bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound Field in Reverberation Chamber at Discrete Frequencies
Authors: Tichy J.
Published: October 2005

In order to find the low-frequency limit of sound power measurements in reverberation chambers at discrete frequencies, the sound field in a 70-ft3 model reverberation chamber has been investigated. Results of both the sound-pressure measurements and averaging along various paths of microphone travel at various frequencies are presented. The influence of the wall absorption on the sound-pressure level fluctuations, averaging and accuracy of sound-power measurements has been investigated. Results of correlation relations are also presented and the validity of existing formulas for sound-pressure variance is discussed.
Standing-Wave Tube for Low-Frequency Measurements in the Presence of Steady Flow
Authors: Gatley William S. , Simon Victor
Published: October 2005

Design, evaluation, and use of a standing-wave tube for determination of reflection factors in the presence of steady flow is described. Measurements in the 50- to 3000-Hz frequency range are possible. The apparatus consists of a 2-in. i.d. × 212-in. o.d. aluminum tube 70 in. long, with a 54 in. long flat surface machined along its length. A 18 in. wide slot 52 in. long is milled along the centerline of the flat surface; the slot is covered by a sliding steel band. Contact between the band and slot is maintained by guide rails and pressurized rubber tubing that bears against the band on either side of the slot. A block containing a microphone cavity is attached to the steel band; the microphone is exposed to the sound field within the tube by a small probe that projects through the slot. Standing wave measurements are obtained by recording rms voltages and distances from an unknown termination affixed to one end of the tube. Accuracy and validity of measurements, as well as current and anticipated applications, are discussed.
Masking Thresholds for Sinusoidal Signals and Noise after Infinite Amplitude Clipping
Authors: Thomas Ian B. , Grupposo Paul J.
Published: October 2005

Sinusoidal signals from two audio oscillators were added linearly and the resulting signal was subjected to symmetrical infinite amplitude clipping. The signal from the first oscillator (the masker) was held constant in amplitude and frequency. The signal from the second oscillator was passed through a variable attenuator and an electronic gate prior to linear addition and clipping. Listeners heard the clipped signal binaurally at a constant SPL of 80 dB throughout. For each frequency of the second oscillator, the attenuator was adjusted to determine the detection threshold for the second signal. Masking frequencies were 1200 and 2400 Hz; signal frequencies ranged from 125 to 8000 Hz in octave steps. Thresholds are roughly constant, averaging 50 dB, over the range of signal frequencies. These thresholds correspond to maximum perturbations in the half period of the masker of about 1.3 μsec and 0.7 μsec, respectively. For white noise as masker, thresholds for sinusoids averaged 30 dB; for a sinusoid as masker, thresholds for white noise detection averaged 25 dB. [Work supported by NIH and NASA.]
Interaural and Idiosyncratic Differences in Monaural Detection with Contralateral Cue
Authors: Taylor M. M. , Smith Sharon
Published: October 2005

Performance in the situation of monaural detection with contralateral cue (MDCC) [Taylor and Forbes, J. Acoust. Soc. Amer. 42, 1194 (A) (1967)] is drastically affected by the relative timing or phasing of the signal and the cue. We find that the phase effect is strongly dependent on both frequency and cue amplitude and that these factors interact. Different subjects perform differently in detail but agree in the main features of the effects of cue phase and intensity. The same characteristic differences among subjects tend to appear whichever ear is used as the signal ear. But there are also consistent interaural differences. When the signal is in the right ear, the cue must be relatively earlier in phase than when the signal is in the left ear. There is also a suggestion that in the cued situation, the energy-detecting mechanism may be less effective with left ear signals in spite of the fact that without the cue, detection performance is the same when either ear is used.
Difference Limen for Duration of Acoustic Bursts, as Dependent on their Envelope Curves and Carrier Signals
Authors: Rozsypal A. J. , Nabelek I.
Published: October 2005

The just noticeable differences in duration of tone and noise bursts with rectangular, triangular and Gaussian envelopes were measured by the method of limits. The equivalent burst durations were 8, 24, 80, and 240 msec. As carrier signal of the pulses, either pure tone or noise of different spectral bandwidths (narrow band, 13-oct band, 1-oct band, and white noise) was used. The central frequency of the carrier signal was 250, 1000, or 4000 Hz. Six persons served as observers. Using the method of analysis of variance, the significance of each of the various signal and individual factors was determined. The most significant was the influence of the pulse duration. Second to it was the factor of individual differences between the subjects. On the third place was the influence of the carrier-signal central frequency. Neither the factor of the envelope curve nor of the carrier-signal frequency bandwidth exhibited any significant influence on the obtained data.
Time Error for Pitch Memory
Authors: Elliott Lois L.
Published: October 2005

Ten listeners judged a 300-msec tone (T2) as higher or lower in pitch than another 300-msec tone (T1) that occcurred 8-sec earlier. The intervening time either was unfilled or contained a 400-msec distracting tone (D) with frequency either inside or outside the critical band of T1, and which occurred either 50-msec after T1 or 50-msec before T2. Performance for the silent-interval condition was as good as has been reported for pitch discrimination with no delay when T1 was 250 Hz but was slightly poorer for T1 at 1550 Hz. The distractor tone diminished pitch discrimination and, for nine subjects, produced constant errors that were generally in the direction of D's frequency. These effects were more pronounced when D immediately followed T1 than when it immediately preceded T2. While effects of the frequency of D (whether inside or outside the critical band of T1) were not clear for all individuals, some consistencies were observed within particular listeners. Results will be related to work of Postman, Wickelgren, and the author's previous studies on development of auditory frequency contours.
Discrimination between Beats and a Pure Tone
Authors: Viemeister N. F.
Published: October 2005

The detectability of a sinusoidal signal masked by a sinusoid of fixed frequency (920 Hz) was measured in a 2IFC task. The signal and masker were gated with fixed starting phase such that the resultant started at maximum amplitude. For fixed duration of the observation interval (T = 500 msec), there was a slight improvement in performance with increasing frequency difference between signal and masker (Δf = 2.0, 4.0, or 6.0 Hz). With Δf = 4.0 Hz, there was a monotonic improvement in performance with increasing duration (T = 125, 250, or 500 msec); the four observers required an average of 6.2 dB less signal power for constant performance with T = 500 msec as compared with T = 125 msec. For a single beat in the signal interval, there was a monotonic improvement in performance with decreasing frequency difference (Δf = 2.0, 4.0, or 8.0; T = 1kΔf). The average improvement was 3.6 dB over the range in Δf. With Δf = 4.0 Hz, T = 250 msec, the average slope of the Weber function was 0.88. Performance in classical intensity discrimination (Δf = 0.0) was better than in some beat conditions. [Supported by a NIH predoctoral fellowship and by the Air Force Office of Scientific Research.]
Dual Concept of Singing Registers
Authors: Oncley P. B.
Published: October 2005

Much of the confusion that surrounds the definition of registers in the singing voice grows out of the confusion of two completely different sets of phenomena. The voice shows two physiologically distinct registers, using different muscular actions, as shown by high-speed motion pictures. The degree of cooperation between these two actions depends on the skill and natural gifts of the singer. There is also a series of changes in voice quality, sometimes designated as “lifts,” which are purely acoustic in origin. Sound spectrograms show that these result from the enhancement of different harmonics of the voice as the frequency is varied while the formant resonances of throat and mouth are held essentially constant. A similar phenomenon can be demonstrated with electronic organs of the formant type. A bass voice may exhibit five or more such “lifts,” while a soprano will have only two or three. These lifts can be helpful in voice classification and are influenced by the vowel and by modifications to it. An understanding of this dual concept is important in voice teaching.
Review of the Literature on Vocal Registers
Authors: Fields Victor A.
Published: October 2005

Many eminent scientists are at work in the field of vocal research, and considerable attention is being focused on the problem of voice registers. However, information that emanates from the laboratory is not easily comprehended by the teacher of singing because it covers such highly technical areas and techniques as physiology, neurology, acoustics, stroboscopy, spectral analysis, and electrical analogs of tonal utterance. There is little reference to the musical expression of the voice, and the communication gap between science and art is evident. Numerous references to vocal registers also appear in the pedagogical literature. But these are often conditioned by feeling rather than fact and are loosely organized, ambiguous, opinionated, and controversial. The situation is compounded by an ambiguous terminology. Subjectivity in the teaching approach is apparent. The teacher observes the singing performance as the embodiment of certain esthetic values, which, in his opion, cannot be dissociated from the vocal act. An approach is needed that will correlate a diversified and widely diffused scientific arena with the pedagogical scene and focus attention on possible pedagogical applications and interpretations of research in this subject.
Physiological Basis for Vocal Registers
Authors: Vennard William , Hirano Minoru
Published: October 2005

The registration of four professional singers was studied by means of hooked-wire electrodes inserted transcutaneously in the following muscles: vocalis, cricothyroid, lateral cricoarytenoid, and interarytenoid. Light registration (falsetto) was primarily aerodynamic, with the musculature active only to maintain the necessary condtions for phonation. Heavy registration (chest) was primarily myoelastic, with only such airflow as needed to maintain the conditions. Cricothyroid activity correlated with fundamental frequency (pitch), but, in falsetto, it was exerting itself too greatly to change with each degree of the scale. Vocalis activity correlated with intensity (loudness) in both registers. In the pitch area corresponding to low falsetto or upper chest, a distinct adjustement was recognized called “head voice” by the men and “mixed voice” by the women. Cricothyroid exertion on a given pitch was greatest for head, about equal for chest and falsetto. Vocalis exertion was greatest for chest, less for head, least for falsetto. When a swell tone was produced, head to chest, vocalis increased for the crescendo and cricothyroid decreased.
Perceptual Studies of Female Chest and Middle Registers in Singing
Authors: Large John , Shipp Thomas
Published: October 2005

A critical portion of a research program into the nature of vocal registers in singing is to establish their perceptual entity. Selected for study were the chest and middle registers as produced by female student singers. The singer-subjects were trained to produce sustained phonation in one register and, while holding constant the parameters of vowel, voice frequency, and over-all intensity, transit to the adjacent register. These recorded stimuli were presented for register judgment to several groups of student singer-judges in order to obtain samples on which there was unanimous agreement as to the register produced by the singer-subjects. These stimuli were subsequently altered to remove the most obvious possible perceptual cues: by splicing out the interregister transition and by low-pass filtering at 1400 Hz. Another group of student singers was presented with the altered stimuli for judgment. The results suggested that the acoustic information during the transition period contributed little to register identification; whereas the low-pass filtering condition had a marked effect on register identification. [This investigation was supported in part by the National Institutes of Health.]
Noise Control for High-Speed Punch Presses
Authors: Bruce R. D.
Published: October 2005

This paper presents octave-band noise levels measured at the operating position of various size high-speed punch presses. Significant noise reductions were achieved through the use of acoustical absorption in the surrounding space and partial enclosure of the openings of the punch press. The noise reduction of the partial enclosure was limited by structural radiation from the frame of the press. This limitation is discussed.
Equivalent Impedance Method for Attentuation in Ducts
Authors: Vaidya P. G.
Published: October 2005

It is suggested in this paper that, within certain limitations, a variety of effects responsible for attenuation in ducts could be lumped together in the form of an “equivalent impedance” attributed to the duct walls. First- and second-order approximations for attenuation for plane and higher-order modes, when such admittance is either very small or very large, are determined if modal coupling is neglected. An integral-equation approach is suggested for the “intermediate” impedance range. An analysis has been conducted in terms of a nonorthogonal but complete set of modes; expressions for relevant modal distribution functions have been determined. Expressions for sound pressure show the usual decay as well as a modulation in attenuation along the length of the duct. A brief discussion indicating the analytical approach to estimate the modifications due to mean flow and shear is also presented.
Effects of Source Extension on Sound Fields Monitored near a Ground Surface
Authors: Panko R. R.
Published: October 2005

A jet engine must be treated as an extended source at propagation distances common in sound measurements in jet-engine static testing. A general analytical solution is developed for the field from an extended source in the presence of reflectors of arbitrary impedance. Numerical solutions are given for several physically motivated model sources, both in free space and in the presence of a rigid-plane boundary. For such a boundary, source extension is found to reduce strongly the sharpness of interference minima. For the case of a finite-impedance plane boundary, such as grass-covered soil, however, source extension is shown to be less influential in reducing the depth of the minima, in agreement with experimental results that have been previously considered paradoxical. Predictions for the finite-impedance case are based upon a method discussed in a companion paper by P. B. Oncley.
Detection of a Potentially Shifting Signal Parameter
Authors: Hinich M. J.
Published: October 2005

Parameter instability or nonstationarity in an input signal plus noise is a potential problem for various signal-processing schemes. In a processor, for example, that hard clips the input, the clipping level must be at the true mean value of the noise in order to avoid severe distortion. A sudden shift in the mean can occur, however, if a large low-frequency transient is present in the noise or if a malfunction occurs in the electronics. Another nonstationarity problem in signal processing arises in matched filtering if there is a sudden change in the amplitude values of several Fourier components of a known signal waveform. If a change occurs, the old matching function is no longer optimal. The problems of a mean shift, a trend change, or an amplitude shift are special cases of the parameter shift problem in the general statistical linear model. The detection of a shift of one parameter is discussed.
Flush-Mounted Pressure Transducer as a Unit of an Acoustic Homing System
Authors: Maidanik G. , Noiseux D. U. , Horwath T. G.
Published: October 2005

A flush-mounted pressure transducer consisting of a porous plate backed by a cavity is described. The employment of the pressure transducer as an elemental unit of an acoustic homing system is discussed. The homing is executed by the motion of the boundary in a direction and an orientation that brings the pressure transducer system closer to a stationary target. The target is assumed to be a localized acoustic source. The target induces a pressure field on the sensitive surface of the pressure transducer producing the signal in the response. In addition, because of the motion of the boundary, the sensitive surface of the pressure transducer is subjected to the pressure field induced by a turbulent boundary layer. The response of the pressure transducer to this pressure field constitutes the noise. The influence of the motion of the boundary on the nature of the pressure fields to which the pressure transducer is subjected is estimated and the filtering action of the pressure transducer is analyzed in some detail. The design criteria that will tend to maximize the signal-to-noise level of this. type of pressure transducer are derived and discussed. [This work was initiated and sponsored by Systems Application Division, MERDC, Fort Belvoir, Virginia 22060.]
Predicting Spacecraft Acoustically Induced Random Vibration Flight and Test Environments
Authors: Kazmierczak F. F. , Ikola A. L.
Published: October 2005

To be considered flight worthy, equipment must be shown capable of withstanding a predicted random vibration environment prior to flight, usually by qualification testing. However, the preparation of reasonable random vibration qualification specifications for equipment is a difficult task. A review of considerable literature on the subject shows that variations of 20 dB between predicted and actual data are not uncommon for several techniques. In most cases, only the results are presented with little explanation as to why such large discrepancies occur. This paper describes the sources of some of these discrepancies and indicates directions that can be taken by industry to achieve more uniform and realistic test procedures. In this context, the nfluence that a variety of significant variables has on the generation of test specifications is discussed. For example, the effects that various types of acoustic excitation (i.e., free field, reverberation, and direct radiation) have on a vehicle structure are examined. The significance of structure is shown by comparison of data from several different vehicle configurations. Included are external fairings, trusses, skin data, and simulated versus actual equipment. Also the effect of techniques on extrapolating data is discussed, including linearity of response, statistical methods, analyzer bandwidth effects, broad-band versus random-sweep random spectrums, and time and amplitude levels with respect to predicted flight severity. As a result of this study recommendations are made for methods of deriving test specifications that more closely simulate the flight environment.
Dynamic Green's Function Technique Applied to Shells Loaded by Moments
Authors: Bolleter U. , Soedel W.
Published: October 2005

Green's function techniques to determine the response of shells and plates to dynamic normal loads have been used widely. Using the gradient of the normal-load Green's function for a given shell, a general method is developed that will determine the response of the shell due to an arbitrary time-varying dynamic moment load anywhere on the shell. This approach is closely related to the treatment of dipole sources in acoustics. Two simple examples are given. The response of a simply supported beam to a dynamic edge moment compares with results obtained by a classical approach. The response of a simply supported rectangular plate to a rotating moment, as it would be created by a rotating unbalance parallel to the plane of the plate, is given as the second case.
Membrane Application of Second-Order Nonseparables
Authors: Moseley Donald S.
Published: October 2005

The Helmholtz wave equation [∇2+ (ω/c)2]W − 0 is customarily solved by the familiar, college-taught method of separation of variables. Separable solutions so obtained can be considered a special—and very important—case in an infinite set of nonseparable solutions of this equation. [See Quart. Appl. Math. 22, 354 (1965).] Known nonseparables of this set can be derived from the separable by repeated application of a generative operator. In view of this, a separable is looked upon as a nonseparable of zero order. An example in two dimensions is w = W exp iωt, where W is amplitude, W(0) = sinax sinby, W(1) = bx cosax sinby − ay sinax cosby, the operator connecting them is b∂/∂a−a∂/∂b, and the frequency eqation for both is (ω/c)2=a2+b2. Some properties of nonseparable members of the set are presented, and application to the transverse displacement of a membrane is illustrated.
On the Forced Vibration of a Nonlinear Stretched String
Authors: Beitin K. I.
Published: October 2005

The response of a stretched elastic string to a periodic motion of one of its supports constitutes a nonlinear eigenvalue problem. To the lowest order approximation, one obtains two coupled Mathieu equations, one for each of the transverse directions. The results indicate that, at a certain critical frequency near resonance, motion normal to the plane of the driving force appears. This nonplanar motion results in a reduction of the amplitude of the planar motion, and a significant increase in the string tension. The theoretical results agree with experimental data obtained elsewhere.
Re-Entry Acoustical Measurements on a Ballistic Vehicle
Authors: Kachadourian George
Published: October 2005

Acoustical measurements, with a ported-hole installation, were made at two points on the conical surface of a high-performance ballistic vehicle during re-entry flight. The instruments were intended to detect the onset of boundary-layer flow from laminar to turbulent flow. The results of the measurements are presented with comparison to the findings of other standard transition sensing instruments. In addition, time histories and spectral analyses of pretransition and transitional acoustic data are presented and discussed. The fundamental design concept of the sensor installation is presented and reviewed. The basic conclusions reached are that the ported-hole acoustic-sensor concept is a feasible one. The usefulness of the acoustical measurement in boundary-layer technology is that information is acquired that is unobtainable by other means presently in use and can, with proper application, be a valuable tool in extending boundary-layer-flow technology.
Discrimination of Filtered-Clipped Speech by Sensorineural Hearing-Impaired Subjects
Authors: Thomas Ian B. , Sparks David W.
Published: October 2005

A form of preprocessed speech known to be highly intelligible to normal listeners was heard by a group of subjects with sensorineural hearing losses. The preprocessing technique involves high-pass filtering (cutoff 1100 Hz, slope 12 dB/oct) and infinite amplitude clipping. Tests with normal listeners in this laboratory have shown that the resulting speech has an intelligibility of 97% under noise-free conditions and an intelligibility of 90% at a signal-to-noise level of 0 dB for PB words after training. Subjects with sensorineural hearing losses and average bilateral SRTs of 65 dB were tested using CID W-22 PB word lists. The subjects heard unmodified speech and then filtered-clipped speech, both at 15-dB sensation level. Discrimination scores for one group of subjects averaged 46% for unmodified and 61% for filtered-clipped speech. For the remaining subjects, presbycusis cases, scores were so variable as to defy analysis. Errors for unmodified speech were due mainly to misrecognition of stops, fricatives, and affiricates; errors for filtered-clipped speech were more frequently due to vowel substitutions and distortions. [Work supported by NIH and NASA.]
Discrimination of Formant Transitions by Listeners with Sensorineural Hearing Losses
Authors: Pickett J. M. , Martin Ellen S.
Published: October 2005

Persons with sensorineural hearing losses usually exhibit a discrimination deficit for audible speech sounds. Some of the most important features of speech are the transitions in the vowel-formant frequencies. How discriminable are these transitions to persons with severe sensorineural losses? We attempted to get a preliminary answer to this question. Synthetic sounds with formant peaks in the spectrum were employed in discrimination trials. The task of the listener was to hear the occurrence of a formant transition in contrast to no transition. An adaptive procedure was used to estimate discrimination threshold of frequency transition. The threshold for listeners with sensorineural impairment was compared with the threshold for normal listeners. Transition durations of 50, 100, 300, and 500 msec were tested in low (0.6–1.2 kHz), middle (1–2 kHz), and high (2–3 kHz) frequency regions. The results indicated that the impaired listeners needed larger and longer transitions for threshold discrimination than did normal listeners and that this difference was greater at high frequencies than at lower frequencies. [Supported partially by U. S. Public Health Service.]
Effects of Intensity on Critical Bands
Authors: Bourbon Walter T. , Hehmsoth Carl J.
Published: October 2005

Critical bands (CB) for antiphasic tonal stimuli (noise zero phase, signal out of phase—N0Sπ) were determined in a band limiting, two-alternative forced-choice paradigm. Signals were 100-msec tone bursts at either 500 or 2000 Hz. Masking noise was at sound pressure spectrum levels of 15 or 45 dB. For each combination of signal frequency and noise intensity, a signal level was determined, which produced average probability correct of 0.54 for the three observers. Band limiting of the noise disclosed the characteristics of the critical band for each stimulus condition. CB for N0Sπ were wider for a noise spectrum level of 45 dB than for a spectrum level of 15 dB. For any given conditions, the CB for N0Sπ was from 18% to 30% wider than the CB determined earlier for N0S0. [Work supported by U. S. Navy Office of Naval Research, Physiological Psychology Branch.)
Model of Binaural Hearing Based on Auditory Nerve Patterns
Authors: Colburn H. S.
Published: October 2005

A model for binaural hearing is presented in which the firing patterns of the auditory nerve are regarded as input to a central processor. The model is a continuation of work by W. M. Siebert on monaural phenomena, and the random-process description of the firing patterns is based on data from N. Y. S. Kiang's studies in the cat. Early work centered on analysis by an ideal central processor and indicated that further restrictions on the use of detailed timing information were necessary. Restrictions on the permissible interaural comparisons of event times result in a model for the central processor in the form of a set of statistics that are used optimally. Predictions of this model are compared with data from binaural unmasking and interaural discrimination. A distinctive feature of the present model is the central rôle played by the observed randomness inherent in the firing patterns of auditory nerve fibers. [Work supported primarily by a grant from the National Institutes of Health and in part by the Joint Services Electronics Program.]
Detectability of a Noise-Signal as a Function of Signal-Masker Phase and Interaural Phase
Authors: Robinson Donald E. , Langford Ted L.
Published: October 2005

Using a two alternative temporal forced-choice technique, the detectability of a wide-band, 128-msec noise signal masked by a coherent, continuous noise was measured as a function of the level of the signal, the phase angle at which the signal was added to the masker and the interaural phase difference of the signal. When the interaural phase difference is 0°, the detectability is found to follow a simple energy-or power-difference model. When the interaural phase difference is 180°, the relation between signal-masker phase angle and signal level required for a constant level of performance is approximately that predicted by the Durlach equalization-cancellation model for binaural signal detection. [Research supported by a Grant-in-Aid from Indiana University.]
Digital Filter Technique for Synthesis of Bassoon Tones
Authors: Plitnik G. , Strong W.
Published: October 2005

The amplitudes of the partials of a bassoon tone can be approximated by a smooth spectral envelope that is somewhat dependent upon the fundamental frequency. The spectral envelope has two peaks at frequencies of about 550 and 1150 Hz. For bassoon tones played in the high register at a dynamic marking of ff, the peaks are of approximately equal amplitude: In the high register, the second peak is about 3 dB lower than the first peak for mf tones and about 13 dB lower for pp tones. The second peak has a somewhat greater attenuation when the instrument is played in the low register. Two digital filters (modeled by the Z-transform method), one resonating at 550 and the other at 1150 Hz and each having an independent amplitude control, were used to approximate the bassoon spectral envelope. A common pulse train was used to excite the filters, and the output of the filters was summed. The filter amplitudes were controlled by an appropriate set of time-dependent exponentials that approximated the rms amplitude of real bassoon tones. Examples of the synthetic bassoon tones are presented.
Trumpet Air-Column Overloading
Authors: Backus John , Hundley T. C.
Published: October 2005

The sound output of the trumpet is rich in harmonics. Since sound-pressure levels (SPLs) in the air column of the instrument are high (measurements of SPL in the mouthpiece range up to 165 dB), it has been suggested that harmonic production is due to acoustic overloading of the air column. This hypothesis has been tested in four different ways: (1) The amount of second-harmonic production was calculated with the use of some simplifying assumptions; (2) trumpet input impedance as a function of SPL was measured; (3) two separate standing waves were set up in the trumpet air column and the difference frequency produced by them was measured; (4) a signal was fed from a driver into the closed trumpet mouthpiece through a capillary tube, and the ratios of harmonic amplitudes in the driver to amplitudes in the trumpet output were measured. Calculated second-harmonic distortion was more than an order of magnitude smaller than measured, and none of the three sets of measurements showed significant air-column overload effects. The conclusion is that acoustic overload is not a primary cause of harmonic generation in the trumpet. [This work was supported by the National Science Foundation.]
New Method for Acoustical Radiation Problems with Mixed-Boundary Values
Authors: Butler John L.
Published: October 2005

A series-expansion method for the solution of acoustical-radiation problems with mixed-boundary values is presented. The condition of a given velocity on a transducer face and a given pressure or impedance on the surrounding boundary is of interest in underwater acoustics. With this mixed-boundary condition, solutions are difficult to obtain using the usual methods in even the simplest cases. In the method presented here, a wavefunction expansion is truncated to include only the number of terms equal to the number of specified boundary values. The solution improves as this number increases, and coefficients may be evaluated through a matrix inversion as in a nearfield-to-farfield prediction method presented previously [J. Acoust. Soc. Amer. 44, 351 (A) (1968)]. The particular case of a radiator on a sphere is treated and results are presented that show that the sound beam is more directive if the remaining portion of the sphere is soft. [Work sponsored by the Office of Naval Research (Acoustics Programs Branch).]
Analysis of Array with Nonlinear Amplifier/Transducer Modules
Authors: DeLaCroix R. F.
Published: October 2005

Procedures for modeling the performance of a transmitting array require either an explicit or implicit definition of the velocity of each radiating element as a function of the electrical input signal and the acoustic pressure on the radiating surface. To date, most array modeling work has been restricted to linear systems where the velocities are computed from the electrical input signal and the linear equivalent circuit for each element in the array. When an array contains nonlinear amplifiers or transducers, this equivalent circuit, in general, will be a function both of the input signal and the pressure on the radiating surface, and the linear analysis techniques cannot be used. Two methods, repeated matrix inversion and iterative lookup, have been developed and applied to the hydroacoustic amplifier/transducer module. In both methods, the nonlinear operating profile characteristics of the coupled amplifier/transducer module are known, either by prediction using a simulation program for nonlinear devices or by measurement. The operating profile is defined by several equivalent Thevenin circuits in the former method and by tabular data in the latter. Several examples show that for larger arrays the latter method requires much less computer time and storage than the matrix method.
Sinusoidal Horns
Authors: Nagarkar B. N. , Mathis T. D. , Ripper A. P. , Finch R. D.
Published: October 2005

It is pointed out that a sinusoid satisfies Salmon's criterion for a good horn shape. Calculations have been made of the throat impedance of sinusoidal horns of various dimensions, including the case of a single globe terminating in a cusp. Depending on the relative dimensions of the mouth and throat, the device may be used as an impedance transformer. Experimental determinations of directivity of an underwater horn have been made and found to compare favorably with conical horns. Finally, it is demonstrated that several musical instruments employ sinusoidal cavities, the bell of the English horn being discussed in particular.
A Mutually Complementary Effect of the Rate and the Amount of Formant Transition in Distinguishing Vowel, Semivowel, and Stop Consonant
Authors: Suzuki Hisayoshi
Published: October 2005

The purpose of this research is to examine the effect of changes in rate and amount of a formant transition in speech sounds. Synthesized wordlike sounds /a:/, /aua/, /awa/, and /aba/ were used as the experimental materials because the motions of first formant frequency are the main cue for distinguishing them, and accordingly, the first formant frequency could be used as the only control factor in the experiment. Eight different transition patterns and 11 different target values between 250 and 790 Hz were prepared as x in a wordlike sound /axa/. The total length of each sound was 450 msec. From the results of listening tests, a distribution diagram of identification for any given sound was obtained. It was found that an increase in the rate of frequency change V reduced the frequency deviation F, necessary to switch an identification of a particular phoneme, and that the locus of boundary values between different words were represented approximately by a formula (V − Vθ) = C/(F − Fθ), where Vθ, Fθ, and C were constants depending on particular word pairs. [Work supported in part by grants from the Air Force Cambridge Research Laboratories and the National Institute of Health.]
Effects of Signal Distortion on Three Listener Performance Tasks
Authors: Gilbert Harvey R.
Published: October 2005

The purpose of the study was to assess the usefulness of three listener performance tasks: learning rate, recall, and listener confidence ratings, as criteria for evaluating speech communication systems by determining if performance on the three tasks varied systematically with type and severity of speech-signal distortion. Lists of 24 words, equal in intelligibility and content but differing in acoustical distortion, were presented auditorily to five groups of 20 listeners. Results showed that learning rate decreased as the amount of distortion associated with the speech signal increased. Listeners were more confident of correct reception of the words as the signal distortion decreased and were more confident of the incorrect reception as the distortion increased. There were no differences in the number of words correctly recalled between the five distortion conditions. It is suggested that the intelligibility score alone is limited in its ability to assess the transmission capabilities of a speech-communication system and that learning rate and listener confidence ratings may provide additional information useful in evaluating speech-communication systems.
Frequency Organization and Response Characteristics of Single Neurons in the Nuclei of the Lateral Lemniscus of the Cat
Authors: Aitkin L. M. , Anderson D. J. , Brugge J. F.
Published: October 2005

Single neurons isolated in the dorsal and ventral nuclei of the lateral lemniscus were studied on and off line with a LINC computer. Best frequencies of cells in the dorsal nucleus are arranged from low to high in a dorsoventral orientation. Data suggest that similar organization exists in the ventral nucleus. The great majority of neurons studied in the dorsal nucleus were sensitive to binaural stimulation, with the contralateral ear supplying the major excitatory drive. With few exceptions, neurons in the ventral nucleus were affected only by contralateral ear stimulation. Discharge patterns generated within response areas of units in both nuclei, as well as spike-count functions, have been studied in detail. Units usually exhibit a sustained discharge, accompanied often by an onset burst, throughout the frequency-intensity domain. At low frequencies, discharges may be locked to individual cycles of the stimulating tone. The first spike latency tends to be minimal at or near best frequency and, regardless of spike counts, is a monotonic function of stimulus intensity.
Vibrational Holography of the Tympanic Membrane in Cats
Authors: Khanna Shyam M. , Tonndorf Juergen , Ropper Allan H.
Published: October 2005

Vibrational holography (Powell and Stetson, 1965) was applied to a study of the vibratory characteristics of the cat's tympanic membrane (TM). Technical difficulties were presented by the TMs small size, low stiffness, and its transparency. Vibrational holograms of the TM for various frequencies and sound-pressure levels are demonstrated. These holograms are pictures of the TM with superimposed isoamplitude contour lines. The first line appears at a peak amplitude of 1.2×10−5 cm, below which vibrations cannot be discerned. Measurements may be extended over a range of approximately 20 dB. Results may be summarized as follows: (1) Vibratory patterns remain essentially unchanged in the first mode up to a frequency of 2000 Hz, with higher modes occurring above that value; (2) at all frequencies, the TM vibrates maximally in the posterior quadrant, less in the anterior, and least in the inferior quadrant; (3) for a uniform amplitude of the TM at its point of maximal displacement, mallar displacements increase first with frequency and decrease steeply at frequencies above 2000 Hz. [Supported by NIH grants.]
Test-Site Measurement of Noise Emitted by Engine-Powered Equipment
Authors: Hillquist Ralph K.
Published: October 2005

This draft proposal, developed by the S3-50 Working Group, presents test-site methods for determining the maximum noise emitted by a wide variety of engine-powered equipment categorized as contributing to community noise. Requirements and procedures contained in the proposal are discussed, as are the considerations made in drafting them.
Diffraction of a Sound Pulse by a Solid Cylinder in Water
Authors: Neubauer W. G. , Dragonette L. R.
Published: October 2005

Motion pictures will be shown of the schlieren visualization of a 5-μsec sound pulse at 6.6 MHz in a time sequence as it is emitted from a source, strikes the cylinder, and produces the various radiated constituents of the diffracted field—i.e., those caused by the creeping wave, the elastic circumferential (Rayleigh-type) wave, and the transmitted refracted longitudinal and shear waves in the cylinder. The sequence of production of the constituent waves on the diffracted field at a given time are also shown as the acoustic pulse is swept across the cylinder normal to its axis. The resolution will also be shown of the constituent waves in the diffracted field of cylinders of copper and aluminum oxide.
An Extension of Larmor's Theorem to Inhomogeneous Media and Its Application to Radiation into the Shadow Zone
Authors: Hudimac A. A.
Published: October 2005

It was shown that the wave field in an inhomogeneous medium satisfy a given discontinuity in pressure and its normal derivative on a continuous surface is the same as that due to related distribution of sources and dipoles. Such discontinuities occur in ray theory on the surface separating the sonified region and the shadow zone. One can distribute sources and dipoles on this surface so that the discontinuities resulting from the ray theory and from the distortions are mutually annihilated. This modification of the ray theory has been checked satisfactorily against wave theory in two cases: (a) diffraction through an aperture in a homogeneous medium; and (b) propagation from a point source in a stratified medium. [This work was supported by the Office of Naval Research.]
Some Wind-Tunnel Test Developments Relating to Fluctuating Pressures of Transonic Shock-Boundary Layer Interaction
Authors: Luksus Edmund J. , Huang Jackson T.
Published: October 2005

A transonic wind tunnel fluctuating-pressure test involved 21.6-in.-diam models of spacecraft shrouds. This large size, coupled with small microphones (116-in. diam) allowed detection of fine-grained effects from mutual interactions between terminal shock, vorticity, and boundary layer condition: sometimes interacting in pairs, sometimes three conjunctively, depending on relative strengths. This paper presents some static pressure and microphone data that suggest vorticity interaction with the shock structure, distorting the shock front. For a model with regularly spaced external corrugations, fluctuating pressure environments are described in terms of circumferentially periodic rippling of the shock that induces a broad zone of intense fluctuations. Coexisting with this zone, and about 3 dB more intense, is a localized environment associated with the highest-order nearfields from the unsteadily undulating shock front. The total environment is inexplicable in terms of shock discontinuity alone and illustrates that designing for decreased pressure fluctuations can sometimes involve more complications than merely decreasing shock strength.
Sound Propagation in a Continuous Isotropic Random Medium
Authors: Neubert J. A.
Published: October 2005

The steady-state propagation of sound from a highly directional source in a medium where the index of refraction (μ = 1 +αn) varies in a continuous isotropic random manner is investigated by means of a Debye asymptotic expansion applied to the stochastic Helmholtz equation: ∇2p+k02μ2p=0, where p is the wave pressure and k0 is the wavenumber. The first-order term for p is shown to involve Lagrangian ray-path correlations and yields, after considerable simplification, a coefficient of intensity variation V such that V2 a is proportional to the range r and the Lagrangian cross-ray integral-scale H1 of the fluctuation n of μ. One of the simplifying assumptions is that α2k02H1r is much less than unity.
Laser Excitation of Microwave Sound
Authors: Cachier G.
Published: October 2005

Ruby lasers can be used for exciting microwave sound in the bulk or from the surface of a crystal, by the mixing of two longitudinal modes separated by a frequency Ω in the gigacycle region. Different mechanisms can be involved; electrostrictive mixing occurs in the bulk, as mentioned by D. E. Caddes (thesis, Stanford University). Pressure of radiation and electrostriction are involved for surface excitation, with lower efficiency. Surface heating does occur even in the case of uncoated dielectrics, being related to surface damage. Our experiments were performed in lithium niobate crystals, where birefringence can be used for forward Brillouin scattering: at 810 MHz, with longitudinal sound in an X-cut crystal; at 480 MHz, with shear sound in a Y-cut crystal. We generated about 0.5 mW/mm2 of sound in the bulk of the crystal. We could not detect pressure of radiation effects, which were rapidly overcome by surface heating effects, producing up to 2 mW/mm2 of longitudinal sound in 20-nsec pulses.
Brillouin Scattering from Sulfur Hexafluoride in the Vicinity of the Critical Point
Authors: Mohr R. , Langley K. H. , Ford N. C.
Published: October 2005

Using techniques described earlier by Ford, Langley, and Puglielli [Phys. Rev. Lett. 21, 9 (1968)], we have observed Brillouin scattering from SF6 near its critical point for two scattering angles: 166° and 45°. Sound velocities deduced from these measurements at (T−Tc) = 3° are Cs = 108±1 m/sec for a sound frequency of 370 mHz and Cs = 98±2 m/sec for a sound frequency of 130 mHz. The dispersion in the sound frequency of about 10% at T−Tc = 3° decreases as the temperature is increased to about 2.5% at T−Tc = 20°, where the sound velocity has increased to 135 m/sec. A comparison is made between these data and existing ultrasonic data, and it is shown that the sound velocities are consistent with a single relaxation frequency, which, however, is temperature dependent. [This work was supported in part by a National Science Foundation Grant.]
Absorption of Light by the Sound Waves of Disordered Crystals
Authors: Whalley E. , Klug D. D. , Wong P. T. T.
Published: October 2005

Photons and phonons can interact in disordered crystals without conservation of wave vector. The absorption of light by the acoustic waves of orientationally disordered crystals, such as ice, and of vitreous silica are discussed in detail. The effect of short-range correlation of orientations has been examined theoretically. When the wavelengths of the excitations are very long compared to a lattice spacing, the absorption of light can be described in terms of a kind of piezoelectric coefficient, the root-mean-square value of which is not zero for orientationally disordered crystals.
Determination of the Vocal-Tract Shape Directly from the Speech Wave
Authors: Atal B. S.
Published: October 2005

Sound propagation through the human vocal tract is studied by quantizing the vocal tract into a finite but arbitrarily large number of contiguous uniform cylindrical sections. The transfer function between volume velocities at the glottis and lips and the corresponding impulse response are obtained by matching the pressure and the volume velocity at the junctions between adjacent sections. It is shown that the frequencies and bandwidths of the poles of the transfer function determine uniquely the areas of the cylindrical sections. The vocal-tract area function is determined directly from the autocorrelation function of the impulse response and the calculation does not involve any iterative or search procedure. The application of this procedure to determine the vocal-tract shape for connected speech is discussed.