bluuebunny/crossref_metadata_2025 huggingface dataset:
Full-duplex speakerphone with acoustic and line echo cancelers
Authors: Kuo Sen M. , Chen Jier
Published: October 2005

In this paper, a complete speakerphone is implemented with an AT&T WE DSP16A microprocessor. This single chip implementation has the advantage of low cost and hence can be applied to the speakerphone installed in a small conference room or a hands-free cellular phone. A robust speech detector is developed to classify four different operation modes; a corresponding gain regulation algorithm is then applied to guarantee the stability of local acoustic and electronic loop. More specifically, it reduces signal levels on both channels when in idle mode, freezes acoustic (or line) echo canceler during the transmit (or receive) mode, and freezes both echo cancelers when double talk mode occurs. The performance of the system is evaluated by computer simulation and tested by real time experiment.
Reflection, refraction, and transmission of vibrations by T junctions in piecewise-continuous beam constructions
Authors: Wendlandt B. C. H.
Published: October 2005

A numerical analog to the laws of conservation and momentum and the constitutive laws of piecewise-continuous materials is developed and shown to be able to describe the propagation of vibrational waves in a composite. The analog considers material strains of up to 30% to permit a first-order description of nonlinear plastic and viscoelastic response of metal syntactic foam composite T junctions to relatively large scale vibrational and acoustic excitations. The computations describe the propagation of direct stresses across the junction and the generation of shear stresses at the T junction corners. Results of propagation studies of Gaussian and sinusoidal wave packets across a T junction are discussed. Results are presented for selected T junction composites. The results of the numerical analog are discussed in terms of an extension of the classical dilatation-torsion wave theory extended to piecewise continuous materials. Techniques to minimize reflections of vibrations or acoustic excitations from T junctions are discussed.
Noise control in the 1990's: A consultant's view
Authors: Goodfriend Lewis S.
Published: October 2005

The acoustical consultant working with both manufacturers and users of industrial machinery must become thoroughly conversant with the client's equipment or facility and then, and only then, can he take the responsibility for recommending process changes and equipment modifications that will result in noise control. Notwithstanding advances in the analytical and instrumentation areas related to noise propagation and transmission, the methods of noise control other than source modification are, in general, similar to, or the same, as those used in the two preceding decades. Some new hardware has become available including noise cancellation equipment. However, no new theories of noise control have appeared, and the materials and hardware available for noise control have changed little over this period. Some proprietary flow control technology is just now appearing. In general, however, improvements in older materials and systems has simplified the use of existing technology. Industries in the chemical process and utility field still depend on passive “silencers” and insulating jacketing to achieve noise control. Active noise control methods are still mostly confined to experimental work. The use of modern instrumentation has simplified the identification of internal equipment sources. The characteristics of today's methods, materials, and equipment are reviewed along with the expected results. It remains the consultant's responsibility to integrate the noise control measures into the equipment, system, or process without adverse effects on the operation. Several examples from industrial applications will be described.
Quiet zones using active control
Authors: Ross Colin F.
Published: October 2005

This paper will review the recent advances in active control technology that allow small zones to be protected in a noisy environment. It will compare the technological approaches that are appropriate to the different types of noise (broad and narrow band) and the source of the noise (distributed or point). The paper will concentrate on the fundamental limits imposed by causality and signal to noise on the performance of such systems. It will finally compare the typical performances available from the different types of system.
A cavity-piston model for acoustical source impedance in a duct
Authors: Prasad M. G. , Wu K.
Published: October 2005

The importance of acoustical source impedance in the performance evaluation of a muffler in terms of insertion loss is well known. Several experimental methods have been used to obtain the acoustical source impedance. However, studies based on analytical approaches are not many. This paper presents a cavity-piston impedance model for an acoustical source based on the combined pressure-velocity source behavior. The present study deals with the analysis of a source comprising a finite length pipe with an oscillating piston as the termination. The impedance curves for the case of oscillating piston reduces in the limit to the well known case of pipe with rigid end termination. The parameters studied are frequency and amplitude of the piston. The application of this study to noise sources are discussed.
Determination of the vibration mode by a short pulse method
Authors: Reinbert P. , Pareige P. , Maze G. , Ripoche J.
Published: October 2005

It is well known that several experimental methods using quasiharmonic insonification allow a direct verification of the resonance scattering theory. They all provide, for elastic cylindrical targets immersed in water, the resonance frequencies and the mode number of each one. So far, pulsed techniques only allowed resonance isolation. Presented here is a new method: the short pulse method of isolation and identification that completes these works and allows a total comparison with theoretical and quasiharmonic experimental results. This method consists in the digitizing of the time signals that characterize the scattering of an elastic target insonified by a short pulse for different angular positions of the receiving transducer. For each so obtained signal, a resonance spectrum is obtained after a spectral amplitude analysis. From these data, a computer processing allows the plotting of identification patterns, and, by the same way, the knowledge of the mode of vibration at a given resonance frequency. This method has been used for the identification of the resonances of targets as cylinders, water-filled or air-filled cylindrical shells, cavities, etc. The results obtained by this new short pulsed method of identification agree with all those already published.
One-dimensional model of turbulence-induced distortion of sonic boom profiles
Authors: Piacsek Andrew A.
Published: October 2005

In a recent paper (AIAA-90-4031), Pierce and Sparrow have suggested that the prediction of the distortion of sonic booms by atmospheric turbulence can be carried out using modification of the Friedlander series theory that gives waveforms as a power series in time relative to wave onset. The present paper explores basic mathematical problems associated with that theory by analysis of a simplified mathematical model. A step pulse in acoustic pressure propagating in the + x direction enters at time t = 0 the region x > 0 in which sound speed c(x) is a random function of position, where this function is drawn from an ensemble with given statistical properties. The wave at any positive x begins with a weak shock that arrives at a time τ equal to the x integral of 1/c and which, for t < τ can be expanded in a power series t > τ. The statistics of the coefficients in this power series are studied with the assumption that the random process c(x) is homogeneous and Gaussian.
Fourier transforms and effective rise times of sonic booms propagating through a relaxing atmosphere
Authors: Kang Jongmin
Published: October 2005

Sharp impulsive sounds, such as sonic booms, typically have sudden pressure jumps (shocks) that are principal contributors to their perceived annoyance. Rise time, the ostensible time over which the sudden pressure rise occurs, is somewhat of an inadequate descriptor because not all profiles are similar and because two profiles with the same over-pressure and rise time may seem markedly different in perceived loudness. A previously developed numerical procedure determines the detailed pressure versus time profile during the interval that the leading shock nominally occurs, taking into account molecular relaxation effects, and the Fourier transform is determined using the known asymptotic behavior of the waveform profile immediately preceding and following the shock. The proposed definition of an effective rise time recognizes that the A-weighted sound exposure of a waveform is a good descriptor of perceived loudness and that Fourier transforms of pressure waveforms with shocks with finite rise times tend to fall off as the inverse square of increasing frequency as one over the square of the frequency. Such considerations lead to a definition of rise time that is inversely proportional to the square root of the A-weighted sound exposure of that portion of the waveform which includes the shock. The basis for this definition is explained, the constant is evaluated, and examples of atmospheric sonic booms are discussed. [Work supported by NASA-LRC and by the William E. Leonhard endowment to Penn State Univ. The author acknowledges the advice of A. D. Pierce.]
Propagation in atmospheric convective-boundary-layer turbulence
Authors: Wilson D. Keith , Thomson Dennis W.
Published: October 2005

Turbulence in the atmospheric convective boundary layer is inhomogeneous and anisotropic. The vertical correlation length of the sound speed field is typically proportional to height from the ground, whereas the horizontal correlation length is proportional to boundary-layer thickness. Solutions for the turbulence strength and diffraction parameters, valid for this particular case, are presented. The solutions differ significantly from those for homogeneous, isotropic turbulence. An intercomparison is made between the theoretical solutions, numerical propagation simulations, and experimental data. For the numerical simulations, rays were traced through wind and temperature fields generated by a large-eddy simulation.
Frequency window analysis of submerged shells with internal subsystems
Authors: Bjarnason Jens , Igusa Takeru , Achenbach Jan D.
Published: October 2005

The far-field radiation from harmonically loaded submerged shells with internal subsystems is studied. The analysis is based on modal expansions derived from Lagrange's equations. The complexity of the problem is reduced by separating terms with respect to a frequency window. Detail is retained for terms within the window, and dominant coupling effects are included for terms outside the window. This frequency window method provides mathematical insight into two important characteristics of the fluid-shell-substructure system: the modal interaction between the substructure and the shell, and the transition across frequency scales from inefficient to efficient radiating shell modes. The study shows that subsystems have significant effects on the acoustics of submerged shell structures, and that the frequency window method is a useful modal approach for analyzing these effects. [Work supported by ONR.]
Time-dependent wave-vector analysis of the near-field pressure of a fluid-loaded cylinder
Authors: Carroll Gerard P. , Baggeroer Arthur B. , Scheer Edward K.
Published: October 2005

The response of a ribbed cylinder to impulsive excitation was measured on a cylindrical scan surface in the evanescent near field of a cylinder and previously reported [J. A. Clark, and D. Feit, L Acoust. Soc. Am. Suppl. 1 84, S87 (1986)]. The present paper describes the application of a modified maximum-likelihood array processing algorithm to the spatial array data in conjunction with short time FFT processing of selected temporal portions of the transient response, to provide high resolution wave-number-frequency-time information about the field. Slowness (reciprocal phase velocity) versus time plots of the response for each frequency band reveal the time of arrival and the phase velocity of the various waves traveling past the array, which are compared to theoretically predicted dispersion curves for a water loaded infinite cylindrical shell. [Work supported by DARPA/ONR.]
Strategies for representing speech with multichannel cochlear implants
Authors: Wilson Blake S.
Published: October 2005

Various strategies for representing speech information with multichannel cochlear implants will be described, including compressed analog (CA), interleaved pulses (IP), and continuous interleaved sampling (CIS) strategies. Results obtained in within-subject comparisons of strategies will be reviewed. In general, these comparisons have demonstrated large differences among strategies. Recent studies with the CIS strategy recorded large individual improvements and established a new standard of open-set speech recognition among seven subjects chosen for high levels of performance with their CA processors. The CIS strategy presents brief pulses in immediate succession across electrode channels, with the pulse amplitudes for each channel reflecting the envelope of the energy in a corresponding frequency band. The high rate of stimulation on each channel is designed to improve the representation of temporal events in speech. while the use of nonsimultaneous pulses is designed to increase the salience of channel cues through elimination of current summation between channels. [Work supported by NIH, through the Neural Prosthesis Program.]
Issues in evaluating wearable multichannel tactile aids
Authors: Weisenberger Janet M.
Published: October 2005

The viability of the tactile system to convey information about speech sounds to hearing-impaired persons has been substantiated in a number of laboratory studies. In particular, the addition of multichannel tactile devices to lipreading can provide considerable additional information in speech perception tasks, as compared to lipreading alone. Further, studies of Tadoma have demonstrated the ability of the tactile system to transmit speech information even in the absence of visual input. The recent introduction of a number of wearable multichannel tactile devices has made it possible to extend the findings from laboratory studies into everyday clinical and educational settings. A number of factors must be considered in attempting to obtain results from these wearable devices in nonlaboratory settings that will equal or even surpass findings from laboratory studies. These include the level of background noise in the environment, the number of channels and speech processing strategy of the device, the nature and consistency of the training procedure employed, and the correlations between the physical stimulus and perceptual confusions. In addition, subject factors that permit one to define what makes a successful user of a tactile aid must be delineated. Each of these considerations will be discussed in light of recent data. [Work supported by NIH.]
Accounting for normal-hearing listeners' perceptions of syllable-initial /d/'s spoken by hearing-impaired talkers
Authors: Rakerd Brad , Holden-Pitt Lisa , Revoile Sally
Published: October 2005

A substantial corpus of data on normal-hearing listeners' perceptions of stop and glide consonants spoken by sensorineural hearing-impaired talkers of widely varying speech production abilities has been collected. This report concerns the authors' first efforts to measure acoustic cues to consonants in these productions and to relate cue presence to perceptual judgments. The focus was on /d/, as produced in citation-form /dVk/ syllables (V = /ɑ/, /æ), by ten severely through profoundly hearing-impaired talkers representing the midrange of speech production abilities among our hearing-impaired adults. The /dVk/ syllables, along with other syllables contrastive for the initial consonant, were presented to normal-hearing listeners who made identification judgments for the syllable-initial consonant and, at the same time, rated their confidence in each judgment. Acoustic analysis of the /dVk/ syllables generally revealed some form of measurable release burst at onset; however, the bursts were often abnormal for /d/ in either their onset characteristics, amplitude, duration, or spectrum. The strength and quality of the talkers' vocalic cues to /d/ idiosyncratically depended upon the identity of the syllable vowel. A token-by-token analysis of the perception data showed that some constellations of /d/ cues yielded relatively high identification accuracy, others yielded high confidence, but only a small subset yielded both. [Work supported by NIH and the Gallaudet Research Institute.]
Development of phone communication aid for hearing impaired
Authors: Kanevsky D. , Gopalakrishnan P. S. , Daggett G. , Danis C. , Epstein E. , Nahamoo D.
Published: October 2005

The goal of this paper is to describe work on the use of TANGORA—an Automatic Speech Recognizer (ASR) that was developed by the Speech Recognition Group at the Watson Research Center—as a communication device that would allow a hearing-impaired person to communicate with hearing individuals over the telephone. In this implementation, the speech of the hearing individual is decoded by the ASR, and the output is displayed on a computer screen for the hearing-impaired person. The general usability of this system could be limited by the degradation in TANGORA's recognition accuracy due to (1) use of public toll-quality telephone lines (instead of high bandwidth, low-noise communication lines) and (2) using it as a speaker-independent system (instead of trained to recognize each user). For these reasons, the present study was aimed at understanding the effect of decoder accuracy and knowledge about the topic of conversation on the comprehension ability of the hearing-impaired individual. The results of some successful experiments with hearing-impaired users are described and analyzed. The results indicate that the hearing-impaired user is able to understand the speech of the hearing user even in the case of low ASR decoding accuracy (around 70%). Such an accuracy level appears to be achievable under the real conditions described above.
Frequency-dependent gain control by the minima in the temporal sound envelope
Authors: van Dijkhuizen Janette N. , Festen Joost M. , Plomp Reinier
Published: October 2005

Conventional automatic gain control acts upon the average sound level, irrespective of whether there is a speech signal or not. As a result, during periods without a speech signal, background noise is amplified to levels experienced as “noisy” by the listener. This annoyance can be reduced by using the level of the temporal-envelope minima, rather than the average sound level, to control the gain: the information-bearing fluctuations typical for speech are preserved, whereas background noise, usually showing much less-pronounced fluctuations, is presented at a nondisturbing level. This study investigates the effectiveness of a four-channel AGC system in which the frequency-dependent amplification factor is automatically controlled by the envelope minima in the respective frequency channel. The reference was a condition without gain control, but with the amplification in the different frequency bands adjusted to warrant 100% intelligibility in quiet. The effect of the gain-control system on the signal appeared to be greatest in the case of stationary sounds, and smallest when a single speaker was present. Results for 10 listeners with a sensorineural hearing impairment show that, for various sounds frequently interfering in practice, with spectra that are comparable to that of the speech, the condition with gain control does not affect the speech-reception threshold in noise, but substantially reduces the subjective impression of noisiness when no speech communication takes place.
Validation of a speech intelligibility test using SRT for hearing aid research
Authors: Nilsson Michael J. , Sullivan Jean , Soli Sigfrid D.
Published: October 2005

Speech reception thresholds (SRT) were measured in the presence of spectrally matched masking noise using an English language speech comprehension test that has been developed to address some shortcomings of current speech tests as measures of hearing handicap [M. J. Nilsson et al., J. Acoust. Soc. Am. Suppl. 1 88, S175 (1990)]. Following procedures used with Dutch materials [R. Plomp and A. M. Mimpen, Audiology 18, 43–52 (1979)], Leq of the sentence materials was matched and then adjusted to compensate for relative differences in difficulty between sentences. Lists of 12 sentences were created with nearly equal distribution of phonemes. SRTs were measured using normal-hearing subjects with unmodified as well as high- and low-pass filtered conditions in an effort to measure the repeatability of the lists for different signal bandwidths. Results of these tests will be presented and the use of these materials in hearing aid research will be discussed.
Perception of /d,n,l/ by impaired- and normal-hearing listeners
Authors: Kozma-Spytek Linda , Revoile Sally G. , Pickett James M.
Published: October 2005

Eighteen moderately to profoundly hearing-impaired and 11 normal-hearing listeners were studied for their use of acoustic cues for perception of /d,n,l/ in /æCæ/ tokens extracted from spoken sentences. The cues were in segments associated with the /d,n,l/ occlusions and with the transitions of the adjacent vowels. The segments' contribution to /d,n,l/ distinctions were examined from identification tests of the /æCæ/ tokens with consonant occlusion and transition segments degraded singly or in combination. Specifically, the consonant segments were deleted or replaced by a synthetic neutral segment; the transition segments were neutralized via substitution of adjacent pitch periods from the respective vowels. The results with normal-hearing listeners showed that the presence of any one of the consonant or transition segments supported a moderate to high level of correct /d,n,l/ identification, depending on the phoneme. In contrast, the hearing-impaired listeners showed subnormal identification of intervocalic /d,n,l/ which was associated with deficiencies in the use of the consonant occlusion and, generally, with greatly reduced use of the vowel transition. [Work supported by a grant from the NIDCD (NIH) and the Gallaudet Research Institute.]
Methods for longitudinal measures of speech nasality in cochlear implant patients
Authors: Matthies M. L. , Perkell J. S. , Williams M. J.
Published: October 2005

The validity of longitudinal measures of nasality in cochlear implant patients has been examined based on acoustic spectra, sound levels, and outputs of nasal and throat accelerometers. Speech materials consist of isolated utterances and reading passages. Preliminary observations indicate the following: The ratio of rms values of nasal and throat accelerometer outputs [Y. Horii, Cleft Palate J. 17, 254–261 (1980)] may be influenced by: (a) variation in the relative levels of the two signals during the recommended calibration maneuver, production of a sustained /m/, and (b) substantial changes in SPL that accompany onset of “auditory” stimulation from a cochlear prosthesis. These observations raise uncertainty about using the throat accelerometer output as a reference and about the sensitivity of this kind of measure to longitudinal changes in nasality across experimental sessions. In addition, measures of harmonic and formant amplitudes from acoustic spectra may be confounded by changes in coupling to tracheal resonances that also accompany the activation of the prosthesis. These observations and additional measures and calibration strategies will be explored further. [Work supported by NIH.]
Ocean acoustics turbulence study (OATS)
Authors: Goodman Louis , Szargowicz Diane , Letcher Stephen , Oeschger John , Balasco Elena
Published: October 2005

Limited in situ measurements from high-frequency underwater acoustic echo sounders have suggested that there may be circumstances in which acoustic scattering from ocean temperature microstructure is sufficiently intense to be observable over volume reverberation due to biologics. A new laboratory program, ocean acoustics turbulence study (OATS), has been undertaken to quantify the nature of such scattering and to compare laboratory results with a recently developed model of microstructure scattering. A buoyant plume characterized by three different types of fluid regions as a function of height, namely laminar, unstable, and fully developed turbulent, is used as the scattering field. Experiments are to be performed in the frequency range from 100 kHz to 1 MHz for scattering angles spanning from near forward to near backscatter. Results to date will be presented. Preliminary results have indicated observable acoustic scattering in all three fluid regions at 1 MHz, with the turbulent regime yielding scattering strengths at a scattering angle of 90 deg of order −80 dB in qualitative agreement with model predictions.
Low-frequency backscattering from a submerged bubble cloud
Authors: Roy Ronald A. , Nicholas Michael , Crum Lawrence A.
Published: October 2005

The results of a recent series of experiments designed to demonstrate resonance backscattering from a bubble cloud are presented. In these experiments, an ≈1-m-diam bubble cloud was generated ≈20 m beneath the surface of a deep-water lake and insonified using a pulsed parametric-array projector. Through measurements of frequency-dependent backscattering, target strengths were determined for frequencies ranging from 500 Hz to 4 kHz. (The individual bubble resonance frequencies ranged from ≈1.5 to ≈5 kHz.) Results indicate an increasing target strength with decreasing frequency, which suggests the presence of a resonance response in the subkilohertz range. Experimental results will be discussed in light of theories describing the collective oscillations of bubble clouds and plumes. [Work supported by ONR, ONT, and AEAS.]
Acoustic backscatter measurements of suspended sediments as part of the 1988 STRESS experiment
Authors: Lynch James F. , Gross Thomas F. , Brumley Blair , Sherwood Christopher
Published: October 2005

As part of the 1988 STRESS (Sediment Transport Events on Shelves and Slopes) experiment, an upward looking 1-MHz backscatter sonar was deployed in 90 m of water off the California coast for a period of 2 months. Dubbed “ABSS” (Acoustic Back Scatter System), this instrument made vertical profiles of the suspended sediment from 1.5 to 27.O m above bottom. Temporal sampling allowed both slow (every half-hour) sampling to look at the long time evolution of the bottom boundary layer and fast (0.5 Hz over 2 min) sampling to look at individual wave-induced suspension. During the course of the development, two major transport events (storms) were seen. in this talk, the ABSS measurement results, the correlation of the suspended sediment profiles obtained to relevant environmental variables, the correlation of the acoustic data to other measurement techniques (e,g., OBS, transmissometer), and the ramifications for coastal boundary layer monitoring are discussed. [Work supported by ONR.]
Physical constraints of shallow water on acoustic communication by aquatic insects
Authors: Forrest T. G. , Miller G. L. , Zagar I. R. , Gilbert K. E.
Published: October 2005

Frequency responses of shallow, freshwater ponds in northern Mississippi were measured. The response has a highpass characteristic with a sharp cutoff frequency due to the modal properties of the system. The cutoff frequency of the system is inversely related to the depth of water at the shallower transducer (projector or receiver). Frequencies below the first mode are nonpropagating, and the overall effect of this environment on propagation is about 50 dB. Several species of aquatic insects communicate in these shallow-water ponds using acoustic signals, and they must contend with the physical constraints imposed by the system. Data on the calling song (long range) of a common aquatic beetle (Tropisternus collaris, Hydrophilidae) are presented and discussed in relation to the propagation characteristics of their shallow pond habitats. [Work supported by USDA.]
Neural network simulation for ranging mechanism of FM-FM cortical neurons in FM bats
Authors: Lin Zhen-Biao , Chittajallu S. K. , Kayalar S. , Wong D. , Yurtseven H. O.
Published: October 2005

A multilayer neural network is designed for modeling FM-FM neurons in the auditory cortex of FM bats. These neurons play a critical role as a “delay-dependent multiplier” to perform cross correlation. Data from FM-FM neurons in Myotis lucifugus were used to train different artificial neural networks. Results show that one hidden layer is adequate for modeling biological FM-FM neurons. More hidden layers give little improvement in precision, but the cost of computation grows linearly with the number of synaptic connections. Very large networks and very high-training cycles lead to the memorization of the training patterns but result in a poor prediction for testing patterns. A neural network model with one hidden layer (15 nodes) is proposed. The results from three trained models showed that for testing patterns not included in the training set, the prediction error was small (MSE = 0.007). The dynamic behavior of the delay-dependent multiplier (described by the contour of 70% of the maximum value) is reasonable from a hunting behavior standpoint. In the search phase (low-repetition rates), a high-output sensitivity and a very wide delay window is necessary for detecting a target at an unknown distance. After detection, the repetition rate increases and the delay width drops dramatically corresponding to focusing to a specific target distance.
Echolocation signals of the smallest odontocetes
Authors: Au Whitlow W. L.
Published: October 2005

Echolocation signals of the smallest odontocetes, Cephalorhynchus commersonii, Cephalorhynchus hectori (genus Cephalorhynchus), Phocoenoides dalli, Phocoena phocoena, and Neophocoena phocoena (family phocoenidae) are compared with those of larger dolphins. Available data seem to indicate that two distinct classes of signals exist. Echolocation signals of Tursiops truncatus, Pseudorca crassidens, and Delphinapterus leucas studied at the Naval Ocean Systems Center have peak frequencies between 100-120 kHz, with high amplitudes (210–225 dB re:1 μPa), short durations (50–70 μs), and wide bandwidths (30–40 kHz). The smallest odontocetes tend to emit signals having peak frequencies between 120 and 140 kHz, with low amplitudes (< 170 dB re: 1 μPa), long durations (170–430 μs) and narrow bandwidths (7–11 kHz). Double pulses are also emitted regularly by the smaller odontocetes and very infrequently by the larger dolphins. The signals used by the smaller animals may reflect an adaptation resulting from constraints associated with their small size and may also reflect differences in the generation mechanism. Some of the properties of high-frequency, narrow-bandwidth biosonar signals used by the smaller odontocetes will be discussed, along with comparative advantages and disadvantages of these signals.
Prospects for low-noise, high-performance chain saws: An achievable goal?
Authors: Keith S. E. , Brammer A. J.
Published: October 2005

The noise of chain saws powered by internal-combustion engines depends on the relative strengths of four major sources; engine exhaust and intake, noise radiated from the structure associated with engine operation (so-called “mechanical” noise), and noise associated with the cutting process. The prospects for developing low-noise, high-performance saws have been explored by rank ordering the source strengths and examining the potential for reducing the sound pressure produced by the most significant source, or sources, at each frequency. At the present state of development, a further reduction in the noise at the operator's ear of approximately 5 dB can be expected by improving the exhaust and intake mufflers of a typical 3-kW saw, but the A-weighted sound level will remain in excess of 100 dB. Control of the mechanical noise will be required to reduce the A-weighted sound level experienced by the operator to 90 dB, within the constraints of minimal increases in weight, size, and cost, and maintenance of mechanical efficiency.
Experimental design of centrifugal fans for minimum noise generation
Authors: Bolton J. Stuart , Konieczny Peter
Published: October 2005

The level of broadband noise generated by airflow through a centrifugal fan has been found to depend on a variety of housing design parameters, e.g., scroll development angle and length, axial and radial inlet clearances, and cutoff clearance. In the absence of complete theories describing the effect of these parameters on the noise generation process, it has been necessary to identify quiet fan designs experimentally. The comparison of noise levels generated by fans having different designs is, however, complicated by the fact that design changes affect a fan's aerodynamic performance as well as its sound power level. Thus it is impossible in general to operate two different fans at the same operating point and thus to establish directly which fan design will result in the least noise generation while fulfilling a specified pumping requirement. In this paper, a procedure is described that allows the effects of aerodynamic performance differences to be scaled out of measured sound power levels, thus allowing fans having different aerodynamic performance to be compared and, in turn, making it possible to establish unequivocally which of several possible designs is the quietest. The procedure will be illustrated through the experimental identification of the optimum housing design parameters for a fan having an impeller diameter of approximately 0.1 m. In addition, it will be shown how a low-noise design established in this way may be physically scaled to meet a range of flow requirements, and how the noise generated by any fan within the design family may be predicted.
Vibration control of a rotating arm using an ultrasonic motor
Authors: Wu Zhen , Bao Xiaoqi , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

Unlike an electric motor, the ultrasonic motor produces torque through ultrasonic vibrations. It has some unique advantages over electric motors such as light weight and small volume; no magnetic noise; and low-rotation speed without gears. Also, because it is driven by the friction force between the stator and the rotor, it has a very quick reponse time which is a highly desired feature in a control system. The motor control characteristics including the response time for speed and position control are presented. Experiments have been performed on a simple robotic system with a rotating arm. The motor can be used to control the arm location as well as actively control the residual vibration of the ann tip.
Optimum structural configuration of a baffled beam for a minimum radiation condition
Authors: Naghshineh Koorosh , Koopmann Gary H.
Published: October 2005

A method has been devised for designing baffled beams that radiate sound inefficiently. The problem has been broken into two steps. First, given the overall length of the beam, a velocity distribution is found that would result in a beam that radiates sound least efficiently. This particular velocity distribution is referred to as the “weak radiator” mode shape. Second, given a choice of material properties, the structural configuration of a beam is found that exhibits the weak radiator mode shape. In the first step, a finite element adaptation of the Rayleigh integral has been employed in conjunction with the Lagrange multiplier theorem to obtain a beam velocity distribution that minimizes the radiated sound power. In the second step, extensive use of finite element modeling, as well as linear programming techniques, has been made. The result is the optimum structural configuration of a beam that exhibits a weak radiator mode shape as a natural mode shape.
Acoustic Bloch wave energy transport and group velocity
Authors: Bradley Charles E. , Blackstock David T.
Published: October 2005

The relationship between the steady-state rate of energy transport and the group velocity is investigated for acoustic Bloch waves in a periodic waveguide. A time-average energy flux relation is derived and used to find the energy transport velocity for an arbitrary periodic waveguide. An apparent disparity between the energy transport velocity and the power delivery is discussed. The group velocity is derived using a Bloch wave generalization of the usual Fourier transform method and is shown to be equal to the rate of energy transport. The integral transform method works well for the boundary value problem as the associated Bloch wave transform is relatively straightforward. The initial value problem, however, involves the inverse Bloch wave transform, the problems associated with which are discussed. [Work supported by the Office of Naval Research.]
Determination of transient acoustic wave fields in continuously layered media using the modified Cagniard method
Authors: Verweij Martin D. , de Hoop Adrianus T.
Published: October 2005

A combination of the Neumann series solution and the modified Cagniard method is used to derive a theoretically exact space-time domain solution for the 3-D acoustic wave propagation problem in continuously layered media. In view of the application of a time Laplace transformation with a real positive transform parameter, the convergence of the iterative Neumann scheme for an arbitrary continuously layered configuration is guaranteed, both in the transform domain and in the space-time domain. The iterates, which represent successively reflected waves, are transformed back to the space-time domain using the modified Cagniard method. Using this method, continuously layered configurations with relatively large horizontal source/receiver distances lead to an unconventional type of integration contour. In contrast to the standard angular wave number/frequency domain analysis, difficulties due to “turning rays” can be avoided. The inverse transformation procedure is demonstrated for the direct wave and the wave due to single partial reflections. Numerical results for these wave constituents are presented.
An approximate numerical solution for the general radiation problem by combining the method of wave superposition and the singular value decomposition
Authors: Fahnline John B. , Koopmann Gary H.
Published: October 2005

In the method of wave superposition, the field due to an arbitrarily shaped radiator is written in terms of the sum of the fields due to a finite number of simple sources enclosed within the radiator. The strengths of the sources are determined by requiring that the sum of their individual fields reproduce the radiator's normal surface velocity at a finite number of locations either exactly or in the least square sense. Through the singular value decomposition (SVD), the dipole matrix, which relates the source strengths and normal surface velocities, can be written as a product of two unitary matrices and a real, diagonal matrix. Each of the unitary matrices represents a set of mutually orthogonal mode vectors, while the diagonal matrix represents the singular values associated with these modes. This decomposition is shown to contain the first N terms of the exact multipole expansion for the solution of the associated boundary value problem.
Acoustic radiation from a chaotic viscous layer
Authors: Thompson Charles , Mulpur Arun
Published: October 2005

The Stokes boundary layer has been shown to exhibit linear instability with increasing amplitude of acoustic excitation. Special consideration is given to the amplitude range above which these disturbances bifurcate from linear stability. It is found that oscillatory modulation present in the basic-state results in successive period-doubling bifurcations for three-dimensional vortical disturbances. The acoustic radiation from these unstable vortical disturbances will be addressed.
A flow-powered very low-frequency underwater tone source
Authors: Elder S. A. , Yoshikawa S.
Published: October 2005

Previous studies of underwater flow excited cavity resonance in streamlined towed models have shown that large amplitude acoustic oscillations can be achieved at frequencies under 40 Hz for towing speeds in the range of 5–15 kn. The present investigation aims to develop an understanding of the phenomenon that could permit its utilization as a nonpowered low-frequency underwater tone source. A resonant cavity was constructed in the form of a rectangular box with a vertical slot cut in the side, allowing uncomplicated prediction of wall vibration and radiation. The box was then mounted in a fiberglass fairing to produce a uniform turbulent boundary layer at the location of the slot. Before towing, identification of those vibration modes that provoke flow into and out of the cavity was performed in the laboratory, using modal analysis. Early tow tank runs are showing that tonal radiation seems to occur at expected range of speeds and frequencies, though the level of the sound is less than desired. Further “voicing” of the device is underway (sharpening the edge of the slot, raising the Q of the resonator by using more resilient mounting. etc.).
Constraints on nonlinear amplification for recruitment of loudness compensation
Authors: Tungthangthum Apichat , Rutledge Janet C.
Published: October 2005

A nonlinear amplification technique has been developed to compensate for recruitment of loudness in sensorineural hearing losses [J. C. Rutledge, “Time-Varying, Frequency-Dependent Compensation for Recruitment of Loudness,” Ph.D. thesis, Georgia Inst. of Technol., 1989]. This technique uses a sinusoidal speech model to incorporate a model of the psychoacoustic masking of sinusoids in normal hearing and in hearing-impaired persons. It operates on both a time-varying and frequency-dependent basis. The drawback is that the model processing may distort the vowel formant structure and thus cause confusions between vowels. Therefore constraints on the relative amplitude levels of the sinusoidal components at different frequency regions should be incorporated into the model. These constraints have been studied and will be discussed.
Reliability, sensitivity, and validity of magnitude estimation, paired comparisons, and category scaling
Authors: Purdy Suzanne C. , Pavlovic Chaslav V.
Published: October 2005

This study investigated the reliability, sensitivity, and validity of speech intelligibility judgments for hearing aid evaluation. Subjects judged the intelligibility of sentences using either magnitude estimation, category scaling, or paired comparisons. Speech recognition scores for CID sentences and NU-6 words were also obtained. Test conditions were selected using articulation index (AI) theory. AI theory predicts that speech intelligibility is monotonically related to the articulation index which depends on the available speech dynamic range and the importance [I(f)] of each frequency band for speech intelligibility. The speech signal was bandpass filtered so that the AI increased monotonically regardless of I(f). Filter conditions were selected that produce an increase in AI for speech materials spanning the range of probable importance functions, namely nonsense syllables, easy speech, and average speech [C. V. Pavlovic, J. Acoust. Soc. Am. 82, 413–422 (1987)]. Speech scores and intelligibility judgments were obtained for each filter condition. Test-retest reliability was poorest for paired comparisons and CID sentence scores. There were no differences in sensitivity among the scaling procedures. Intelligibility judgments and NU-6 scores were more sensitive than CID sentence scores to differences among conditions. The results indicated that intelligibility judgments are valid measures of speech recognition.
On measurement of structural intensity in thin-walled structures
Authors: Pavic G.
Published: October 2005

In order to measure structural intensity in a thin-walled structure (shell), one has to employ intensity expressions given in terms of physical quantities that (a) are measurable and (b) refer to the external surface of the shell. These quantities are surface strains and displacements or displacement derivatives—either velocities or accelerations. Intensity expressions, which can serve as a starting basis for measurements, have been established for flat plates, circular cylindrical shells, and spherical shells. The expressions are given in terms of neutral-surface displacement and strains, which are reference quantities for any theoretical analysis and, consequently, have to be translated to the external surface domain. Intensity in a flat plate consists of two contributions: one due to extensional, the other due to flexural effects. The shell, in addition, has the influence of curvature, which couples the in-plane and the normal components of motion. As a result, large number of strains and displacement components have to be simultaneously detected in order to produce intensity readings correctly. The number of transducers required to measure these quantities is even larger, because some of the quantities are given in a differential form, implying use of multipoint finite difference schemes in practical measurements. Furthermore, some transducers, such as accelerometers, cannot measure at the body surface but somewhat above it, which necessitates corrections in readings of in-plane motions. This and other reasons (transducer cross-sensitivity, surface loading) make conventional vibration transducers impractical for this work. Preference in practical measurements should go to non-contact methods which still have to be developed. This paper describes the nature of the intensity expressions related to thin shells. Examples are given of a circular cylindrical shell in contact with an acoustic medium. Various possibilities are described for measurement of intensity using conventional transducers. Sources of measurement errors and limitations are discussed in some detail. Finally, new measurement concepts are shown, aimed at improving accuracy and reducing difficulties encountered with conventional methods.
Flexural intensity measurements in a beam using a three-point measurement
Authors: DeJong Richard
Published: October 2005

A method for obtaining the flexural intensity vector in a vibrating beam has been developed using the measurement of the transverse motion at three closely spaced points. This method is superior to the two-point method in that it accounts for both the shear and bending components of the energy flow in the beam. The intensity vector can be accurately measured near discontinuities in the beam, where near-field components cause errors in the two-point method. The new method is also superior to the four- or five-point methods that use a full finite difference approximation to the flexural wave equation in that it is more compact in space and less sensitive to instrumentation errors. The new method does use an approximation that makes it sensitive to phase errors at low frequencies. The accuracy of the method and the sensitivity to phase errors are investigated using simulations and measurements on beams with discontinuities.
The effects of fluid loading on the radiation from plane ribbed panels
Authors: Maidanik G. , Dickey J.
Published: October 2005

The impulse response of an infinite regularly ribbed fluid-loaded panel is used to calculate the spectral response and radiation efficiency of these structures when they are excited by mechanical (line) drives. The linear response quantities, pressure and velocity, are displayed in the wave-number-frequency plane, where the patterns show many interesting features connected with the periodicity of the ribs, the mechanical damping, and the fluid loading. The combination of the linear-response quantities to form the quadratic quantities, energy and intensity, is discussed. The near-field and far-field responses in the fluid are calculated and used to determine the intensity on the panel and in the far field. These quantities are then integrated and used to determine the radiation efficiency of the panel.