bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle separation by ultrasonic forces
Authors: Woodside Steven M. , Groeschl Martin , Benes Ewald , Bowen Bruce D. , Piret James M.
Published: July 2002

A simple, effective device has been developed to separate mammalian cells from growth medium using the ultrasonic forces on suspended particles in a standing wave field. The ultrasonic force distribution in this acoustic separation device has been analyzed to provide a basis for further optimization and scale-up of the separation system. Measurements of the force distribution in the liquid using a microscope-based imaging system were compared to laser interferometric measurements of the velocity amplitude distribution on the transducer and reflector surfaces of the ultrasonic resonator. The axial force followed the surface velocity, being highest near the center, and approaching zero near the walls. The transverse force distribution and the local gridlike surface amplitude variation had characteristic wavelengths of 1.4 mm. These results suggest that the force distribution is determined predominantly by the response of the reflector and transducer to the standing wave. This understanding of the force distribution simplifies the modeling of particle retention and facilitates resonator design. By selection of appropriate resonator dimensions and construction materials, and modeling of the ultrasonic force on the particles, enhanced flow-through capacity and particle retention efficiency can be achieved.
Acoustic methods for transport properties measurements in gases
Authors: Gillis Keith A. , Mehl James B. , Moldover Michael R.
Published: July 2002

Two novel acoustic resonators have been developed, one for measuring the viscosity and a second for measuring the Prandtl number of gases. For viscosity measurements, a double Helmholtz resonator, called the Greenspan viscometer, is used. This resonator consists of two chambers connected by a small duct. The Greenspan viscometer has a single, isolated, low-frequency mode that is fitted to determine the gas’ viscous diffusivity. The Greenspan viscometer may be used for absolute measurements if the dimensions of the duct and chambers are accurately known. Otherwise, the viscometer may be calibrated with argon or helium. For Prandtl number measurements, a cylindrical resonator that has been modified by inserting an array of short, parallel plates halfway between the ends is used. The lower longitudinal modes of this resonator are fitted to determine the Prandtl number. The odd order modes are attenuated primarily by the viscous diffusivity; the even order modes are attenuated primarily by the thermal diffusivity. Detailed acoustic models of both resonators have been developed and are necessary to realize the full precision and accuracy of these techniques. Transport property measurements of several gases will be presented. [This work is supported in part by the Office of Naval Research.]
Excess attenuation by reactive obstacles at a noise barrier edge
Authors: Fujiwara Kyoji , Kim Chul-hwan , Ohkubo Tomonao
Published: July 2002

The excess attenuation by small obstacles with a reactive surface installed at the noise barrier edge was studied. So far, the absorbing obstacle has been used to obtain large attenuation, keeping the barrier height constant. It was found that an obstacle with a soft surface at the barrier edge can suppress noise more effectively than the absorbing one does. To realize this soft surface an arrangement of one-quarter wavelength acoustic wells was used. Although these acoustic wells behaved as the soft surface in a certain frequency range, at a barely lower frequency range the sound pressure level behind the barrier was amplified. To overcome this negative effect a new arrangement of wells tuned to several different resonance frequencies is studied. As a result, the excess attenuation by a small round obstacle of 53 cm width and 33 cm height installed at the edge of a 3-m barrier is about 4.7 dB (OA) at the ground 25 m behind the barrier. When the barrier has a T shape and is of 2 m width and 5 m height, the excess attenuation is 7 dB (OA). Details of the cross sections of these barriers will be presented.
Scale model experiments on the insertion loss of wide and double barriers
Authors: Wadsworth Glenn J. , Chambers James P.
Published: July 2002

The insertion loss of wide and double barriers is investigated through scale model experiments. Such configurations are common in outdoor sound propagation problems such as highway barriers and raised or depressed roadways. The Biot–Tolstoy–Medwin time domain wedge formulation for multiple diffraction [J. Acoust. Soc. Am. 72, 1005–1013 (1982)] is used to predict the acoustic field directly in the time domain. Evaluating the insertion loss at discrete frequencies or in octave bands is accomplished via the fast Fourier transform (FFT). Comparisons to other frequency based models will also be presented.
An acoustic radiometer
Authors: Simmons Timothy G. , Denardo Bruce , Larraza Andrés , Keolian Robert
Published: July 2002

An electromagnetic radiometer is a well-known physics demonstration and toy. When exposed to light of sufficient intensity, the vanes rotate in the opposite direction if radiation pressure were the mechanism. That is, the reflective white side leads the absorptive black side. This occurs due to thermal effects associated with the gas in the bulb, and can be overcome only with a very high vacuum. To demonstrate the effect of radiation pressure, we have built an acoustic radiometer consisting of an aluminum T-beam with a 10-cm-square pane attached to each end. One side of a pane is acoustically reflective (aluminum) and the other is acoustically absorbing (foam). The device is pivoted with a V-jewel bearing and a steel pin, and is placed in a transparent chamber with a uniform broadband noise field (2.5–15 kHz). A minimum sound-pressure level of roughly 125 dB (re: 10−12 W/m2), which yields a theoretical net force corresponding to 2 mg on each pane, produces rotation in the ‘‘correct’’ sense with the absorptive side leading the reflective side. The apparatus will be demonstrated during the talk. [Work sponsored by the Office of Naval Research.]
Proactive concert sound management: The essential ingredient for community acceptance of outdoor concert venues
Authors: Cann Richard G. , Cavanaugh William J.
Published: July 2002

Residents living adjacent to outdoor music venues have often objected to sound emissions. With increased sound power now available from loudspeakers, the situation is exacerbated, threatening the existence of music venues. Venues have demonstrated that by using a fixed installation system to manage and control concert sound emissions effectively, the friction with the community can be reduced substantially. An essential ingredient of the amelioration process is making automatic sound emission reports available to amphitheater sound engineers and management as each concert proceeds. Sharing these same reports with citizen activists immediately after each concert helps develop trust. Case histories will be presented.
Comparison of predicted and measured noise levels for refinery units
Authors: Brittain Frank H. , Gmerek Mark M.
Published: July 2002

Predicting noise levels from new refinery units is a vital part of environmental assessment and designing units to meet noise limits. The accuracy of those noise predictions is a very important concern. The simplest way to assess the accuracy of predictions is to compare predicted and measured noise levels. This is usually difficult, because measured levels are strongly affected by noise from adjacent units and by atmospheric effects on sound propagation. Further, actual noise levels of significant sources often deviate from expected levels used in the noise prediction model. Thus to meaningfully compare predicted and measured levels, the actual noise source levels for the major sources, atmospheric conditions, and noise levels from adjacent units must all be accounted for. Predicted and measured levels are compared for two large refinery units. Measurements were made at locations where noise from adjacent units has little effect and close enough so that atmospheric conditions have little impact on the measured levels. Measured operational noise levels of major sources were used to update the noise prediction model. Accuracy of the predictions is evaluated.
Measurement of the radiation impedance of a pipe with a circular flange
Authors: Dalmont Jean-Pierre , Nederveen Cornelis J.
Published: July 2002

The radiation of an open pipe with an infinite flange, as well as that of an unflanged pipe has been explicitly calculated by, respectively, Norris and Sheng [J. Sound. Vib. 135(1), 85–93 (1989)] and Levine and Schwinger [Phys. Rev. 73, 383–406 (1948)]. The radiation of real tubes, i.e., with a finite wall thickness or a finite circular flange, is not accurately known. The aim of the present measurements is to determine the radiation of tubes with various flanges and their frequency dependence. The radiation impedance has been deduced from the measurements of the input impedance of a short tube. As the differences between the different situations can be very small, the impedance sensor must be accurately calibrated. Results are reproducible and are in good agreement with a calculation using a boundary elements method (software, Rayon). It is observed that the curves obtained are not limited by the case of the infinite flange and the case of the unflanged pipe. This is probably caused by a resonance effect due to the diffraction at the edges of the flange.
Experimental investigation on nonlinear standing waves by two tube structure
Authors: Liu Ke , Maa Dah-You
Published: July 2002

Nonlinear standing waves have been studied in a structure consisting of two lengths of tubing with different diameters. The measurement system of the experiment is presented. A new high-power loudspeaker driver (300 W) is used as a sound source to excite the large tube of 45 mm diameter through a small hole near one end which is closed. Preliminary nonlinear theory is proposed, and a resonance diagram of the tube structure is given. The main properties of nonlinear standing waves were obtained. At the end of smaller tube, a sound-pressure level (SPL) of nearly 177 dB has been obtained with a low distortion. The phenomena of saturation and properties of the output at the end of the smaller tube as well as their relation with the input were investigated. Increasing the diameter of the structure directly with a modern high-power loudspeaker produces high intensity in a more extended space. Experiments are in progress. [Work supported by the National Natural Science Foundation of China.]
Simple model for temperature gradient formation in a short stack
Authors: Muehleisen Ralph T. , Atchley Anthony A.
Published: July 2002

There has been much analytical, numerical, and experimental work investigating steady-state thermoacoustic phenomenon. However, much less work has been done on time-dependent problems such as the evolution of the thermoacoustic temperature gradient in a short stack of plates. If the time scale of the acoustics is much shorter than that of the thermodynamics of the stack itself, the acoustics can be assumed to be in steady state while the temperature gradient in the stack is formed. With this assumption, the thermoacoustic heat flux between the stack plates will be of the form Q=(C1+C2∂T/∂x)p2. This gives rise to a temperature gradient that rises exponentially in time with a time constant proportional to the thermal conductivity of the stack and the acoustic pressure squared. There is an additional exponential temperature rise from viscous heating. The model is shown to match measured temperature gradients very well. [This work was supported by the Office of Naval Research and the American Association for Engineering Education.]
Estimates of temporal resolution at low and high spectral frequencies
Authors: Eddins David A.
Published: July 2002

The auditory system must encode dynamic acoustic stimuli throughout the audible spectrum. This coding is limited by the temporal resolution of the ear. Unfortunately, the results of several investigations disagree on the way in which temporal resolution varies with stimulus frequency. While gap-detection thresholds measured with sinusoidal signals change little over the frequency range of 200–2000 Hz, gap and amplitude modulation detection with narrow-band noise is more variable. Eddins [J. Acoust. Soc. Am. 93, 470–479 (1993)] showed that modulation detection is not frequency dependent from 500 to 4400 Hz, however, there are few measures of modulation detection above this frequency range. In the present experiment, thresholds for modulation depth were obtained as a function of modulation frequency. Narrow-band noise carriers had upper- cutoff frequencies ranging from 3200 to 12 800 Hz and bandwidths from 400 to 3200 Hz. Temporal modulation transfer functions (TMTF) demonstrated the typical low-pass characteristic. The form of the TMTF did not vary with noise bandwidth or frequency region from 3200 to 9600 Hz. Sensitivity to modulation increased with increasing bandwidth. For lower modulation frequencies, thresholds were slightly reduced at 12 800 Hz. These results indicate that modulation detection varies little over a very broad range of frequencies.
Effects of carrier level on the processing of highly detectable envelope fluctuations
Authors: Wojtczak Magdalena , Viemeister Neal F.
Published: July 2002

A modified 2AFC matching procedure was used to measure the modulation depth that yielded similar perceived envelope fluctuations for different carrier levels. In one case, the standard was a 60-dB SPL 1-kHz tone that was amplitude-modulated at 16 Hz, with a modulation depth that produced highly detectable envelope fluctuations. The comparison had the same carrier and modulation frequencies as the standard, and its level ranged from 15 to 85 dB SPL. The data indicate that the higher the carrier level, the less modulation was needed to produce the same perceived fluctuation depth. For broadband noise carriers, however, the data indicate that approximately the same modulation depth was needed to obtain subjectively similar envelope fluctuations for all carrier levels tested. These results are similar to those observed for detection of AM, and they suggest that the level effects seen for detection extend to suprathreshold AM processing, i.e., Weber’s law for broadband noise and a ‘‘near-miss’’ for sinusoidal carriers. [Work supported by NIDCD Grant No. DC00683.]
Auditory motion aftereffects with a two-component adapter
Authors: Uematsu Hisashi , Kashino Makio
Published: July 2002

Auditory motion aftereffects have been used to investigate mechanisms used to detect changes in interaural time differences (ITDs). In this paper, auditory motion aftereffects with two-tone adapters were used to examine how the ITD-change information from each frequency band is integrated. In the experiment, a complex tone with 250- and 500-Hz components was used as an adapter. The magnitude of the auditory motion aftereffect for a physically stationary 500-Hz test tone was measured using various combinations of direction and adapter component. Apparent sound movement was produced by varying only ITDs. The results showed no difference in the magnitude of the aftereffect between the 500-Hz tone adapter and the complex adapter when the two components moved toward the same direction. On the other hand, the aftereffects disappeared when the two components of the adapter moved in opposite directions. This suggests that the integration of ITD-change information from each frequency band is not a simple linear summation. Mechanisms of across-frequency integration will be discussed.
Vibration measurement of the tympanic membrane using the time-averaged speckle pattern interferometry
Authors: Wada Hiroshi , Takeuchi Masataka , Hozawa Koji , Gemma Takashi , Nara Makoto
Published: July 2002

In this study, using the time-averaged electronic speckle pattern interferometry, the sinusoidal phase modulation technique by a direct modulation of laser injection current, and the digital image processing technique, an attempt was made to develop a system for measuring a small vibration in nanometer order. The vibratory responses of the guinea pig’s tympanic membrane were measured. At the frequency of 1500 Hz, the whole part of the tympanic membrane vibrated almost in phase. The maximum amplitude was about 30 nm. At the frequency of 2500 Hz, the tympanic membrane had two local maxima in the posterior and inferior portions. At the frequency of 3000 Hz, the four peaks around the manubrium were seen. The number of the peaks increased with an increase in frequency and the vibration mode became more complicated. The results of this study indicate that the vibration amplitude is detectable in nanometer order by this system even when the stimulus level is small, e.g., 60 dB SPL. Consequently, the system developed by our group has a potential for clinical applications. [Work supported by the Ministry of Education of Japan.]
Comparison of psychophysical and single-unit thresholds in response to electrical stimulation of the cochlea in guinea pig
Authors: Pfingst Bryan E. , Montney Lisa M. , Bledsoe Sanford C.
Published: July 2002

Recent studies have shown that the spatial pattern of currents used on individual channels of cochlear implants can have a large effect on speech recognition and other measures of electrical-stimulus perception. This study is one of a series that seeks to understand the neural patterns of response underlying these effects. Guinea pigs were deafened in one ear by local perfusion of an antibiotic and implanted with an electrode array in the scala tympani. Psychophysical strength-duration functions (detection threshold versus electrical pulse duration) were obtained in guinea pigs trained using positive reinforcement, operant conditioning techniques. Single-unit data were obtained from inferior colliculus in the same animals, or in guinea pigs deafened and implanted in a similar manner. In these preparations, thresholds for neural responses were near the psychophysical thresholds at all phase durations, and the thresholds for the most sensitive neurons were several dB below the psychophysical detection thresholds. Thus, the paradoxical discrepancies between neural responsiveness and behavioral stimulus detection observed in previous comparisons made across animal models do not occur in this preparation. This seems to be a useful preparation for determining the spatiotemporal patterns of neural activity that underlie electrical-stimulus perception. [Work supported by NIH-NIDCD Grant No. DC00274.]
Nonlinear wave propagation from a discrete annular array: Theory
Authors: Kargl Steven G. , Roy Ronald A. , Edson Patrick
Published: July 2002

Theoretical investigations of finite amplitude wave propagation from bounded beam sources has been considered by Lee and Hamilton [J. Acoust. Soc. Am. 97, 906–917 (1995)] as well as others. These researchers have restricted their analyses to a source geometry of either an unfocused circular piston or a weakly, spherically focused circular piston. When the peak pressure does not exceed approximately 150 MPa, the Khokhlov–Zabolotskaya–Kuznetsov (KZK) nonlinear parabolic wave equation yields numerical solutions in agreement with experiments. However, little research has been reported on finite amplitude wave propagation from an array of discrete sources. Time domain simulations, based on the KZK equation, will be discussed for an eight element discrete annular array immersed in fresh and sea water. The source signal is typically a short sine wave tone burst with a center frequency of 500 kHz. The transitions from linear acoustics to nonlinear acoustics will be discussed, and comparisons between a spherically focused circular source and a properly phased array will be presented. While some data from recent experiments may be shown, the scope of this talk will be restricted to the theoretical treatment and the numerical simulations for the discrete annular array. [Work supported by ONR.] by Edson
Application of the three-wave interaction to the problem of acoustical monitoring of complicated media
Authors: Rybak Samuil A. , Zozulya Oleg M.
Published: July 2002

In a nonlinear medium with resonant dispersion the three-wave interaction is considered. The medium consists of oscillators distributed in eigenfrequency range. The quadratic nonlinearity is taken into account in surrounding compressible medium. The three-wave interaction in such medium is sensitive to the changing of the medium parameters. Space and time scales of energy transfer among the interacting waves are determined. The eigenfrequency distribution leads to the effective Landau attenuation of wave amplitudes and results in finite time interaction among waves. On the other hand, this finite time permits the same efficiency of interaction not only for waves exactly satisfying the resonant conditions but also for wave packets. In the particular case of Lorentz distribution the influence of the distribution parameters on the energy transfer is determined. Some exact solutions expressed in special functions describing the three-wave interaction are obtained. [Work was partially supported by Russian Foundation of Basic Research.]
Application of nonlinear interaction of sound waves in sound reproduction
Authors: Dong Weiguo , Wu Qunli , Ling Shih Fu
Published: July 2002

Audio sound reproduction using the nonlinear interaction of sound waves is investigated. Special emphasis is given to the sum and difference frequencies generated by the nonlinear interaction of two sound waves in a duct. The numerical and experimental results for scattered sum and difference frequency sound are presented and compared. The relationship between the difference frequency and the two primary sound waves are studied. It is found that the flat frequency response of the difference frequency can be achieved by adjusting the amplitudes of two primary waves. Finally, the sound reproduction using a single bi-frequency source is also investigated. The results for sum and difference frequency generation of this case are compared with those of the dual sources.
Linear and nonlinear modeling techniques for cochlear mechanics
Authors: Grosh Karl , Parthasrathi Anand , Nuttall Alfred
Published: July 2002

New experimental techniques have made possible the measurement of the cochlear response to electrical, mechanical, and acoustical stimuli as never before possible. By controlling the various inputs to the cochlea, these measurements hold the promise for delivering sufficient information for developing morphologically based cochlear mechanics models capable of representing the amplification and nonlinear dynamics seen in the data. Nonlinear dynamics takes the form, for example, of harmonic generation and compression. Activity may take the form of outer hair cell mediated force generation. These new data in part motivate the need for new modeling techniques to accurately and efficiently simulate the response arising from the morphology and possible activity of the cochlea. In this paper, hybrid methods are presented for three-dimensional cochlear models which generalize to include activity and nonlinearity in a straightforward fashion. These methods are based on modal–finite element and boundary element–finite element hybrid methods. This approach enables the inclusion of as much structural inhomogeneity as needed for the accurate simulation of the underlying response. The framework for the inclusion of activity, nonlinearity, and inhomogeneity (e.g., radial variation in morphology) is given. Results for time harmonic forcing (e.g., stapes motion) are presented.
Rejecting a cochlear-partition model with constant mass
Authors: Wilson Timothy A.
Published: July 2002

The question of whether a simple low-order, linear, passive model of cochlear-partition dynamics can account for ‘‘global’’ (overall stiffness change, range of best frequencies and best places) and ‘‘local’’ (peakiness of frequency- and place-selectivity, amount of phase-angle change around the best place or frequency) attributes of cochlear response to tones in Békésy’s observations in cadavers remains unresolved. With answering that question the goal, a simple stiffness-damping-mass model of cochlear-partition dynamics with constant mass and exponentially varying stiffness and damping, was investigated computationally using a box-cochlea model of cochlear hydrodynamics. Constrained only by Békésy’s reported change in stiffness by about two orders of magnitude, the model’s global and local response attributes were determined over a reasonably exhaustive set of mechanical parameter values. It was found that the only combinations of mechanical parameters resulting in reasonable cochlear maps had magnitude-response shapes neither qualitatively resembling nor quantitatively consistent with observations by Békésy or anyone else, postmortem or in vivo.
A signal detection theoretic analysis of the Carney model of auditory processing
Authors: Collins Leslie M. , Gresham Lisa C.
Published: July 2002

Computational models of human auditory processing provide a platform on which to apply signal detection theory (SDT) directly to the ‘‘output‘‘ of various peripheral processes. Theoretical performance predicted by standard SDT analyses which do not incorporate such models often substantially exceeds measured performance. These discrepancies are commonly compensated for by adding a physiologically unspecified source of ‘‘internal noise.’’ By applying SDT to auditory models it is possible to evaluate whether the performance predicted at various stages of the auditory system provides a more accurate estimate of human performance than standard approaches which incorporate internal noise. Our previous work indicates that integrating SDT with a deterministic model of the human auditory system affords theoretical performance predictions that match experimental measurements more closely than traditional approaches. In the work presented here, SDT is integrated with Carney’s model of auditory processing [Carney, J. Acoust. Soc. Am. 93 (1993)]. This model incorporates physiologically based models of the basilar membrane and inner hair cell mechanisms, as well as a nonhomogeneous Poisson process to model nerve discharge times. The performance predicted by this model is presented, and its relationship to previous results and to modeling assumptions is discussed. [Work supported by NIH.]
On the effects of a subharmonic masker on the loudness of a pure tone
Authors: Ozawa Kenji , Hellman William S. , Inoue Yoshinori , Suzuki Yôiti , Sone Toshio
Published: July 2002

Loudness matching functions between a 1-kHz tone in quiet and in the presence of a 70 dB(SPL) 0.5-kHz subharmonic masker were studied to determine the alterations in loudness due to intensity shifts at the stimulus frequency arising from the generation of the second harmonic of the masker. Such effects are understood to be due to a quadratic nonlinearity occurring in the inner ear transduction process. In the experiment, masked thresholds were measured at 30° phase angle intervals of the stimulus. Matching functions were obtained for phase conditions corresponding to minimum and maximum thresholds. Both the shape of the matching functions and their relative displacement from each other were consistent with the predictions of the vector summation model [Clack et al., J. Acoust. Soc. Am. 52, 536–541 (1972); Schubert, J. Acoust. Soc. Am. 45, 790–791 (1969)]. Assuming that the threshold shifts were due to constructive and destructive interference between the 1-kHz tone and the second harmonic of the masker, a single effective matching function was constructed by means of the vector summation model. This calculation demonstrated the ability of loudness matching to probe nonlinear cochlear mechanisms. Matching functions generated from several proposed loudness functions were compared with the data.
Convolution formulation for high-frequency leaky wave scattering enhancements for solids and shells with truncations: Evaluation of the surface integral and experimental and computational tests
Authors: Marston Philip L. , Gipson Karen , Morse Scot F.
Published: July 2002

Leaky waves reflected at truncations of elastic objects in water can cause high-frequency backscattering enhancements for ranges of orientation angles [Morse et al., J. Acoust. Soc. Am. (accepted for publication)]. The backscattering can be much greater than for rigid objects having the same shape, size, and orientation. Such enhancements are relevant to the interpretation of sonar images and are usually associated with relatively flat portions of the outgoing wavefront. The typical leaky wave attenuation length can be much less than the largest dimension of the scatterer, rendering global resonances to be unimportant. One approach to approximating these enhancements is to evaluate a two-dimensional convolution integral for the outgoing leaky wave amplitude on the surface [P. L. Marston, J. Acoust. Soc. Am. 102, 358–369 and 1628–1638 (1997)]. In some cases this integral may be approximated as a one-dimensional integral. It is also necessary to approximate leaky wave reflection coefficients at truncations and to evaluate a propagation integral for the far-field amplitude. Some mechanisms to be discussed give large enhancements from reflected Rayleigh waves on tilted cylinders and cubes and from Lamb waves on cylinders. [Work supported by the Office of Naval Research.]
Vibroacoustical modeling and modal analysis of a double wall panel
Authors: Pietrzko Stan Josef
Published: July 2002

In this paper results are reported of analytical and experimental vibroacoustical modal analysis of a double wall panel. Both mechanical vibrations of panel walls as well as the modal behavior of acoustical field in cavity were identified. Special interest was focused on identification and modeling of interaction and coupling between vibratory behavior of the walls and acoustical field in the cavity and their influence on drop of the transmission loss of the panel, as measured in the laboratory. The identification was carried out using a set of combined vibratory and acoustical frequency response functions measurements as response due to random noise force and controlled volume velocity source. The identified global complex modes of the panel and an estimated model of the panel employing general parameters were of high quality. It was confirmed by very good orthogonality of the identified vibratory and acoustical mode shapes and high correlation values between the measured and synthesized frequency response functions. This result provides a robust basis for the numerical study of the transmission behavior of the panel in the low-frequency range. Application of this result on optimum placement of force actuators to increase of transmission loss over a lower-frequency range by means of active noise and vibration control will be presented.
An analytical model for bandlimited response of vibroacoustic systems
Authors: Sum K. S. , Pan J.
Published: July 2002

In this paper, an analytical method for predicting bandlimited time-averaged energies in vibroacoustic systems is presented. A vibroacoustic system is considered where a flexible boundary structure is directly excited by some external forces and an enclosed sound field is driven through an acoustic-structural coupling. This method allows for the reduction in computational effort compared to the classical modal coupling method especially for analysis in the medium frequency range where there is a large number of dominant acoustic and/or structural modes. The vibroacoustic problem is also extended to consider cases of structure-borne sound where the sound field is subject to coupling with various vibrating boundary structures. The prediction accuracy of the present method will be compared to the classical modal coupling method and its computational efficiency is demonstrated by means of numerical examples.
Building acoustic models for speech recognition
Authors: Scattone Francesco
Published: July 2002

This paper reviews the methodology currently used at Dragon Systems to build a speech recognition system for a new language, with particular focus on the training of acoustic models. Issues concerning the selection and use of suitable speech corpora are discussed and experimental results from recent experiences in developing large vocabulary continuous speech recognizers in several European languages are reported.
Spoken language technology research at Microsoft
Authors: Huang X. D.
Published: July 2002

The goal of ongoing work is to develop spoken language technologies for use by a broad audience of computer users and in a wide range of applications. The current work in support of this broad objective falls into four main areas: speech recognition technology code-named Whisper (Windows Highly Intelligent Speech Recognizer); speech synthesis technology code-named Whistler (Windows Highly Intelligent Stochastic Talker); spoken language understanding technology code-named Leap (Language enabled applications); and the Microsoft Speech Software Developer’s Kit that facilitates full integration of speech into applications. This paper describes ongoing R&D effort and technical challenges in these areas. Not only are technology components being created that can be shared for the whole spoken language system, but also solutions are being created for application developers to author compelling speech-enabled applications. To realize this vision of speech enabling the whole computer, not only should critical technology components be improved (i.e., Whisper, Whistler and Leap), but also a tighter integration of these spoken language technology components should be evangelized with broader applications and interfaces to enhance and extend the entire user experience. A number of groups have started developing SAPI-compliant technology components and applications such as telephony, wireless PDA, accessibility, and desktop agent. More information can be found in http://research.microsoft.com/stg.
Recent advances in speech recognition at IBM research
Authors: Gopalakrishnan Ponani S.
Published: July 2002

This paper will review the work going on at the IBM T. J. Watson Research Center on speech recognition systems dealing with real world speech data. Such data includes voice mail messages, broadcast news data, and live interaction with natural language systems. Many problems need to be addressed in order to improve speech recognition accuracy, including speaking style, accents, spontaneous speech phenomena, and different acoustic environments. Some of the methods used for detecting the signal and background condition, fast adaptation to new environments, and for handling pronunciation variations in spontaneous speech will be outlined. Speech recognition results on a variety of materials will be presented and analyzed, with a discussion of the significant problems that remain to be solved in order to obtain acceptable recognition performance on such material.
Natural speech dialogue systems
Authors: Steinbiss Volker
Published: July 2002

The application of speech recognition and understanding to real-life situations generates new scientific problems. To illustrate the latter, the example of an automatic switchboard system is given that can be used in a very natural communication style. It is based on a high-end speech recognizer that outputs a word lattice which is subject to further evaluation by a speech understanding and a dialogue component. Although word error rates are above 20% for this task, the integration of additional knowledge sources like the telephone directory and the dialogue history can add to both the acoustic and the language model in order to achieve highly improved performance. As recognition is not perfect, the user has to confirm what the system understood. In order to avoid lengthy confirmations, it was requested to base the level of confirmation (repeated question, explicit or implicit confirmation) on the probability that the request was understood correctly. This was formulated within the statistical framework of speech understanding and successfully implemented into our prototype system. The degree of reliability controls the further dialogue flow. Other useful applications of this reliability measure will be described.
Up-to-date state and outlook for the intensity measurement method in underwater acoustics
Authors: Shchurov Vladimir
Published: July 2002

The acoustic intensity measurement method consisting of four components of the acoustic field [acoustic pressure p(t) and three orthogonal components of the particle velocity vector V(t){Vx(t),Vy(t),Vz(t)} simultaneous measurements] did not occupy a suitable place in underwater acoustics until now. Simultaneous measurement of four components of the acoustic field enables one to construct a point receiving system possessing direct characteristics in a wide frequency range (for example, from 10 to 100 Hz). By now unconventional results of investigations of underwater acoustic noises, reverberation, point source capacity, seismic noises, and underwater navigation were obtained. The intensity measurement method has given one a chance to research the acoustic field characteristics that have never been revealed during measurements of only acoustic pressure, i.e., characteristics connected with energy flux density vector. For example, a compensation of opposite energy fluxes of ambient noise and tone or signal similar to noise; horizontal energy flux of dynamic noise connected with propagational direction and the extent of wind near-surface roughness; splitting of ambient noise total field energy density into an isotropic component connected with the isotropic (diffuse) part of the field and an anisotropic one connected with the anisotropic (coherent) part of the field related to the energy transfer in the ocean. The isotropic component (possessing zero averaged flux) existence in the field of ambient noise allows for decreasing the threshold noise level for receiving systems measuring acoustic intensity, thus enables one to research a thin structure of the acoustic field of the noise and signal. Measurements of only acoustic pressure cannot give one such information. The acoustic intensity measurement method development will allow for constructing the most up-to-date acoustic devices for oceanologic processes dynamic investigation on the bases of ambient noise and sounding signal vector characteristic measurements.
Preliminary project for the rebuilding of ‘‘LA FENICE’’ theater of Venice: Acoustic aspects
Authors: Strada Mauro , Pompoli Roberto
Published: July 2002

After a fire destroyed ‘‘La Fenice’’ Theater of Venice, the Town Council decided it should be rebuilt, being a place of memories for Venetians and people worldwide, committing to the Prefect, named Delegate Commissary, the management of the operation, compiling of a Regulated Contract until reconstruction is finished. He set up an expert workgroup for the drawing up of the Contract which is of main importance in the competition for judging the works. They decided to start the rebuilding of the theater as it was and where it was, preserving at least the internal and external aspects of the ‘‘SaleApollinee’’ halls, and the ‘‘SalaGrande’’ hall. They also decided to give freedom to the designers of the companies invited to the competition, concerning the stage aspects and all the facilities areas (halls for rehearsal, dressing-rooms, etc.). The problem has been the acoustic characteristics of the ‘‘Sala Grande,’’ which had to appear aesthetically as it was, nevertheless the materials were not going to be the same as before the fire, due to newer safety fireproof requirements. This article deals with all acoustic problems and the several stages of historical-critical deepening of the acoustics of the theater before the fire, brought into effect during the compiling of the Regulated Contract.
The acoustics of the Italian opera house, ‘‘Teatro di San Carlo’’ in Naples, Italy
Authors: Maffei Luigi , Iannace Gino , Ianniello Carmine , Romano Rosario
Published: July 2002

Teatro di San Carlo is reported to be the oldest existing European opera house. This horseshoe-shaped theater was opened on the 4th of November 1737, 41 years before the opening of La Scala in Milan and 51 years before the opening of La Fenice in Venice. Surprisingly, no objective acoustical data were found in the open literature for San Carlo. Therefore, the authors were stimulated in carrying out measurements of modern objective criteria in the above-mentioned opera house. As the theater hosts both symphonic/classical and opera concerts, two sets of measurements were carried out. The first one with the stage fitted for performing symphonic and classical music, and the second one with fitted scenery and the orchestra pit open, for performing opera concerts. Measurements in the unoccupied hall, yielded now classical, objective criteria (RT, EDT, C80, G, LE, and LF) at specific locations both on the main floor and in the boxes. The sound source was located along the longitudinal axis of the stage under the proscenium arch.
Acoustic conditions of the San Francisco War Memorial Opera House and its renovation
Authors: Paoletti Dennis , Graffy Kurt , Tedford Larry , Wetherill Red
Published: July 2002

The War Memorial Opera House is one of the most culturally significant performing arts venues in San Francisco. The San Francisco Opera organization (which includes the performers, designers, systems, and facilities) is known worldwide for the quality of its performances. The Loma Prieta earthquake which occurred just south of San Francisco in October 1989 was the impetus for the major renovation to the War Memorial Opera House currently in progress. This paper will report on the history of the San Francisco Opera House and the current renovation. It will also touch on some of the peripheral facilities and projects resulting from the renovation. Paoletti Associates has enjoyed a long-standing professional relationship with the San Francisco Opera organization, and the San Francisco War Memorial Board of Trustees, having been involved in a number of various studies for them over the past 20 years. They recognize the importance of acoustics, and they are quite concerned about the historical and cultural reputation of their performing arts facilities.
Scattering by two spheres: Theory and experiment
Authors: Bjo/rno/ Irina , Bjo/rno/ Leif
Published: July 2002

Extensive studies of scattering of acoustical signals by targets of different regular shapes have formed a useful background for attempts to develop procedures for remote monitoring of suspended materials in marine environments as, for instance, measurements of characteristic parameters of suspended sediments. The scattering properties of single regular-shaped particles have been studied in depth by several authors in the past. However, single particle scattering cannot explain all features of scattering by suspended sediment. When the concentration of particles exceeds a certain limit, multiple particle scattering becomes important. As a first step in the investigation of mutual interactions between several particles, the acoustical scattering by two spheres has been studied theoretically and experimentally and the results are reported in this paper. The study has mainly been focused on three issues: (1) to develop a simplified theory for scattering by two elastical spheres; (2) to measure the scattering by two spheres in a water tank, and (3) to compare the theoretical/numerical results with the measured data. A number of factors influencing multiple scattering, including the geometrical distribution of particles, their shape, size, and material properties are taken into consideration in the studies to be reported. Broadband signals were used for the experimental studies.
A new method of ultrasonic hydrophone calibration using KZK wave modeling
Authors: Bleeker Hendrik J. , Lewin Peter A.
Published: July 2002

Most commercially available ultrasonic transducers exhibit finite amplitude distortion in water during hydrophone measurements needed to comply with regulatory requirements. The frequencies observed due to finite amplitude distortion can easily exceed ten times the transducer center frequency and 100 MHz. Typically, hydrophone calibrations are supplied only up to 15 or 20 MHz and do not exhibit a flat response. The frequency response above 15 MHz should be known to accurately represent the acoustic information, especially for high-frequency transducers ranging between 7.5 and 15 MHz. A new hydrophone calibration technique has successfully predicted the frequency response of hydrophones up to 100 MHz. A circular source transducer was first characterized and then modeled using the KZK wave propagation model. This model accounts for diffraction, absorption, and nonlinearity. The transducer frequency response was measured with a hydrophone and compared to the simulation. This difference characterized the frequency response of the hydrophone and was used to estimate the hydrophone calibration. The estimated calibration at 20 MHz was checked and provided good agreement with the manufacturer calibration supplied. Acoustic measurement accuracy will be improved if the hydrophone frequency response is deconvolved from the actual acoustic transducer response.
High-frequency backscatter measurements of bovine tissues with unfocused and focused transducers
Authors: Maruvada Subha , Shung Kirk K.
Published: July 2002

In order to improve resolution of ultrasonic imaging, high-frequency scanners which are employed in the range 20–50 MHz are needed. As a result, it is critical to obtain data on ultrasonic scattering and attenuation in this frequency range. At these high frequencies, it is not feasible to make scattering measurements with unfocused transducers, therefore focused transducers are needed. Using the standard substitution method to calculate the backscatter coefficient, as is used with unfocused transducers, yields erroneous results for focused transducers. The assumption that the reflected echo from a perfect reflector in the far field can be calculated as though the transducer acts like a point source does not hold for focused transducers. Therefore a method is presented for focused transducers where the flat reflector is substituted by a particulate reference medium whose backscatter coefficient is well known and documented. Unfocused transducers in the range 10–20 MHz will be used in comparison with focused transducers to measure backscatter. For 15–35 MHz, focused transducers will be used. Results for the backscatter coefficient will be presented for various bovine tissues.
An A-mode ultrasound technique for tracking the advance of coagulation front in laser irradiated tissue
Authors: Sun Zhigang , Ying Hao , Bell Brent , Motamedi Massoud , Lu Jialiang
Published: July 2002

This communication presents an A-mode ultrasound technique for automatically determining the advance of coagulation damage front in laser irradiated tissue. The basic assumption underlying our technique is that the waveform of the echo signal scattered from a tissue region undergoing coagulation should be changing more rapidly than tissue regions where no coagulation is taking place. In this technique, we first track rf echo signals scattered from many small tissue regions during heating by computing the cross-correlation coefficient between two consecutively acquired echo signals. We then use the resulting coefficients as a measure of waveform change to determine the position of coagulation front via an automatic procedure. To test our technique, we carried out ten in-vitro experiments in which pig liver samples were irradiated using an Nd:YAG laser with fluence in the range of 32.4–112.0 W/cm2 for 290 s. A 10-MHz broadband single-element spherical focused ultrasound transducer was used to detect the thermal coagulation front. The mean-square difference between ultrasonically and histologically determined coagulation depths was 1.0 mm, whereas the mean coagulation depth was 7.2 mm. This good agreement between ultrasonically and histologically determined results shows the potential of our technique for monitoring coagulative tissue damage during thermal therapy.