bluuebunny/crossref_metadata_2025 huggingface dataset:
Towed array processing as a spatial Kalman filter problem
Authors: Sullivan E. J. , Candy J. V.
Published: October 2005

A moving towed array essentially constitutes a system intended to provide a series of measurements that are sequential in space. This type of process fits quite naturally into an iterative measurement process that can be realized as a spatial predictor-corrector form of a Kalman filter. It is shown how this concept is formulated and constitutes a generalization of the overlap-correlator synthetic aperture algorithm [E. J. Sullivan and S. Stergiopoulos, J. Acoust. Soc. Am. 86, 158–171 (1989)]. Examples will be given that demonstrate how this scheme constitutes a self-consistent synthetic aperture algorithm capable of determining estimates of the bearings of multiple sources, both correlated or uncorrelated. It will also be shown how the method provides coherent synthetic aperture processing over integration times that are significantly longer than the coherence time of the source signals.
Subjective and objective parameters of sound within fabric structures
Authors: Chesnokov Andrei N.
Published: October 2005

An investigation of acoustics in 15 circuses with fabric roofs has been carried out. Objective acoustical parameters (reverberation time, clarity C80, and others) have been measured and questionnaires from the audience in the circuses have been obtained. Features of circuses acoustics are the decrease in reverberation times at low frequencies, echo (in halls with impervious fabric roofs), and high levels of background noise. The background noise levels in circuses before a performance were equal LA=46–56 dBA. The questionnaire contained subjective acoustical attributes: Timbre, balance, reverberance, spaciousness, echo, loudness, clearness, audibility of background noise, background noise affect on speech legibility, and others. Average mark estimates and results of measured noise level in halls (LA) have been subjected to factor analysis. Three factors have been extracted that can be interpreted as (1) overall acoustical impression of the music sound in a circus, (2) disturbing influence of the background noise, and (3) clarity of music and speech sounding.
The Great Hall at Cooper Union: A study of its acoustical problems
Authors: Raichel Daniel R. , Dragan Tanya , Wilkerson Winston
Published: October 2005

The Great Hall, a place for public assembly in the lower level of the Foundation Building at the Cooper Union in New York City, is steeped in history. Constructed in 1859, it was the site where Abraham Lincoln have his ‘‘Right Makes Might’’ speech that catapulted him to the Republican presidential nomination. Many prominent speakers, including Mark Twain, feminist Victoria Woodhull, Theodore Roosevelt, Woodrow Wilson, labor leader Samuel Gompers, and very recently President Clinton, graced the podium, a tradition that continues to this day; and the hall also accommodates musical events and theatrical productions. The Great Hall underwent reconstruction nearly 20 years ago, but recent concerns about its acoustical properties led to the authors’ measurements of the reverberation times in different parts of the 900-seat auditorium. Reverberation times exceeding 3 s in the 125- to 1000-Hz range point up the existence of excessive echoes that made speech comprehension difficult for many members of the audience. Solutions are being developed to lower the reverberation times and to provide flexibility for meeting the requirements of different types of events, with due regard for the landmark status of the Foundation Building.
Spectral properties of transmission in a simulated room
Authors: Strong William J. , Li Sining
Published: October 2005

Transmission of sound in a large room was simulated by means of an image method incorporating artificial diffusion. The simulation model was validated by comparing the standard deviations of its transmission spectra to theoretical and experimental results obtained by others. Several combinations of source and receiver positions were simulated in order to assess their effects on spectral variability. A single source and single receiver arrangement resulted in the greatest variability as expected. Other combinations, including single-source/two-receiver (to represent two ears), two-source (to represent spatial extent of source)/two-receiver, and five-source/five-receiver, were used to assess their effects. The effects of frequency modulation and critical bands of the ear were also simulated. In an attempt to relate simulation results to stability in perception, a limit of 6-dB difference in relative harmonic levels between received tones and source tones was chosen as the criterion. On the basis of this criterion, a single-source and two-receiver arrangement incorporation critical band effects and frequency modulation was found adequate to provide stable perception.
Prosodic variation for text-to-speech synthesis
Authors: Hirschberg Julia
Published: October 2005

Appropriate intonational variation is critical for text-to-speech synthesis to convey appropriate meaning and improve naturalness. While in the past it has been thought that a full linguistic analysis is prerequisite to the generation of appropriate intonational features, in recent years considerable progress has been made in assigning prosodic variation in text-to-speech synthesis for unrestricted text, using simple and currently available techniques for text analysis. Techniques for varying pitch range, prominence, and phrasing based on such text analysis will be discussed. Also discussed will be techniques, such as phrasing and accent assignment procedures. Such automatic training allows quicker development of new prosodic variation procedures and also allows such procedures to be tailored to particular speaking styles or applications.
GEST: A computational model of speech production using dynamically defined articulatory gestures
Authors: Browman Catherine P. , Goldstein Louis , Saltzman Elliot , Rubin Philip E.
Published: October 2005

A computational model of speech production that produces speech for English utterances, using dynamically defined articulatory gestures, will be described. The model is comprised of three submodels. The first part, the linguistic gestural model, generates a gestural score specifying the identity and relations of the gestures involved in the desired utterance. This gestural score is input to the second part, the task dynamic model [e.g., Saltzman and Munhall (1989)], which generates the movements of the various model speech articulators. These movements serve, in turn, as input to the third part, the vocal tract model [Rubin etal. (1981)], which determines the resulting area functions and acoustic signal. Attention will be focused on the integrated system and the first part, since the second and third parts of the model have been described elsewhere.
Segmental aspects of speech synthesis
Authors: Macchi Marian
Published: October 2005

A phonemic segment has different acoustic-phonetic realizations depending on many contextual factors, e.g., nearby phonemes and position in the syllable, word, and phrase. Appropriate acoustic variation in the phonemes is necessary for intelligible, natural-sounding synthetic speech. Two basic approaches to achieving these variations are: (1) articulatory synthesis, which models the human vocal apparatus, attempting to automatically account for the desired acoustic variability and (2) acoustic synthesis, which bypasses the articulatory level and operates on acoustic patterns directly, either by controlling phoneme-based format targets and transitions or by concatenating prerecorded units. In a phoneme-based system, whether articulatory or acoustic, the necessary acoustic variations for each phoneme are produced entirely by rules whose goal is to capture linguistic and articulatory regularities. However, knowledge of these rules is incomplete. The rationale for concatenative systems is that by recording and storing multiple variants of each phoneme, or units longer than phonemes, the units themselves incorporate some of the acoustic variation. Basic units for concatenation range in size and phonetic nature from phonemes or allophones, through dyads or diphones, polyphones, and demisyllables, to units covering polysyllables or words. This talk discusses interactions among the modeling approach, the basic unit, and the rules for combining units.
Results of acoustic optimization of a point-driven, thin-shelled cube using the boundary element method
Authors: Kruger Daniel H. , Mann J. Adin , Spalding Amy , Holman Keith
Published: October 2005

The sound power radiated by a thin-shelled cube is calculated from simulated acoustic velocities (equal to the normal shell velocity) using the boundary element method (BEM) [K. A. Cunefare and G. H. Koopmann, J. Vib. Acoust. 113, 387–394 (1991)]. Optimization techniques are then used to predict velocity distributions that result in the minimum output sound power. In future work, recommendations for the addition of passive noise control materials will be defined on the basis of achieving the calculated optimal velocity distribution that will result in the minimum radiated sound power. These criteria are tested on a point-driven, thin-shelled cube in an anechoic chamber. The normal shell velocity is measured using a laser velocimeter. Again, sound power is calculated and the optimal velocity distribution is determined using the BEM. Accuracy of power predictions, based on experimental power measurements and computational examples, as a function of frequency and vibration pattern are studied.
Structure-property relationships in polymer interpenetrating networks for use as broad band damping materials
Authors: Coughlin Christopher S. , Samuels Mary Q. , Capps Rodger N.
Published: October 2005

In the search for broadband damping materials, it is desirable to have polymers with a broad and high loss region in shear or extension, covering the entire temperature and frequency range of interest. Interpenetrating networks, IPN’s, are materials composed of two or more crosslinked polymers intimately and irrevocably intertwined. The resulting distribution of microenvironments can result in a material with a high mechanical loss broadened over that of either polymer component alone. Several series of polyurethane/epoxy IPN’s have been prepared for possible use as broadband damping materials. All IPN’s showed apparent true IPN behavior with no or very small scale phase separation. Dynamic mechanical analysis revealed that the temperature of the loss peak may be varied over a wide temperature range with formulation. Further work has focused on incorporating a more flexible epoxy component and/or a plasticizer, and comparison of viscoelastic behavior to observed damping in constrained layer structures. [Work supported by ONR.]
Progress report on the continuing activity based on the May 1993 special workshop on the ASA’s role in noise and its control
Authors: Hoover Robert M.
Published: October 2005

A discussion meeting is being sponsored by the Technical Committee on Noise to present the progress that has been made to date on the recommended actions that were developed by the working group participants of the May 1993 Special Workshop on the ASA’s role in noise and its control. The results of the May workshop will be summarized. Representatives of each working group will present a discussion of the progress on specific initiatives that have been begun. These will include any collaborative actions being taken with the cooperation of other Technical and ASA Standing Committees.
Point–source/point–receiver ultrasonics: A versatile materials characterization tool
Authors: Sachse Wolfgang , Weaver Richard
Published: October 2005

The essential elements of a point–source/point–receiver ultrasonic system include a broad bandwidth, small-aperture source generating elastic waves with a broad angular spectrum and a receiver with similar characteristics to detect them. By moving the source or receiver and stacking the received waveforms, one generates a scanimage that provides a view of the complete elastic wave field in a test specimen. Wave arrivals are related to the speeds of propagation of various wave modes in various directions and the signal amplitudes reflect the propagational characteristics of the material. An interpretation of the scan images requires an understanding of the propagation of transient elastic waves in a bounded structure. Recent developments on both the forward and inverse problems are summarized and the full solution of the forward problem for the response of a general axisymmetric anisotropic viscoelastic plate is reported. The computed results are compared to measured waveforms in viscoelastic and transversely isotropic materials. Also reviewed are the approaches for processing single wave forms and scan images to recover the elastic and viscoelastic properties of a test specimen. Extensions of this approach to materials of arbitrary anisotropy and layered microstructures are also considered. [Work supported by Cornell’s Materials Science Center (NSF) and the Office of Naval Research (Physical Acoustics and Solid Mechanics Programs).]
Ultrasonic nondestructive evaluation of a layered medium
Authors: Kinra V. K. , Zhu C. , Jamminet P. , Iyer V.
Published: October 2005

This paper is concerned with developing a technique for an ultrasonic determination of the acoustical properties (thickness, wave speed, density, attenuation) of the individual layer in a layered medium. The layered medium is surrounded by an identical host medium (water) of infinite extent on either side. Normally incident plane longitudinal waves are considered. Transfer functions have been calculated in time domain as well as in frequency domain. A satisfactory comparison between the theory and the experiment was observed for a three-layered medium (forward problem). An inverse problem is defined as a simultaneous determination of several acoustic parameters from the measured transfer functions. A systematic analysis of the sensitivity of the transfer functions to the acoustic parameters has been carried out. The following inverse problems have been solved for a three-layered medium: three thicknesses for a three-layered medium; and wave speed and thickness of any one of the layers (given those of the remaining two layers). Finally, relative merits of the time-domain and the frequency-domain approaches have been studied. [Work supported by Texas Advanced Technology Program.]
High-resolution velocity measurements in the superconducting state of the heavy fermion compound UPt3
Authors: Lin S.-W. , Zhang H. , Levy M. , Sarma Bimal K. , Jin C. , Lee D. M.
Published: October 2005

Ultrasonic measurements have been used very successfully in investigating multi-phase superconductivity in the heavy fermion compound UPt3. Further probing of the superconducting properties in UPt3 demands even higher resolution in both ultrasonic velocity and attenuation measurements. In order to achieve this, a new approach was used in measuring ultrasonic velocity and attenuation, in which a digital dynamic control technique was utilized in the conventional pulse-echo method. With this approach, longitudinal ultrasonic velocity and attenuation of frequencies up to 450 MHz were measured on a single crystal UPt3 sample in the superconducting state. The overall resolution in the velocity measurement is in the order of 0.1 ppm. This enables us to determine a complex superconducting phase diagram for UPt3 with unprecedented accuracy. Superconducting phase boundary lines were traced even within the transition width. The critical property of converging phase transition lines is thus determined unambiguously. This in turn provides crucial information for the understanding of unconventional superconductivity in UPt3. [Work at UWM supported by ONR and at Cornell by NSF.]
High-frequency hearing loss in old (25+ years old) male dolphins
Authors: Ridgway S. H. , Carder D. A.
Published: October 2005

Eight bottlenose dolphins (four male, four female) were studied in an acoustic response time task [Ridgway etal., J. Acoust. Soc. Am. 89, 1967–1968 (A) (1991)]. The animals were trained to station 1 m below the water surface and respond to a stimulus tone (St) delivered through a hydrophone located 1 m in front of the blowhole. St duration varied from 60 to 450 ms and frequencies were 20, 40, 50, 60, 70, 80, 100, and 120 kHz. St were 120 dB (re: 1 μPa peak to peak at 1 m) ±24 dB in 6-dB steps. With the dolphin at 1-m depth and 1 m from the St hydrophone, the trainer started a randomly variable 3- to 20-St block. The computer selected St from a file in random sequence and interval (1.1 to 2.1 s in 0.1-s steps) and offered St via a St generator. Animal responses (ARs are the whistle or pulse train) were received by another hydrophone, digitized, and stored. Each AR file with 20 to 200 St was edited on a CRT display of a 700 ms St window. No-AR trials, noisy trials, and wrong ARs were identified. Three males (ages 25, 29, and 35) exhibited hearing disability at the four higher frequencies. One female (age 33) showed some loss above 80 kHz, but two females (age 32 and 36) responded to all frequencies as did a male (age 9) and a female (age 13).
Reactions of bottlenoise dolphins, Tursiops truncatus, and migrating gray whales, Eschrichtius robustus, to experimental playback of low-frequency man-made noise
Authors: Tyack Peter L.
Published: October 2005

Playback experiments of low-frequency noise to two species of cetacean were linked to measurements of transmission loss in order to relate responses to received sound level. Coastal observation sites were selected to allow visual tracking of animals using theodolites. The Tursiops playbacks involved a population resident near Sarasota, FL, using a 800–900 Hz M-code stimulus with a source level of 170 dB re: 1 μPa at 1 m. The identification of individual dolphins of known sex and age with predictable movement patterns permitted repeat playbacks to monitor habituation. The Eschrichtius playbacks were performed as the whales migrated past Big Sur, CA; each whale was only exposed once during its migration. A single airgun (source level=226 dB) and several continuous (source levels 151–163 dB) stimuli associated with offshore oil industry were used. Observation of ≳3500 migrating whales showed significant responses. Whales slowed down and altered course at ranges of 1–3 km, some near 0 dB SNR. Half of the whales avoided exposure to continuous stimuli at levels ≳117–123 dB, to airgun pulses at levels ≳170 dB. Bottlenosed dolphins exposed to continuous M-code at levels near 120 dB showed no such avoidance response.
A great depth class V flextensional transducer design
Authors: Letiche Michel
Published: October 2005

Flextensional transducers consist of a piezoelectric or magnetostrictive driver and a mechanical shell. The shell, excited on its first bending mode, amplifies the acoustic radiation. In a first part, the coupling between the driver and the shell is analyzed. The relative resonance frequency of each element determines the resonance frequency of the transducer and its radiated acoustic power. Furthermore, in most cases, operating depth is a significant limitation in the design of this kind of source—classical flextensional transducers on the work market are typically depth limited at about 200 or 300 m. To avoid the effects of the hydrostatic pressure, mechanical filters have been developed. The aim of these devices is to make the driver and the shell independent under static conditions. An equivalent scheme model is used to understand and to design this filtering element. Theoretical results are presented and a great depth class V flextensional transducer has been developed using this original technology. Its acoustic and static behaviors have been optimized with an axisymmetric B.E.M./F.E.M. numerical code. Finally, theoretical results are discussed in comparison with experimental ones obtained with the CERDSM facilities in Castillon Lake. Finally acoustic performances of this low-frequency, high power, and great depth transducer are shown. [Work supported by DRET.]
Reciprocity assessment of single transducers
Authors: Ge Li-Feng
Published: October 2005

Although most conventional transducers are usually regarded as reciprocal at nominal signal level, it is still necessary to ascertain that the presumed reciprocal transducer is indeed reciprocal or possesses sufficient reciprocity in reciprocity calibration practice. A conventional reciprocity check involves a system comprised of the two transducers and the gaseous, liquid, or solid medium and its boundaries. This paper tries to give an absolute method for reciprocity assessment without the need of any other auxiliary transducer. The principle is that if the imaginary part of the electrical impedance of a transducer (i.e., the capacitance for piezoelectric-type or the inductance for electrodynamic-type transducers) varies linearly with its mass load impedance, the transducer is reciprocal. So, the linear correlation coefficient could be considered as a reciprocity index. The theory is applied to evaluate the reciprocity of a piezoelectric and an electrodynamic vibration generator. The coefficients are determined as 0.9915 (at 10 kHz) and 0.9773 (at 1 kHz), respectively. With the data processed by a complex least-square-fitting code [L.-F. Ge, J. Acoust. Soc. Am. 91, 2326 (1992)], the relevant coefficients are adjusted to 0.9987 and 0.9724. Thereupon, the transducers can be regarded as reciprocal at their respective working frequencies. The assessment has been verified by the accurate calibration results.
Transient behavior of time-domain wind instrument models
Authors: Hoekje Peter L.
Published: October 2005

An important playing characteristic of a musical wind instrument is its transient response, which is well suited for calculation by time-domain models. Typically, the instrument air column is described by a time-domain response (either impulse response or reflection function), and a reed valve by a flow control equation and harmonic oscillator dynamics. Since important musical effects have been observed for changes in harmonicity of instrument resonances on the order of 10 cents (0.6%), calculations intended to show such effects need to specify the instrument response with appropriate resolution. In one calculational experiment, the air column resonance frequencies are adjusted in the frequency domain, then the corresponding time-domain response is calculated and the dynamical model run. The results show significant changes in transient response due to minor changes in air column response or in reed resonance. In addition to FFT methods, the transient behavior of spectrum partials may be tracked by applying the Hilbert transform to individually filtered harmonics and finding their instantaneous frequencies and amplitudes. Alternatively, a system of nearly harmonic oscillators with varying phases, frequencies, and amplitudes may be fit to the transient waveform. Each of these methods has unique benefits and difficulties.
The influence of clarinet and saxophone reed responses on sound production
Authors: Keefe Douglas H. , Waeffler Serge
Published: October 2005

Performers of reed-driven woodwinds understand the important role that the reed plays in the production of aesthetically expressive musical sounds, yet the current status of musical acoustics theory and experiment concerning the reed is ambiguous. Benade (1976) stressed the importance of the reed resonance in controlling the tuning and tone color of reed-driven woodwinds, and Thompson (1979) experimentally measured such tuning effects using a metal reed with a quality factor (Q) of about 10. However, the Q of a clarinet reed has been reported to be about 3. Time-domain simulations of a clarinet with a Q of 3 did not show the predicted entrainment of the playing frequency to a subharmonic of the reed frequency (Keefe, 1992). Measured responses of moist clarinet and saxophone reeds using mechanical impact excitation have been obtained in a configuration in which the experimenter’s thumb applies the static force of the reed against the mouthpiece. This is intended to mimic the lower lip of the player under playing conditions. Results indicate Q’s in the range of 5–10. Time-domain simulations of sound production demonstrate that entrainment can occur in these higher-Q regimes.
Behavioral and hearing responses of pinnipeds to rocket launch noise and sonic boom
Authors: Stewart Brent S.
Published: October 2005

Loud launch noise and sonic booms from some military space vehicle launches from Vandenberg Air Force Base impact pinnipeds on the mainland and at San Miguel Island, California, and may cause stampedes, temporary threshold shift or, less likely, permanent hearing damage. Maximum fast A-weighted (MFXA) sound levels approximately 4.8 miles downrange during the launch of three Titan IV rockets were 93.2, 92.7, and 93.0 dB; average sound exposure levels were between 98.9 and 101 dB. Harbor seals fled into the water in response but many returned to land within several hours. A sonic boom was recorded at San Miguel Island during one launch. Its peak flat sound-pressure level was 129.5 dB and maximum fast A-weighted sound level was 86.2 dB; virtually all of the energy was below 500 Hz. Pinniped behavioral responses were mild and brief. Predicted overpressures for focused sonic booms from the Titan IV rocket are substantially greater (≥150 dB). Noninvasive hearing tests using ABR and OAE techniques are being used to determine if pinnipeds suffer temporary threshold shifts or permanent hearing damage from exposure to those sonic booms.
Walrus response to offshore drilling operations
Authors: Brueggeman Jay
Published: October 2005

Walrus response to drilling operations in the Chukchi Sea was evaluated between 25 June and 19 October, 1989. Aerial and vessel observations of walruses were conducted at three prospects in conjunction with acoustic measurements of the operations. Walrus response was evaluated before, during, and after they passed the drillsite relative to various sound sources. Over 350 groups comprising approximately 4500 walruses were observed in the prospects. Walrus response was greatest during ice management, when the icebreaker crisscrossed the prospect. Animals moved deeper into the pack ice, where the noise level from the icebreaker was an estimated 15–25 dB above ambient (97 dB). Once ice management stopped or became more focused at the drillsite, walruses began to reoccupy formerly used areas. Under these circumstances, walruses displayed some behavioral responses that rapidly decreased beyond 0.46 km (0.25 nmi) from the icebreaker. Walruses showed little response to other drilling operations. These results show that walruses reacted to icebreaker activities, but responses varied according to the intensity of ice management. This variability offers opportunities to incorporate precautions to minimize disturbance to walruses during future drilling operations.
Detection of salt-marsh mosquito swarms in remote mangrove swamps
Authors: Mankin Richard W.
Published: October 2005

Swarms of Aedestaeniorhynchus mosquitos produce sounds that can be detected from 10–50 m at 25–35 dB (re: 20 μPa) in a quiet environment. The loudness of the swarms is above the 21-dB acoustical background between frequencies of 0.6 and 3.4 kHz in an isolated salt marsh, but below the 40–60 dB background of a typical urban environment. Individual Ae. taeniorhynchus have wingbeat frequencies (±standard error) of 441±21 Hz and 703±17 at 24 °C, detectable from 3 cm at 22–25 dB in an anechoic chamber. In the marsh, females beat their wings at 400–500 Hz and males at ≳800 Hz, depending on their size and the temperature. Because of their low wingbeat sound intensities, the only individual Ae. taeniorhynchus mosquitoes that can be detected are those flying within 2–5 cm of the microphone. These frequency and loudness measurements suggest that it is technologically feasible to construct an acoustical device for remote surveillance of Ae. taeniorhynchus swarms or individuals attracted to a bait. Further studies to correlate detection of wingbeat sounds with numbers of mosquitoes captured at a bait are in progress.
Time-frequency spectrograms of impulse scattering by shells: Quantitative comparisons with ray theory for Lamb wave contributions
Authors: Hughes D. H. , Marston P. L.
Published: October 2005

The Wigner distribution function (WDF) and quantities derived from it were used to investigate high-frequency scattering processes for a spherical shell in water [D. H. Hughes, Ph.D. thesis, Wash. State Univ. (1992)]. The investigation includes: (i) display of Gaussian smoothed WDF for ka as large as 500 with smoothing functions of different time and ka resolution; (ii) measurements of the leaky Lamb-wave decay rates from the smoothed WDF for different ka regions showing good agreement with ray theory based on complex partial-wave index poles; and (iii) evaluation of a derived quantity, the local temporal variance of the WDF as a function of frequency, showing how the temporal spread changes near a resonance [D. H. Hughes and P. L. Marston, J. Acoust. Soc. Am. 94, 499–505 (1993)]. The temporal variance at resonance was in general agreement with the ray theory predictions for the dominant scattering contribution. Structure in the smoothed WDF was also investigated for the prompt backward wave contribution that causes a prominent scattering enhancement at high frequencies. [Work supported by ONR.]
Ambient noise in shallow seas: Propagation issues
Authors: Dyer Ira
Published: October 2005

Whatever the source of ambient noise in a shallow sea, propagation to a distant receiver shapes in a major way its spectral character, its temporal properties, and its coherence or spatial distribution functions. Any one ambient noise mechanism is generally an incoherent superposition of a large number of similar elemental sources. Thus propagation modeling for ambient noise must address the multiple source question, and as well the modeling can take advantage of simplifications often afforded by multiple path averaging. In this context, the main confounding elements of shallow sea propagation including, but not limited to, downward refraction, sloping bottoms, sediment interaction, rough bottom scattering, and water column fluctuations are reviewed. In such complicated propagation channels the noise is modified in important detail, although much of its character remains broadly recognizable.
Spatial structure of ambient noise in shallow water
Authors: Buckingham Michael J.
Published: October 2005

Apart from the nature of the sources, ambient noise in shallow water is distinguished from that in deep water through the proximity of the bottom. As with acoustic propagation, the bottom introduces a modal structure into the noise, evident through noise eigenrays with discrete grazing angles that are characteristic of the modes. There is also a continuous noise component, associated with overhead sources. Since it is largely controlled by the bottom, the modal structure is characterized by the geoacoustic properties, including the stratification, of the sediment. As the modal structure determines the directionality, or equivalently the spatial coherence in the vertical, it should be possible, through measurements with vertically aligned hydrophones, to establish the bottom properties through measurements of the noise field in the water column. For example, the sound speed of a fluid sediment close to the water–seafloor interface can be estimated from observations of the vertical noise coherence over the frequency range 500 Hz to 1 kHz (M. J. Buckingham and S. A. S. Jones, J. Acoust. Soc. Am. 81, 938–946 (1987)]. This inversion technique can be extended to the case of a shear supporting bottom and, at sufficiently low frequency, may yield information on the sub-bottom structure. [Research supported by ONR.]
Acoustic echo cancellation for stereophonic teleconferencing
Authors: Sondhi M. Mohan , Morgan Dennis R. , Hall Joseph L.
Published: October 2005

In long-distance telephony, echoes arise due to impedance mismatches at various points in the telephone circuit. Adaptive line echo cancelers have been used successfully for over a decade to combat this problem. Echoes also arise in teleconferencing, due to acoustic coupling between microphone and loudspeaker in each conference room. This problem is similar to the line echo problem; however, the echo paths are much longer and much more variable in this case. In this paper a further complication that arises if stereophonic transmission is used for teleconferencing is discussed: There is an inherent nonuniqueness in estimating the echo paths. It appears that the only way to resolve this nonuniqueness is by somehow decorrelating the signals in the two stereo channels. Several methods of decorrelation are discussed and how they affect adaptive echo canceller performance as well as stereophonic perception is shown.
New systems for intercommunications—Synergy of acoustics and telecommunications
Authors: Holden Mark A.
Published: October 2005

Proper room acoustics for audio teleconferencing and video teleconferencing facilities has been, at best, a matter of guesswork. In this paper, room acoustic treatments are varied in material and location within a typical conference room and the results studied using binaural analysis techniques. The relationship between room acoustics, speech intelligibility, speech interference, and mechanical noise levels in regard to teleconferencing systems will be explored in a quantitative manner, including the effects of ‘‘echo cancelling’’ technology.
Architectural acoustics design parameters for teleconferencing facilities
Authors: Paoletti Dennis A.
Published: October 2005

Audio and video teleconferencing equipment and room facilities have emerged as one of the fastest growing areas of communication and business technology. The acoustic environment is an extremely important component in (determining) the success of the teleconferencing experience. Additionally, other environmental factors such as: architectural space planning, design aesthetics, color, thermal, lighting, operations, etc. must also be considered. This paper will present a summary of the significant acoustical parameters and key environmental factors that impact the design and functional use of audio and video teleconferencing facilities, whether teleconferencing equipment is portable or permanently built-in. (This paper acknowledges the work of Michael Sullivan, Kurt Graffy, and John Whitcomb, audiovisual consultants and teleconferencing systems designers at Paoletti Associates, Inc.)
Audio for video teleconferencing
Authors: Berkley David A.
Published: October 2005

Video teleconferencing, especially that supported by inexpensive low-bit rate connections, is an exploding area. It is clear that there are severe trade-offs to be made as bit-rate is lowered. However, although everyone agrees that audio is a vital part of audio/video teleconferencing, little is understood about what trade-offs are involved in optimizing the audio and the relationship between the audio and video on a specific type of conference link. The relationship between audio and video transmission delay, camera tracking errors and lag, audio bandwidth and other related issues are discussed. Implementation of experiments, based on the HuMaNet [D. A. Berkley and J. L. Flanagan, AT&T Tech. J. 69, 87–97 (1990)] platform, is also described.
A binary method for measuring the electroacoustic characteristics of hands-free telephones
Authors: Bareham John R.
Published: October 2005

Hands-free telephones often are designed with performance features that make it difficult to obtain meaningful electroacoustic measurements using simple methods. Compressors, limiters, threshold detectors, noise guards, and other more complex speech-sensitive functions change the telephone’s electroacoustic characteristics depending on the type and level of signal applied to it. To realistically account for such variables, electroacoustic characteristics of several hands-free telephones were measured using a binary method, in which two signals were applied to the device simultaneously. The first signal was a bias, which temporarily caused the telephone to operate in a well-defined manner. Bias signals used in this work included noise, noise bursts, and speech fragments. The second signal was used for the actual measurement. It was applied at a low level relative to the bias, so the effect of the bias was not disturbed. The measurement signal used was a series of very fast sine sweeps, processed using an enhanced time delay spectrometry algorithm. This method was chosen to enable simulated free-field measurement of the telephone in an ordinary room. The measurement setup will be described, and measurement results will be shown and explained. Benefits and limitations of the method will be discussed.
A new artificial ear for telephone measurements
Authors: Krebber Winfried , Böhme Stefan , Gierlich Hans W.
Published: October 2005

Opinion tests show the importance of the acoustical leakage between the handset and the human ear for the subjective speech transmission quality of telephone sets. Artificial ears, which are now used for telephone measurements, do not allow measurements with variable leakage. Using an artificial ear formed as an individual human ear does not lead to reproducible results. Both problems are avoided by this new ear. It has a simplified shape, which is determined by only a few geometrical parameters. Thus the transmission characteristics can be described by a mathematical model. Nevertheless it approximates a human ear, referring to the dependence of the leakage and the transmission characteristics on the force applied to the handset. Measurements using the artificial ear are reproducible and show high conformity with measurements of handsets at human ears. Implemented in an artificial head, the ear can also be used to measure hands-free telephones. The directional characteristics of the artificial ear in a free sound field show all main structures of monaural outer ear transfer functions.
A modified complex starting field for shipping traffic noise modeling
Authors: Burkhalter Christopher J.
Published: October 2005

In current ambient noise modeling efforts, commercial shipping is considered a major contributor to overall noise levels and is modeled accordingly. The propagation of shipping noise from the many sources to the receiver is effected by use of any of a number of high-fidelity acoustic models. Almost all of these models require an initial condition in the form of a vertical pressure field that is stepped out numerically in range. This starting field usually takes one of several forms: a simple or modified Gaussian distribution around a source depth, a normal mode starter, a simple image (acoustic dipole) starter, or a Pade-approximated parabolic equation starting field. The implications of a near surface source are discussed, as well as effects of low- versus high-angle propagation models and the effects of complex reflection from the necessarily turbulent surface. Additionally, the use of the Gaussian distribution as a sufficient starting approximate is analyzed for long-range, deep-water results. [Work supported by ONR and NRL.]
Description of a noise model for shallow water: RANDI-III
Authors: Breeding J. Ernest , Bradley Marshall , Hebert Melanie , McBride Walt
Published: October 2005

Version III of the research ambient noise directionality (RANDI-III) noise model is described and illustrated. The objective of the model is to make predictions of the ambient noise at low to mid frequencies (10 to several hundred Hz) for highly variable environmental conditions typical of shallow water and coastal areas. The receiver can be either a horizontal or vertical line array. Shipping and local wind are assumed to be the dominant sources of noise. Ships are treated as discrete sources of noise. The ship noise is propagated to the elements of the receiver using a wide-angle finite element parabolic equation. The contributions from all ships are added coherently. The environmental and shipping information are automatically extracted from several databases. [Research supported by The Office of Naval Research, Program Element 62435N with technical management provided by the Naval Research Laboratory, Stennis Space Center, MS.]
A ray-model theory on spatial correlation and vertical directivity of surface-generated ambient noise in shallow water
Authors: Zhang Renhe , He Yi , Zhu Baixian , Guan Dinghua
Published: October 2005

The ambient noise in shallow water is more complicated than that in the deep sea, and it has greater geographical and seasonal variations since there is a strong bottom interaction. A theoretical model of ambient sea noise including surface-noise sources and a stratified medium ocean is discussed. The noise sources are assumed to be statistically independent directional point sources distributed over the sea surface. The effects of the surface–source feature, velocity profile, and bottom property on ambient noise are studied. In general, the ray theory is suitable for calculating the contribution of near-field sources, whereas the normal-mode theory is appropriate for far-field sources. In this paper, a ray-mode theory suitable for near- and far-field sources is developed. The concise formulas for calculating the intensities, spatial correlation, and vertical directivity of ambient noise are present and some numerical simulations are given.
Application and comparison of neural nets for marine mammal call classification
Authors: Potter John R. , Mellinger David
Published: October 2005

Recent work has successfully applied a linear matched filter to calls made by Bowhead whales recorded off the coast of Alaska in frequency-time (spectrogram space) to detect and classify marine mammal calls. This method relies on an empirical matrix weighting for the matched-filter coefficients. A neural net, trained on spectrogram estimates as the feature vector space, offers two advantages over this approach; (a) the equivalent weighting matrix is determined by training and may coverage to a more optimal solution and (b) the response of a neural net is nonlinear and can embody more sophisticated responses. A simple three-layer feedforward neural net is ideally suited to this application and has been implemented on 204 calls, of which 163 were used for training and 31 kept as ‘‘unseen’’ test data. The neutral net was configured to identify both whale calls and other mammal interference. The success rate including failures in both estimates on training data was 88%. The combined false-positive and false-negative whale detection errors on unseen data was only 7%, which compares very favorably with any other known method. The neural net approach is compared with the matched filter and the role of the hidden neurons and equivalent weighting matrix are discussed. [Work supported by the Office of Naval Research.]
Fortuitous underwater acoustic measurements of baleen whale vocalizations by large aperture arrays
Authors: D’Spain G. L. , Hildebrand J. A. , McDonald M. A. , Hodgkiss W. S.
Published: October 2005

Over the past several years, the Marine Physical Laboratory has designed, built, and deployed innovative, large-aperture sensor systems in order to measure the low-frequency properties of the ocean acoustic field. In many of these experiments, baleen whale vocalizations have been a significant feature of the infrasonic sound field. For example, finback whale (Balaenoptera physalus) sounds have been recorded by a 120-element, 900-m, vertical line array of hydrophones. Finback whale sounds were also recorded by a 12-element, 165-m, vertical array of ‘‘TRIFAR’’ elements (i.e., each element records simultaneously the three components of acoustic particle velocity and pressure). In addition, blue whale (Balaenoptera musculus) signals were the overwhelming feature of a data set recorded by some neutrally buoyant, freely drifting, acoustic particle motion/acoustic pressure sensors. Finally, new-design ocean bottom seismometers (OBS) have recorded both finback and blue whale signals. Where possible, these measurements are used to estimate both the position and the actual time signature of the source by removing the effects of multipath arrivals.
The characteristics of the radiated noise from open grid and bascule bridges
Authors: Cuschieri J. M.
Published: October 2005

When vehicles travel across the grid section of an open grid or bascule bridge, noise is generated which for most type of grid configurations has a very strong tonal characteristic in the frequency range between 150 and 250 Hz. To investigate the mechanism by which this noise is generated, and identify possible noise mitigation procedures, a series of measurements of both sound and vibration levels have been performed on 12 bascule bridges with different types of grid. The grid types can generally be classified into three configurations, two of which are of a rectangular or square shape, while the third configuration has diagonal members and is generally referred to as four-way grid. For the rectangular-shaped grids, both the vibration and the sound spectra exhibited a dominant peak at a frequency that scaled with the speed of the vehicle and a typical length of the grid spacing. For the four-way grid, the spectrum did not show a very strong peak, but was more broadly distributed in frequency. The general overall sound level was not much different from one bridge grid type to another. The grid is an open structure and its radiation efficiency in the 200-Hz region is very low. This makes the tire a potentially significant source of noise. [Work sponsored by FDOT.]
Active control of sound power using acoustic basis functions
Authors: Naghshineh Koorosh , Koopmann Gary H.
Published: October 2005

An improved method of active structural acoustics control is presented that is based on the minimization of the total power radiated from any structure expressed in terms of a truncated series sum. Each term of this sum is related to the coupling between the orthogonal eigenvectors of the radiation impedance matrix (referred to as ‘‘basis functions’’) and the structural surface velocity vector. The basis functions act as surface velocity filters. These acoustic basis functions are found to be weak functions of frequency but their corresponding weighting coefficients increase monotonically with frequency. The minimization of the radiated power is shown to result in a structural surface velocity vector that couples poorly to those acoustic basis functions that account for high efficiency sound radiation. This strategy is demonstrated numerically for a clamped-clamped baffled beam in air. An unexpected benefit of the control strategy described is that it provides a rational procedure for selecting the number and placement of actuators and sensors on a structure for effective control. This development is significant since this procedure doe not require apriori knowledge of the dynamics of the structure.