bluuebunny/crossref_metadata_2025 huggingface dataset:
A time domain formulation of the absorption limited transient parametric array
Authors: Stepanishen Peter R.
Published: October 2005

The impulse response of the absorption limited transient parametric array is developed using a time-dependent Green's function approach. A simple closed-form expression is developed for the farfield spatial and time-dependent impulse response of the parametric array. Farfield pressures are expressed as a time convolution of the impulse response and a source function. Numerical results for the farfield pressures resulting from a Gaussian-modulated carrier are presented to illustrate the spatial and time-dependent characteristics of the field. Additional numerical results are presented for the farfield pressures resulting from the pulsed excitation of a simple model of an ultrazonic transducer. These latter results are compared to existing experimental data and noted to be in general agreement. [Work supported by ONR.]
Application of array processing to active noise cancellation in underwater acoustics
Authors: Gan W. S.
Published: October 2005

In this paper, array processing is applied and extended to wide, distributed noise sources. Array processing increases the speed of computation of FFT and Green's function. For narrow-band noise, a linear array of sensors is used. The array propagation vector and the weight vector are derived. In order to obtain optimal solution for noise cancellation, four correlation matrices are derived. Adaptive filters and Widrow's mean-square error algorithm are used. The optimal “Wiener” solution for the Wiener-Hopt equation in matrix form is obtained. For broadband noise, Wiener linear minimum mean-square error filtering is also used. The spectral density function of the noise component to be cancelled is derived. The broadband Wiener solution which is a generalization of the narrow-band case is obtained.
Laboratory-scale simulation of under-ice reflectivity at low frequencies
Authors: McLanahan T. , Diachok O. I. , Wales S. C.
Published: October 2005

Under-ice reflectivity is dominated by sea ice ridges, long, randomly spaced, randomly oriented rubble piles of broken ice. The effective low-frequency shear and compressional velocities of these formuations have been estimated to be between 1100–1700 and 2700–3400 m/s, respectively (Diachok, Proceedings International Congress on Acoustics, 1986). To be consistent with these estimates, Lucite, a readily available and easily machined material, for which Vs = 1260 m/s and Vp = 2600 m/s was used to construct laboratory scale analogs of sea ice ridges situated on a thin plate. Both parallel and randomly oriented ridge models were construtted, and the effects of ridge elasticity and orientation on under-ice reflectivity (amplitude and phase) were examined for 0.67 < ka < 6 (k = wavenumber and a = mean depth). Initial reflection coefficient data at the lowest frequencies are approximately consistent with Twersky's predictions for reflectivity from both hard and soft half-cylinders on a soft boundary. Higher frequency results, including phase versus grazing angle, will also be reported, and implications for under-ice propagation modeling will be discussed.
Arctic low-frequency propagation loss from shallow cracks in ice plates
Authors: Chamuel Jacques R. , Brooke Gary H.
Published: October 2005

At the 111th Meeting of the Acoustical Society of America, the authors reported on the effects of shallow cracks in floating ice plates on lowering the flexural wave dispersion curve creating discrepancies in plate thickness determination. In this paper, the effects of shallow cracks in sea-ice plates on low-frequency propagation loss in the water waveguide underneath the ice are demonstrated using laboratory ultrasonic models. Air-filled shallow cracks extending near vertically in the ice plate present sharp impedance discontinuities to the low-frequency water acoustic waves coupled to the ice plates. Upward refraction in arctic water increases the interaction of the acoustic waves with the cracks causing distributed backscatter along the water waveguide. The importance of the cracks increases as the effective water waveguide depth is decreased. Experimental laboratory results are presented for shallow water waveguide conditions. The new findings may explain the very high backscatter levels and high propagation losses of low frequencies observed in the Arctic. [Work supported by DREP.]
Geoacoustic scattering from seafloor features in the ROSE area
Authors: Dougherty Martin E.
Published: October 2005

A strong “refraction branch diffraction” has been observed on ocean bottom hydrophone data from the Rivera Ocean Seismic Experiment (ROSE). Modeling of the interaction between seismic/acoustic energy and the ocean bottom has shown that this arrival could be caused by scattering from common seafloor features. Seismic/acoustic wave propagation was computed for models of marine seismic refraction lines using a 2D heterogeneous formulation of the elastic wave equation. These models demonstrate that a significant amount of energy is diffracted from seafloor structures such as hills and valleys when both the direct water wave and the refracted compressional wave (traveling through the upper crust) are incident upon a structure. Since much of the diffracted energy travels through the crust, the diffracted arrivals appear on the refraction branch of the seismograms at large ranges. Energy partitioning at the seafloor of the two incident wave types produce both compressional (P) and shear (S) diffracted phases in the upper oceanic crust. The large models used also clearly demonstrate the existence of phases which are theoretically possible but rarely identified in marine seismic data such as the pseudo-Rayleigh wave and the P and S interference head waves.
Acoustics of the Highland, Irish, and Baroque harps
Authors: Firth Ian M.
Published: October 2005

Measurements of the string lengths of the extant Highland and Irish harps and the harps of the Baroque period show that there has been a consistent scaling rule used in the construction of the harp from the 14th Century to modern times. Acoustical measurements on extant instruments in museums using portable equipment show that modes of vibration of the soundboards of these instruments can be correlated. Over this period the method of construction of the harp has altered considerably from the Highland and Irish, made of a sound chest hollowed from the solid with string arm and column without any glued joints to the modern harp made of many pieces with a spruce soundboard. The change in construction took place in the Baroque period and measurements show that the modern harp maintains the string scaling rules of the earliest harps of the western seaboard of Europe but incorporates the lighter and more complicated construction of the Spanish type of harp played in the Baroque period. The measured acoustical modes of vibration of a Spanish harp of the Baroque period suggest that the modern concert harp is descended from that type.
Acoustical studies on p′i-p′a and cheng
Authors: Feng Shih-yu
Published: October 2005

Improved holographic interference patterns of the vibrational modes of the front plate of a p′i-p′a will be shown. Most of the modes lie below 2000 Hz and those having larger amplitudes of vibration lie between 320 Hz to 1300 Hz. Vibrations of the front plate due to plucking of the strings have been studied. It is found experimentally that any one of the three strongest plate modes can be excited when the fundamental frequency of the plucked string is equal to or is a subharmonic of the frequency of that mode. The p′i-p′a sound generated by plucking the string is picked up by a sound level meter and the Fourier components are obtained by using a digital storage oscilloscope coupled to an Apple II computer. Because of the lack of an anechoic chamber, the sound level meter was placed not more than 1 m from the front plate. Even with this limitation, it was discovered that the sound pressure levels associated with different mode patterns decreased, with increasing distance, at different rates. This seems to mean that listeners at different distances from the player would hear music of different tone quality. Holographic vibration patterns and frequency response curves were also obtained for another Chinese musical instrument, the cheng. Efforts were made to identify various wood or air resonances. The cheng is a much larger instrument than p′i-p′a, and both its front and back plates can vibrate strongly.
On the usefulness of active sound intensity for sound power determination
Authors: Nicolas J.
Published: October 2005

In order to examine the limitations associated with this technique, a systematic study of the various parameters affecting intensity measurements to determine sound power will be presented. The effect of the finite approximation, phase mismatch, inter-active intensity, the number of points, and the spatial distribution of the points will be discussed, keeping in mind actual measurement conditions. Some in-situ experimental studies will be presented. For a typical section of a textile machine, the power measured via ISO 3744 in a semianechoic field compared well with that measured in a semireverberant room using intensity, confirming the validity of the technique. Further, it will be shown that intensity can be used to differentiate the noise emitted by the frame from that of the spindle. A systematic way of including a criterion of precision will be proposed. This leads to a tolerance which gives the degree of confidence on the measurement and which points out clearly unfavorable conditions.
A statistical analysis of the estimation error of sound power measured by sound intensity techniques
Authors: Wu Mei Q. , Crocker Malcolm J.
Published: October 2005

The difference between the exact power passing through the measurement surface and the sound power estimated from a finite number of sound intensity measurements is defined as the estimation error. Based on the expression of the error derived in a previous paper [M. Q. Wu and M. J. Crocker, Proc. INTER-NOISE 86, 1129 (1986)], the statistical properties of the error were studied and frequency histograms of it were drawn for the cases where the sound source was assumed to be a point monopole with random locations over the source surface and the measurement surface was a 1-square-meter square parallel to the source surface. It is found that if the measurement distance is 0.3 m and if four sound intensities are measured over the measurement surface, then for 89% confidence the estimation error will be less than 0.9 dB. If the measurement distance is increased to 0.5 m, then for 99% confidence the estimation error will be less than 0.5 dB. Some estimation of the necessary number of sound intensity measurements for a given error limit has also been conducted.
Radiation efficiency as a factor in the design of engine components
Authors: Pettyjohn Steve
Published: October 2005

The importance of radiation efficiency as a factor in the design of engine components is shown. The sound power reduction of a two-piece engine gear cover was the goal. In the past, the action taken was to reduce the vibration amplitude. This ignores the role of radiation efficiency, often assumed to be one. Wallace [C. E. Wallace, J. Acoust. Soc. Am. 51, 926–945 (1972)] has shown how to analytically calculate radiation efficiency. Three models of the gear cover were developed. The standard gear cover comprises the flat steel plate attached to the block and an aluminum shell covering the gears. The first model, ♯1, greatly stiffened the shell; the second model, ♯2, greatly stiffened the flat plate; and the third model, ♯3, reversed the units, i.e., an aluminum shell was attached to the block and thin steel cover was used to enclose the gears. The model showed decreasing sound power levels from ♯1 to ♯3. A prototype part made up to the specifications of number ♯3 showed sound power measurements, using acoustic intensity methods, in close agreement with predictions.
Calculated B/A parameters for n-alkane liquids
Authors: Hartmann Bruce , Balizer Edward
Published: October 2005

The B/A parameters for a series of n-alkane liquids of chain lengths n = 5,7,8,9,12,16, and ∞ (i.e., molten polyethylene) were calculated from an analytic PVT equation of state, supplemented with experimental heat capacity data. The density, thermal expansion coefficient, sound speed, and sound-speed derivatives (with respect to temperature and pressure) all vary in a systematic manner with chain length and approach the polyethylene values asymptotically. The pressure derivative of the sound speed is calculated much more accurately than the temperature derivative; but since the pressure derivative term dominates, the overall accuracy of the calculations is dose to the experimental accuracy. Calculated density values agree with experiment to within 0.2% while B/A values, which require a second derivative of the density, are within 5% of the values calculated numerically from experimental sound speeds in the literature.
Relationship between extra-high-frequency hearing and cardiovascular endurance in noise-exposed industrial workers
Authors: Donahue Amy , Diefendorf Allan O.
Published: October 2005

Extra-high-frequency audiometry may have a clinical use as an indicator of the traumatic effects of noise. The purpose of this study was to determine if cardiovascular endurance has a relationship to the extra-high-frequency thresholds of hearing. Industrial workers (ages 27–30, with normal hearing in the conventional frequency region) exposed to daily noise doses of 85–88 dBA served as subjects. Cardiovascular endurance and extra-high-frequency thresholds were determined for 50 subjects. A two-factor ANOVA (Group × Frequency) revealed no significant differences in the extra-high-frequency thresholds of two groups of industrial workers with varying cardiovascular endurance. For 50 subjects, no significant correlations existed between the thresholds of hearing at the extra-high frequencies and cardiovascular endurance. It was concluded that cardiovascular endurance cannot be used to determine individual susceptability to the noxious effects of noise.
Mathematical model of the effect of limited stapes displacement on hazard from intense sounds
Authors: Price G. Richard , Kalb Joel T.
Published: October 2005

As a follow-on to an idea presented earlier [G. R. Price, J. Acoust. Soc. Am. 56, 195–197 (1974)] an integrated mathematical model of the external, middle, and inner ears has been developed for the cat ear. It allows the calculation of stapes displacements (among other values) in response to any free-field sound pressure. An absolute limit to displacement of about 20 μ peak to peak is assumed, based on the dimensions of the annular ligament and in accord with the measurements of Guinan and Peake [J. Acoust Soc. Am. 41, 1237–1261 (1967)]. Where hazard from intense impulses, such as gunfire, are concerned, the effect of this limitation on stapes displacement is profound, producing a spectral bias (higher velocities being transmitted at high frequencies) as well as the blocking of transmission into the cochlea when amplitudes exceed the limiting values. This action may in part explain why low-frequency impulses are much less hazardous than their energy content would seem to indicate as well as why hearing losses are not more severe for very intense sounds (150 dB and up) commonly found around weapons.
Ascending and descending thresholds of pure tones
Authors: Young I. M. , Lowry L. D.
Published: October 2005

Fixed frequency Békésy threshold measurements were made for subjects with normal hearing and hearing impairment. Ascending (no sound to sound) and descending (sound to no sound) methods were used for both continuous tones and tones interrupted 212 times per second with attenuation rates of 2.5 and 5.0 dB/s. For ascending method, the ratio of time to reach the first appearance of tone by slow and fast attenuation rates was 2:1. For descending method, the ratio of time to reach the first disappearance of tone was 1.6-1.7:1. There were no observable differences in these ratios for various frequencies, starting intensities, interrupted and continuous tones, and for subjects with normal hearing and hearing impairment. The ratio of 2:1 was the same as the speed of mechanical attenuation rates. The ratio of 1.6-1.7:1 may suggest that the slower attenuation rate decreased speed of machine relatively slower than mechanism of adaptation. In conventional automatic audiometry, pulsed tones are interrupted 212 times per second with an off-time of 200 ms. For this stimulus, substantial amount of adaptation can be demonstrable even in normal ears if threshold is approached from above-threshold stimulus levels. The results were compared and discussed with our previous data in that an offtime of 700 ms or longer is required for complete recovery from adaptation when descending method is used.
Perceptual basis for the compact-diffuse distinction for consonants
Authors: Hawkins Sarah , Stevens Kenneth N.
Published: October 2005

A distinguishing acoustic property of velar obstruents is a prominent midfrequency “compact” spectral peak (roughly 800–2000 Hz). Is there evidence for a qualitatively different auditory response for sounds with compact as opposed to diffuse spectra? We generated two ten-item series of bursts by exciting a group of resonators with white noise and systematically varying the relative amplitudes of the spectral peaks corresponding to formants 2 to 5. Stimuli at one end of each continuum had a compact, k-like spectrum and at the other end a diffuse p-like or t-like spectrum. The bursts were appended to short, transitionless vowels with or without intervening aspiration. Identification functions were obtained for the syllable-like stimuli (with response alternatives p t k b d g) and for the isolated bursts (using an ABX paradigm). The results suggest that a sound with a compact spectral peak can cause a distinctive perceptual response when that peak is sufficiently narrow and projects well above adjacent spectral minima. Responses are also influenced by the amplitude of the burst in relation to the following vowel and by the burst duration. Possible mechanisms underlying this distinctive response are discussed. [Work supported in part by NINCDS.]
Importance of various frequencies to perception of continuous discourse
Authors: Pavlovic Chaslav V. , Studebaker Gerald A. , Sherbecoe Robert L.
Published: October 2005

Normal-hearing subjects estimated intelligibility of continous discourse passages spoken by three talkers under various conditions of filtering and noise interference. The relationship between the intelligibility of continuous discourse and the articulation index (transfer function) was different from any found in ANSI S3.5-1969. Also, the lower frequencies were found to be relatively more important for the intelligibility of continuous discourse than for identification of nonsense syllables and other types of speech for which data are available except for synthetic sentences.
Sound scattering by fluid cylinders of finite length
Authors: Stanton T. K.
Published: October 2005

The scattering of incident plane waves by penetrable fluid finite-length circular cylinders for all frequencies is described. The results appear to be valid for all frequencies for lengths much greater than the diameter of the cylinder and limited to low frequencies (ka ≪l) when the length is comparable to the diameter. By neglecting end effects, we are able to approximate the volume flow per unit length of the scattered field of the finite cylinder by that of the infinite cylinder. The solution is obtained by integrating this volume flow along the length of the cylinder. This approximation restricts the solution to geometries where the direction of the incident wave is normal or near-normal to the lengthwise axis of the cylinder. The results are compared to those from other theories and to data. Under the same limiting conditions that the other theories were derived, the solution in this paper is identical to those. There was good to excellent agreement between this solution, when appropriately truncated to include just the first few modal terms, and lead cylinders and preserved shrimp. Finally a simple heuristic “high-pass” model is also derived and shown to pass through the data and asymptotically approach the rigorous solution at extreme values of ka. [Work supported by ONR.]
Amplitude and spectral characteristics of low grazing angle backscattering
Authors: Koenigs Paul D.
Published: October 2005

Acoustic backscattering from the sea surface at grazing angles in the region of 5 deg is affected by shadowing. Under these conditions the equations presented by Bass et al. [IEEE Trans. Antennas Propag. AP-16 (5) (Sept. 1968)] may be combined to form a single equation. The agreement between experimental data near 1 kHz and the unified equation is good. The frequency shift of the backscattered acoustic energy is dependent on wave height and period through the horizontal orbital particle velocity. The frequency spread of backscattered energy is still dependent on the same particle velocity but is diminished because the wave troughs are preferentially insonified. The experimentally determined values of backscattering strength compare favorably with other reported low-frequency, low grazing angle data.
Frequency resolution and speech discrimination in persons with sensorineural hearing loss
Authors: Thibodeau Linda , Van Tasell Dianne J.
Published: October 2005

Two experiments were conducted to evaluate frequency resolution and speech discrimination in a group of seven subjects with nearly equivalent flat, sensorineural hearing losses. In experiment 1, percent correct detection of a 2000-Hz tone was measured as a function of notch width in band-reject noise. In experiment 2, percent correct discrimination of synthetic speech syllables differing in spectral content in the 2000-Hz region also was evaluated as a function of notch width in the same band-reject noise. Two indices were determined from the percent correct functions obtained in each experiment: (1) the rate at which performance improved as notch width increased, and (2) the notch width at which 100% detection or discrimination occurred. Correlations among the four indices were computed. Moderate correlations were observed between tone detection and speech discrimination in notched noise. [Work supported by NIH and PHS.]
Temporal processing abilities of hearing-impaired listeners
Authors: Espinoza-Varas B. , Watson C. S.
Published: October 2005

It has been suggested that deficits in speech processing associated with hearing impairment may result in part from deficits in basic temporal processing abilities. Performance of 16 sensorineural hearing-impaired listeners, whose mean heating loss ranged from 25–95 dB, was studied with a battery of discrimination tasks [Watson et al., 1. Acoust. Soc. Am. Suppl. 1 71, S73 (1982)]. The tasks included discrimination of: (a) duration of a 1.0-kHz tone; (b) temporal jitter within a train of square pulses; (c) temporal order of two sinusoidal frequencies; (d) temporal order within sequences of syllables; (e) detection of a variable duration test tone, embedded in a nine-tone sequence; and (f) frequency and intensity of 1.0-kHz tone. Stimuli were presented over headphones, with 6 dB/oct frequency pre-emphasis, or in the field while the subjects wore their hearing aids. The sensation level was in all cases held constant at 25–30 dB. Although there were notable individual differences, the average performance in the temporal processing tasks with tones [i.e., tasks (a), (b), (c), and (e)] was remarkably similar to that of a group of a control normal listeners (n = 33). However, the hearing-impaired listeners exhibited expected deficits on each of four speech processing measures (SRT) discrimination scores, syllable identification, and temporal order of syllables). No strong correlations were found between temporal processing abilities and degree of hearing loss. It therefore appears unlikely that deficits in speech processing could be explained in terms of deficits in the temporal processing abilities here studied.
Discriminability of frequency-response irregularities in hearing aids
Authors: Sullivan Jean A. , Levitt Harry , Hwang Jain-Yih , Hennessey Ann Marie
Published: October 2005

Frequency-gain characteristics of a large number of hearing aids were measured using a computer-based system for the automated measurement of hearing aids [Levitt and Sullivan, Hear. Instrum. 37, 16–18 (1986)]. Irregularities in the frequency-gain characteristic were specified in terms of the peak-valley ratio and bandwidth of each spectral peak. Typical frequency-response irregularities were then simulated on a digital master hearing aid and the detectability of both single and multiple peaks was measured using an adaptive paired-comparison technique. The average peak-valley detection threshold for single peaks was approximately 6 dB for normal-hearing subjects and 11 dB for hearing-impaired subjects. The average detection threshold for a typical set of four multiple peaks was approximately 6 dB for hearing-impaired subjects. [Research supported by NIHR.]
The detectability and acceptability of time and frequency amplitude clipped speech
Authors: Neuman Arlene C. , Levitt Harry , Toraskar Jayashree
Published: October 2005

Thresholds of detectability and acceptability of unfiltered and filtered speech clipped in the time and frequency domain were obtained on normal hearing listeners. Speech signals were digitized and the clipping of the signal in the time or frequency domain was done through a digital master hearing aid. All subjects were able to detect very small amounts of clipping (less than 1%) in both the time and frequency domains. However, the intelligibility of the speech continued to be acceptable until approximately 25% of the signal was clipped. More clipping could be tolerated in the time domain than in the frequency domain. Prefiltering of the speech (high-frequency boost) allowed increased clipping in the time domain. [Research supported by NIH.]
Boundary layer transition as a source of noise and vibration
Authors: Lauchle Gerald C. , Josserand M. A.
Published: October 2005

When laminar flow over a rigid or flexible surface becomes unstable, an intermittent flow state occurs. This intermittent flow regime, called the transition region, is where turbulent spots are created, and then grow as they convect downstream at a velocity typically equal to 0.7 times the free-stream velocity. The spots eventually coalesce to form the beginning of the fully developed turbulent boundary layer. The statistics of the velocity or pressure fluctuations in the transition region are essentially stationary in time, but nonhomogeneous in the streamwise direction. Fundamentally, it has been argued that this region is capable of creating monopole sound radiation, e.g., Lauchle [J. Acoust. Soc. Am. 69, 665–671 (1981)] and Sornette and Lagier [Acustica 55, 255–267 (1984)]. Also, it has been suspected that a transitional boundary layer can induce wall vibrations. These issues have been under study for some time. We have completed a set of measurements on the. space-time statistics of turbulent spots in a naturally occurring transition zone and from them developed an analytical model for the wavenumber-frequency spectrum of the pressure fluctuations. Based on this model, it appears that the transition zone wall pressure is less intense than that of a fully developed turbulent layer by a factor equal approximately to the intermittency factor. This presentation will review the current research findings on wall pressure fluctuations and radiated sound caused by boundary layer transition. [Work supported by Applied Research Laboratory under NAVSEA contract.]
Wave vector-frequency spectra of nonhomogeneous fields
Authors: Strawderman Wayne A.
Published: October 2005

The utility of wave vector-frequency spectral analysis for the description and interpretation of hydroacoustic and structural-acoustic fields has been amply demonstrated over the past decade in both theoretical and experimental applications. In the majority of these applications, the statistics of the random fields of interest were assumed to be stationary and homogeneous. While many of the hydroacoustic and structural-acoustic fields of practical interest can be considered stationary, few can be considered homogeneous. Structural-acoustic fields are nonhomogeneous owing to the space-varying nature (e.g., boundaries) of practical structures. In hydroacoustics, the natural growth of the turbulent boundary layer results in a nonhomogeneous pressure field at the boundary. This paper addresses the application of wave vector-frequency analysis to the description and interpretation of nonhomogeneous, but stationary, fields. Whereas only one definition of the wave vector-frequency spectrum exists for a homogeneous, stationary field, several alternative definitions of the wave vector-frequency spectrum are possible for the nonhomogeneous, stationary field. The utility of these various spectral forms for the analysis and interpretation of nonhomogeneous, stationary fields is assessed.
Flow-induced noise and vibration of confined jets
Authors: Ng Kam W.
Published: October 2005

An experimental program was conducted in the acoustical water tunnel to determine the flow-induced noise and vibration on pipes due to various flow restrictors. Several flow restrictor configurations were tested for a range of flow velocities (up to 15 m/s). The flow configurations tested include: pipe flow, and flow restrictors with circular, coannular, rectangular cross-sectional areas, as well as multiple circular and slot jets. Wall pressure fluctuation and acceleration measurements were made using miniature hydrophones, flush-mounted on the inside wall of the pipe, and accelerometers mounted on the outside wall. Spectral and cross-spectral densities of the wall pressure and acceleration signals were determined. Experimental results showed that the flow-induced noise levels vary with the pipe axial location. The peak noise is located at the vicinity of the end of the jet potential core (six jet diameters downstream of the jet). Correlation of noise versus velocity showed a velocity to the 4.8th power relationship. Normalized noise spectra were obtained for the various flow configurations. The spectral shapes of the various flow configurations are quite similar, except that the coannular and slots jets show more high-frequency noise. The pipe-wall structural resonances were identified by correlating the various hydrophone signals. These resonance frequencies were consistent with the results obtained by impact testing. Furthermore, results from the correlation of hydrophone signals showed the existence of coherent structures, which probably control the generation of turbulence generated noise, near the exit of the jet.
Evaluation of ASR front ends using synthetic vowel-like sounds
Authors: Hermansky Hynek , Javkin Hector Raul
Published: October 2005

Analysis techniques and distance metrics interact in their effectiveness as the front end of the automatic speech recognizer (ASR). Synthetic vowel-like sounds were used to compare different ASR front ends, focusing on cepstrally smoothed standard LP analysis and the recently proposed perceptually based LP (PLP) analysis combined with the LP cepstral distance and the root power sum (RPS) distance metrics. (1) The findings of Kamm and Kahn [J. Acoust. Am. Suppl. 1 78, S82 (1985)] that standard LP overemphasizes the importance of higher formats were confirmed. The tonality scale inherent in PLP representation alleviates this problem. (2) In PLP, as opposed to LP, the contribution of a formant change depends much more on the particular vowel in which it occurs. (3) LP is less sensitive to changes in formant bandwidth than PLP. (4) RPS is less sensitive to the overall spectral slope changes than the cepstral metrics. (5) With PLP, RPS emphasizes the dominant formant more than the cepstral metric. (6) All examined techniques are sensitive to the harmonic structure of speech. The re-analysis of published formant frequency jnd experiments suggests this sensitivity might not be inconsistent with human perception.
Vocal tract areas from LPC—A comparison of several techniques
Authors: Larar J. N. , Schroeter J. , Sondhi M. M.
Published: October 2005

The need for good initial estimates of cross-sectional vocal tract areas [e.g., Schroeter, Larar, and Sondhi, J. Acoust. Soc. Am. Suppl. 1 80, S19 (1986)] has renewed our interest in LPC techniques. Starting with speech synthesized from a vocal tract model with known cross-sectional areas [Schroeter and Sondhi, J. Acoust. Soc. Am. Suppl. 1 78, S6 (1985)], LPC-derived areas that closely approximate the areas used to control the synthesizer are sought. In a comparative study, the LPC method used to derive the predictor polynomial (autocorrelation, covariance, and stabilized covariance methods) as well as its particular application with respect to location of pitch epochs is varied; pitch synchronous and asynchronous analyses are performed with different assumptions regarding the glottal termination. Spectral shaping and source components in the inverse filter are removed and formant shifts due to yielding wall losses are considered. Areas are computed using the standard Wakita recursion [Wakita, IEEE Trans. ASSP-27, 281–285 (1979)] proceeding from the glottis to the lips with the first supraglottal section set to the known value (used for synthesis). Results are presented for steady vowels and for voiced segments produced with a time varying vocal tract.
Segerstrom Hall—A review of concept, design process, and results
Authors: Marshall A. Harold
Published: October 2005

The recently opened Segerstrom Hall in Orange County, California is a 3000-seat directed reflection sequence (DRS) hall that responds in a unique asymmetrical way to the competing demands for theater and symphony. This paper reviews the origins of this concept, the design process by which it was realized, and the model study at 1:10 scale carried out in New Zealand. Comparisons between modeled results and final results in the hall will be presented.
Intelligibility of ICAO spelling alphabet words as a function of LPC narrow-band processing and bit error rate
Authors: Schmidt-Nielsen A.
Published: October 2005

The intelligibility of ICAO spelling alphabet words was tested to determine the kinds of confusions that occur under severely degraded digital voice conditions. The test conditions included a 2400 bit/s linear predictive coding (LPC) voice processing algorithm with random bit error rates of 0%, 2%, 5%, 8%, and 12%. The ICAO alphabet (ALFA, BRAVO, CHARLIE,…) was developed for communication under degraded conditions, and the words have been selected with the object of minimizing confusions. Scores on a standard intelligibility test, the Diagnostic Rhyme Test (DRT), were obtained for comparison and to determine a prediction function from DRT scores to spelling alphabet performance. The types of confusions that were obtained with the narrow-band digital speech with bit errors showed a number of substantial differences from the types of errors normally found with spelling alphabet words tested in noise. The most frequent error was that PAPA was heard as ALPHA (but ALPHA was virtually never heard as PAPA). As is to be expected, scores on the spelling alphabet words fell monotonically with falling DRT scores but were considerably higher than the DRT scores for the same conditions up to 5% errors; after that, the spelling alphabet scores dropped off rapidly to levels as low as the DRT scores.
An identification of the approximations in stepwise coupled modes
Authors: Evans Richard B.
Published: October 2005

The stepwise couple mode method was developed to compute the acoustic field in a range-dependent ocean environment. The goal of this development was to eliminate the one-way and limited aperture assumptions that are made in the parabolic approximation. Having eliminated these approximations, it was expected that the stepwise coupled mode solution could serve as benchmark for range-dependent propagation in the same way that the normal mode solution serves as benchmark for range-independent propagation. Any numerical solution has some inherent approximations and associated conditions under which the resulting errors are small. The approximations and errors should be well understood in a reliable benchmark. The purpose of this talk is to begin to address this issue by identifying the approximations in the stepwise coupled mode method. Some of the errors which result form these approximations will also be discussed. [Work supported by NORDA.]
Benchmark models by the method of finite differences for VLF pulse propagation in bottom-interacting ocean acoustics
Authors: Stephen R. A.
Published: October 2005

A suite of benchmark models are proposed for VLF pulse propagation in bottom-interacting ocean models. The models are: (i) a homogeneous medium; (ii) a flat seafloor with a sharp transition from water to basalt; (iii) a flat seafloor with a linear gradient in elastic parameters between water and basalt; (iv) a flat seafloor with a linear gradient in elastic parameters overlying a sharp transition to basalt; (v) a flat seafloor with a uniform sediment layer overlying a basaltic basement with continuously increasing elastic parameters with depth; (vi) a range-dependent model of water over Plexiglas with a step in the Plexiglas offset from the source; and (vii) a range-dependent waveguide problem for a shot over the continental shelf propagating out over the continental slope. Solutions to all of the above problems have been obtained using finite difference solutions to the elastic wave equation. The range-independent models have been solved using discrete wavenumber techniques. All models are based on physically realistic models for which either laboratory or field data are available.
Convergence rate of codes for numerical quadrature techniques for classical ray tracing
Authors: Floyd Edward R.
Published: October 2005

The estimated residual error (or its bound) for numerical quadratures is usually expressed in terms of a derivative of some order of the integrand or some residual factor of the integrand after factoring out a countable number of zeros and singularities that occur along the integration path. The order of the derivative is a function of the number of sample points for evaluating the integrand. Regrettably, the magnitudes of these higher-order derivatives are difficult enough to estimate for even analytic sound velocity profiles. In practice, observed sound velocity profiles, which are usually given in tabular form and include measurement errors, exacerbate our inability to assess the magnitudes of these higher-order derivatives. An estimate of the residual error expressed in terms of a first derivative would be far more practical for both analytic and observed sound velocity profiles.
The neglected role of musicians in the preliminary planning of concert halls
Authors: Finn Robert
Published: October 2005

A common complaint among musicians is that they are almost never involved in the preliminary planning stage when a new concert hall is being built. The basic planning which determines the acoustical properties of the finished building is thus left to architects, acousticians, and engineers, who are usually nonmusicians. There are certain criteria which the musicians—who must, after all, live with the hall long after the architects and acousticians have departed—consider basic. There are building materials they prefer for acoustical reasons, and configurations they consider better than others. What are these considerations, and how subjective are they? Do they have any validity when measured against the scientific data of the experts? Is it possible for the scientific community to learn from the experiences of practicing musicians who play in the halls they design—and conversely, would the musicians profit by paying closer attention to the work of scientists and acousticians?
The effect of nonlinear distortion of biomedical ultrasound on acoustic cavitation
Authors: Church Charles C.
Published: October 2005

Previous theoretical studies of acoustic cavitation postulated as the driving pressure a Gaussian pulse, a sine wave within a Gaussian envelope, or a pure-tone sine wave. In this study, the harmonic components of a distorted sine wave are calculated following the method of Blackstock [J. Acoust. Soc. Am. 39, 1019–1026 (1966)]. The magnitudes of these harmonics are attenuated as a function of frequency and distance from the transducer and are summed using a constant phase shift. This produces a waveform quite similar to those seen in the laboratory. Distorted waves produced at 1, 3, 5, and 10 MHz are used to derive Cramer's equations for nonlinear bubble dynamics [Cavitation and Inhomogeneities in Underwater Acoustics, edited by W. Lauterborn (Springer, New York, 1980), pp. 54–63]. Typical bubble radius versus time curves and transient cavitation thresholds (R/Rn, > 2.0) are shown. Due to the shifting of energy from the fundamental to the harmonics and to attenuation, these thresholds are generally higher than for pure sine waves. [Work supported by NIH.]
Array shape estimation via piecewise subarray beamforming
Authors: Caveny Deanna M. , Del Balzo Donald R. , Becklehimer Jeffrey L. , Ioup George E.
Published: October 2005

Deformation produced when towing a linear array can remove L-R ambiguities in conventional beam patterns, provided the beamformer knows the deformed array shape. In practice, however, this shape is usually unknown. Thus it is desirable to have a processor that determines the shape and uses this information to form the beams. A method which accomplishes this goal forms beams for subapertures separately assuming that they are approximately linear. A maximum likelihood estimation method [M. J. Hinich and W. Rule, J. Acoust. Soc. Am. 58, 1023–1029 (1975)] has previously been used to associate an angle with each of the subapertures. Given the subarray bearing angle they calculated a mean and a median to estimate the full array bearing angle. In this study, after the main angle was determined, using conventional methods, a piecewise linear array was constructed by placing the subarrays together with estimated correction angles. To test the performance of the approximated array shapes, beamforming was carried out using the new piecewise linear array and the modeled data for the original deformed array. Systematic errors were investigated as well as various methods for smoothing the piecewise linear array.
Effect of a voltage shading of the ceramic stack on the bandwidth of a radiating Tonpilz transducer
Authors: Boucher D. , Tocquet B. , Decarpigny J. N. , Debus J. C. , Tierce P.
Published: October 2005

In addition to the main resonance, the analysis of classical Tonpilz transducers points out the existence of several maxima of the transmitting voltage response which are associated to various structural modes (dilational modes of the stack, flexural modes of the headmass). However, though the electromechanical coupling of the first mode is large, the other modes are generally less effective. In this paper, the effectiveness of a particular mode is shown to depend upon a simple relation, for each ceramic ring of the stack, between the phase of its electrical excitation and the sign of its longitudinal strain. This fact is clearly demonstrated with the help of a finite element modeling, using the ATILA code [J. N. Decarpigny et al., J. Acoust. Soc. Am. 78, 1499 (1985)]. These results suggest various voltage shadings of the ceramic stack which reinforce particular modes. Thus various frequency ranges can be effectively obtained with the same transducer, as confirmed by a detailed study that is based on numerical simulations as well as in-water measurements.
The effect of electrode stiffness on the piezoelectric and elastic constants of a piezoelectric bar
Authors: Mofett Mark B. , Ricketts Donald
Published: October 2005

Electrodes that are stiff and thick compared with the underlying piezoelectric substrate material can substantially change the effective piezoelectric and elastic constants from those values which would be obtained in the absence of electrodes. A simple analytical model for the stress distribution inside a composite piezoelectric plate, consisting of two outer electrode layers and one inner piezoelectric layer, is used to calculate the effective g31, g32, and g33 piezoelectric constants, as well as the effective sij (i, j = 1,2,3) elastic compliance coefficients. Numerical results for copper-clad poly (vinylidene) fluoride (PVDF) plates are presented. [Work supported by the Office of Naval Technology and by Raytheon Submarine Signal Division, Acoustic Transduction Research and Development Project (DR).]
Results of simultaneous acoustic measurements around a large horizontal axis wind turbine
Authors: Hubbard Harvey H. , Shepherd Kevin P. , Willshire William L.
Published: October 2005

A unique set of experiments is described in which simultaneous acoustic measurements were made at 18 locations around a large horizontal axis wind turbine in a circular array having a radius of 200 m. Results are presented for frequencies from 3–3000 Hz, for power output values from 0.1–2.1 MW and for several rotational speeds and skew angles. Additional data for simultaneous measurements using a linear array will be presented to illustrate sound propagation in both the upwind and downwind directions to distances of several kilometers. [Work supported by DOE.]
Signal processing for windmill noise measurement
Authors: Walker Bruce
Published: October 2005

Measurement of noise from wind-powered generators (windmills) often must be done in acoustically hostile environments, with ambient winds of up to 15m/s and operation of large numbers of noise sources (other windmills, highways, etc.) in the same vicinity. In addition, the frequency spectra produced by some commonly encountered windmills extend well into the infrasonic range, where microphone/wind-interaction noise is most troublesome. By using autocorrelation and cross-correlation processing and homodyne filtering, it has been possible to resolve windmill noise data from signal-to-noise environments as poor as 15 dB with good repeatability. The paper will discuss how these processing techniques have been implemented on a desk top computer with a minimum of expense. The paper will also include an audio demonstration of the noise characteristics of a variety of windmills.
Criteria for low frequency and infrasound from wind-energy farms
Authors: Buntin Jim , Brown Robert E.
Published: October 2005

Criteria for low frequency and infrasound were developed under contract to Kern County, California, to allow assessment of potential public reaction to wind-energy farm developments. Recent literature was reviewed regarding possible annoyance, physical discomfort, and perception of sound in the frequency range of 2–125 Hz. Criteria suggested by a number of authors were compared to determine commonality of recommended sound pressure levels versus frequency in one-third octave bands. The suggested criteria were than evaluated as to whether they addressed the issue of annoyance, rather than perception. A set of criteria was then proposed which incorporated empirically derived criteria intended to minimize community reaction, incorporating a 5-dB penalty for the impulsive components which are sometimes present in low frequency and infrasound produced by wind-energy farm installations. The resulting criteria represent a balance between sound pressure levels which are perceptible and those which are expected to result in community annoyance.