement on the sound production of flue instruments has not yet been obtained. This paper discusses three jet deflection models proposed by several authors by means of the time-domain approach. Simulations of an organ flue pipe where the blowing pressure is changed as a parameter are carried out. These models in common provide oscillations in the fundamental pipe resonance mode and in the higher modes (overblows). They also provide the underblow regimes of oscillation when the blowing pressure is lower. Differences among the models appear in the number of the underblow regimes and in the levels of harmonics of oscillations. Transition among the oscillation modes would also be a clue to compare the models. The results should be compared with an experiment of the artificial blowing of a pipe in the wide range of blowing pressure, which is in progress.
Sound absorption by seats in concert halls, occupied and unoccupied, and average sound absorption by the interior surfaces of halls.
Authors: Beranek Leo L.
Published: October 2005

Average sound absorption coefficients were determined for the interior surfaces of concert halls based on measurements in five halls in which all finishes had been completed before installation of seats. Fifteen halls were selected for detailed analysis and divided into three groups with seats that are (1) lightly upholstered, (2) medium upholstered, and (3) heavily upholstered. Assuming relative humidites of 50% for unoccupied and 70% for occupied halls, ‘‘acoustical’’ areas (added 0.5-m edge effect) for seating blocks, and the above, average interior-surface, absorption coefficients, the sound absorption coefficients for occupied and unoccupied seats were calculated from reverberation measurements. Among the three groups, it is found that there are large differences in absorption coefficients for the seats at all frequencies, but particularly at low frequencies. The values are markedly different from those previously published [L. Beranek, J. Acoust. Soc. Am. 92, 1–39 (1992)]. Where possible, photos and visual analyses of the chairs are made to compare with the data.
Sound absorption of occupied chairs as a function of chair design and audience clothing.
Authors: Kirkegaard Dana L.
Published: October 2005

In 1989, a series of experiments was initiated at Riverbank Acoustical Laboratories to study the detailed relationships between chair design and audience absorption. Chairs were measured occupied and unoccupied. Many chairs were disassembled and tested as individual chair components to confirm specific correlations between design and data. Chair manufacturers responsed by redesigning chairs for further testing. Each series of tests was designed to minimize the number of experimental variables. An unupholstered reference chair provided a baseline for each series of occupied tests. The baseline measurements provide a means of comparing occupied chair measurements made with different occupants and/or changes of clothing. They also establish baseline absorption values for an audience in minimally absorptive chairs. Results of these occupied chair measurements show that differences in chair design are most highly correlated with data below 500 Hz, which ranged from 2 to 8 Sabins/person. Above 500 Hz, data ranged from 6 to 11 Sabins/person as a function of chair design and seasonal changes in occupants’ clothing. Results support the hypothesis that chair design and seasonal clothing are critical in concert halls and other rooms with low residual absorption. [Research supported by Irwin Seating, JG Seating and Country Roads.]
A new methodology of applying measured acceleration and forces or pressures as excitation on powertrain models for noise prediction.
Authors: Vlahopoulos Nickolas , Stark Richard D. , Kargus Walter
Published: October 2005

Numerical methods can be used to compute the vibration of powertrain systems or components and the corresponding radiated noise. Specifically, the finite-element method can be utilized in computing the structural vibration. The structural response will constitute the boundary conditions for the boundary-element method in computing the radiated noise. In this work a new methodology is presented, it allows a combination of measured accelerations, and forces or pressures, to apply as excitation. The innovative elements of this work are: (i) the methodology utilized in prescribing the acceleration at certain parts of the structure; and (ii) integrating the vibration analysis within the acoustics software and creating a single process for computing the noise. A generic six-cylinder engine model is used as an example to demonstrate the new capabilities. The structural finite-element model is utilized to compute the modal basis of the structure. Acceleration measured at the bearing locations, and pressure loads applied at the cylinder head (simulating combustion) comprise the excitation. The modal basis of the structure, the loads, the structural model, and the acoustic boundary-element model are utilized within the acoustics software in comparing the structural vibration and the corresponding radiated noise.
Predictive acoustic modeling applied to the control of intake/exhaust noise of internal combustion engines.
Authors: Davies Peter O. A. L.
Published: October 2005

The application of validated acoustic models to intake/exhaust system acoustic design is described with reference to a sequence of specific practical examples. These include large turbocharged diesel generating sets, truck engines, and high-performance petrol engines.
Side branches in automotive intake systems as noise generators.
Authors: Selamet A. , Radavich P. M.
Published: October 2005

It is well established that the coupling of flow induced vortices and acoustic resonances in a closed side branch can lead to the production of both large wave amplitudes in this duct and excessive noise levels in the main duct. The present study concentrates on the propagation of noise in an automotive intake system induced by the closed side branch of an exhaust gas recirculation tube. The effects of (1) altering the side branch length, and (2) the addition of an area expansion in the side branch are investigated to modify the acoustic resonance characteristics. [Work supported by Ford Motor Co.]