bluuebunny/crossref_metadata_2025 huggingface dataset:
Little known and ignored facts in automatic audiometry
Authors: Young I. M. , Lowry L. D.
Published: October 2005

Automatic audiometric findings may be affected by various factors such as contralateral ear making, starting frequency, starting intensity, different stages of same disease entity and exposure to stimulating sound. These findings are seen mostly on steady tones shown by amplitude reduction and threshold drift. This paper is concerned with automatic audiometric results which have been little known or ignored by many investigators. Our data show that, in certain subjects with sensorineural hearing impairment, masking presented to opposite better ear produced striking effects on steady tones in affected worse ear. Various starting frequencies produced marked effects on separation between pulsed and steady tone tracings if hearing was tested starting at suprathreshold intensity. A subject diagnosed as an early endolymphatic hydrops retested within three hours following an episodic attack displayed varieties of findings. Subjects with acoustic trauma and abnormal adaptation were exposed to pure tone stimuli. They showed changes in loudness recruitment going from straightline and reverse decruitment to asymptotic. There were also marked reduction in amplitude and elevation in threshold of steady tones.
Prediction of the ability of discrimination of speech sounds by hearing impaired children
Authors: Hiki Shizuo , Fukuda Yumiko
Published: October 2005

A computer program designed for predicting the acoustical limitation of discrimination of speech sounds by hearing impaired children is described. In this program, the kind of identifiable phones and the probable confusion among the phones are estimated based on the aided frequency characteristic of each individual hearing impaired child. The program is currently being used to find the most appropriate methods of prescribing hearing aids and evaluating use of the aided characteristics, especially in the courses of extending the highest limit of the frequency range or depressing the low frequency components and of utilizing directional microphones and telephone pickup coils mounted in the hearing aids.
Interval biases in 3AFC experiments
Authors: Johnson David M. , Watson Charles S. , Kelly William J.
Published: October 2005

Performance on several three-alternative, temporal forced-choice discrimination tasks (3AFC) was found to vary significantly over the three possible temporal positions of the signal on each trial. First observed in a ten-tone pattern discrimination task, this temporal-interval effect was also found to occur in a battery of 22 detecton and discrimination tests, designed for the study of individual differences in auditory capabilities by Johnson, Jensen and Watson [J. Acoust. Soc. Am. 67, S58 (1980)]. Interval-specific indices of d′ and β were derived by decomposition of the 3 × 3 stimulus-by-response matrices for each task into 2 × 2 matrices. These measures suggest that the temporal-interval effect is typically the result of a combination of decreased sensitivity in the early intervals and relaxed-decision criteria for the later ones. Listeners with overall high levels of auditory resolving power in the individual-differences test battery show the least temporal-interval effect in 3AFC tasks. This last result suggests a dependence of both overall discrimination performance and the temporal-interval effects on the relative efficiency of short-term auditory memory. [Work supported by NIH.]
Time and frequency in the digital world for the nondigital person
Authors: Gray Augustine H.
Published: October 2005

An elementary tutorial on the concepts of the time and frequency domains in the digital world. A qualitative discussion of problems such as aliasing and quantization errors, as well as a brief overview of the tools used in theoretical studies (modeling and spectral analysis) and design such as FFTs and z transforms.
Decisions and options in the evolution and design of a microprocessor-controlled acoustic analyzer
Authors: Raventos William A. , Berry Craig B.
Published: October 2005

The paper first overviews the scope of the total instrument design, and then narrows to examine specifically the design philosophy of the RT-60 measurement section. The designers first had to look at not only the specific “manual” methods of calculation, but further programming was called for to “educate” the computer to act and make decisions in a way paralleling its human counterparts. The designers had to anticipate problems and weaknesses stemming from the computer's literal interpretation of all instructions. Decisions concerning certain compromises resulting from the implementation of primary design goals are discussed. Specifically, the areas of internal source and external trigger corrections, linear regression calculations, system resolution, smoothing, automatic averaging, and internal and external data formatting and display are discussed.
Dispersion of acoustic waves by heterogenous materials
Authors: Sutherland Herbert J. , Drumheller Douglas S.
Published: October 2005

During the past ten years, Sandia National Laboratories has been engaged in a program to investigate the behavior of stress waves in heterogenous materials. The classes of materials which have been studied are metal-metal composites, metal-polymer composites, and Fiberglas-polymer composites. The various internal geometries include laminated, fiber-reinforced, and particulate-loaded materials. Extensive data have been collected from experiments using low-amplitude, sinusoidal pressure waves. These data illustrate the effects of the degree of periodicity of the reinforcing geometry on the dispersive characteristics of the material. They also show how the geometric dispersion due to the reinforcing geometry interacts with the material dispersion due to the presence of the polymer constituents. The theoretical implications of these data will be discussed. It will also be shown how these findings lead to an improved understanding of the behavior of transient wave phenomena.
Multiple scattering of waves: T-matrix formalism
Authors: Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

The T-matrix formalism for studying the scattering of time-harmonic acoustic, electromagnetic and elastic waves by obstacles of arbitrary shape has been discussed in the literature for layered obstacles, finite number of obstacles and statistical distribution of obstacles. The above problems are appealing, for the analytical challenges that they present as well as the diversity of applications to many practical problems in science and engineering. More importantly, the T-matrix approach is such that one can easily write down analogous descriptions for all three wave fields namely, the acoustic, electromagnetic and elastic fields. The method also lends itself to numerical computations for higher frequencies of the incident plane wave as well as more realistic geometries for the inhomogeneities. The purpose of this paper is to present a brief survey of the T-matrix approach to study multiple scattering and present some new results for finite number and statistical distribution of scatterers. We will compare this approach to other existing methods.
Scattering of focused ultrasound in water by spherical micro-particles
Authors: Edwards P. L. , Jarzynski J.
Published: October 2005

The scattering of focused ultrasound in water by three different types of microspheres (∼25-75 μm diam), with ka < 1, was studied. The three scatterers were a spherical glass bubble, solid polystyrene spheres, and hydrogen bubbles. The measurement arrangement consisted of two transducers (transmitter and receiver) of 0.5-in. diameter and with focussing lenses mounted on their faces. They were positioned so that their focal regions overlapped and their axes were 60° apart. A swept frequency ultrasonic signal was used, of 30-μs duration, in which the frequency increased linearly from 3.5-6.8 MHz. The glass bubble was mounted on a nylon filament and positioned in the overlapping focal regions. The polystyrene spheres were in solution, and reflections were obtained as they drifted through the focal regions. The hydrogen bubbles were generated by electrolysis and reflections obtained as they rose through the focal regions. From the shape of the echo envelope the frequency dependence of the scattered-pressure amplitude was determined for each scatterer, and significant differences were observed between the echoes from the solid scatterers and the gas bubbles. The experimental results are compared with theoretical predictions.
Acoustic backscattering in water at the Rayleigh angle
Authors: Neubauer Werner G.
Published: October 2005

An acoustical pulse confined to a finite beam in water, incident on a plane solid surface generates a specular pulse. Also, a pulse radiated from the Rayleigh wave, which is generated on the surface is generated adjacent to and partially overlapping the specular pulse. It has been found that at the Rayleigh angle there is also a backscattered pulse propagating in the opposite direction to that of the incident pulse. This pulse seems to be a reflection from the Rayleigh wave which is itself being generated over the incidence region. This was first reported by Sasaki [Jap. J. Appl. Phys. 2 (1963)]. Schlieren photographs and stroboscopic schlieren motion pictures will be presented, as well as hydrophone measurements showing the form and properties of this pulse.
Identification of the auditory nerve neurotransmitter
Authors: Wenthold Robert J.
Published: October 2005

Several lines of evidence suggest that glutamate or aspartate is a neurotransmitter for the auditory nerve. Both amino acids are concentrated in terminals of the auditory nerve and two enzymes associated with the metabolism of glutamate and aspartate, glutaminase and aspartate aminotransferase, are present in terminals and fibers of the auditory nerve. Glutamate and aspartate are released from slices of the cochlear nucleus and their release is decreased by lesion of the auditory nerve. The auditory nerve neurotransmitter is pharmacologically similar to glutamate and aspartate. Immunocytochemical localization of aspartate aminotransferase in the cochlear nucleus will also be discussed.
Microchemical mapping studies of neurotransmitter chemistry in the cochlear nucleus
Authors: Godfrey Donald A.
Published: October 2005

Quantitative histochemical procedures [O. H. Lowry and J. V. Passonneau, A Flexible System of Enzymatic Analysis (Academic, New York, 1972), pp. 219–260] have been applied together with a mapping approach to study the distributions of neurotransmitter systems in the cochlear nucleus. The methods involve quick-freezing of tissue, followed by frozen sectioning, freeze-drying, dissection of sections with microknives, weighing of samples on microbalances, and direct chemical assays in microliter volumes. Structures as small as 20 μM per edge can be chemically analyzed by these methods, and the histological locations of all samples are recorded, allowing direct comparisons with anatomical and physiological data for the same locations. The distributions of proposed transmitter amino acids and of the enzymes of acetylcholine metabolism have been mapped in the cochlear nuclei of rats and cats. The effects on these distributions of transections of anatomical pathways are being studied. Results so far suggest that, in the rat cochlear nucleus, most cholinergic synapses may be related to centrifugal, or feedback, pathways to the nucleus.
Light and electron microscopic autoradiographic approaches to the chemistry of auditory brain stem nuclei
Authors: Schwartz Ilsa R.
Published: October 2005

A fresh brain slice preparation has been developed which allows the simultaneous characterization of the anatomical localization of radioactively labeled substances in a variety of different auditory brain stem areas. Labeled substances may include putative neurotransraittcrs, ligands for receptor binding sites and antibodies to specific proteins. Varying incubation conditions can be applied to adjacent slices, avoiding the complication of differences between non-inbred animals. These slices can be examined at both the light and electron microscopic level. Differential distributions of label in cells and synaptic terminal populations in the cat cochlear nucleus following incubations with putative neurotransmitter tritiated amino acids suggest differences in the chemical properties of at least three classes of terminals in the dorsal cochlear nucleus. Studies are underway to describe the differential labeling patterns in several auditory nuclear groups and to characterize the conditions under which they occur. [Work supported by NIH.]
Introcellular responses of hair cells in the alligator lizard: Dependence on tone frequency and level
Authors: Holton Thomas , Weiss Thomas F.
Published: October 2005

Receptor potentials of hair cells in the basal region of the basilar papilla of anesthetized alligator lizards were recorded with micropipettes. The steady-state tone response consists of a dc component and ac components at multiples of the tone frequency. The isopotential contour (“tuning curve”) of the dc or the fundamental ac component has a sharply tuned “tip” on a more broadly tuned region. The dependence of receptor potential components on sound-pressure level (“level functions”) was measured at different tone frequencies. These functions saturate at high sound-pressure levels; the maximum value of the dc component is independent of frequency, while the maximum value of the fundamental ac component decreases with increasing tone frequency. Shapes of level functions at tone frequencies in the tuning curve “tip” differ from those at other frequencies, suggesting the presence of a frequency dependent non-linearity in hair cell transduction. (Research supported by NIH.)
Vibration sensitivity in the bullfrog inner ear
Authors: Baird Ra. A. , Lewis E. R.
Published: October 2005

Eighth-nerve studies with dye-filled electrodes reveal the peripheral origins of vibration-sensitive units and extend previous physiological observations of such units by L. Cazin and J. Lannou [C. R. Soc. Biol. (Paris) 169, 1067–1071 (19751]. We find that these units are distinguished from auditory units by high sensitivity to substrate-borne vibration (thresholds between 0.001 and 0.01 g) and low sensitivity to airborne sound (thresholds over 80 dB SPLI, with C. F.s from 20 Hz to more than 100 Hz for both stimulus modes. Auditory units originate in the amphibian or basilar papilla; vibratory units originate in the saccule or lagena. Vibratory units from either organ exhibit resting discharge frequencies from 0 to 80 spikes/s and exhibit phase-locking of individual spikes to sinusoidal vibratory stimuli up to 150 Hz. For stimulus frequencies below resting discharge frequency, most units respond with two or more spikes per stimulus cycle, thereby maintaining average discharge frequency at or above resting frequency. Occasionally a unit responds with one spike per cycle to stimulus frequencies below resting frequency. At low stimulus intensity, phase-locking is incomplete. Some lagenar (not saccular) vibratory units are sensitive as well to head position. [Research supposed by NSF Grant BNS-8005834.]
Relationships between trapezoidal EP variations and auditory nerve fiber responses in gerbils and guinea pigs
Authors: Sokolich W. G. , Oshima W. , Strelioff D.
Published: October 2005

It has been shown [Sokolich et al., J. Acoust. Soc. Am., 59, 963–974 (1976)] that most gerbil auditory nerve fibers show one of three time patterns of response to acoustically-evoked trapezoidal time patterns of EP change. Pattern “A” is characteristic of fibers with CFs below 2 kHz, pattern “B”, of fibers with CFs between 3 and 6 kHz, and pattern “C”, of fibers with CFs above 8 kHz. Although all three patterns contain four distinct response components reflecting both static and dynamic aspects of trapezoidal EP change, the patterns differ in that the sign of one or more components depends on fiber CF. The present comparative study reveals that pattern “A” is exhibited by all guinea pig fibers with CFs below and by many fibers with CFs above 7 kHz. Nonetheless, some guinea pig fibers with CFs above 7 kHz show pattern “B”. In spite of the difference in the dependence of response pattern on CF, all patterns observed in both species support the conclusion that neither excitation nor inhibition of auditory nerve fibers is uniquely related to specific aspects of either static or dynamic changes in EP or to associated aspects of basilar membrane motion.
Coding of stimulus intensity by neurons in the anteroventral cochlear nucleus of kittens
Authors: Brugge J. F. , Kitzes L. M. , Jayel E.
Published: October 2005

The effects of stimulus intensity on the number of spikes evoked in AVCN neurons was studied in kittens 4 to 45 days old. For neurons whose spike-count functions saturated, the number of dB required to raise that count from 10% to 90% of maximum (DRI) was determined at various frequencies within the response area. For kittens younger than 14 days the shapes and slopes of the curves are remarkably similar over a wide frequency range within the response area. The functions rise sharply to a maximum and commonly in young animals decrease abruptly. The mean DRI increases with age. At 4-5 days the DRI at CF ranges between 10 and 18 dB; during the second week these values vary from 6 to 27 dB. Between 14 and 20 days the functions achieve the shapes and slopes of those seen in older kittens and those described for the cochlear nuclei and auditory nerve of adult cat. At 20 days the DRI varies between 13 and 56 dB. As thresholds diminish over the first 2 weeks, tuning curves change from being initially shallow to increasingly “V” shaped.
A piezoelectric polymer evanescent wave generator
Authors: Powers James M.
Published: October 2005

To determine the response of a hydrophone to high wavenumber (short wavelength) waves, a method of generating high wavenumbers at relatively low frequencies is needed. The method to be presented uses a 22 element planar array of long thin (10 cm × 0.34 cm) piezoelectric polymer transducers, stacked side by side. When adjacent elements are electrically driven in phase opposition, an evanescent wave in the nearfield is generated whose wavelength (0.68 cm) is equal to twice the element spacing and is independent of the driving frequency. This wavelength corresponds to a wavenumber (K = 9.3 cm-1) which is, for example, 17 times higher than a 3.0 kHz propagating wave in air (K = 0.55 cm-1). The transducers are air-filled cylindrical half-sections of thin films (30 μ) piezoelectric polymer (polarized PVDF), a design which allows long thin elements to be made with relative ease and inexpensively. Also presented is a method of evaluating the array which uses a spatial Fourier transform to determine the generated nearfield wavenumber spectrum. [Work supported by NAVSEA 63R-12.]
Model for a complaint tube polymer hydrophone
Authors: Ricketts Donald
Published: October 2005

A mathematical model of the compliant tube polymer hydrophone has been developed, which facilitates the evaluation of its low frequency electroacoustic sensitivity and maximum operating pressure. Developed by the Naval Underwater Systems Center/New London Laboratory (NUSC/NL), this type of hydrophone is comprised of the complaint tube (an air-filled tube of flattened oval cross section and closed ends), a plastic spacer plate which attaches to the flattened surface of tube, and the piezoelectric polymer (PVF2) film. The PVF2 film is bonded to the surface of the plastic plate. It is shown that the sensitivity is enhanced by the use of the spacer, rather than bonding the PVF2 film directly to the flattened surface of the compliant tube. Moreover, there is an optimal spacer thickness that maximizes hydrophone sensitivity. Numerical results are presented for a steel compliant tube polymer hydrophone. The theoretical model has been applied to the NUSC steel compliant tube polymer hydrophone, with excellent agreement between the predicted and experimental values for hydrophone sensitivity and maximum operating pressure. [Work supported by NUSC.]
Acoustic analysis of some speech discrimination abilities of normal and language impaired children
Authors: Tallal Paula , Stark Rachel
Published: October 2005

The ability of 35 language impaired (LI) and 38 normally developing children between the ages of 5 and 9 years to discriminate between speech stimuli using an operantly conditioned, nonverbal motor response was investigated. Six syllable contrasts (/ba/ vs /da/, /da/ vs /ta/, /ε/ vs /ae/, /dab/ vs /daeb/, /sa/ vs /sta/ and /sa/ vs /∫s/) were selected to investigate discrimination of various temporal and spectral cues. Results demonstrated that the pattern of difficulty in discriminating the six stimulus pairs was different for the LI and normal children. The LI group made most errors on syllables which were differentiated by consonants and fewest errors on those differentiated by vowels. The normal group made most errors discriminating between syllables including fricatives and brief vowels and fewest errors on stimuli differentiated by stop consonants or vowels in context. The LI group was significantly poorer than the normals in discriminating all syllables that incorporated brief temporal cues followed rapidly in succession by other acoustic cues. They also were impaired in discriminating /sa/ vs /∫a/. Constraints demonstrated by LI children may be attributed to abnormalities in mechanisms involved in auditory masking.
Measuring the acoustic phonetic range of American and Japanese speakers using minimax LPC vector sets
Authors: Dorsey Eric , Bernstein Jared
Published: October 2005

A method is described for estimating the size of the “phonetic space” used by a speaker. Our minimax method chooses a given size subset from a set of LPC vectors in such a way that the maximum rms log spectral distance from any vector in the superset to its nearest neighbor in the subset is minimized. This maximum distance is a measure of the acoustic dispersion of the superset in the LPC domain. The measure shows individual differences and may show general interlanguage differences in the size of acoustic phonetic space. So far we have derived minimax subsets containing 32, 64, 128, and 256 LPC vectors from sets of 7500 that describe the spectra of large segments of raw speech from one American and from one Japanese speaker. The minimax measure is consistently about 0.8 dB smaller for the Japanese speaker, indicating that his speech spanned a smaller region in LPC acoustic space. We will analyze at least one more Japanese and one more American speaker by November 1980.
Vocal tract area functions from inverse scattering experiments
Authors: Resnick J. R. , Sondhi M. M.
Published: October 2005

Some new methods of deconvolution and of area function computation have been applied to the problem of inferring vocal tract area functions from measurements of the acoustic transient response at the lips. Results with test cavities and with real human subjects will be presented.
Improving the signal-to-noise-ratio of a noisy speech signal
Authors: Sondhi M. M. , Schmidt C. E. , Rabiner L. R.
Published: October 2005

In this talk we will describe an algorithm for increasing the SNR of a very noisy speech signal. The basic structure used for the signal processing is a channel vocoder; the noise reduction is accomplished by adjusting the channel gains on the basis of estimated noise levels in each channel. We will demonstrate how the noise cancellation is affected by the number of channels used, by the method used for estimating channel gains, etc. Results of informal listening tests will be presented.
Hybrid adaptive filtration for seismic event location
Authors: Schnitta-Israel Bonnie , Fletcher Donnie C.
Published: October 2005

Certain techniques of adaptive filtration, time delay estimation, and minimum variance parameter estimation were synthesized into a hybrid adaptive filtration technique and applied to a problem in seismic event location. The hybrid adaptive filtration was applied to a body of geophone measurements collected of a strong impulsive source. The seismic waves were recorded by an array of nine three-component geophones arranged in a cross at ranges of 5, 11, and 17 km. An earlier attempt to process this data by a variant of conventional beamforming was only successful in one-third of the 5-km events. The hybrid adaptive filter had excellent results for all 5-km events. Actual signal detection was evident in the 11-km events. [Work supported by ONR Earth Physics Program.]
Echo-echo correlation (EEC)
Authors: Green M. D.
Published: October 2005

Traditional coherent processing of large BT product waveforms in active acoustic detection suffers apparent loss in echo energy due to channel multipath and/or target highlights. High resolution sonar used with targets at long ranges requires massive array processing and fast correlation, with heavy display loads. Echo-Echo Correlation (EEC) is a new technique which finds the auto-correlation of the echo, independent of pulse characteristics, multipath, or target velocity. For a given probability of detection, required decision thresholds are much lower with EEC than with standard procedures. The ECC output is not distorted by unknown Doppler, yet target velocity is readily computed. The computations are easily carried out in the time-domain, and the display load is greatly reduced. Two experiments using EEC have been completed. The first was a deep ocean, bottom bounce operation using a submarine as a target and a surface ship as the sonar source. The EEC results were equal to or superior than those from the standard coherent technique. The second compared the losses caused by target multipath for EEC and the standard technique. The latter suffered much higher losses as a function of target aspect, bandwidth, and pulse type. EEC showed negligible losses.
Comparison of spatial coherence of bottom-interacting sound for Abyssal Plain and Abyssal Hills sites
Authors: Berkson J. M. , Morris G. B.
Published: October 2005

Acoustic reflectivity experiments were conducted over two different ocean bottom types in the northeast Pacific. Explosive sources were dropped at ranges up to 50 km from a vertical hydrophone array that was suspended near midwater depth. The experimental geometry allowed time isolation of the bottom-interacting arrival. The bottom-interacting arrival received by the array was processed to obtain spatial coherence for frequencies in the 20- to 250-Hz band. The behavior of spatial coherence vs frequency, grazing angle, and sensor separation is distinctly different for the two sites. At the Abyssal Plain site, coherence is nearly 1.0 at grazing angles 10° to 25°, decreases with increasing grazing angle until about 60°, and then increases after 60°. At the Abyssal Hills site, coherence is low (about 0.3 for 280-m sensor separation) and variable for 10° to 60°, and increases after 60°. The results are consistent with the combined effects of scattering from a rough interface and changing sensor geometry with grazing angle. [Work supported by NORDA and Naval Electronic Systems Command.]
Dependence of infrasonic ambient noise levels on wind speed and surface wave properties
Authors: Diachok O. I.
Published: October 2005

Near-coincident ambient noise and wind speed measurements were made over a frequency range 2–20 Hz on a 3400-m-deep bottom-mounted hydrophone in the North Atlantic for wind speeds between 5 and 50 knots. Above about 5 Hz, spectrum levels were dependent on wind speed, w, and frequency, f, approximately as w4/f2. The wind speed dependence is in reasonable agreement with the theory of noise generation through near-surface atmospheric turbulent pressure fluctuations. The observed spectral shape differs from previous measurements and may be site-dependent. Below about 5 Hz, the measured wind-dependence of spectrum levels was consistent with computations based on (1) the theory of noise generation by nonlinear interaction of surface waves propagating in opposite directions, (2) Hasselman's prescription for the wind dependence of the surface wave spectrum [J. Phys. Ocean. 6, 200–228 (1976)], and (3) Tyler's characterization of the directionality of the sea surface wave field [Deep Sea Res. 21, 989–1016 (1974)]. Comparison of the measured spectrum, with theory requires consideration of the predicted source spectrum, which is proportional to 1/f7 (approximately in agreement with data), its directionality and the source to receiver transfer function.
Measurements of shallow water ambient noise due to breaking surf
Authors: Wilson O. B. , Wolf Stephen N. , Ingenito Frank
Published: October 2005

Horizontal directionality of ambient noise was measured at ranges up to 4 km from the eastern shore of Monterey Bay, California. Water depths at the sites ranged from 8 to 73 m. A steerable cardioid receiving pattern was formed using signals telemetered from dipole and omnidirectional hydrophones suspended from tethered buoys. With no nearby shipping, whenever the maximum of the cardioid pattern was directed toward the beach, noise levels in the range 20 to 500 Hz were greater than those obtained when the maximum was directed seaward. This difference (seaward versus shoreward), which depended on range from the beach and on frequency, was 7 dB at 100 Hz at the 4-km site. Surf beat was clearly audible when the cardioid maximum was steered shoreward at ranges as great as 2 km. The measurements, made when wind and surf were high, suggest strongly that under some conditions breaking surf can contribute significantly to ambient noise in fairly deep continental shelf waters. [Supported by the NPS Foundation Research Program and the Naval Sea Systems Command.]
Application of experimental modes for solving helicopter vibration problems
Authors: Wood E. R. , Gupta B. P.
Published: October 2005

Helicopter vibration reduction frequently requires detuning airframe natural frequencies from well-defined frequencies of excitation. If airframe detuning proves impractical, vibration reduction is generally achieved by use of vibration control devices. The most common vibration control device is the fixed or variable-tuned vibration absorber. For either effective detuning or efficient absorber design, accurate information is required with respect to airframe natural frequencies and mode shapes. Due to complexity of the airframe structure, classical finite element models often are inadequate for defining design changes necessary for either detuning or determining an effective location for vibration absorbers. Also, these finite element models are both time-consuming and costly to develop and use. In work at Hughes Helicopters considerable success has resulted from application of classical theory to carefully obtained experimental airframe modes and natural frequencies for establishing effective vibration reduction methods. The manner by which this is accomplished is summarized in the paper. Airframe detuning is achieved through application of stiffness changes in selected aircraft locations or by changes in mass distribution at response solution using modal superposition. In both cases, theory is applied to experimental airframe eigenvectors and eigenvalues.
Standards Committee S3 on Bioacoustics
Authors: Yost W.
Published: October 2005

The current status of standards under preparation will be discussed. In addition to those topics of interest including hearing conservation, noise, dosimeters, hearing aids, etc., consideration will be given to new standards which might be needed over the next few years.
T-matrix formulation of Acoustic wave scattering by layered elastic obstacles immersed in water
Authors: Varadan V. K. , Peterson B. , Varadan V. V. , Pillai T. A. K.
Published: October 2005

The subject of wave scattering from layered elastic obstacles of arbitrary shape immersed in a fluid finds many potential applications in underwater acoustics. In spite of the mathematical unity present in the description of the three classical wave fields, namely acoustic, electromagnetic and elastic, due to the coupling by boundary conditions of the rotational and irrotational parts of the elastic field that propagate at distinct wave speeds, many problems with layered elastic bodies defied solution. With solid-fluid interfaces, the problem is even more difficult since the wave equations governing the regions in the solid and fluid are different, admitting different solutions that must be coupled at the interface through continuity conditions of pressure and particle velocity. The available results are limited to this elastic shells in water using shell theory approximations. In this paper, we propose a T-matrix approach to study acoustic wave scattering from layered elastic objects such as oblate and prolate spheroids, finite cylinders, infinite two dimensional cylinders, etc., and present numerical results for bistatic, backscattering and total scattering cross sections for a range of frequencies and for different angles of incidence, and for different thickness of the layer.
Computation of rigid body scattering by spheroids and finite cylinders using T-matrix approach
Authors: Varadan V. K. , Varadan V. V. , Pillai T. A. K. , Dragonette L. R. , Flax L.
Published: October 2005

The periodic structure of the backscattered spectrum of elastic and acoustic waves from smooth obstacles has been indicative of diffraction effects similar to the geometrical diffraction concepts in optics. The waves do go around the obstacle (diffraction) and consequently one observes periodic multiple echo returns. Such circumferential waves have been named Franz waves, after W. Franz who first discussed the existence of such creeping waves in his work on the diffraction of electromagnetic waves by conducting spheres and cylinders. In the present paper we present a Franz wave analysis of the backscattered spectrums of spheroids and finite cylinders of various aspect ratios. The backscattered spectrum is calculated using the T-matrix approach, and a Franz wave velocity is predicted for spheroidal and cylindrical obstacles. Comparisons of the acoustic and elastic cases are made wherever possible.
T-matrix analysis of the resonances in sound scattering from elastic spheroids in water
Authors: Dragonette L. R. , Flax Lawrence , Varadan Vijay K. , Varadan Vasundra V.
Published: October 2005

The acoustic scattering by elastic prolate spheroids in water is computed by the T-matrix method. Resonances in the range ka < 10, where k is the wavenumber of the incident sound wave and a is the length of the semi-major axis, are isolated by comparing the rigid and elastic solutions. The effects of circumferential waves on the frequency response of the elastic target are derived.
Radiation and attenuation of waves in a random medium: The mean energy flux
Authors: Wenzel Alan R.
Published: October 2005

A theoretical analysis of the wave field radiated by a point source in a weakly inhomogeneous one-dimensional random medium has been carried out. The analysis is based on a perturbation technique and includes all single- and double-scattering terms, as well as some scattering terms of higher order. An approximate expression, valid when the absorption of the medium is small, has been obtained for the mean energy flux of the wave as a function of propagation range. This expression shows that, as a consequence of backscattering by the random inhomogeneities of the medium, the mean energy flux decreases more rapidly with range than it would due to absorption alone. This more rapid rate of decrease of the mean energy flux with range can be regarded as an excess attenuation of the wave as a result of the randomness of the medium. An interpretation of this result in terms of energy conservation is given. [Work sponsored by NORDA.]
Ultrasonic scattering from rough cracks in solids
Authors: Adler Laszlo , Lewis D. Kent , de Billy M. , Cohen-Tenoudji F. , Quentin Gerard
Published: October 2005

The problem of ultrasonic scattering from cracks with random rough surfaces such as a fractured surface in solids is considered. The rough crack is embedded in diffusion bonded titanium. From ultrasonic measurements (both in the time and in the frequency domain) parameters of the crack are determined and compared to actual values. These parameters include: size, shape, orientation, rms roughness, spatial correlation, length, and density distribution of roughness. [This work was supported jointly by the French CNRS and by the Center for Advanced NDE operated by the Science Center, Rockwell International, for ARPA and AFML.]
Loudness magnitude adaptation at 60 dB SPL
Authors: Weiler Ernest , Sandman David
Published: October 2005

Fishken et al. [J. Acoust. Soc. Am. 61, S61 (1977)], Scharf and Horton [J. Acoust. Soc. Am. 63, S16 (1978)], and Canevet et al. [J. Acoust. Soc. Am. 67, S21 (1980)] report that direct magnitude estimation of a continuous sound does not yield adaptation above 30 dB SL. To investigate the phenomena further, we presented a 1 kHz 60-dB SPL tone to the right earphone of ten listeners for a 7-min period, with and without an additional ipsilateral (reference) intensity. The initial 60-dB intensity was defined as a magnitude of 60. Using the method of successive magnitude estimations at 30-s intervals, there was found to be no consistent or significant change in the judged magnitude of a continuous 60-dB sound. This agrees with the above referenced studies. However. when a 20-dB increment (80 dB SPL) was added for 5 s every 30 s, subsequent magnitude estimations declined immediately, permanently, progressively, and significantly (p < 0.01) for the majority of subjects. It had been hypothesized that the “reference” intensity would allow for a perceptual cue to the declining sensation of a stimulus otherwise “known” to be unchanged. The results do not rule out the possibility of direct effects induced by the 80-dB “reference.” Either explanation concludes that loudness magnitude adaptation can be measured above 30 dB, and at 60 dB specifically, with the modification of technique described.
The effective dynamic moduli and density for composite viscoelastic materials
Authors: Kligman R. , Madigosky W.
Published: October 2005

By extending the self-consistent field technique of Chaban [Sov. Phys.-Acoust. 10, 298 (1965) and 11, 81 (1965)] we have derived general expressions for the dilatation modulus and density of composite viscoelastic materials. The range of validity extends to values of wavenumber times void radius equal to two, corresponding to the truncation of the partial wave analysis. The effective modulus exhibits resonance behavior in the neighborhood of [k1a] equal to 0.27 for various void volume concentrations and for a range of damping constants. This corresponds quite closely to the resonance that Meyer, Brendel, and Tamm [J. Acoust. Soc. Am. 30, 1116 (1958)] calculated. The moduli exhibit other resonances and stiffness regimes as well. The effective density exhibits sharp double peaks in the region of k1a approximately 0.43 and 0.46 for a range of concentrations and damping constants. For large values of k1a approaching two, the ratio of the effective density to the density of the host material approaches unity. The density, in the long wavelength limit (or static approximation) shows some disagreement with that obtained by Chaban, while the effective moduli in this limit is quite similar to Chaban's to first order.
Effects of accent on the performance of an isolated-word recognizer
Authors: Gupta V. , Mermeistein P.
Published: October 2005

Universal access to word recognizers connected to the switched telephone network requires careful consideration of the anticipated population of speakers. To this end recognition performance on a 20-word vocabulary was investigated for two groups of speakers. One group consisted of 22 native English-Canadian males, a linguistically homogeneous group. The second consisted of 31 male French-Canadian speakers with widely varying degrees of French accent. Applying a modified version of the clustering technique used by Rabiner [IEEE Trans. Acoust. Speech Signal Process ASSP-27, No. 4 (Aug. 1979)] six reference templates per word were created by clustering 2 productions of each word by eleven speakers and used to recognize an equal number of productions from eleven other speakers. The recognition rate was 95%. A similar experiment on the French-Canadian speakers resulted in only 83% recognition. Increasing the reference data to 24 speakers and ten templates per word increased the recognition rate, but only to 90%. The variation in recognition rate for individual French-Canadian speakers of English is also significantly higher than that for English-Canadian speakers. The results suggest that where words from a linguistically nonhomogeneous group are to be recognized, a significantly larger number of reference templates per word may be required for acceptable recognition.
Microcomputer and signal-processor system for speech processing
Authors: Upton J. W. , Johnston J. D. , Flanagan J. L.
Published: October 2005

Digital hardware implementation is described for a system that combines the control and storage capabilities of a microcomputer with the arithmetic capabilities of a high-speed signal processor. The Motorola MC68000 design module is used as the microcomputer, and the Bell Labs Digital Signal Processor (DSP) is utilized as the high-speed arithmetic unit. The computer and processor communicate via their normal data ports, and both can communicate directly with analog-to-digital and digital-to-analog converters. The MC 68000 module incorporates 32K bytes of dynamic random access memory, and the DSP provides single-instruction integer multiples in 0.8 μs. Circuit features are described for digitally encoding, storing, processing, and outputing speech signals at a variety of digital rates.
Comparison of vector and scalar quantization techniques for LPC speech compression
Authors: Juang Fred B. , Wong David Y.
Published: October 2005

Vector and scalar quantization techniques for LPC filter coefficients are compared. Geometric comparisons are made in the coefficient space and spectral distortion comparisons are made along a number of distortion measure scales. Spectral and statistical characteristics of the quantization errors for both techniques are also examined in detail. Correlations to listening comparisons of output synthesis speech will be presented. Taped examples will also be played.
Investigations into the quality limitations of LPC speech
Authors: Stevenson Dale C.
Published: October 2005

LPC (Linear Predictive Coding) speech is characterized by several types of degradation which limit both the intelligibility and naturalness of the reconstructed speech. The present paper reports the results of systematic investigations into the information-bearing elements of the residual waveform (i.e., the error signal obtained by inverse filtering the input speech waveform using the predictor coefficients). Using computer-aided manual stylization of the residual waveform, we find that it is possible to produce very high quality LPC speech. The traditional LPC “buzziness” can be completely eliminated, as can the monotone, synthetic quality of the reconstructed speech. If the temporal location of the important speech events in the residual (e.g., pitch pulses, noise bursts) is faithfully reproduced at the synthesizer, intelligibility is not significantly impaired. Furthermore, if a pitch pulse extracted from a residual waveform from the talker's voice is used as the excitation source for the voiced speech segments, the resulting speech is perfectly natural and possesses the bassy, resonant quality of natural speech. The implications for the design of LPC coders are discussed.
Effects of freeway noise on academic achievement of elementary school children
Authors: Lukas Jerome S. , DuPree Russell B.
Published: October 2005

California law requires noise abatement for classrooms in which noise levels from a freeway exceed 50 dBA. In contrast, the Federal Highway Administration's criterion level is L10 = 55 dBA. This discrepancy reflects, in part, a lack of hard data regarding how noise from external sources affects the educational process. About 100 classrooms in 15 schools comparable with respect to certain socioeconomic variables but at different distances from freeways were studied. Noise levels inside the third and sixth grade classrooms with and without children were measured. In addition, teachers' voice levels and certain indications of classroom performance were obtained during three days of observation in each classroom. The Los Angeles Unified School District and the California Department of Education provided scores for each classroom on standardized tests of academic achievement in reading and mathematics. Preliminary analysis of the data indicates that achievement in reading and mathematics is poorer as noise levels increase, a finding consistent with previous studies. However, our data indicate that the coefficients of correlations between noise levels without children and achievement are higher if the levels are C-weighted rather than A-weighted, and that L1 and L5 are better predictors of achievement than are the other Lxs. [Work supported by F.H.W.A. and California Departments of Transportation and Health.]
Techniques for in-situ measurement of pipeline noise
Authors: Brittain Frank H.
Published: October 2005

A variety of problems exist in the in-situ measurement of noise radiated by pipelines, including noise from other sources and reverberant noise. Measurements of noise radiated by several pipelines were made using a microphone tube and an accelerometer mounted directly to the pipe wall. The results of these measurements are compared and the effect of frequency and pipe diameter are indicated.
Angles of peak sound radiation from axisymmetric duct inlets
Authors: Posey Joe W. , Clark Lorenzo R. , Silcox Richard J.
Published: October 2005

The radiation of isolated spinning modes from five axisymmetric duct inlets having very different contours is examined experimentally in the absence of flow. It is found that when a mode is well cuton (cuton ratio ξ ≫ 1), the radiation pattern is much the same as if the duct were terminated at the inlet throat. However, as ξ decreases, the radiation pattern becomes more sensitive to the shape of the inlet. A physical model based on the concept of an effective plane of radiation explains the observed behavior and results in a simple expression for the angle of maximum radiation. This expression involves only two variables, ξ and the normalized inlet radius at the station where the contour has a slope of unity.
Axial fan noise with modulated stator blade spacing
Authors: Krishnappa G.
Published: October 2005

This paper describes the investigations carried out to examine whether unevenly spaced stator blades can be advantageously used to reduce the blade passing frequency tone generated by rotor wake interaction with the stators. Experiments were carried out on a single stage axial fan of 305-mm diameter with 18 rotor blades followed by 19 stator blades at one-fifth and 2 rotor blade chord distances. The spacings between the stator blades were varied with 5° and 10° modulation amplitudes. Farfield noise measurements made inside an anechoic test cell with symmetric and modulated blades showed significant changes in the directionality of the blade passing frequency tone with no apparent reductions in the peak tone levels. The generation and propagation of acoustic modes by rotor-stator interaction for the case of modulated stator blades were theoretically examined in the light of the experimental results. Although the modes generated by symmetrical stators were attenuated, the sound energy was distributed to the additional modes thus causing no drastic reduction in the radiated energy.