bluuebunny/crossref_metadata_2025 huggingface dataset:
Propagation of Waves of Acoustic Frequencies in Curved Ducts
Authors: Rostafinski W.
Published: October 2005

Propagation of long waves (very low frequencies) in curved ducts has been solved analytically and the results published [82nd Meeting of the ASA, J. Acoust. Soc. Amer. 51, 154(A) (1972)]. It was found that the basic mode of propagation is characterized by a wave pattern totally different from that known in a straight duct. To examine the propagation of shorter waves, in the acoustical frequency range, a systematic study of the pattern of higher modes has been done. Fact solutions up to the fourth mode are presented. Analysis applies to ducts with long and short radii of curvature of arbitrary width. The results are compared with propagation in a straight duct and important differences in the behavior of waves are noted. Analysis was made possible by the use of Bessel functions of the order (n + 12).
Acoustic Propagation in Ducts with Varying Cross Sections
Authors: Navfeh Ali H. , Telionis Demetri P.
Published: October 2005

The method of multiple scales was used to derive the equations that describe the spatial and temporal variation of the amplitudes and phases of acoustic modes propagating in slowly varying hard-walled or lined ducts. The analysis was carried out for rectangular as well as circular ducts. These equations were also derived from the conservation of energy. For large-admittance or high-frequency modes, an approximate expression was obtained for the attenuation. This expression shows that all possible acoustic modes are attenuating. The results also show that varying the cross-sectional area can lead to elimination of some of the acoustic modes.
Mechanical Impedance Properties of a Toy Xylophone and Two Steel Drums
Authors: Pallett David S.
Published: October 2005

A series of informal measurements of the mechanical driving point impedance properties of a toy xylophone and two steel drums is described. The motivating factor for these measurements was to establish the feasibility of accurate identification of the fundamental pitches for the various segmented regions of the steel drum from mechanical impedance data. Complicating factors, which limit the accuracy of these measurements, are indicated. It is shown that interesting mechanical properties of the toy xylophone can readily be demonstrated. Successful measurements were conducted upon a large steel drum which indicate that: (I) the fundamental component of the free decay or the frequency for the lowest principal resonance is nominally a major third above the indicated pitch, but that (II) variations from this tuning of ± 1 semitone are common in the lowest octave; (III) variations of ± 3 semitone are common in the upper octave; and (IV) the subjective impression of tonal purity is correlated with the absence of modal degeneracy or coupling in the fundamental mechanical resonance.
Acoustic Attenuators for Brass Wind Instruments
Authors: Smith Perry , Stein John , Martin Daniel W.
Published: October 2005

The acoustical radiation from trumpets, Flugelhorns, trombones, and French and baritone horns has been greatly attentuated, without the adverse effects that conventional mutes have upon the natural timbre of the tone and the acoustical impedance at the player's lips. The new lightweight attenuators [Patent 3,555,956] are mounted upon the horns in contrast to a previous type [Patent 2,618,191] demonstrated at a Society meeting in 1947 by the present senior author. The absorptive part of the attenuator and the enclosed microphone lie just outside the open-end reflection region of the horn mouth, minimizing reaction upon the resonant horn and its modal frequencies. Listening to the enclosed microphone by earphones allows a performer to practice in relative privacy. A classroom of brass students so equipped can be taught individually, in groups or in ensembles by one teacher through a versatile communication system.
Precise Complex Tone Generation by Digital Table-Lookup Techniques
Authors: White Stanley A.
Published: October 2005

Complex arbitrary periodic waveforms may be generated by simple table-lookup means. An important trade-off exists between the number of points of that waveform which is stored in the memory and the interpolation complexity. A simple frequency-generation technique is analyzed, and the attendant accuracy requirements (word length) are developed. Next, the relationship between the amplitude of the points stored to represent the waveform and its frequency spectrum are derived in a review of the discrete Fourier transform. The transfer functions (and frequency responses) of the buffers associated with the memory and the interpolator, as well as the transfer functions of the interpolators proper are derived. Shown also are the effects on the frequency response of the generator system as a function of the number of interpolation points and the order of the interpolator. The mathematical model of the interpolator is in exact agreement with measured data. The system is easily mechanized by a read-only memory, an accumulator, adders, and simple logic. Applications have been to communications, sonar, vibration testing, and music synthesis.
Backscattering from a Finite Rigid Cylinder
Authors: Eisler T. J. , New R.
Published: October 2005

The backscattering cross section of a finite rigid cylinder is calculated for plane-wave incidence at various aspects using both the Kirchhoff approximation and Keller's geometrical theory of diffraction. In the Kirchhoff method, the first term in the asymptotic expansion of the Kirchhoff integral in inverse powers of ka is used, where a is the radius of the cylinder, k is the wavenumber of the incident radiation, and the length of the cylinder is assumed to be of the same order of magnitude as the radius. In Keller's method, only singly diffracted rays are considered. The calculations are compared with experimental results of Dunsiger [J. Sound Vibration 13, 323 (1970)]. In the special cases of beam and end-on aspect, there is specular reflection in the backscattering direction. In these two cases, the backscattering cross section is plotted as a function of ka using higher-order terms in the asymptotic expansion of the Kirchhoff integral and multiply diffracted rays in the Keller method. These results are compared with the geometrical acoustics cross section.
The Radiation Patterns of Acoustic Multipole Sources in Motion
Authors: Gaunaurd G. C. , Eisler T. J.
Published: October 2005

A study is presented of the radiated part of the pressure and velocity fields produced in free space by the arbitrary motion of point acoustic sound sources. Three types of multipole sources (monopoles, dipoles, and quadrupoles) are analyzed in detail, especially for the extreme cases of rectilinear and circular motions. Extensions to all the higher-order multipoles are also given. The solid angle distribution and the combined frequency and solid angle distribution of the radiated power are studied in further detail for point sources, forces, and stresses in general arbitrary motion. Particularizations for the cases of rectilinear and circular motions are given, and the instantaneous radiation patterns are plotted in various cases. Some examples are worked out and some applications to the theory of sound radiation from rotating machinery are given as particular cases of the general theory. The total radiated power from each type of multipole undergoing each considered motion is also given. The analysis has applications when modeling the acoustic radiation produced by moving submerged bodies.
Acoustic Radiation in the Near- and Farfield of an Annular Ring Using Impulse Response and Fast Fourier Transform Techniques
Authors: Stepanishen P. R.
Published: October 2005

An application of impulse response and fast Fourier transform techniques is presented to investigate transient and steady-state pressures in the near and farfield of a baffled piston with a specified velocity. As a specific example, and exact expression for the impulse response from an annular ring to an arbitrary point is presented. Time-dependent pressures in the field are expressed as a convolution integral involving the piston velocity and an impulse response. For harmonic fields, the pressure at a point is related to the Fourier transform of the impulse response at the point. The Fourier transform of the impulse response is evaluated exactly for on-axis points and points at large distances from the ring, and the results are seen to agree with the classical steady-state results. In general, the Fourier transform of the impulse response must be evaluated numerically and the use of fast Fourier transforms is proposed as a convenient method of evaluating the transform. The use of the approach to obtain nearfield pressure contours over a wide frequency range is also discussed and several numerical considerations are noted.
Sound Pulses Radiated in Air by Creeping Waves on Rigid Spheres and Cylinders
Authors: Vogt Richard H.
Published: October 2005

The diffraction of sound pulses by metal spheres and cylinders in air was observed under conditions where the radiation from creeping waves could be compared with the specularly reflected pulses. The amplitudes of the radiated and reflected pulses were compared for various angles of scattering and for a range of frequency parameter (ka) from 8 to 20. The results were in agreement with theory in the case where the calculations were available. The attenuation of the creeping waves was determined from the decrease in amplitude of the sound pulses radiated tangentially as the creeping waves traversed increasing arc lengths along the surface of the body. In the case of pulses derived from truncated sinusoids two or three cycles in duration, the attenuation agreed with the steady-state theory in the observed range of frequency parameter from 8 to 40.
Transient Radiation from a Point-Excited Infinite Elastic Plate
Authors: Stuart Alan D.
Published: October 2005

The acoustic pressure radiated by an infinite elastic plate excited by an impulsive point force has been determined. The effects of shear and rotary inertia in the plate have been included to ensure the proper high-frequency response. The calculation for the steady-state case has shown two distinct peaks or lobes in the farfield radiation pattern. The inverse two-sided Laplace transform reveals that the nature of the transient pressure waves are dependent on the point of observation relative to the three regions separating the two steady-state peaks. Precursor waves that arrive before the retarded time of the fluid medium were found to exist only in two of these regions, while the region about the normal to the plate contained only causal waves.
Measurement of the Critical Masking Interval
Authors: Penner M. J. , Cudahy E.
Published: October 2005

The critical masking interval, the time period during which noise is effective in masking a brief click, was measured in two experiments. The first paradigm was the temporal analog of Fletcher's critical band experiment. That is, the click was presented in the temporal center of the noise, and threshold was measured as the masker duration was decreased. The second paradigm investigated the temporal analog of Greenwood's [J. Acoust. Soc. Amer. 33, 484–502 (1961)] masking experiment wherein a click was moved through the noise burst. The two paradigms yielded similar numerical estimates of the critical masking interval (about 20 msec), although the critical masking interval was not affected by the stimulus' bandwidth.
Frequency Discrimination and Detection of Homophasic and Antiphasic Tonal Signals in Noise
Authors: Robinson Donald E. , Dolan Terence R.
Published: October 2005

Psychometric functions generated in a 2ATFC detection paradigm were compared to psychometric functions generated in a 2ATFC frequency-discrimination paradigm (see Henning, J. Acoust. Soc. Amer. 41, 4 (1967)]. For frequency discrimination, two tones were presented, one in each of the two observation intervals. The observer's task was to indicate in which interval the signal of higher frequency occurred. With a frequency difference of 15 Hz, the psychometric function for frequency discrimination of homophasic signals was parallel to and slightly displaced to the right of the psychometric function for detection of homophasic signals. The psychometric function for frequency discrimination of antiphasic signals, however, had a significantly lower slope than the psychometric function for detection of antiphasic signals. Performance for frequency discrimination of antiphasic signals was similar to performance for detection of antiphasic signals at low S/N ratios and similar to detection of homophasic signals at high S/N ratios. The data are discussed in view of current models of binaural signal processing.
Masking of Pure Tones by Frequency Modulated Tones
Authors: Young I. M. , Wenner C. H.
Published: October 2005

Pure-tone threshold measurements were made in the presence of frequency modulated tones in subjects with normal hearing. For a given masking intensity, effects at the carrier frequency of the FM tones, were found to be similar for a different frequency deviations and modulation rates. As masking intensity increased, effects at the carrier frequency increased linearly. Frequencies above and below the carrier frequency demonstrated a spread of masking being greater above the carrier frequency. This effect increased considerably for intensities above 60 dB re 0.0002 dyn/cm2. As the modulation increased for a given frequency deviation, masking effects at frequencies above the carrier frequency behaved similarly to pure-tone masking. Upon increasing the frequency deviation for a given modulation rate, masking effects produced at frequencies higher than the carrier frequency were comparable to narrow-band noise. In comparing the masking at the carrier (center) frequency, the most effective method was narrow-band anise, then the FM tone, and the least effective method was pure tone.
Some Factors Affecting the Perception of Auditory Patterns
Authors: Watson C. S. , Benbassat C. A. , Kelly W. J.
Published: October 2005

Auditory patterns, each composed of a sequence of 10 tones 40-msec long with frequencies between 250 and 900 Hz, were played in pairs. The patterns within each pair were either the same or differed by a Δf added to one of the 10 tonal components. Just detectable values of this Δf are quite small when the same patterns are used on every trial and when listeners know which tonal component may be changed [Watson and Wroton, J. Acoust. Soc. Amer. 51, 113(A) (1972)]. Presenting a new pattern on each trial was found to make the task significantly more difficult; however, the increase in difficulty was uniform whether one, two, four, or eight tonal components comprised the catalog from which the one to be varied was selected. Decay of the “auditory image,” studied by varying the interval between standard and comparison patterns, was found to proceed at a rate similar to that for single tones.
Detection of Alterations of One Component in a Multiple Tone Complex
Authors: Patterson James H.
Published: October 2005

Experiments were conducted to determine the relative detectability of an increment, a decrement, and a phase shift of one component of a harmonic series of sinusoidal components. Data will be presented showing the detectability of these three types of alterations of one component as a function of the frequency of the component being altered. The results are interpreted in terms of the time-frequency resolving power of the auditory system.
Two-Tone Unmasking
Authors: Leshowitz B. , Cudahy E.
Published: October 2005

The detection of a brief tonal signal in the presence of a two-tone masher was investigated. The composite masher consisted of a gated sinusoid of constant amplitude (80 db) added in quadrature with a continuous sinusoid. The frequency of the masher was 200 Hz higher than that of the signal. As the level of the continuous masher was increased from 60 to 85 dB, signal threshold actually decreased by 15 dB. This “unmasking” effect is interesting because simple stimulus-oriented models of detection cannot account for the data. Two-tone unmasking may be related to saturation effects reported for single units in the cochlear nucleus [R. L. Smith, J. Acoust. Soc. Amer. 52, 117 (1971)]. [This research was supported by an NIH grant.]
Central versus Peripheral Control of Vowel Duration
Authors: Condax Iovanna , Krones Robert
Published: October 2005

Although in English the vowel [I] is shorter than [i:], [ɔ], and [æ], only the [I]/[i:] difference is traditionally recognized as linguistically significant, i.e., something the speaker “knows” and has control over. The differences between [I]/[ɔ,æ], however, are usually attributed to constraints of the speech production mechanism. We tested this description by observing the effect on vowel durations of having speech produced without the normal speech organs, namely by having several subjects “speak” [sIs] “sis”, [si:s] “cease”, [sɔs] “sauce,” and [sæs] “sass,” using a finger-operated switch that controlled a speech synthesizer. Although in normal speech, the subjects produced all four vowels with statistically significant duration differences, in the order [I <i: < ɔ < æ], when “speaking” with the synthesizer only [I] was significantly shorter than the rest. We interpret these results as (1) supporting the traditional claim that the [I/i:] difference is part of the English speaker's linguistic competence, but (2) countering the claim that the [I]/[ɔæ] difference is determined by the constraints of the speaking mechanisms and is not part of the speaker's linguistic competence. [Supported by the National Science Foundation and the Office of Naval Research.]
Epenthetic Stops between [l] and Following Sibilants
Authors: Javkin Hector R. , Ohala John J.
Published: October 2005

An interesting phenomenon in phonology, one that has played a significant role in sound change, is the appearance of epenthetic stops between /l/ and /s/ in words such as “false” and “pulse,” i.e., /fɔlts/, /pʌlts/. This occurs because of the failure to release the /l/ contact before making the /s/ articulation. But such epenthetic stops are much less likely to occur when there is a /z/ following the /l/. We considered three possible explanations for this: (1) /z/ has a less complete area of closure than /s/ so the combined areas of closure for /l/ and /z/ do not form a complete stop; (2) complete closure can occur in both situations, but the oral air pressure buildup is smaller with /z/ so that the atop is less perceptible, (3) differences in the timing of the tongue gestures for /s/ and /z/. Preliminary investigations with one subject using a dynamic palatograph with computer display plus sampling of intraoral air pressure, suggested the probable correctness of (2). [Research supported by National Science Foundation and University of California President's Undergraduate Fellowship.]
Some Temporal and Autonomic Correlates of Sentence Production
Authors: Melamed Barbara G. , Jarvella Robert J.
Published: October 2005

Sentences were obtained containing verbs that refer to cognitive states or processes and are grammatically capable of taking sentence complements (e.g., “know,” “think,” “amaze,” and “delight”). The sentences were elicited in sentence production tasks by giving the verbs as lexical content or asking questions containing them. Some control conditions were also employed, including subject reading of some of the sentences aloud. Concurrent measures of speaking onset and duration, heart-rate variability, and galvanic skin response were taken during production of the sentences. Grammatical properties of the sentences are described and related to these temporal and autonomic variables.
Silent Interval and Vowel Duration Effects on Pause Magnitude Estimation in Intrapause and Interpause Environments
Authors: Rupf John A. , Ruder Kenneth F.
Published: October 2005

The stimuli for this experiment were derived from two sentences, each containing the words free criminals. In one sentence these two words occurred within a phrase, and in the other sentence a phrase boundary occurred between the words. The vowel duration in free and the silent interval preceeding criminals were systematically and independently varied. Vowel durations of 100, 200, 300, 400, 500, and 600 msec were paired with silent intervals of 0, 50, 100, 150, 250, and 500 msec for both sentences. Subjects were asked to make direct magnitude estimates of the perceived pause between free and criminals in each of the stimulus sentences. Results indicated that given durations of vowel and silent interval result in similar perceived pauses in intraphrase position than in interphrase position. Power law scaling exponents were larger for vowel duration than for silent interval in all conditions. [This research supported by the National Institutes of Health.]
Temperature Rise in Biological Tissue during Focused Ultrasonic Irradiation: Some Theoretical Subtleties
Authors: Pierce Allan D.
Published: October 2005

During focused irradiation, the absorption of ultrasound causes a net increase of temperature in the focal region. A topic of some current interest is the extent to which the temperature history or the peak temperature reached correlates with the probability of lesion formation. Because of the practical difficulties associated with measurement of very rapid temperature rises, theoretical models are sometimes used to infer the temperature history during intense but short duration pulse irradiation. The existing models [Pond, J. Acoust. Soc. Amer. 47, 1607 (1970)] Robinson and Lele, [J. Acoust. Soc. Amer. 51, 1333 (1972)] neglect a number of effects that might warrant some study. Among these is the fact that, for a given acoustic power output, the intensity at the focus may tend to decrease with time because when the medium becomes heated by the wave, the medium tends to refract wave energy away from the higher temperature and, hence, higher sound speed regions. In the present paper, it is shown that the fractional decrease in intensity is of the order of 0.05(ΔT)12, where ΔT is the temperature rise in degrees centigrade (typically, 30°C). Possible implications of this and other effects in the reinterpretation of intensity versus damage threshold irradiations duration time data are discussed quantitatively.
Parametric Acoustic Arrays
Authors: Fox C. C. , Akervold O. L.
Published: October 2005

Parametric acoustic array performance has been demonstrated with several different transducers. Three-inch-diameter transducers with primary frequencies between 250 and 300 kHz have produced good parametric acoustic beams at 10, 20, and 40 kHz difference frequencies with nearly constant beamwidth across this frequency band. A parametric acoustic array operating at 20-kHz difference frequency was compared to a 100-kHz conventional transducer for bottom profiling capability in Lake Washington. Echograms were obtained demonstrating the capability of the lower frequency beam to produce subbottom, as well as bottom returns.
Mathematical Model for a Standing Wave Acoustic Parametric Source
Authors: Van Buren A. L. , Rogers Peter H.
Published: October 2005

A standing wave acoustic parametric source (SWAPS) has been proposed as a small, efficient, low-frequency, nearly omni-directional underwater sound source. SWAPS is envisioned to be a cylindrical tube driven on one end by a piston transducer and terminated on the other end by a thin plug of pressure release material to form a resonant cavity. When the piston is driven at two neighboring resonance frequencies, the resulting large amplitude primary sound waves mix non-linearly to produce secondary sound waves. The secondary wave at the difference frequency is of low frequency so that it passes easily through the relatively thin tube walls and radiates to the farfield. The farfield radiation at the difference frequency is calculated by use of the virtual source density method. The results are expressed in terms of a quality factor which represents the resonance properties of the cavity. Comparison is made to a traveling wave acoustic parametric source using the same piston transducer.
Parametric Detection of a Low-Frequency Plane Wave by a Circular Piston Beam
Authors: Rogers Peter H. , Williams A. O. , Barber James M.
Published: October 2005

Westervelt's prediction [J. Acoust. Soc. Amer. 35, 535–537 (1963)] that an acoustic signal of low frequency can be detected by a parametric endfire array—i.e., by nonlinear interaction with a “pump” beam of high frequency—is analyzed in the case of a plane wave of low frequency and a highly directional beam from a circular plane piston used as a pump. To first-order perturbation theory, at field point (r,z), the z component of particle velocity for the interaction component at the difference frequency is proportional to the product of the piston-beam function at (r,z) (but calculated at the difference frequency) and the response function of a truncated endfire array of length z (calculated at the low frequency). The receiving directivity of the system is thus determined by the endfire response function alone, regardless of the piston's properties. The piston-beam function is, however, a factor in determined the system's receiving sensitivity. Work continues on generalizing the theorem to arbitrary directional pump transducers.
Investigation of the Parametric Radiator as a Wide-Band Calibration Source
Authors: Konrad W. L. , Navin J. G.
Published: October 2005

The parametric difference frequency radiator appears to offer advantages over conventional sources used for hydrophone calibration, i.e., wide bandwidth with a single transducer, narrow beamwidths, and short pulselengths. The combination of these characteristics promises simplification of calibration procedures and elimination or reduction of boundary reflection problems. Experiments are described which measure the performance of the parametric source for calibration purposes and which point out some of the special problems inherent in this new technique.
A Closed Form Expression for the Source Level of a Finite Amplitude Parametric Array
Authors: Bartram James F.
Published: October 2005

In a Letter to the Editor [J. Acoust. Soc. Amer. 52, 1042(L) (1972)], the author has derived a closed form expression for the on-axis farfield pressure of the secondary wave generated by a finite amplitude parametric array in which the primary waves are collimated plane waves. This formulation takes into account the effects of absorption and saturation due to shock formation. The present paper shows that this solution can be modified to account as well for spherical spreading and diffraction. It is even possible to treat nearfield buildup effects in a rather crude fashion. The thus modified expression remains in closed form, and is therefore useful for system engineering purposes.
A Computer Algorithm for Predicting Propagation of Intense Acoustic Signals of Arbitrary Waveform
Authors: Pestorius F. M. , Blackstock D. T.
Published: October 2005

The plane-wave propagation law dt/dx = [c0+βu]−1 ≐ c0−1[1 − βu/c0] is used as the basis of a computer algorithm to calculate the distortion of a finite-amplitude wave. Here x is distance, t time, u particle velocity, and c0 small-signal sound speed; for gases β = (γ + 1)/2, for liquids β = 1 +B/2A. Starting with a time waveform of arbitrary shape, we use a finite-difference form of the above law to calculate the wave shape at successive small distances. After each step in distance the waveform is scanned for multivaluadness to determine whether shocks have formed. When a shock is identified, its propagation is described thereafter by the weak-shock relation (dt/dx)s ≐ c0−1[1 − β(ua + ub)/2c0], where ua and ub are values of u ahead of and behind the shock, respectively. In growing, decaying, and merging, the shocks ultimately determine the shape and amplitude of the wave. The algorithm has been tried on several initial signals, including N waves, sinusoids, and randomly generated waveforms. In general, the algorithm gives excellent agreement with known analytical results. Comparison has also been made with experimental data on pulsed sinusoidal waves in a tube. The algorithm has been developed as a tool to study propagation of very intense noise. [Work supported by ONR, AFOSR, and USN Postgraduate school.]
Finite-Amplitude Losses in Spherical Sound Waves
Authors: Merklinger Harold M. , Mellen Robert H. , Moffett Mark B.
Published: October 2005

Using an approach suggested by Westervelt [3rd Int. Congr. Acoust., Stuttgart (1959)], the excess absorption in a plane, traveling sound wave due to nonlinear effects can be predicted with remarkably accuracy. The same approach is applied to spherically diverging sound waves evaluated for a number of cases of practical importance in underwater acoustics, and compared with existing data.
Aspects of the Finite Amplitude Interaction of Multiple Tone Signals
Authors: Pridham Roger G.
Published: October 2005

Two results are given that pertain to the effects of finite amplitude distortion on a multiple tone (i.e., multiple sinusoid source) signal. The first result is a second-order perturbation solution to plane-wave Burgers' equation for a multiple-tone source with arbitrary amplitude and phasing. This solution is interpreted to predict the spectral distortion of the primary waves at moderate levels. The second result concerns the relationship of the shock distance for fixed source tone levels and frequencies to the relative phases of the source tones. It is shown that the shock distance is minimized when the source components are in phase. However, the shock distance maximization problem is shown to be equivalent to the classic peak factor problem, which has so far defied solution. While an exact maximization is not possible, a procedure is given for phase selection that yields shock distances that are considerably greater than the minimum shock distance when many source tones are present. It is pointed out that shock distance maximization may significantly reduce distortion effects. This is particulary true if the shock can be made to occur in the farfield.
Transient Pressure Attenuation by Nonlinear, Resilient, Cylindrical Scatterers
Authors: Geers Thomas L.
Published: October 2005

Temporal convolution techniques [T. L. Geers, J. Acoust. Soc. Amer. 51, 1640–1651 (1972)] are used to obtain solutions for the problem of transient acoustic scattering by nonlinear cylindrical scatterers. These scatterers behave like cavities during the initial stages of motion, but then offer increasing dilatational resistance with increasing deformation. In contrast to the results of previous studies [M. L. Baron, J. Appl. Mech. 24, 501–505 (1957) and J. Appl. Mech. 28, 135–136 (1961)], it is found that such “modified cavities” are indeed capable of effective transient pressure attenuation in the surrounding fluid without the generation of unacceptable pressure pulses at later times. Parameter studies for plane, step-exponential incident waves are performed to establish suitable ranges for the modified cavity stiffness parameters.
Laser Excited Broadside Acoustic Array
Authors: Westervelt Peter J. , Larson Richard S.
Published: October 2005

A high-power modulated laser beam in a fluid acts like a broadside acoustic directional array at the modulation frequency. The laser is assumed to generate a beam having average power P0 with 100% modulation at the frequency ω. The radiated acoustic intensity I at a distance r far from this source is I = (αβωP0)232ρ0c0(πrcp)2 [1α2+k2 cos2θ], in which, α is the intensity attenuation coefficient for the laser beam, θ is the angle measured from the laser beam direction, k = ω/c0, β is the coefficient of thermal expansion, cp is the specific heat per unit mass, c0 is the speed of sound, and ρ0 is the density. Maximum radiation occurs at θ − π/2, in a direction perpendicular to the laser beam. [This work was supported by the U.S. Office of Naval Research.]
Receiving Calibration and Beam Pattern Measurements of a Large Sonar Array with a Parametric Transmitting Array
Authors: Truchard J. J. , Willette J. G.
Published: October 2005

A classical problem encountered in the receiving calibration and beam pattern measurement of a large, conventional sonar array is the difficulty involved in producing a plane wavefront at the face of the large array when reflecting boundaries are present. In this paper, an attempt will be made to show that the parametric transmitting array can be used to minimize this problem. Two experimental beam patterns are presented for the case of an 8-ft aperture array receiving at 5 kHz. One beam pattern was taken by using an omnidirectional 5-kHz source. The other was taken by using a parametric array sound source having primary frequencies of 70 and 75 kHz—thus, a difference frequency of 5 kHz. Theoretical results are presented for the parametric array which demonstrate the uniformity of phase and amplitude across the 8-ft aperture. The feasibility of absolute receiving calibration with the parametric array is discussed.
Application of External Aerodynamic Diffusion to Reduce Shrouded Propeller Noise
Authors: Longhouse R. E.
Published: October 2005

A major portion of the noise from V/STOL aircraft fan or shrouded propeller systems occurs during the hover mode. External diffusion of the exhaust flow during this mode significantly increases the thrust/power ratio. Attendant with the flow diffusion is a reduction in fan blade aerodynamic loading. The latter effect suggests a potential source of reducing the fan discrete-frequency noise. Results of model shrouded propeller tests to study the noise reduction associated with external diffusion are presented. [NASA is acknowledged for partial sponsorship of this work.]
Holographic Study of the Disturbances Generating Supersonic Jet Noise
Authors: Salant Richard F. , Wu J. H. T. , Handa Hisayuki , Sorrow Jerry W.
Published: October 2005

Optical holography has been used to study the noise-generating disturbances within supersonic nitrogen and helium laboratory-scale jets. Mach angle measurements indicate that the average convection velocity of such disturbances is 77% of the jet velocity for the nitrogen jet in the Math number range of 2.8–3.4, and is 67% of the jet velocity for the helium jet in the mach number range of 1.5–3.0. The length scale of the disturbances in the nitrogen jet has been lot,rid to contain a primary peak at 0.20–0.45 jet diameters, and a secondary peak between 0.45–0.77 jet diameters. The amplitude of the secondary peak, relative to the primary peak, increases in the downstream direction. In addition, the peak length scales shift upwards in the downstream direction. [This work was sponsored by the Department of Transportation.]
On Protuberance Noise Environments
Authors: George Ballard W.
Published: October 2005

A review of three-dimensional or local protuberance environments is presented with emphasis on the role of the boundary layer. The boundary layer is observed to participate significantly in the generation or propagation of acoustic disturbances throughout the adjacent region. Deductions on boundary layer quantitative effects are made based on data presented by (1) Robertson (1969) and (2) various other investigators. These data are respectively associated with relatively high and low (or roughness) regimes of proturberance height with respect to the boundary layer thickness. Insights are also obtained from the data on two-dimensional and axisymmetric steps contributed by various researchers in the past decade. Highest fluctuating pressures, forward and aft of cylindrical protuberances, typically occur in cases where protuberance height is on the order of 1.0–2.0 boundary layer thicknesses. Cylindrical protuberance configurations, having a minimum height (h) of 0.125 boundary layer thickness (δ), caused a local increase in rms fluctuating pressures (relative to undisturbed case) of 4.0 or more in all cases tested. Comments are included on roughness (h/δ < 0.1) noise sources and amplitudes as a function of height and distribution parameters.
Noise of High Speed Jets with Rough Combustion
Authors: Abdelhamid A. N. , Harrje D. T. , Plett E. G. , Summerfield M.
Published: October 2005

An experimental program to demonstrate the effect of unsteady combustion processes in a combustion-augmented jet flow is described. Characteristics of noise for several combustors, having different flame holders and several lengths, operating in a jet temperature range from 1100°C to 1500° and a jet Mach number range from 0.2 to 0.35 (jet exit velocity ranging between 400 and 800 ft/sec) are presented. Data were collected from six B&K 14-in. microphones positioned at an angular separation of 15°in a quadrant of 50-ft radius from the 2-in. diam nozzle exit. Kistler type 601 pressure transducers are mounted in the duct wall of the combustor which is held on a pylon 12 ft above the ground. The experimental data collected and analyzed to date shows a directivity pattern with a nearly circular pattern, which has a peak in the vicinity of 45° to 60° from the jet axis. Comparison of internal pressure fluctuations with the farfield noise shows many simularities in the spectrum, an observation which is verified by the strong cross correlation between the two signals. Combustor and flame holder geometry are found to affect the level and frequency content of the noise. [Supported by NASA grant.]
Low Frequency Noise of Gas Turbines
Authors: Hoover R. M.
Published: October 2005

With many electric utility gas turbine installations, the most difficult noise problem has been the control of low-frequency noise radiated to the community from the turbine exhaust. In this paper a number of case histories are discussed leading to some suggestions for noise control design goals for the 31.5-Hz octave band. Some material will be presented on noise spectra, noise control measures, and noise specifications for gas turbines pertinent to low frequencies.
AMRL Dynamic Pressure Chamber
Authors: Powell Robert G.
Published: October 2005

The AMRL dynamic pressure chamber is an infrasonic simulator expressly designed for biomedical research. This device simulates the low-frequency (0.5–30 Hz) noise spectrum associated with jet aircraft and rocket launches. Being an electrohydraulic device, it can simulate periodic, random, or impulsive types of environment. This wide dynamic range simulator (104–172 dB SPL) is characterized in terms of its frequency response, linearity, and distortion. Additional information concerning safety circuits, subject accommodation, and mechanical design are also presented.
Simplified Theory for Predicting the Transmission Loss Characteristics of Double-Panel Constructions
Authors: Sharp Ben H.
Published: October 2005

One of the problems in attempting to predict the transmission loss of a double-panel construction has always been the rather cumbersome analytical expression that is involved in the calculation. However, even if the calculation is simplified by the use of a computer, the resulting values often bear little resemblance to the measured values. It has long been realized that the disagreement is a result of mechanical connections between the individual panels and the presence, or absence, of absorption material in the cavity, neither of which are taken into account in the classical theory. By simplifying the general acoustical characteristics of double panels, it is shown that it is possible to include these two factors and accurately calculate the transmission loss with the aid of simple expressions. The simplicity of the solution makes it possible to develop optimum interpanel connections and panel configurations using materials of different mechanical properties and to design constructions to meet specific acoustical criteria. [This work was conducted under contract to the U. S. Department of Housing and Urban Development.]
Effect of Room Size on Field Sound Transmission Loss Measurements
Authors: Sepmeyer Ludwig W.
Published: October 2005

As part of the qualification testing and quality control program for the University of California Residential Building Systems (URBS) project, a field test mockup building was constructed. This facility was designed so that the test walls, having nominal ratings of 40 and 50 STC, could be measured in three different room sizes similar to those of future dormatories without disturbing the test wall to effect the change in room size. The results of the measurements will be shown and the differences discussed.
Transmission of Sound through Enclosures
Authors: Holmer C. I.
Published: October 2005

The exact description of sound transmission through an enclosure depends, in general, on the details of the source radiation characteristics, coupling of the source to the enclosure acoustic space, and coupling of the acoustic space to the resonant and nonresonant motion of the enclosure walls. Moreover, for an extended source, and a relatively small and absorptive enclosed space, an exact description is beyond the present state of the art. In this paper, a simple design procedure based on an energy flow analysis is described, which provides good lower bound estimates of enclosure performance. The performance parameter that is calculated is the lower bound of a space average, or radiated power insertion loss. When formulated in this way, the performance is reciprocal in the sense that it is independent of whether transmission is from outside to inside or inside to outside. Above the first enclosure volume resonance, the result is PIL ⩾ TL + 10 log A/S where PIL is the power insertion loss, TL is the field incidence transmission loss of the enclosure walls, A is the sabine absorption of the enclosure interior, and S is the radiating area of the walls. A result that is applicable below the first enclosure resonance is also presented. A number of experimental results are presented which confirm the analysis procedures. [Work supported in part by General Electric Co., Aircraft Engine Group, Cincinnati, Ohio, and NASA-Langley Research Center.]
Comparison of Reverberation-Room and Impedance Tube Measurements on Carpets
Authors: Poulin Maurice , Northwood T. D.
Published: October 2005

Carpet is a material difficult to define in terms that relate to its sound absorbing capacity. Accordingly there is use for a simple method of measuring its sound absorption. The reverberation room method (ASTM C423) provides the definitive measure for random incidence absorption when large specimens are available. The impedance tube method requires only small specimens but measures normal-incidence absorption, which is not a useful measure of performance in rooms. For some materials, deemed “locally reacting” with respect to the incident sound, one may calculate random-incidence absorption from tube data, but this cannot be assumed, especially for a loose ensemble of components such as carpet. Accordingly the correspondence between the two methods of measurement was studied for a range of carpet specimens. Results indicate that calculations from impedance tube data, corrected according to the locally reacting assumption and taking account of diffraction effects in the reverberation room, yield lower absorption coefficients than are obtained directly in the reverberation room. Since a good correspondence is found with truly locally reacting materials, it is inferred that carpet does not thus qualify.
Operational Methods in Determining the Acoustical Green's Function of a Right Parallelepiped with Perfectly Reflecting Walls
Authors: Selvaggi J. A.
Published: October 2005

The rules of LaPlace transforms are involved in the solution of ∇2φ − 1v2 ∂2φ∂t2 = δ(x−a)δ(y−b)δ(z−c)δ(t). The boundary conditions of a perfectly reflecting wall are applied. The solution displays the effect of the position of the source on the amplitude response. The acoustic potential is determined by V̄ = −∇φ. Real convolution extends the solution to any time dependent input.
Auditory sequence and phonetic classification
Authors: Studdert-Kennedy Michael
Published: October 2005

The distinctive characteristic of speech perception, as compared with purely auditory perception, is phonetic classification. The process is one of transforming an auditory pattern into a sequence of nonauditory, abstract segments. The listener therefore brings to bear both auditory and nonauditory, or linguistic, capacities. The former set limits on what he can detect, the latter assign perceptual weights to portions of the auditory patterns and so determine the phonetic percept. The transformation of the auditory pattern into a phonetic percept may enable the listener to evade some of the constraints of auditory masking, to extend the limits of auditory memory and to increase his capacity for temporal resolution. These ideas are discussed and illustrated with examples from recent work on voice onset time, the perception of temporal sequence, and prosody.
Identification of the temporal order in three-tone patterns embedded in eight-tone sequences
Authors: Divenyi Pierre L. , Hirsh Ira J.
Published: October 2005

Highly trained listeners identified three-tone patterns that were part of an eight-tone sequence. The patterns constituted the six random permutations of three temporally contiguous tones composing a 1/3-octave span (890, 1000, 1118 Hz). The five nonpattern “background” tones were randomly chosen, in each trial, from a 2/3-octave range. Three parameters were investigated: duration of each component tone, temporal position of the pattern within the sequence, and the band from which the background tones were chosen. Subjects had no difficulty identifying the patterns even at very short durations (18 msec/tone), whenever the patterns occupied initial or final position in the sequence, or whenever the frequency range of the background was remote from that of the pattern. However, in those conditions where the pattern was in the middle of the sequence, the average duration for threshold performance (d′ = 1.0) was longer: about 90 msec when the background-frequency range enclosed that of the pattern, about 65 msec when the background range was located slightly above the pattern range, and about 35 msec when it was located slightly below the pattern range. The experiments constitute an auditory analogy to visual figure-ground effects and demonstrate that an auditory figure can be perceptually separated from the ground on the basis of either temporal or spectral differences. [Supported by NINDS Grant No. 03856.]
Tonal intervals are perceived categorically by musicians with relative pitch
Authors: Siegel W. , Sopo Robert
Published: October 2005

Musicians with relative pitch were tested in interval-naming and magnitude-estimation experiments. They judged 20 intervals ranging over five musical categories, from unison to a major third. The results indicated that, for some musicians, the naming distributions showed sharp category boundaries, as with speech continua, and the magnitude-estimation functions showed discrete steps corresponding to the standard musical categories. Some subjects used only five different numbers in the magnitude estimation task, even though there were 20 physically different intervals. Post-experimental interviews revealed (a) that subjects who categorized believed that most of the stimuli were “in tune” even though three-fourths were inaccurate musically; and (b) that tonal intervals possess unique sound qualities. We conclude that categorical perception is not unique to speech, but may occur for other physical continua which subjects learn to identify over a protracted period of time.