bluuebunny/crossref_metadata_2025 huggingface dataset:
Laboratory Simulation of Sonic Boom and Its Effects on Sleep and Human Performance
Authors: O'Brien D. M. , Hart F. D. , Levere T. E.
Published: October 2005

As a part of a larger program concerned with the effects of acoustic energy on sleep and human performance, an electromechanical sonic boom simulator has been designed and constructed. The operational characteristics and performance of the simulator will be discussed. Preliminary results on the effect that the sound stimulus has on sleep and performance will be described and compared with other research investigations. [NASA Langley Research Center is acknowledged for support of this work.]
Capacitance Microphone Static Membrane Deflections
Authors: Warren J. E. , Hamilton J. F. , Brzezinski A. M.
Published: October 2005

The nonlinear equations for the static deflections of the moving electrode due to the electrical fields between the electrodes in capacitance microphones are presented. These equations are valid for the historic method of constant bias voltage and the more recently developed polymer electret biasing. The equations were solved numerically for boundary conditions of circular and annular membranes. Due to the nonlinearity of the electrical attraction forces, certain values of the microphone parameters exist for which the deflections can become unstable. The results compare closely with past solutions and experimental deflection data obtained on constant-bias voltage microphones using a laser interferometer.
Large-Amplitude Piezoelectric Properties of Standard and Sapphire Whisker-Reinforced Lead Zirconate-Titanate Ceramics
Authors: Feith K. E. , Kerr G. S. , Taylor R. J.
Published: October 2005

The dynamic strain amplitude of sapphire whisker reinforced and nonwhisker reinforced types I, II, and III piezoelectric ceramics was measured as a function of increasing electric field until fracture occurred. The 1-in.-diam by 0.2-in.-thick disk specimens were poled in their [33] direction and excited at their planar resonance. The direct measurement of radial displacement amplitude allows accurate assessment of the nonlinear behavior of piezoelectric and elastic constants from low to very high excitation fields. Test results show that previous determinations of peak dynamic tensile strengths, based on calculations which assume linear d constants, can result in large error. In addition, the investigations show the whisker-reinforced ceramics exhibit linearity and excellent performance to excitation levels unattainable by their nonwhisker-reinforced counterparts. [This work sponsored in part by ONR Code 468.]
Vowel and Speaker Identification in Natural and Synthetic Speech
Authors: Meltzer David , Lehiste Ilse
Published: October 2005

The purpose of this study was to develop a simple means for evaluating the relative quality of synthesizers. A set of 10 monophthongal English vowels was produced by a man, woman, and child. These vowels were synthesized on a Glace-Holmes synthesizer, using values measured from spectrograms. In addition, synthetic stimuli were generated on the basis of averages published by Peterson and Barney [J. Acoust. Soc. Amer. 24, 175–184 (1951)]. In the latter set, formant values for men, women, and children were combined with the respective fundamental frequencies, resulting in 9 different combinations for each of the 10 vowels. The 150 stimuli were presented, in random order, to 60 trained listeners for both vowel and speaker identification. The overall vowel identification score for the normal set (all three speakers combined) was 79.46%; the over-all speaker identification score (all 10 vowels combined) was 90.03%. The corresponding scores for the set synthesized from measured spectrograms were 50.87 and 69.73%, respectively. The differences from the normal set (−28.59 and −20.30%) constitute an evaluation measure for the performance of the synthesizer (and the synthesizers). Results of the listeners' responses to the set of vowels synthesized from averages will also be discussed.
Design of Nonrecursive Digital Filters Using Linear Optimization Techniques
Authors: Mohammed A. , Hubley B. A.
Published: October 2005

The coefficients of nonrecursive digital filters have been determined by linear programming techniques to provide a specified frequency response with or without some constraints on the time response. Filters having real or complex coefficients are considered. The real and imaginary parts of the frequency response may be constrained to meet composite requirements on bandwidth, passband ripple, side-lobe level, and response slope along any part of the frequency axis. In addition, the time response may include monotonic, concave or convex, and magnitude restrictions. Constraints may be imposed in order of priority with the solution obtained when a limit of feasibility is reached. Examples of low-pass, bandpass, and complex asymmetric filters would be presented and the results compared with published ones.
Signal Design for Reverberant Acoustic Channels
Authors: Scharf Louis L. , Harthill W. P.
Published: October 2005

In active sonar, system performance can be limited by reverberation noise that is signal related and nonwhite. Therefore, when attempting to optimize system performance, one is confronted with the task of optimizing signal design. The signal design approach taken in this paper is a structured one in the sense that the receiver is assumed to be a matched (rather than optimum) detector, and the admissible signals are required to be composed of weighted sums of harmonically related sinusoids. The requirement arises quite naturally out of a representation of the reverberation noise spectrum in terms of the signal spectrum. This representation enables us to state the signal design problem as one of minimizing a quadratic form (proportional to the matched filter output variance) under certain signal energy and time-bandwidth constraints. The actual minimization problem is a nonlinear programming problem with linear and nonlinear constraints. Results of a steepest descent computer algorithm for solving the problem are presented for example detection problems. Some examples show as much as 3-dB improvement over a detector that merely uses CW signals. The direction of future work to solve signal design problems for optimum filters using the same approach is indicated.
Vocal Cord Model for Singing
Authors: Titze Ingo R. , Strong William J.
Published: October 2005

A thick membrane is approximated by a set of 16 masses, allowing for 32 degrees of freedom. The restoring forces are a combination of longitudinal tension and material elasticity. Thus the vibration becomes stringlike for high frequencies (high tension in the ligaments, or cord edges) and springlike for low frequencies (elastic properties of the vocalis muscle). Longitudinal tension and medial compression define the statics of the system of coupled masses, and the air flow determines the dynamics. Vibrato can be introduced by slowly modulating either the subglottal pressure or the cord length, i.e., the crico-thyroid muscular tension. Registration is accomplished by manipulating the elastic properties and the tension on the vocalis muscle. Various falsetto modes, including horizontal phasing along the edge of the cord, are set up by a medial compression adjustment. The set of coupled equations is programmed on a small computer which includes a graphic display.
Two-Dimensional Perspectives of Three-Dimensional Surfaces with Automatic Hidden-Line Elimination
Authors: Graham Nancy , Rabiner Lawrence
Published: October 2005

In digital signal processing, one is often faced with displaying a function of two variables. To examine this surface on a two-dimensional medium, such as a piece of paper or a computer scope face, one is forced to resort to clever alternatives. For example, a sound spectrogram uses intensity of blackness of the marking to show the spectrum amplitude as a function of time (x-axis) and frequency (y-axis). In a scope display, intensity modulation can serve as a third variable in making a “three-dimensional” display. In this paper we discuss a novel algorithm for perspective display of a three-dimensional surface. The algorithm includes automatic elimination of hidden lines. To produce a perspective of the surface, the program needs only a mathematical description of the surface over a rectangular grid, and the x, y, z coordinates of the viewing (vantage) point. By changing the vantage point in a continuous manner, one is able to “examine” the surface in detail, as though it were physically there. A movie film, composed and generated interactively on the DDP-516 computer, will illustrate the algorithm.
Bias-Free Loudness Judgments for White Noise
Authors: Warren Richard M.
Published: October 2005

Loudness judgments are especially sensitive to experimentally induced biases. An earlier study [R. M. Warren, “Elimination of Biases in Loudness Judgments for Tones,” J. Acoust. Soc. Amer. 48, 1397–1403 (1970)] eliminated known biasing factors (by using only single judgments from large groups of unpracticed subjects and employing symmetrical response ranges), and found that half loudness (12L) for tones corresponded to half sound-pressure level (12P) or 6-dB attenuation. The present study extended this procedure to white noise, using 12 separate groups of 30 subjects. It was found that 12L = 12P from about 45 through 90 dB. This relation held for both loudspeaker and diotic headphone stimulation. These results are in agreement with the theory which considers that subjective magnitude estimates for sounds are based upon familiarity of the listener with the relation between level of stimulation and distance from the source. Half L corresponds to the effect of doubling distance and hence corresponds to 12P (or 12 sound energy). It is suggested that the sone scale, which considers 12L = 0.32P (or 10-dB attenuation), reflects the systematic influence of known biasing effects.
Setting Tolerable Limits of Noise Exposure with Respect to Hearing Impairment
Authors: Kryter K. D.
Published: October 2005

The threshold of impairment to hearing is reached, according to the American Academy of Opthalmology and Otolaryngology (AAOO) [Trans. Amer. Acad. Opthalmol. Otolaryngol. (1959), pp. 236–238], when the hearing levels indicate an average loss of 25 dB for the audiometric frequencies of 500, 1000, and 2000 Hz. It would appear from published data [e.g., W. L. Baughn, “Noise Control—Percent of Population Protected,” Int. Audio 5, 331–338 (1966)] that by the age of 60 yr some 40% of men working 8 h/day in steady noise of an intensity of 80 dBA (60% in noise of 90 dBA) will have hearing impairments greater than the AAOO criterion. In contrast, only about 11% of the men in the general U. S. population have hearing impairments greater than that magnitude [A. Glorig and J. Roberts, “Hearing Levels of Adults by Age and Sex—United States 1960–1962,” U. S. Department of Health, Education, and Welfare]. It can be deduced that the AAOO threshold of hearing impairment is reached, as the result of the noise exposure, in some small percentage of men when the noise is at a level of 65 dBA and men are exposed 8 h/workday for more than 20 yr. The tolerable limits of 90 dBA for 8 h/workday specified for industry to meet the “Walsh-Healey Act” is to be questioned.
Noise Character of a Riding Lawn Mower
Authors: Faulkner L. L.
Published: October 2005

The ANSI 1971 safety specifications for riding power lawn mowers recommend a maximum sound-pressure level of 95 dBA at the operator's ear location for a stationary mower with blade in operation and at maximum-governed engine speed. Sound surveys were made to determine the levels at various positions about a tractor mower and the relative importance of the blade versus the engine as a noise source was determined. It was found that improvements in the exhaust muffler would produce no more than a 3 dBA reduction. Effects of engine speed, frame excitation, and partial covers were considered as possible modifications without altering the basic engine configuration. Several 5− to 8-hp engines were evaluated including a dynamically balanced engine with the result that the dBA levels were not appreciably different.
Speech Communication in Office Landscape
Authors: Krishnan P. V. , Sulewski James E.
Published: October 2005

Assuming the existence of a free field in an office landscape, the speech communication at a work station is studied in terms of articulation index and speech intelligibility under two situations: with a continuous masking background sound and with a masking background sound in addition to intruding speech sounds from a neighboring work station. It is shown that the effect of intruding speech sounds from a neighboring work station results in a reduction in speech intelligibility. In a landscape provided with a masking background sound equivalent to an NC-40, the articulation index at a distance of 5 ft from a speaker at a work station is approximately 0.8 for face-to-face communication. However, with intruding speech sounds from a neighboring work station situated 30 ft away, the articulation index is reduced from 0.8 to 0.6. For the above situation at a work station, the articulation index would therefore fluctuate between 0.6 to 0.8, depending on whether intruding speech sounds are present or absent, respectively. Based on the landscape equation [81st meeting of the Acoustical Society of America, April 1971, J. Acoust. Soc. Amer. 50, 97(A) (1971), paper H4] the results of field tests on the noise reduction provided by screens will be discussed with particular reference to speech privacy considerations.
Role of Acoustics in Sound System Design
Authors: Sprinkle Melvin C.
Published: October 2005

The poor performance of many sound reinforcement or announcing systems can be traced to the failure of the system designer to consider the acoustical environment in which the loudspeakers will be installed. Loudspeakers are often selected because of their reputed “penetrating power” or coverage angle or power handling capacity. No attention is paid to acoustics in general or those of the listening rotan in particular. This paper considers the acoustical properties of the room in which the loudspeakers are installed as an important part of sound systern design. It develops the concept of a critical distance, and from it criteria which govern the loudspeaker-to-listener distance for optimum intelligibility of the reproduced sound. A sound system is, basically, an information transmission device, and if it fails to deliver intelligible information to its listeners, then it fails in its mission. The critical distance is a function of the room constant and the directivity factor of a given type of loudspeaker. As a by-product, criteria for microphone type and location are developed. Formulas are given whereby the critical distance may be calculated as well as the sound-pressure level dropoff distance. Information is provided by which the acoustic gain requirements of the sound system may be assessed. The use of these methods will ensure that the listener is supplied with clear and understandable sound, even in rooms with a “hostile” acoustical environment.
Strong Seismic Wave Generation Mechanisms durin Large Rocket Launches and Static Tests
Authors: Dalins I. , McCarty V. M.
Published: October 2005

Large-amplitude (50 μ) seismic waves of acoustic origin generated during rocket launchings can be classified in three categories: pure seismic (mostly shear waves with velocities exceeding the ambient atmospheric sound velocity), air-coupled waves due to resonance, and direct ground loading due to overpressure. These wave components propagate with ambient sound velocity. Various characteristics of these waves as recorded during various Saturn launches and test firings will be discussed in some detail. Positive identification of resonantly coupled waves from disturbances that are generated by ground loading will also be discussed, together with instrumentation employed in these studies.
Normal Modes, Virtual Modes, and Alternative Representations in the Surface Duct Problem
Authors: Labianca F. M.
Published: October 2005

The surface duct model first proposed by W. H. Furry [D. E. Kerr, Propagation of Short Radio Waves (McGraw-Hill, New York, 1951), pp. 140–174] has formed the basis for most studies of surface duct transmission loss. Most recently, Pedersen and Gordon [J. Acoust. Soc. Amer. 47, 304–326 (1970)] have improved the accuracy of the computations necessary for the implementation of this model. At first sight, Furry's analysis appears very different from the virtual mode treatment of duct leakage [F. M. Labianca (to be published)]. The connection between the two approaches is established. Each treatment is shown to yield an alternative representation of the solution. The virtual mode results follow from an eigenfunction expansion of the solution, whereas Furry's treatment yields an alternative residue representation. The virtual mode theory of duct leakage is shown to be both conceptually more satisfying and computationally simpler than the theory of Furry. [Work supported by the Office of Naval Research under contract.]
Acoustic Response of External Ear with Progressive Wave Source
Authors: Shaw E. A. G.
Published: October 2005

The acoustic response of the human external ear has been measured with simple progressive waves at grazing incidence. The waves are launched from a short duct mounted on a source plate which can be pressed against the region of the head surrounding the ear at any desired angle. Measurements on a model ear at eardrum position and at the center of the blocked meatus show virtually identical angular dependence of acoustic gain up to at least 15 kHz. The blocked meatus response curves of eleven real ears have been measured from −15° to +135° relative to the horizontal forward direction over the frequency range 0.3–20 kHz. From −15°to +15° all ears have one or more sharp minima of response between 6 and 10 kHz which are critically dependent on angle. In contrast, from 60° to 90° all ears have response curves which are relatively smooth and insensitive to angle up to at least 12 kHz and in some cases to 20 kHz. These characteristics are closely associated with the geometry of the concha but independent of the shape of the pinna flange. An earphone based on this new knowledge offers the prospect of more accurate audiometry and appears feasible.
Network Representation of the External Ear
Authors: Gardner Mark B. , Hawley Mel S. , Hawley Mel S.
Published: October 2005

Two of the basic requirements of an ear model design are that the transfer characteristic of the ear canal and the impedance as measured at the eardrum closely agree with results obtained on real ears. In the case of the electrical model, this requires that the number of sections used to represent the ear canal provide an upper cutoff well beyond the highest frequency under study. This is particularly true where the effect of canal taper is of interest. While the reactance of the eardrum and its connected structures can be rather closely approximated both electrically and mechanically, an equally conforming representation of the widely variable resistive component is more difficult to achieve. The present paper will outline how well each of these characteristics can be represented, in turn, by one-, two-, three-, and four-mesh networks.
Combined Effects of Noise and Vibration on Mental Performance
Authors: Sommer H. C. , Harris C. S.
Published: October 2005

Two experiments were conducted to determine the combined effects of noise and vibration on mental performance. In experiment I, 10 subjects were tested on a combination short-term memory and subtraction task during exposure to four different intensities of noise. Another group of 10 subjects was tested using the same noise intensities in combination with 0.25 g (peak) vertical vibration at 5 Hz. Noise alone, and vibration with low-level noise (80 and 90 dB re 0.0002 dyn/cm2 had no adverse effects on task performance, while the highest level of noise (110 dB) combined with vibration to produce a significant reduction in the number of correct responses. In experiment II, the second group of subjects used in experiment I was tested during exposure to the following conditions: no vibration (control), vibration at 5 Hz–0.25 g, 7 Hz–0.30 g, and 11 Hz–0.50 g, all combined with 80-dB noise. Subsequently these same vibration conditions were presented with 107-dB noise. High-intensity noise and vibration combined to produce a greater decrement in performance than either stressor alone. Vibration at 5 Hz was a more sensitive frequency for mental subtraction performance than 7 and 11 Hz when the three frequencies were presented in conjunction with high-intensity noise.
Motor Vehicle Noise Assessment by Semireverberant Testing
Authors: Harford K. D. , Siddon T. E.
Published: October 2005

The feasibility of a new approach to vehicle noise monitoring, providing an effective alternative to “side-of-the-road” enforcement is under study. This new approach involves the measurement of vehicle noise in the semireverberant environment of Motor Vehicle Testing stations. Initial studies have shown that the reverberant amplification can be predicted from the room constant. Comparisons between semireverberant and freefield measurements show that the same noisiest vehicles can be identified under both test conditions. Modal patterns have little effect on A-weighted indoor readings. Tests are continuing to evaluate other factors including changes in the frequency spectrum, consistency of the room constant, selection of engine speed, and the importance of engine load. The statistical distribution of the noise levels from a large sample of vehicles is being recorded to determine levels for legal limits.
Interaction between Resonators and their Surroundings
Authors: Czarnecki Stefan
Published: October 2005

The phenomena of acoustical and mechanical resonances are very important in acoustics: (1) The effect of acoustical resonances are used in room acoustics in the construction of resonant absorbing panels; (2) acoustical resonantors are used in the construction of mufflers; (3) the resonance effect determines the quality of musical instruments; and (4) mechanical and acoustical resonances cause an increase in noise produced by machines. In particular cases, different resonator theories are used. In this paper a common theory for resonators, based on the interaction between resonators and their surroundings, is given. It is demonstrated that the conditions of the surrounding medium strongly effect the properties of resonators. By changing the conditions of the medium surrounding the resonators, different changes of resonator parameters can be obtained, namely, changes of sound absorption and sound reinforcement and changes of resonance frequency or selectivity of resonators. The experimental results confirm the above considerations.
Acoustic Propagation in Waveguides with Sinusoidal Walls
Authors: Salant Richard F.
Published: October 2005

The propagation of acoustic waves through a plane waveguide consisting of two rigid sinusoidal walls, is examined analytically. It is found that the phase difference between the walls, the wall wavenumber, and the mode number strongly influence both the form of the disturbances generated by the walls, and the conditions under which these disturbances become very large.
Infinitesimal and Finite-Amplitude Effects in a Real Duct
Authors: Coppens A. B. , Sanders J. V. , Winn J.
Published: October 2005

Further measurements of the nonlinear behavior of standing waves in an air-filled rigid-walled duct were carried out in an effort to test the agreement between theoretical development of Coppens-Sanders and experimental results for standing-wave amplitudes near shock formation. The pressure waveforms observed at the rigid end of a 6-ft tube driven near its gravest mode were recorded on analog tape, digitized, and Fourier analyzed for all harmonic components with amplitudes greater than 1% of the fundamental. It was found that, while the shapes of the experimental curves were in essential agreement with the theoretical predictions, the frequency at which each harmonic peaked was greater than that predicted, the difference becoming greater as harmonic number increased. These results inspired a careful restudy of the infinitesimal-amplitude behavior of the duct. It was found that while the experimental attenuation coefficients agreed with those predicted by the Rayleigh-Kirchhoff treatment of wall losses (at least up to frequencies for which cross modes are possible), the experimentally determined phase speeds differed. The direction and amounts of these differences seem sufficient to explain the discrepancy between experiment and the finite-amplitude predictions. The finite-amplitude theory was generalized by replacing the Rayleigh-Kirchhoff predictions with the observed infinitesimal amplitude behavior of the system.
Traveling Ionospheric Disturbances
Authors: Silverman S. M. , Tuan T. F.
Published: October 2005

The T.I.D. of 13 May 1964, discussed by Theme appears to have had unusually high amplitude and would seem well suited for further investigation into its possible extension into the southern hemisphere as well as the possible presence of a simultaneous northbound wave. With f-plot data, supported by tabulated hourly values, as well as, in some cases, the actual ionegram, we have found some evidence for an extension of the wave into the southern hemisphere with a phase change of 180° in accordance with Thome's predictions. Preliminary investigations into a northbound wave seem to reveal a disturbance traveling at different velocity from the southbound T.I.D.
A Reexamination of Reaction Time to Segments and Syllables
Authors: King J. W. , Hoffman M. , Daniloff R. G.
Published: October 2005

This study reports subject auditory reaction times to syllables (CVC, CCV, and VCC in construction) and to their constituent segments. A target syllable or segment was located randomly in each of 288 lists each containing 10 nonsense syllables. Stimulus material was presented via earphones to 12 normal hearing subjects who heard the target syllable or segment spoken before each list. Reaction time was measured from the beginning of the target to the depression of the response button by the subject. Response times, false alarms, and misses were recorded from a frequency counter on a data printer. Analysis of data indicated that, within limits, subjects reacted equally fast to syllables of different constructions, given similar durations. Contrary to the findings of Savin and Beret [J. Verbal Learning and Verbal Behavior, 1970], subject response to syllable initial segments was significantly greater than to the entire syllable. Segment response times within a syllable generally increased according to segment position from initial to final.
Contour Plots of Speech with Subglottal-Rate Time Resolution Provide New Insight Into Perceptual Cues
Authors: Stewart J. L.
Published: October 2005

An electronic analog ear having 24 sections has a space-time pattern that can be converted to a contour pattern in the manner of a “Voiceprint.” Each section signal is half-wave rectified and low-pass filtered to 400 Hz so as to retain several harmonies of fundamental voice pitch. Contours are generated with high speed commutation of the 24 section signals, a delay line smoothing device, and a level clipper. The actual experimental system, which is frequency scaled downward by a factor of 20 is described. A number of example patterns are shown for both speech and nonspeech sounds. Cues are revealed which allow the central nervous system to make localization measurements on the basis of envelope periodicity. A voice pitch mechanism is demonstrated which depends upon periodic pattern projections into the cochlea in a manner which is not well described with spectra.
Transient Sounds Due to Implosion of Simple Structures under Hydrostatic Pressure
Authors: Reader W. T. , Chertock G.
Published: October 2005

Experiments have been performed with a small simple structure which is designed to implode under hydrostatic pressure, and to generate sound by such processes as tearing, inrush of water, compression of internal air, and impact. The associated theory predicts the motion and deformation of the structure, and also analyzes the radiated sound as the sum of multipole components. Experiments were conducted at depths of 40, 200, and 500 ft; the structure's motions were measured by accelerometers, and the radiated sound pressures versus time were measured with hydrophones at up to eight locations about the implosion. The measurements are in substantial agreement with the theoretical predictions. In particular, they confirm that the dominant contribution to the sound is simply the monopole component p(R,t) = ρV̈/(4πR), where V̈ is the second time derivative of the volume enclosed by the wetted surface.
An Equivalent Circuit for Oval, Flextensional Transducers
Authors: Brigham G. A.
Published: October 2005

The combined integral-differential equations of a piezoelectrically driven, radiating, oval shell are put into integral form and solved by an iteration process. The solutions for maximum pressure, drive-point impedance, and maximum dynamic shell stress are calculated and shown to compare favorably with two experimental transducers that were separately tested over a 1-oct bandwidth. Finally, the integrals in the drive point impedance expression are interpreted in a direct way as the oval equivalent of algebraically known impedances for the more elementary case of a circular ring transducer. By so doing we apply bounds on the “modal” stiffness and inertia as functions of oval shape and also bound the acoustic loading components both external and internal to the shell.
Saturation Effects in the Westervelt End-Fire Parametric Radiator
Authors: Mellen R. H. , Konrad W. L. , Nelson J. L.
Published: October 2005

Westervelt's theory for the end-fire parametric radiator [P. J. Westervelt, “Parametric Acoustic Array,” J. Acoust. Soc. Amer. 35, 535–537 (1963)] includes only second-order interaction of two primary frequencies to produce radiation at the difference frequency. When higher-order saturation effects are included, harmonics of the difference frequency become important. Experimental measurements of the growth and radiation patterns of several difference frequency harmonics are presented.
Parametric Sonar Receiving Experiments
Authors: Konrad W. L. , Mellen R. H. , Moffett M. B.
Published: October 2005

Pump saturation and noise effects on the performance of underwater acoustic receivers utilizing medium nonlinearity for beam forming are discussed. Experimental data is presented illustrating the effect of medium saturation on the receiving beamwidth and the performance limitations resulting from spurious modulation of the pump source.
Wavefield Reconstruction and Acoustic Holography
Authors: Graham T. S.
Published: October 2005

Acoustic holography has been shown to be a useful tool for studying single frequency acoustic wavefields [Acoustical Holography (Plenum Press;, New York, 1969), Vol. II, Chap. 25; T. S. Graham, PhD thesis, The Pennsylvania State University (Mar., 1969) (unpublished)] allowing visual observation of the wavefield to be studied. To obtain greater insight into holographic reconstruction of acoustic wavefields the process of holographic reconstruction of a monopole and a dipole has been analyzed revealing interesting features of the holographic process. It is shown that the monopole reconstructs in the focal plane of an infinite hologram as J1(Kr)/r while the dipole reconstruction produces a sin(Kr)/r pattern. The results of this analysis may be extended to more general cases of acoustic wavefield reconstruction because the dipole and monopole are the building blocks of the Helmholtz formulation of acoustic boundary value problems.
Ultrasonic Absorption in Aqueous Solutions of Deoxyribose Nucleic Acid
Authors: O'Brien William D. , Christman Christopher L. , Dunn Floyd
Published: October 2005

The ultrasonic absorption of aqueous deoxyribose nucleic acid (salmon sperm, M≃106) solutions were studied as a function of pH in the acidic region over the frequency range 5–50 MHz at 10° and 25°C. The alkaline pH range has previously been investigated [J. Chim. Phys. 66, 81 (1969)]. The double helical structure of the DNA molecule breaks down as a result of the acid and alkaline titrations causing the base-base hydrogen bonds to be substituted for base-solvent hydrogen bonds. The ultrasonic absorption titration curves for DNA show peaks around pH 2.6 and 12 which are attributed to hydrogen bond transfer. Proton transfer, which has been implicated in aqueous protein solutions, is considered unimportant as the mechanism responsible for the DNA absorption peaks. [This work is supported by the Institute of General Medical Sciences, National Institute of Health.]
Some Perspectives and Recent Findings in Shallow Water Acoustics
Authors: Urick R. J.
Published: October 2005

Shallow water acoustics has had in this country a long, though sporadic, history dating back to World War II, when the acoustic mine stimulated feverish activity in the subject. Yet, in spite of the impressive body of theory, model studies, and field data that has accumulated in subsequent years, many aspects of this most difficult branch of underwater acoustics are not understood. Many of its complications are due to the temporal and spatial variability of the shallow water medium and its boundaries. For example, we have found the transmission of shallow water sound to vary with direction and time at one location and to be different at apparently similar locations. Such variations make acoustic prediction difficult, and necessitate on-the-spot measurements at the place and time that data is required. To this end, we have developed and tried out at a number of coastal locations an airborne method of data collection using sonobuoys, explosive sound signals, and simple, portable recording equipment. The transmission results have been summarized by loss contour charts showing the transmission environment around a receiving point in shallow water.
Comparison of Power Flow Predictions Using Statistical Energy Analysis with an Exact Calculation
Authors: Remington Paul J. , Manning Jerome E.
Published: October 2005

The time-averaged power flow between two rods vibrating in compression and coupled by a spring is calculated using two Statistical Energy Analysis techniques, the mode-to-mode approach, and the wave approach. The two techniques which yield the same results are shown to agree with an exact closed-form calculation when the latter is averaged in sufficiently broad frequency bands. The comparison is made for both well separated modes and overlapping modes.
Optimal Design of Vibrators for Specified Characteristic Functions
Authors: Brace R. M.
Published: October 2005

The usual approach to problems involving axial and transverse vibration, for an elastic bar or beam, is to find the characteristic values (natural frequencies) and characteristic functions (mode shapes) for known boundary conditions. This generally is done by solving a Sturm-Liouville or related problem. In an inverse or design problem, a characteristic function is proposed perhaps along with a corresponding characteristic value and the characteristic equations are used to solve for the unknown mass or area distribution. Both types of problems have been solved in the literature. It usually has been assumed that a vibrator (its mass distribution) can be found for whatever characteristic functions have been proposed. In fact, this is not always so. For example, consider a fixed-free rod vibrating axially. Suppose that the first characteristic function is specified to have uniform, nonzero strain. This violates the boundary condition at the free end, however. Many other such examples exist. This work considers inverse design where the specified characteristic function does not satisfy boundary conditions or even continuity. Using calculus of variations, a method is developed where the difference between the specified (impossible) function and an attainable characteristic function is minimized. This attainable function is then used to synthesize the bar or beam. This is done for linearly elastic materials vibrating either axially or transversely. Examples include the application of the technique to the design of ultrasonic resonators.
Interpretation of Ultrasonic Signals in Terms of Phase Difference of Vocal Fold Vibration
Authors: Hamlet S. L.
Published: October 2005

The amplitude variation of a continuous wave ultrasonic signal received through the larynx during phonation at low pitches suggests that the signal may contain information on the phase difference between vibration of the upper and lower edges of the vocal folds. Vertical placement of transducers was systematically varied during sustained phonation at constant vocal frequency and intensity. It was anticipated that the time relationships between ultrasonic and speech signals recorded simultaneously would change as the ultrasonic beam passed from predominantly through the upper edge to predominantly through the lower edge of the vocal folds. Transducers with different beam characteristics were tried on several speakers, but good results were obtained only for a male with a bass voice, using a narrow 5-MHz beam. Data from this subject showed the lower edge of the vocal folds closing slightly before the upper, and the lower edge opening before the upper also, but with a greater phase difference on opening. Results indicate that potential exists for obtaining information on phase difference in vocal fold vibration with a continuous wave ultrasonic technique, but more work needs to be done on determining the optimum transducer characteristics. [This investigation was supported by NIH Grant DE 00248-02.]
Evoked Response to Amplitude-Modulated Filtered Signals
Authors: Butler R. A.
Published: October 2005

A test stimulus consisting of square waves repeated 200 times/sec and filtered so as to bandpass 1000–1250 Hz, was presented once each 5 sec. Other stimuli—a 200-Hz tone, a 1000-Hz tone, or a train of filtered signals identical to the test stimulus—intervened once per second between successive test stimuli. The question asked was, “What is the influence of each intervening stimulus condition on the responsiveness to the test stimulus?” The results showed that the 1000-Hz tone and the filtered square waves suppressed greatly the evoked response (N1P2 component) to the test stimulus. The 200-Hz tone did not. These data suggest that the N1P2 component of the evoked response reflected the acoustic spectrum of the filtered signal, not its modulation rate. If N1P2 can be taken validly as an index of auditory cortex activity, one can infer from these results that periodicity differences in stimulation at the periphery are not converted into place differences at the level of the auditory cortex.
Perception of Amplitude-Modulated Signals in the Goldfish
Authors: Fay Richard R.
Published: October 2005

Judgments of stimulus similarity between AM signals and other simple and complex tones were obtained from goldfish using a stimulus generalization paradigm in combination with a classical respiratory conditioning technique. Several groups of fish were conditioned in inhibit respiration upon the presentation of an AM signal (400 Hz modulated at 100% by 40 Hz), and subsequently tested for generalization to other signals differing in degree of complexity, carrier frequency (fc), and modulating frequency (fm). All stimuli were presented at approximately 30 dB above threshold. Obvious generalization decrements occurred to test signals differing in fc while no decrements occurred to test signals differing only in fm. For subjects trained to AM signals and tested with pure tones, little generalization occurred to any test frequency in the range including fc and fm. Thus, while there is a great perceptual difference between an AM signal and a pure tone at fc, the major sensation evoked in fish by these AM signals is determined primarily by fc, and not by fm. The results suggest that for the fish, whose ear is assumed to analyze primarily in the time domain, envelope periodicity does not generally determine the quality of an AM signal.
Model for the Acoustic Impedance of a Perforated Plate Liner with Multiple Frequency Excitation
Authors: Rice Edward J.
Published: October 2005

The one-dimensional, time-varying equations of momentum and continuity describing the fluid mechanics in a perforated plate liner are integrated numerically in time to obtain instantaneous values of the orifice velocity and displacement. An arbitrary orifice pressure can be used to excite the system. In this way spectral noise excitation can be simulated. This approach is of value since previous experiments have shown that excitation at one frequency can effect the nonlinear acoustic impedances at other frequencies. A quasi-steady nonlinear resistance term was added to the differential equations to account for the effects of orifice velocity and displacement as well as grazing flow. This term was obtained from steady-flow experiments but was assumed to be valid instantaneously. This assumption was at least partially justified by excellent agreement with single-frequency acoustic-impedance measurements over a large range of sound pressure levels without grazing flow. A comparison of the theory with experimental results will be shown. These will include two frequency tests (in which the pressure amplitude at one frequency is varied) and single-frequency impedance measurements in the presence of grazing flow. The effects of some typical noise spectra on liner impedance will also be shown.
Fluctuating Forces on Rotating Airfoils and their Relationship to Radiated Sound
Authors: Heller H. H. , Havden R. E. , Widnall S.
Published: October 2005

This paper describes the results of a study on the role of aerodynamically induced fluctuating forces in sound generation by axial-flow compressors. For this purpose, the technology was developed and implemented to measure fluctuating forces directly on rotating airfoils using miniature differential pressure sensors and an FM telemetry link. Under the assumption of full coherence of the force field on the blade, radiated sound power was predicted from the force measurements on blades and compared with measured sound power. Both broad-band radiation from a single rotating arifoil and discrete-frequency radiation due to interaction of multibladed stator/rotor configurations were investigated. The results indicate the necessity to obtain information on the details of the hydrodynamic force field for accurate prediction of the radiated sound spectrum. [This study was supported by the Acoustics Branch, Loads Division, NASA Langley Research Center, Hampton, Virginia.]
Cross-Correlation Analysis of Flow Noise with Fluid Dilatations as Source Fluctuation
Authors: Siddon T. E. , Rackl R.
Published: October 2005

A recently developed diagnostic technique for aerodynamic noise involves cross correlation between various types of source fluctuation and the resulting radiated sound [T. E. Siddon, Int. Congr. Acoust. 7th (1971)]. The technique yields explicit quantitative information on the volume distribution of source strength, the spectrum from unit volume, and the local correlation volume. Following Ribner's dilatation model of jet noise, the present paper considers “pseudosound” pressure as the source fluctuation. By moving a single probe around in the jet and cross-correlating with the farfield radiation, the character and distribution of the basic pressure sources is obtained. Preliminary experiments in a model air jet indicate difficulties arising from aerodynamic and acoustic contamination of the correlation functions. Special pressure probe configurations are described which minimize this contamination.
Estimating Ocean Wind Wave Spectra by Means of Underwater Sound
Authors: Williams R. G.
Published: October 2005

Measurements of the spectrum of ocean surface reradiated acoustic signals generated by an omnidirectional, sinusoidal source are used to estimate the ocean surface wave-height spectrum. Plane-wave physical optics theory is applied to a long-crested sea surface model to verify Marsh's hypothesis, that for low sea states the spectrum of acoustic waves reradiated by the rough moving sea surface consists of a specular component at the transmitted frequency and a scattered component, which is the weighted surface wave-height spectrum. The approach employs theories by Parkins, Clay and Medwin, and Pierson. The weighting function applied to the surface spectrum depends on signal frequency, experimental geometry, and mean-square wave height. CW signals at 127 and 1702 Hz were transmitted from fixed, omnidirectional sources to receivers 4.5 and 31 km downrange. Additionally, wave height was monitored continuously by resistance wave staff. The time series records of sound pressure level and ocean wave height were analyzed for spectral content. Agreement between theory and experiment is good when the acoustic sideband levels are not more than 25 dB below the level of the specular component.
Resonant Structure in Echoes from Schooled Marine Fish
Authors: Holliday D. V.
Published: October 2005

Explosive acoustic sources have been used to ensonify aggregations and schools of commercially important marine fish. Narrow-band spectral analysis of the echoes from these targets reveals significant structure in the frequency range 200 Hz–5 kHz. The targets were sampled biologically, three yielding northern anchovy (Engraulis mordax), one consisting of a mix of anchovy and jack mackerel (Trachurus symmetricus), and the last sample containing an aggregation of seven species of rockfish (Sebastes), whitefish (Caulolatilus princeps}, and striped perch (Embiotica lateralis). The results of the direct biological sampling are combined with theoretical predictions for the resonant swimbladder response and are compared with the experimentally observed resonances.
Second-Order Statistics in the Frequency Domain of Surface Reverberation from a Fresh Water Lake
Authors: Shooter J. A. , Plemons T. D. , Middleton D.
Published: October 2005

Reverberation is in general a non-stationary process. An indirect but informative way of observing the magnitude of the nonstationarity is to compute the co-intensity spectrum, which is the two-dimensional Fourier transformation of the covariance matrix. An experiment described by T. D. Plemons in the previous paper was used to generate surface reverberation from a fresh water lake. The estimated co-intensity spectra of the reverberation were then computed from 150 returns for each of the two types of transmission. The results clearly show the data to be nonstationary. In addition, these particular data are shown to be locally nonstantionary due to the asymmetry of the covariance matrix. The effects of the asymmetry are to distort the main diagonal of the co-intensity spectra as compared with the energy spectra of the transmitted waveform. [This work was sponsored by the U. S. Naval Ship Systems Command.]
General Result for the Power Spectrum of the Signal Reflected from the Rough Sea Surface, and its Application to Backscatter
Authors: Clarke Richard H.
Published: October 2005

A general formulation is given of the power spectrum of the fluctuation in the signal received by way of reflection from a rough sea surface, in terms of an arbitrary wavenumber-frequency spectrum of the surface waves and an arbitrary source directivity function. The basis of the formulation is the resolution of fields into their angular plane-wave spectra; a Kirchhoff-type boundary condition is applied at the surface. The formulation will be applied to the specific situation of backscatter, and the extreme cases of acoustically slightly rough and very rough sea surface examined in detail. The relevance of these results to experiments, to sonars, and to radar-backscatter sensing of the sea surface will be discussed.