bluuebunny/crossref_metadata_2025 huggingface dataset:
Formant discrimination in femalelike vowels as a function of F1−F0 Bark distance
Authors: Hughes Dennis L. , Diehl Randy L.
Published: October 2005

Hughes and Diehl [J. Acoust. Soc. Am. 95, 2978(A) (1994)] reported that discrimination of first formant frequency for both single and multiple formant stimuli was strongly influenced by both a formant/harmonic interaction and F1−F0 Bark distance. No evidence for a peak in discriminability near F1−F0=3.0–3.5 Bark was observed, however. The current study extended these findings to stimuli more characteristic of female talkers. Listeners performed a formant discrimination task on one of five series of four-formant stimuli varying in F1−F0 distance. F1 ranged from 3.2 to 7.7 Bark within a series, and F0 from 1.75 to 2.75 Bark between series. Preliminary results confirm both the strength of the formant/harmonic interaction and the lack of a peak in discriminability at F1−F0=3.0–3.5 Bark. Results also point up the need for a more adequate characterization of how formant frequency is represented in the auditory system. [Work supported by NIDCD.]
Whale ears: Structural analyses and implications for acoustic trauma
Authors: Ketten D. R.
Published: October 2005

Over 75 species of dolphins and whales are spread throughout every aquatic habitat. Although echolocation abilities of some dolphins are well documented, little is known about hearing in most whales. Dolphin signals range as high as 200 kHz, while baleen whales routinely produce 10- to 20-Hz signals. Whales have, therefore, two important auditory considerations: (1) the broadest signal range of any mammal group; and (2) the only mammalian ears adapted to underwater hearing. In this study, three-dimensional morphometric models of middle and inner ears from noncaptive toothed and baleen whales were used to estimate their hearing ranges. The analyses show echolocating species have basilar membrane stiffness coefficients 3× that of bats. Baleen whales have stiffness coefficients lower than elephants that hear infrasonics. Ganglion cell densities in whales are 2× bat and 3× human values. These data suggest echolocating dolphins may use multiple, parallel processed signal detection mechanisms. Cellular hypertrophy of inner ear support structures (stria vascularis, spiral ligament, basement membrane, etc.) in all whales may mean whales have inner ear mechanisms that decrease the potential for acoustic trauma. [Work supported by ONR Grant No. N00014-92-J-4000.]
Late night fish choruses in the shallow waters off San Diego
Authors: D’Spain G. L. , Berger L. , Richardson A. M. , Clapp G. , Rice J.
Published: October 2005

Two major experiments, SWellEx-1 and SWellEx-3, and one engineering sea test recently have been conducted in 200-m-deep water 8 miles west of the mouth of San Diego harbor. SWellEx-1 was conducted in August of 1993, the engineering sea test in May 1994, and SWellEx-3 in July 1994. For both of the summertime SWellEx experiments, an unusual oscillation in the background levels between 275–550 Hz and 575–700 Hz was observed, typically starting around midnight local time and lasting until sunrise. The repeating pattern to the oscillations is that of a 3–5 dB increase in spectral levels, which lasts on the order of 20 s, and then followed by 25 s or so of lower levels. Azimuthal beamforming has indicated that the predominant direction of this ‘‘cycling sound’’ is from near coastal waters. In the data from the May 1994 engineering sea test, no such cycling sound was present. The character of these signals, i.e., their spectral content, their diurnal variation, their seasonal variation, and their directionality, correspond to those described in year-long, single-hydrophone measurements made from a shallow water tower off San Diego in the early 1960s and ascribed to sounds made by fish of the croaker family [G. A. Clapp, NEL Tech Mem 1027 (1966)]. Additional properties of these signals, including a recording of the sounds made by a single individual, will be presented. [Work supported by ONR Code 321.]
Microphone monitoring by charge injection calibration
Authors: Frederiksen Erling
Published: October 2005

Charge injection calibration is a new method for monitoring operation conditions of measurement chains consisting of a microphone with preamplifier, cables, and conditioning amplifier. The method replaces the insert-voltage calibration technique which is frequently used with large or unmanned systems. A great advantage of the new method is its ability to check the transducer which is practically ignored by the insert-voltage calibration. From a remote voltage source, a constant charge is ‘‘injected’’ into the microphone capacitance and preamplifier input circuit using a small capacitance integrated with the preamplifier. This leads to an output signal that is inversely proportional to the combined impedance of the transducer and input circuit. An accidental change in the microphone impedance—which is a good transducer condition indicator—would appear as a change in the preamplifier output. High stability and extremely high leakage resistance (typically 1014Ω) are required for the charge injection capacitor (typically 0.2 pF). This problem was solved and the (patented) method was found to work reliably over a wide frequency range (2 Hz–200 kHz). The new method is less costly and simpler to implement. It also preserves the systems resistance to extraneous electrical fields. The method and its ability to indicate malfunctioning are discussed.
Traceability of acoustics and vibrations standards at the National Center of Metrology in Mexico
Authors: Echeverría-Villagomez J. S.
Published: October 2005

After the creation of the Mexican Primary Laboratory of Metrology, primary standards on acoustics and vibrations are being established for the first time in the country. For this task, CENAM staff has relied on the technical assistance of the corresponding groups at NIST and NRC. The process has involved several specific features due mainly to the particular needs and conditions of the Mexican laboratory. On the acoustics side, for the instrumentation of the reciprocity method for microphone calibration, the altitude of the site at which CENAM is located and the consequent low pressure lead to the proposal for a pressure-controlled chamber. Both the proposal and its completion has been carried out at NIST, with direction of its staff and participation of CENAM staff. The stage in which the project is at the moment will be shown. Also the instrumentation and methods used for giving traceability from CENAM to transfer and working standards of external customers. On the vibrations side, instrumentation of the reciprocity method for accelerometer calibration has been achieved with the Bouche Labs 5000CR system. Besides an interferometric system is being obtained as a complementary aid and for cross checking purposes. Traceability to transfer and working standards at CENAM is already being accomplished through the comparison method. An evaluation of the systems performance will be presented and a first estimation of their uncertainties will be discussed.
Velocity of sound measurement in liquids
Authors: Shi-ming Zhu , Wong George S. K.
Published: October 2005

Sound velocities in pure water at various temperatures were measured. A PZT transducer sends a 2-MHz pulse towards a target stationed at an accurately known distance of 120 mm away. The transit time between the forward pulse and the reflected pulse was measured precisely with statistical averaging and a reference timebase derived from the NRC cesium frequency standard. The transducer-target probe and liquid chamber was immersed in a temperature controlled bath that was under the control of a computer. Measurements were repeated with known concentrations of alcohol and distilled water. Uncertainties of the measurements will be discussed. The authors would like to thank Lu-Jie of the Tongji University for his contribution to the construction of the measurement circuits.
On comparing noise metrics applied to hearing conservation
Authors: Earshen John J.
Published: October 2005

A number of different metrics are in use for measuring and reporting exposure to noise for hearing conservation including noise dose, time-weighted average level, sound exposure, and sound exposure level. Functions for computation of individual metrics from measurement of acoustic pressure vary widely. Functions defining particular metrics in some instances contain choices of parameters (e.g., exchange rates and threshold levels). In most instances, once a metric has been evaluated for a particular time profile of acoustic pressure, it is not possible to convert it to another metric if the original time function is not retained. In addition to the defining functions, dynamic and frequency response characteristics of measuring instruments have influences on results obtained and can present obstacles to conversion among metrics. Large bodies of data exist which only contain the finally processed metric. The degree to which comparisons can be made because of recent changes in TLV requires inferential interpretation of the values of specific metrics which are produced by time functions that are identified only in a statistical sense. This paper examines the inferential relationships among prominent metrics for various classes of sound-pressure profiles as obtained with measuring instruments meeting ANSI and IEC performance standards.
Comparison of daily noise exposures in one workplace based on 3-dB vs 5-dB exchange rates and criteria recommended by the ACGIH versus OSHA
Authors: Petrick Michelle , Royster Larry , Royster Julia D. , Reist Parker
Published: October 2005

In May 1994, the American Conference of Governmental Industrial Hygienists (ACGIH) recommended as a threshold limit value (TLV) for noise exposure an 8-h equivalent level of 85 dBA, based on a 3-dB exchange rate. The U.S. Department of Labor’s Occupational Safety and Health Administration (OSHA) requires that employees be included in a hearing conservation program (HCP) if their 8-h time-weighted average (TWA) noise exposure equals or exceeds 85 dBA based on a 5-dB exchange rate. To investigate the number of additional employees who would be included in the HCP at one industrial facility if the ACGIH TLV were used, new personal dosimetry samples were collected for all noise-exposed employees. Employees at this facility have low noise exposures characterized by time-varying or intermittent noise and impact components. To allow analysis of each sample using both exchange rates, each monitored worker wore either two single-setting dosimeters or one double-setting dosimeter. Based on this data the potential impact if OSHA changed its present procedures for determining employee noise exposure will be presented.
Noise exposure measurements of the Tokyo String Quartet
Authors: Royster Larry H. , Royster Julia Doswell
Published: October 2005

During the Spring 1994 Meeting of ASA a special concert was given by the Tokyo String Quartet. During the first part of the program the Tokyo String Quartet played two music selections using each of four different sets of instruments: Old Italian instruments and modern instruments crafted by Carleen Hutchins, Curtin and Alf, and Robert and Deena Spear. The Tokyo String Quartet had previously agreed to allow noise dosimeter monitoring of their exposures during the first half of the program. In addition, one member of the audience also wore a noise dosimeter during the performance. The measured L(eq) values across instrument groups for the audience member exhibited a range of 0.7 dBA for the first musical selection and 0.6 dBA for the second selection. The remaining recorded database findings and its analysis will be presented. The authors are grateful to the members of the Tokyo String Quartet for allowing them the opportunity to obtain additional musician noise exposure information.
Sampling strategy for noise dosimetry measurements
Authors: Sachs Felix Z.
Published: October 2005

The U.S. Army has adopted most of the new ACGIH TLVs as criteria in its hearing conservation program. Most significant to the Army program was the change from a non-time-weighted inclusion criterion to the 8-h time-weighted average noise exposure level (TWA). The TWA must now be identified for all Army civilian personnel subjected to hazardous noise exposure and for soldiers working in noise-hazardous industrial operations. This can be accomplished without making noise dosimetry measurements on every single individual suspected of being exposed to hazardous noise. The U.S. Army Environmental Hygiene Agency Technical Guide 181 on noise dosimetry and risk assessment was developed as a guide for evaluating types of noise exposure patterns and includes sampling strategies for dosimetry measurement of TWAs. The statistical basis of the sampling approach will be discussed in some detail. Other changes in the Army hearing conservation program resulting from the adoption of the TLVs will be outlined.
New method dose for a 24-h estimation of occupational and nonoccupational noise
Authors: Menshov Alexander A.
Published: October 2005

Over 24 h the influence of occupational and nonoccupational noise may be distinguished by three periods: job, rest, and sleep. If the level of noise for each period is described in dBA there is no possibility of summing up these levels and receiving mean arithmetical values (average daily) because dBA is a logarithmic value. But if one describes levels of noise in doses there is a possibility of receiving a ‘‘medium-weighted’’ dose of noise load for 24-h because the doses are arithmetical values and it is possible to sum up and divide the total. If the dose level during the work is 1 dose −80 dBA, at rest 1 dose −40 dBA (one dose), and during sleep 1 dose −30 dBA (Ukraine and Russian sanitary standards), then the medium-weighted sanitary standard for the 24-h level of noise is one dose. The increase of the level for each a third 24-h period at 3 dBA above the norm will increase the dose level twice (two doses); at 6 dBA it will increase to four doses; at 9 dBA it will increase to eight doses; at 12 dBA, to sixteen doses, etc. If such high doses for each period are summed up and are then devised in three, a real medium-weighted dose of noise load for 24 h above the standard, which is 1 dose, will be found. This method is simpler than estimating the noise load above the standard for each third period of a 24-h influence of noise.
Detection of direct and indirect sonic booms from space shuttle landings
Authors: Cates Joseph , Sturtevant B. , Kanamori Hiroo , Mori J.
Published: October 2005

Two hundred seismic stations covering over 50 000 square kilometers in Southern California were used to analyze the sonic boom patterns from the landing of STS-42 in November 1993 and STS-58 in January 1994 at Edwards Air Force Base (EAFB). The instrument ground motion traces show separate arrivals which can be identified as the primary boom, creeping waves generated at the edge of the primary boom carpet, and multiple indirect sonic booms refracted from high altitude. The measured arrival times are compared with the results of linear ray tracing calculations through reference temperature and wind profiles for EAFB. The ray calculations accurately predict the measured arrival times and wavefront angles for the primary sonic boom and the creeping waves in shadow regions, and accurately predict the wavefront angles for the indirect booms. Ray theory using the reference atmosphere fails to predict indirect boom arrival time, observed multiple booms within the first shadow region, and extensive overlap of the multiply refracted sonic booms. These results suggest that boom exposure under the real atmosphere may be larger than previously expected.
Sonic boom rise time
Authors: Cleveland Robin O. , Blackstock David T.
Published: October 2005

The rise time of a sonic boom shock in air depends strongly on the relaxation processes of nitrogen and oxygen. Stratification of the atmosphere leads to significant variation of the relaxation processes with altitude. J. Kang [Ph.D. thesis, Penn State (1991)] argues that the shock profile can adjust quickly enough to changes in attenuation that it always appears to be in steady state. If correct, then rise time at the ground can be calculated from local conditions only. A time domain computer algorithm, based on work by Lee and Hamilton (‘‘Time domain modeling of pulsed finite-amplitude sound beams,’’ submitted to J. Acoust. Soc. Am. in March 1994), is presented for a Burgers-type equation. The algorithm includes the effects of nonlinear distortion, thermoviscous absorption, molecular relaxation, and ray tube spreading. A parametric study of the effect of change in relative humidity shows that the steady-state assumption is not justified for sonic boom shocks in the atmosphere. A sonic boom propagated through a real atmosphere is shown to have a rise time that, in all cases run so far, is shorter than that of a steady-state shock calculated using atmospheric properties at the ground only. [Work supported by NASA.]
Short term fluctuations in the sound field within a shadow region near the ground
Authors: Havelock David I.
Published: October 2005

An acoustic shadow region can be created near the ground by an upwardly refracting atmosphere or masking by prominent terrain features. Acoustic energy arrives deep within the shadow region principally by scattering from turbulence in the insonified region above the shadow. It is expected that the structure and dynamics of the turbulence ultimately determine the characteristics of the sound field observed in the shadow region. By identifying observable characteristics of this sound field, it is hoped that useful relationships between meteorological dynamics and sound field fluctuations within the shadow region can be established. A large array of microphones has been deployed on an asphalt runway to investigate the sound field fluctuations in a refractive shadow. The frequency range being investigated is 40–1000 Hz, at ranges up to 700 m. The evolution of the sound field over the period of a few seconds is discussed. Examples of the observed sound field are presented.
A change in sperm whale (Physeter macroephalus) distribution correlated to seismic surveys in the Gulf of Mexico
Authors: Mate Bruce R. , Stafford Kathleen M. , Ljungblad Donald K.
Published: October 2005

From 7 to 29 June 1993, vessel surveys for sperm whales were conducted in the Gulf of Mexico off the Louisiana coast. Ninety sperm whales were seen in water 600 to 1400 m deep. On four of the first five survey days, whales were found routinely in an area 100 km S.E. of the Mississippi River before a seismic survey operation began (0.092 whales/km). Within the seismic operations area, whale abundance changed significantly to 0.038 whales/km during the first two days and then to 0.0 whales/km for the following five days (p value <0.001). During the first two days of seismic activity, whales were only seen around the periphery of the seismic area. Survey effort for the last 5 days (920 km) and revealed only one group of four animals 61 km S.W. of the seismic survey area and also 56 km N.E. from another active seismic survey. Although the observation of seismic survey activity was serendipitous, it was highly correlated to numbers of sperm whales. This relationship deserves further investigation. If validated, additional efforts will be needed to identify areas used by sperm whales and assure that the effects of simultaneous seismic surveys do not overlap and prevent sperm whales from using important habitat.
Basic understandings of whale bioacoustics: Potential impacts of man-made sounds from oceanographic research
Authors: Clark Christopher W.
Published: October 2005

The recent increased public awareness and concern over the potential impact of acoustic sources for oceanographic research, particularly the source for the Acoustic Thermometry of Ocean Climate (ATOC) study, has raised the difficult issue of assessing both short-term and long-term effects. A baseline study in Kauai, HI has been underway for two seasons as part of the Marine Mammal Research Program associated with ATOC. This research specifically addresses the questions related to short-term (<4 months), small scale (<30-km radius zone of influence) issues using traditional visual and acoustic field methods. This includes shore-based and aerial observations, passive hydrophone array tracking, and aerial survey methods. These efforts, conducted prior to any operation of an ATOC source, provide a baseline measure of the level of short-term impact under ‘‘normal’’ conditions off Kauai, where normal includes regular exposure to noise from small craft, ships, helicopters, and airplanes. Potential long-term impact is addressed through statewide aerial surveys and through integration of the inter- and intra-seasonal variability of whale behaviors and distributions. Results of the Kauai research will be presented and discussed in terms of baseline impact and the need for standards.
Scattering of sound by turbulence into a shadow region
Authors: Stinson Michael R.
Published: October 2005

The sound field above ground due to a point source in an upwardly refracting atmosphere has been computed to determine the nature of turbulent scattering into an acoustic shadow region. A Green’s function parabolic equation (GFPE) method that includes turbulence via a phase screen approach [X. Di and K. E. Gilbert, J. Acoust. Soc. Am. 92, 2405(A) (1992)] is used for the simulations. Flat ground with finite surface impedance and a logarithmic sound-speed profile are assumed, and propagation ranges of 1 km are considered. Different realizations of a turbulent atmosphere were generated employing a Gaussian spectrum to describe the turbulence. For 500-Hz source tones, it was found that the components of the turbulence spectrum that contributed most to the scattered field in the acoustic shadow region corresponded to dimensions of the order of 2–5 m; this scale of structure can be understood in terms of a Bragg reflection condition. The sound pressure at a receiver position in the acoustic shadow appears to be dominated by contributions from a small number of localized scattering regions.
A new adaptive differential microphone array
Authors: Elko Gary W. , Pong Anh-Tho Nguyen
Published: October 2005

An adaptive differential microphone has been implemented by combining two omnidirectional elements to form back-to-back cardioid directional microphones. By combining the weighted subtraction of these two outputs, any first-order array can be realized. If certain simple constraints are placed on the combination weighting, the null location can be constrained to defined angular regions. Three algorithms that control the constrained adaptation are presented and discussed for the array: the LMS algorithm, Newton’s algorithm, and a time-varying least-squares Wiener filter. A real-time implementation utilizing an AT&T DSP32C digital signal processor is also described.
An adaptive subband differential microphone
Authors: Cezanne Juergen , Pong Anh-Tho Nguyen
Published: October 2005

In a previous talk, ‘‘A new adaptive differential microphone array’’ by Elko and Pong, a differential microphone has been introduced that adapts its directivity pattern to the particular acoustic environment to provide for a good signal-to-noise ratio. There, the selected pattern remains more or less constant with respect to frequency. In this talk an approach is described that contains one more degree of freedom. The spectrum of the signals is partitioned in uniform subbands and different directivity patterns are adaptively chosen in each subband. This allows to cancel multiple noise sources with nonoverlapping spectra. An LMS-based algorithm will be derived with focus on a low computational load and a short delay for the desired signal. Consequences on the speed of adaptation are discussed. Further, experimental results of a first implementation with 33 subbands on a PC-based DSP32C board will be presented. The measurements verify the ability of the algorithm to cancel multiple noise sources with disjoint spectra without distorting the desired signal.
Minimum error sound source localization
Authors: Rainton D.
Published: October 2005

A novel approach to the problem of computing the direction of arrival (DOA) of a sound source using a two-element microphone array is presented. Typically, the DOA is computed by peak picking from the resulting cross-correlation function. In order to improve such estimates it is usually desirable to pre-filter the signals prior to cross correlation. However, proper selection of these pre-filters is often problematic. The proposed algorithm adapts the filters during an initial training session to directly minimize the number of location estimation errors. The only information provided is the signal DOA, no explicit knowledge of the signal or noise spectra are required. It is assumed however that the overall signal/noise statistics are long term stationary over the training and subsequent testing. Examples of both linear and nonlinear filter design are presented for a talker location identification task.
Propagation in range-dependent poro-elastic media
Authors: Collins Michael D. , Kuperman W. A. , Siegmann William L.
Published: October 2005

Biot’s theory of poro-elasticity is derived for heterogeneous media and reduced to a system of three coupled equations. Previous formulations of this problem include a redundant fourth equation. The reduced system factors into incoming and outgoing wave equations and may therefore be solved with the parabolic equation (PE) method, which is useful for range-dependent problems. The operator square root is approximated using rational-linear functions that were originally designed for the elastic PE and provide accuracy and stability. An initial condition for the poro-elastic PE is obtained with the self-starter, which has been generalized to handle compressional and shear sources in poro-elastic media. Qualitative tests involving the propagation and reflection of slow and fast compressional wave beams and shear wave beams demonstrate that the poro-elastic PE handles all wave types. A solution based on the wave-number spectrum has been developed to test the poro-elastic PE quantitatively. The PE and spectral solutions are nearly identical for problems involving a water column overlying a poro-elastic sediment. A nonlinear relationship involving the coefficients of the wave equation and the Biot moduli has been worked out so that the natural parameters (i.e., porosity, density, wave speeds, and attenuations) may be used as inputs to propagation models.
A new high-frequency ocean bottom backscattering model
Authors: Chotiros Nicholas P. , Boyle Frank A.
Published: October 2005

A new model of acoustic backscatter from the ocean bottom is presented. Based on the analysis of existing data, three main physical mechanisms have been identified. These are gas bubbles, sediment grains, and interface roughness. Gas bubbles are particularly prevalent in shallow water sediments. A single-scatter approximation is used to model the bubble scattering. Scattering from sediment grains is a multiple-scatter problem which is still under investigation, but an empirical relationship is available. Scattering from interface roughness is modeled in terms of a Kirchhoff–Helmholtz scattering integral. The total backscattering strength is an incoherent sum of the three contributions. It is found that the interface roughness is dominant near normal incidence. The other two mechanisms tend to dominant at shallow grazing angles. [Work supported by Naval Research Laboratory, Stennis Space Center under the MCM Tactical Environmental Data System (MTEDS) project.]
Acoustic form function for porous solid spheres: Comparison between theory and experiments
Authors: Commander Kerry W. , Lim Raymond , Huskey Theodore W. L. , Baker Steven R. , Kargl Steven G.
Published: October 2005

An underwater acoustic scattering experiment was performed on three porous solid spheres of varying grain size to determine their acoustic form functions. The spheres were constructed from bonded glass beads, sized to yield permeabilities in the range of fine to medium grained sand. Measurements of required material and lattice parameters were determined on analogous cylindrical samples, including a measurement of the dry lattice moduli per the method described by Garrett [S. L. Garrett, J. Acoust. Soc. Am. 88, 210–221 (1990)]. Quantitative agreement between the acoustic measurements and predictions from a theoretical Biot model [S. G Kargl and R. Lim, J. Acoust. Soc. Am. 94, 1527–1550 (1993)] was found but only at the low-frequency end (<20 kHz) of the measurements and for the smaller grained spheres. Although the measured and predicted form functions were still qualitatively similar at higher frequencies, deviations due to inhomogeneities in the porous spheres became evident. For each discrete frequency measurement, the spheres were rotated 360 deg and variations in the backscattering strength noted. For values of ka where little variation with sphere orientation was obtained, there was good agreement with the theoretical model.
Moderate frequency acoustic penetration of a sandy shallow water sediment
Authors: Chotiros Nicholas P. , Kristensen Åge , Michelozzi Enzo
Published: October 2005

An experiment was conducted to investigate acoustic penetration of a sandy shallow water sediment, in the band 500 Hz to 2 kHz, in a site off LaSpezia, Italy. Acoustic sensors were buried in the sediment, forming a sparse three-dimensional array, to measure the sediment penetrating signals. The sound source was a sparker. The collected signals are processed coherently to give direction and speed of the sediment acoustic waves. From a theoretical point of view, the medium is treated as a poro-elastic solid governed by Biot’s theory of acoustic propagation. It is predicted to support two acoustic waves. Comparisons are made between theory and experiment. [Work supported by Office of Naval Research, Ocean Acoustics Program, Code 11250A, under the initiative for basic research in the physics of moderate to high frequency acoustics.]
The effect of roughness on acoustic penetration of the ocean bottom
Authors: Moe John E. , Jackson Darrell R.
Published: October 2005

The acoustic intensity penetrating a rough surface is analyzed using Rayleigh–Rice perturbation theory. When the grazing angle of the incident field is below the critical angle in relation to the mean surface, only the zero-order component of the transmitted field is evanescent; the higher-order components contain downward traveling waves. For an incident field below the critical angle, first-order computations using parameters appropriate to a sandy bottom show that the field below the rough surface can be much greater than the corresponding field below a flat surface. These computations are carried out using a low-frequency cutoff for the bottom relief spectrum. With regard to the accuracy of the calculation, both the short-wavelength portion of the relief profile that is retained as well as the long-wavelength portion that is discarded are considered. It is shown that the rms height of the portion retained and the rms slope of the portion discarded are sufficiently small to lend confidence in the perturbation approach. Further work is required, however, to unequivocally establish the accuracy of the method. [Work supported by ONR.]
On measuring sediment/Biot properties in shallow water at moderate to high frequencies
Authors: Abawi Ahmed , Hodgkiss W. S. , Kuperman W. A. , Collins Michael D.
Published: October 2005

A broadband line array is being designed and constructed to study the acoustics of shallow water in the moderate to high-frequency regime. The 64-element array will consist of nested apertures half-wavelength spaced at 4, 8, and 16 kHz with a total bandwidth of 2–20 kHz. The intention is to study both the forward and inverse problem, the latter with respect to sediment properties. The poroelastic parabolic equation [Collins etal., this meeting] is being used for simulations to (1) aid in the design of the array, (2) study the forward problem, and (3) investigate the potential observables with respect to the inverse problem. In particular, it is of great interest as to whether effects related to the Biot description are observable by measuring waveguide propagation. The use of the parabolic equation formulation will allow for a consistent extension to range-dependent environments in a future study. [Work supported by ONR Code 321OA.]
Finite difference simulations of propagation in a shallow water environment
Authors: Schneider John B. , Broschat Shira Lynn , Flynn Patrick J.
Published: October 2005

The propagation of acoustic energy in a shallow water environment is studied using a two-dimensional, staggered-grid finite-difference model. Such a model allows one to view the propagation of energy in the time domain throughout the region of interest. Since fields are available ‘‘everywhere,’’ the model can be used to guide the development of robust schemes for the detection of scatterers in the water column or buried in the sediment. In addition, it can be used to benchmark approximate models for acoustic propagation and scattering in shallow water. This paper considers the effect of different physical features on the possible identification of scatterers. Such scattering mechanisms as top and bottom roughness and inhomogeneities in the water column are considered. Monte Carlo simulations are used to gauge the relative effects of these features. Frequencies on the order of 7.5 kHz are considered for depths up to 30 m. The implementation used here includes several enhancements over traditional finite-difference models. For example, typical finite difference models approximate continuously varying material interfaces by an interface that appears like a staircase—the material properties change only at discrete location. For this research a conformal technique is used to model more accurately the continuous interface. [Work supported by ONR.]
Optimum beam widths for seafloor scattering problems
Authors: Stephen R. A.
Published: October 2005

Gaussian beams are often used for the insonifying field in scattering problems from interfaces. They have the advantage of restricting the grazing angle content of the incident field while localizing the scattering region on the interface. However a disadvantage is that the beams spread significantly. For oblique incidence, the width of the beam can vary significantly over the region of interaction on the interface and the scattering problem defined in these terms has an inherent propagation component. Analytical work has been carried out for the propagation of Gaussian beams in homogeneous and heterogeneous media [for example, Cerveny etal., Geophys. J. R. Astron. Soc. 70, 109–128 (1982)]. For a given propagation distance there is an optimal initial beamwidth that will minimize the width of the beam along the whole path. Consequently for a given angle of incidence and a given incident amplitude threshold, there will be a minimum surface scattering area. Optimum beamwidths can be defined and these should be used by all investigators in order to standardize results. [Work supported by Office of Naval Research.]
Problems associated with the renovation of existing music practice facilities
Authors: Walsh David P.
Published: October 2005

The acoustical design of music practice and rehearsal facilities is always an interesting and challenging task. However, the challenges increase significantly when the project is a renovation of existing facilities rather than a new design. In renovation projects, extensive investigation and evaluation of the building structure and construction assemblies are required since, in a great number of cases, the original drawings are no longer available. It is also not unusual for undocumented modifications to have been completed to the structure over the years. A working knowledge of outdated construction techniques and materials is typically required. This paper presents a case study of the renovation of the practice and rehearsal facilities for a university music department originally constructed in 1956. The original wall and ceiling systems did not provide satisfactory airborne sound isolation between practice rooms and major modifications were begun less than a year after opening. These modifications improved the overall degree of sound isolation between practice rooms somewhat, however, they were not completely satisfactory. This paper discusses the current modifications, together with the complications inherent in working on a building over 30-years-old for which minimal information on the original construction assemblies was available.
The application of a biologically inspired controller to control sound transmission
Authors: Carneal James P. , Fuller Chris R.
Published: October 2005

A biologically inspired control approach for reducing sound transmission through a distributed elastic system has been theoretically and experimentally verified for narrow-band excitation. The control paradigm approximates natural biological systems for initiating movement, in that a low number of signals are sent from an advanced, centralized controller (analogous to the brain) and are then distributed by local rules and actions to multiple actuators (analogous to muscle fiber). A local learning rule that was developed from linear quadratic optimal control theory and solved apriori was implemented. The investigation considered a plate excited by normal plane wave, oblique plane wave, and reverberant acoustic fields. Radiated sound power was the defined cost function and therefore used as the controller error signal. Four control inputs in the form of piezoelectric actuators were mounted on the plate in a two-by-two array. Results indicate that increases in transmission loss of approximately 18 dB are attainable for off-resonance excitation. In general, comparisons of theoretical and experimental data show good agreement. This investigation has demonstrated that the biological control approach has the potential to control multimodal response in distributed elastic systems using an array of many actuators with a reduced order main controller. Thus significant reductions in control system computational complexity have been realized by this approach. [Work supported by NASA Langley.]
Seat-dip phenomenon
Authors: Greenberg David , Burroughs Courtney
Published: October 2005

The ‘‘seat-dip phenomenon’’ is so called because an anomalous attenuation (dip) in the frequency response of auditoriums is found to be caused by the presence of rows of seats. As sound from the stage grazes over seats, it is subject to broad attenuation of the low frequencies from 75 to 300 Hz. This frequency dip can be as much as 20 dB below the sound level without the presence of seats. Experiments were performed with a simple 1:10 scale model of an auditorium floor. It is found that the dip is caused by a coincidence of effects rather than the single effect dominant in the literature. The effects are considered. (1) A standing wave between the seat and source with nulls relating to the quarter-wavelength distance, (2) half-wave cancellations where reflected and/or diffracted waves interfere with the on-coming wave, and (3) the propagation of the sound of interest at nearly zero degrees over the seats. It is shown that the standing waves and sound pressure cancellations associated with each successive row of seats occur at frequencies that are very close to each other. The effect of frequency spreading of (1) and (2) are presented.
Stable dereverberation using microphone arrays for speaker verification
Authors: Surendran A. C. , Flanagan J. L.
Published: October 2005

The impulse response of a reverberant environment, in general, is a nonminimum phase and cannot be inverted. But an exact inverse of the environment can be obtained by modeling the room as a multiple input–output (MINT) system [M. Miyoshi and Y. Kaneda ICASSP (1986)]. In this report, this model is applied to a microphone array and is used as a front-end processor for a speaker verification system. The G matrix is inverted using row action projection (RAP), an iterative approach to solving a system of linear equations. Starting from an initial guess, the solution is repeatedly projected onto each hyperplane of the equation system until it converges. The method is stable, robust to noise, and converges to the pseudo-inverse solution. In computer-simulated experiments, the signal-to-reverberant-noise ratio is found to improve with the number of microphones in the array. A speaker verification system using the array is evaluated at various signal-to-competing-noise ratios (SCNR). Results suggest that verification performance can be substantially elevated in adverse acoustic environments.
A multisensor connectivist model for the preprocessing of the speech signals
Authors: Kuyel Turker , Hixson Elmer L.
Published: October 2005

Due to the inherent redundancy of the speech data, the design of a redundancy reducing speech preprocessor is very important. Preprocessor design is also very important because it can greatly reduce the computational load on the later stages of speech processing. A special laboratory oriented method in speech data acquisition, which is called near-field spectral wave number estimation is implemented. In this method multiple microphones are used. The goal is to incorporate air flow velocity into speech feature vector. This extra feature is used in addition to the short time cepstrum of the sound data to make the final speech vectors. The speech vectors are then quantized into a determined number of categories using a self-organizing neural network. These quantized and extended vectors are then used for the modeling of higher speech constructs such as phonemes and words. The preprocessing scheme reduced the computational complexity considerably at the expense of slight reduction of the recognition accuracy.
Position-tolerant differential microphones for noisy environments
Authors: West James E. , Elko G. W. , Morgan D. R. , Kubli R. A.
Published: October 2005

Directional microphones are best noted for their noise reduction properties in communication systems. Close-talking differential microphones are particularly useful when the noise environment disturbs the ability to communicate without error, such as in public and cellular telephony, aircraft communications, etc. These differential microphones work best when they are placed within 1 cm from the lips of the talker where the sound field has a large gradient. For a plane-wave sound field the sensitivity rises proportional to ωn, where n is the order of the difference. Users of differential microphones do not always correctly position the sensor at the proper distance from the mouth and therefore the sensitivity of the microphone may also rise proportional to ωn especially at high frequencies. A method is described of correcting for this high-frequency gain without significantly degrading the noise canceling properties of first- and second-order differential microphones.
Sound attenuation in a cylindrical tube due to evaporation–condensation
Authors: Mao Yi , Sabatier James M.
Published: October 2005

The influence of evaporation–condensation processes on the sound propagation in a cylindrical tube were studied in an attempt to understand the sound attenuation in porous materials. In the theoretical model, the tube wall was rigid and kept a constant temperature. A very thin layer of water on the wall was allowed to evaporate into or condense from the sound field propagating in the tube. In addition to the acoustical, thermal, and vorticity modes in Kirchhoff’s theory, there exists a mass-diffusion mode. The sound attenuation was obtained by applying the boundary conditions on the tube wall to these four modes. Analytic expressions for the asymptotic behaviors of both high and low-frequency limits were derived. While the sound attenuation due to viscosity could be identified, those due to thermal conduction and evaporation–condensation were coupled. The sound attenuation due to the evaporation–condensation process would increase to a substantially large level when the percentage of vapor in the tube was high, but it still underestimated the experimental results in porous materials. [Work supported by ONR.]
Wave dynamics and flow in multiple-porosity media
Authors: Margulies Timothy S.
Published: October 2005

The purpose of this paper is to describe the fluid flow and dynamics of wave propagation in multiple-porosity media (such as applied to porous rock with fissures of different sizes). Coupled partial differential equations for matrix deformation and Darcy flow with compressible mass conservation equations obtained from continuum mixture theory are developed. For the limiting case of a single porosity medium the transient response (pressure decay) solution for drilling into a gas saturated rock layer, for example, that is homogeneous and isotropic, will be derived exactly by transformation of the nonlinear diffusion equation describing the motions. Furthermore, a Burgers equation which admits solitons will be presented. Finally a generalization to the case of dual/triple continua will be treated.
Propagation of sound in a lined circular duct with sheared mean flow
Authors: Wu Jinlong , Hamilton Mark F.
Published: October 2005

This presentation describes an analytical investigation of the propagation of sound in a lined circular duct with sheared mean ambient flow. The main assumptions are that the ambient flow is turbulent and unaffected by the sound, the Mach number for the flow is small compared to unity, the thickness of the viscous boundary layer is small in comparison with the radius of the duct, and the acoustical lining is locally reactive. The mean flow profile away from the wall is assumed to be uniform, but the profile within the boundary layer can take one of several analytic forms. Outside the boundary layer, the acoustic mode structure is described by Bessell functions. The solution within the boundary layer is expressed in terms of Kummer functions, and the dispersion relation is obtained by matching the inner and outer solutions, taking the wall impedance into account. The dispersion relation is solved numerically for the attenuation and phase speed of the sound as a function of mode number, complex wall impedance, boundary layer thickness, and flow profile within the boundary layer. Both upstream and downstream propagation are considered. Comparisons are made with published numerical results.
Studies of the relationships between ear canal and cochlear signals for external tones and spontaneous and distortion product otoacoustic emissions, and their connection with middle ear transmission
Authors: Talmadge Carrick L. , Tubis Arnold
Published: October 2005

Some knowledge about the transmission characteristics of the human middle ear may be obtained by comparing ear canal levels of external tones and spontaneous emissions of the same frequency, which when used with another tone give similar ear canal levels of distortion product otoacoustic emissions. It is assumed that the cochlear activity patterns of an external tone of frequency f2 and a spontaneous emission of frequency f2, which produce the same levels of ear canal cubic distortion products when used in conjunction with an external tone of frequency f1 and fixed level, are very similar. The degree of similarity is studied using nonlinear active cochlear models that give spontaneous emissions [Talmadge and Tubis (1993)]. The relationship of the cochlear activities at the place of peak excitation and at the base of the cochlea is also studied in detail. The model results indicate that the comparison of ear canal levels of external tones and spontaneous emissions, which are equivalent with respect to the production of distortion product emissions, may be used to give estimates of the reflection and transmission of cochlear waves at the stapes. [Work supported by the Deafness Research Foundation.]