bluuebunny/crossref_metadata_2025 huggingface dataset:
Directional Filtering of Summed Arrays
Authors: Frosch R. A. , Clay C. S.
Published: September 2005

In a system for which we have complete control of both the outgoing signal and the spacing of elements in a receiving array, proper choices of the signal and the array spacing allow us to treat the array as a 2-terminal device, summing all elements outputs together with no time delays, without losing the ability to make directional discriminations. After summing, the output of the array is passed through a delay-line filter designed for the input signal, array spacing, and direction of interest. The output of the filter is a correlation function peaked for the proper signal arriving in the correct direction. In general, the side-lobe structure and signal-to-noise performance will be poor, but special choices of signal and spacing exist for which both characteristics are acceptable. [Columbia University, Hudson Laboratories Informal Documentation No. 14. This work was supported by the Office of Naval Research under Contract Nonr-266(84).]
Collapsible Anechoic Treatment for High-Intensity ASD Facility
Authors: Tyzzer Franklin G. , Sperry William C.
Published: September 2005

A collapsible layer-type treatment having a normal incidence-absorption coefficient greater than 96% between 50 and 7000 cps was designed for the ASD Sonic Fatigue Facility at Wright Field. Requirements included a maximum thickness of 6 ft, a surface density less than 10 lb/ft2, ability to withstand 160-dB sound pressure levels, 250°F temperatures at high humidity, and collapsibility for semireverberant room use. A layer-type system fulfilled requirements of collapsibility, and its normal incidence absorption could be measured in impedance tubes over the required frequency and intensity ranges. A high-intensity facility was developed for 160-dB SPL in a progressive wave in two 3-in.-diam tubes below 2000 cps and in a 0.75-in. tube at 1500 and 7000 cps. Acoustic resistances of layer material increased with particle velocity, but the absorption of layer systems was not critically dependent on layer resistance. Curves of αn are shown for 5- and 6-layer systems with irregular layer spacing and tapered resistance per layer. Many acoustical materials failed at high intensity, but skeletal polyurethane foam had desirable acoustical and mechanical properties and withstood accelerated fatigue tests which are described.
Equivalent Linearization Techniques
Authors: Caughey T. K.
Published: September 2005

The method of equivalent linearization of Kryloff and Bogliubov is generalized to the case of nonlinear dynamic systems with random excitation. The method is applied to a variety of problems, and the results compared with exact solutions of the Fokker-Planck equation for those cases where the Fokker-Planck technique may be applied. Alternate approaches to the problem are discussed, including the characteristic function method of Rice.
Approximate Power Spectral Density of the Response of a Nonlinear System to Stationary Random Excitation
Authors: Butler Thomas G.
Published: September 2005

An approximation is obtained for the power spectral density of the response of a hard-spring resonator to a class of random inputs by 2 methods of equivalent linearization. Comparison of the theoretical spectral densities is made with those obtained experimentally from an analog computer with white-noise excitation.
Computed Frequency and Angular-Distribution Irregularity of Normal Modes in Rectangular Rooms
Authors: Sepmeyer L. W.
Published: September 2005

Results obtained with the computer program described in papers G5 and G6 at the 61st meeting of the Society are presented. Both frequency and angular mode spacing indices have been computed for each half-octave band over the first 4 octaves of normalized frequency for rooms with dimension ratios ranging from 313 to 1, to 1 to 1. Considerable variation in the frequency spacing criterion exists not only with changes in room dimensions but also from one half-octave band to the next, when only tens of modes are present in a band. When hundreds are present, the modes become Poisson distributed. No clearly defined optimum room dimension, as predicted by Bolt, emerges from this study. The angular distribution index is more regularly behaved with rather definite stratification apparent as a function of the room height/length ratio, when the height direction is taken as the angular reference. For rooms having satisfactory mode distribution, an approximate formula has been developed for determining the lowest midband frequency for which a room may be used for measurements of continuous spectrum sounds. The formula turns out to be a constant divided by the cube root of the volume where the constant is a function of the measuring bandwidth and the number of normal modes required therein. For 20, 12, and 9 modes in one, 12, or 13, octave bands, the constants are 1160, 1285, and 1355 cps, respectively.
Determination of 10 Log a for PWL Measurements
Authors: Engstrom J. R.
Published: September 2005

To determine the absorption in a reverberation chamber for PWL measurements. the reverberation-time method (using the Sabine formula) is preferable to the calibrated-source method. This preferred method, which is independent of the source or measuring-equipment calibrations, involves a device attached to a graphic level recorder to indicate the reverberation time on an electronic counter. The 10 log a factors for three reverberation chambers determined with this device are compared to determinations which were obtained with: (1) a graphic level recorder and (2) a calibrated source.
Reflection of Short Sound Pulses from a Corrugated Surface
Authors: Courts H. R. , Wittenborn A. F.
Published: September 2005

The reflection of sound pulses from corrugated surfaces has been a problem of interest in architectural acoustics for some time. This problem has been examined by simulating the process on a digital computer. The simulation has been carried out in such a manner that the reflected pulse can be obtained from the computer in analog form, so that the pulses can be listened to. Recordings of the direct and reflected pulses are presented, so that the effects of the reflection process can be demonstrated audibly for a variety of geometries, pulse lengths, frequencies, and reflecting surfaces.
Speech Synthesis from Stored Data
Authors: Estes S. E. , Kerdy H. R. , Maxey H. D. , Walker R. M.
Published: September 2005

The synthesis of speech by joining together segments derived from natural speech has not proven to be satisfactory with segments smaller than words, especially because of discontinuities in pitch and formant frequencies at the junctions. It appears that segmentation of the control signals for an analog synthesizer may avoid these difficulties. This paper describes an experimental system to investigate this method. A library of synthesizer control signals corresponding to subword segments of speech is now being developed. The equipment used to generate the library of control signals, as well as that used to synthesize connected speech from the library, is described. The synthesizer is a transistorized terminal analog of the cascade type. The synthesizer control signals are originally derived from functions drawn on a transparent plastic belt by opaque tape and scanned by a CRT and photomultiplier. The control-signal functions are varied until the speech segment being studied is satisfactory. The resulting control signals corresponding to the speech segment are then automatically digitized and recorded on punched cards for addition to the library. Connected speech may be generated by computer assembly of the synthesizer control signals corresponding to a sequence of speech segments. In the assembly of connected speech from the library segments, pitch and timing may be specified independently of the sequence of segments if desired.
Computer Simulation of a Formant-Vocoder Synthesizer
Authors: Flanagan James L. , Coker Cecil H. , Bird Carol M.
Published: September 2005

A speech synthesizer of the formant-vocoder type is described in which vocal antiresonances (zeros) as well as resonances (poles) are taken into account. The synthesizer is simulated by sampled-data operations on a large-scale digital computer. Digital-to-analog conversion of the output permits listening to the synthetic sounds. Voiced sounds are generated by periodic (glottal) excitation of one branch of the circuit. Transfer functions for vowel and vowel-like sounds are described by 4 poles. Nasal consonants are represented by 5 poles and 1 zero. Voiceless sounds are generated by noise excitation of a separate branch. Fricative consonants are described by 1 zero and either 1 or 2 poles. Frequencies and bandwidths of the poles and zeros are independently controllable, although certain vocal constraints are capitalized upon to relate their values. Amplitude of voiced and voiceless excitation and pitch are also controlled. Performance of the synthesizer with band-analyzed control data is demonstrated. Special computer input equipment for facilitating automatic extraction of the control data from real speech is also described.
Acoustical-Impedance Characteristics of Some Sintered Metals
Authors: Coles James J. , Doelling Norman
Published: September 2005

An experimental study is being undertaken to investigate some of the relationships between acoustical-impedance characteristics and manufacturing parameters for sintered metals. The manufacturing parameters to be investigated are particle size, forming pressure, and percentage by volume for pore former. A simple physical model is presented. [This work is being supported by the Gilman Engineering and Manufacturing Company.]
Response Spectra for Nonlinear Dynamical Systems
Authors: Fox Herbert L.
Published: September 2005

We consider the response spectrum of a dynamical system described by Lr(t)+εN[r,ṙ,r̈⋯]=f(t), for which L is a linear differential operator in time, N is a nonlinear analytic function of the response r(t) and its derivatives, and f(t) is a Gaussian random process with a given power spectrum. A perturbation technique is applied, which yields the spectral density of the response in a series in powers of the coupling constant ε. The methods is, therefore, applicable only if the system remains stable in the range of ε. Some general properties of the expansion are presented, and a sample calculation of a perturbed spectrum is outlined. The method is applicable to such problems as Brownian motion with nonlinear viscous forces and the coupling of energy from a nonlinear mode into other modes in a complex structure.
New Analog Device for Studying Long Ducts Carrying a Mean Flow and an Acoustic Signal
Authors: Doelling Norman
Published: September 2005

Representation of long ducts by passive L-C networks is useful only in a limited frequency range, owing to the large number of dissipative inductors which must be used. A new active analog has been developed which overcomes the effects of dissipation. The device also can represent the effect of different upstream and down-stream acoustic-phase velocities resulting from a mean flow. Applications of the system and comparison with standard analog networks are shown.
Sound Radiation from Perforated and Other Pervious Vibrating Surfaces
Authors: Ingard Uno
Published: September 2005

Conventionally, the study of sound radiation from vibrating boundaries refers to impervious boundaries. By allowing the surface to be pervious, we introduce into the problem an additional parameter that can be varied independently. Using the conventional radiation characteristics for piston sources as reference, we show by special examples that reductions, as well as gains in radiated power, can be obtained by such surface treatment. Therefore, this kind of “radiation control” might be of practical interest both in noise-control and communication applications. [This work was supported in part by the U. S. Army Signal Corps, the U. S. Air Force Office of Scientific Research, and the Office of Naval Research under Contract No. Nonr-1841(42).]
Review and Comments
Authors: Jeffress Lloyd A.
Published: September 2005

Three classes of binaural phenomena have been receiving considerable attention during the past several years. They are: the localization of airborne sound, as from loudspeakers, etc.; the lateralization of sounds conducted to the ears via earphones, permitting independent control of interaural differences of level and of phase (time); and the binaural phenomena of masking, or rather of unmasking. The three are closely related, and data from all three help give us some insight into the brain mechanisms responsible for the phenomena. The speakers to follow will undoubtedly discuss all three aspects of binaural hearing, will explain some, and will probably leave us with more problems to puzzle over than we had before.
Behavioral and Physiological Mechanisms
Authors: Neff William D.
Published: September 2005

From anatomical, physiological, and psychophysiological investigations, it appears (a) that nerve impulses aroused by sound striking the two ears interact in a lower brain-stem center of the auditory system, probably in one part of the superior olivary complex; (b) that the neural information which is necessary for localization of sound in space remains in the form, “time differences between nerve impulses.” as it is transmitted to higher centers of the brain; and (c) that the auditory areas of the cerebral cortex are essential for the full utilization of this neural information which makes possible the accurate localization of sound in space.
Hydrophone Preamplifier for Use in Multiple Hydrophone Arrays
Authors: Weiss B. F. , Barber L. M.
Published: September 2005

A compact, versatile, and reliable hydrophone preamplifier designed for use in multiple hydrophone arrays is described. The preamplifier is used in the frequency range 2 to 5000 cps (−3 db points) and has a dynamic range in excess of 80 db. The equivalent electrical self-noise is below that of a sea state 0. One vacuum tube for impedance matching and seven transistors for voltage and power amplification are used in the preamplifiers. A total of up to 5 preamplifiers is contained in a cylinder 6 in. in diameter and 12 in. in length. A large amount of negative feedback is used to insure gain stability. The preamplifiers are designed for use with crystal hydrophones with sensitivities greater than −110 db re 1 v/μbar and capacitances of more than 5000 μμf.
Quantitative Analysis of Flute Design
Authors: Benade A. H. , French J. W.
Published: September 2005

The Theobald Boehm empirical flute-design procedure is checked by direct calculation from first principles. Effects of open- and closed-tone holes, head-joint taper, cork position, embouchure size, and the player's lip position are dealt with quantitatively. The dominant effect is at the embouchure where the length correction is Δl=(c2/8π2r) (fp2−fn2)−1. Here, r is the 17-mm cork-to-embouchure distance, fn the played frequency, and fp a parameter (1350 cps) which is essentially the frequency of a Helmholtz resonator made by plugging the bore wtih a second cork a distance r below the embouchure. In the low register, the net distance between the low D hole and the embouchure is calculated to be 70.8 mm smaller than a half-wavelength, whereas Boehm requires a reduction of 68.5 mm. The nature of this 2.3-mm discrepancy is discussed in the light of current practice, along with the wider implications of the theory for the design of flutes.
Shift in the Location of Resonant Frequencies Caused by Large Electromechanical Coupling in Thickness-Mode Resonators
Authors: Onoe M. , Tiersten H. F. , Meitzler A. H.
Published: September 2005

The frequencies of fundamental and overtone resonance in a thickness-mode piezoelectric resonator depart from an integral multiple relationship when the electromechanical coupling of the resonator material becomes large. This behavior can be explained by the fact that large electromechanical coupling significantly lowers the resonant frequency of the fundamental mode with respect to the overtones. The resonant frequencies have been calculated as a function of the electromechanical coupling coefficient and the mode number for thickness modes in poled ceramics. (The theoretical analysis for thickness-mode resonators is given in a separate paper by Tiersten.) The measured resonant frequencies of both thickness-dilatational and thickness-shear mode resonators made from BaTiO3, PZT-5, and PZT-7 ceramics were found to show good agreement with theory. An important practical application of this anharmonicity is in the determination of the shear coupling coefficient k13, direct measurement of which has hitherto been difficult. This coupling coefficient, along with k33 and kt, can now be obtained from the ratios of the resonant frequencies of the fundamental and overtone modes.
Ultrasonic Research at the Ultrasonic Research Laboratory of the Hungarian Railway Scientific Research Institute
Authors: Greguss P.
Published: September 2005

The ultrasonic research supported by the laboratory can be classified into two main parts: nondestructive material testing and active application of sonic and ultrasonic energy.

In the field of nondestructive material testing, theoretical and experimental attempts have been made on the correlation of the internal stresses of manufactured parts and of the propagation properties of ultrasonic waves. The investigations made up to present proved that, by measuring ultrasonic velocities with an accuracy of 0.1%, the residual stress distributions in metals can be detected. Now, efforts are made to construct a measuring device suitable not only for laboratory tests but also for technical investigations. Some experimental studies have been made on the problem of appointing the size and shape of imbedded scoria and other inclosures in metals, and interesting correlations were found between the identifiableness of the enclosure and the ultrasonic method applied. Some preliminary experiments were carried out in order to test the effect of ultrasonic irradiation on electroluminescent panels and in slightly ionized gases. Work has begun on the development and application of airborne and hydrodynamic acoustic generators to different technological processes, such as combustion, heat exchange, emulsification, etc. The laboratory cooperates with the I. Gynecological Clinic and has developed several methods and devices for ultrasonic therapy. One of their last works deals with the acting mechanism of the resolving gallstones by ultrasonic irradiations.
Damage-Risk Criteria for Line Spectra
Authors: Ward W. Dixon
Published: September 2005

Damage-risk criteria in current use assume that pure tones are 10 db more dangerous than broad-band noise. However, Thompson and Gales [J. Acoust. Soc. Am. 33, 1593 (1961)] have recently shown that 5-min exposures to 110-db sound-pressure level (SPL) produced the same temporary threshold shift (TTS) whether the TTS-producing agent was a pure tone or a band of noise of any width up to an octave; this was true for stimuli centered at 500 and at 3200 cps. In an attempt to extend the generality of their findings, the present study compared the effects of short exposures to (1) a 1200- to 2400-cps band of noise and (2) a 1650-cps pure tone, at intensities up to 125-db SPL. The results indicate that at 115-db SPL and above the pure tone will indeed produce more TTS than the broad-band noise. However, one cannot say just how much more dangerous the line spectra are, because the two types of stimuli shift different test frequencies by different amounts (and by different ratios). Certainly a single-decibel correction applied to all levels and to any frequency range is a gross over-simplification. (This research was supported by grants from the National Institute of Neurological Diseases and Blindness.)
Noise Attenuation of Current Ear-Protective Devices
Authors: Webster J. C. , Rubin E. R.
Published: September 2005

Ten ear-protective devices—three plugs, three muffs, two phone-in-muff combinations, one phone-in-muff in protective helmet, and one plug-muff combination—were tested for noise attenuation. The psychophysical method of binaural threshold shift (occluded ears minus open ear) for half-octave bands of noise using three trials on five experienced listeners was used. When averaged over all frequencies at half-octaves (60–8000 cps), the V-51R plug under a Willson sound-barrier muff gave the best attenuation; the Sharpe HA-10 earphone, the Willson sound-barrier muff, and the David Clark 372-HPF muff gave almost equal and the next best attenuation; the Zwislocki resonant plug showed only slightly less attenuation than the three muffs; the V-51R and ComFit plugs were nearly equal with somewhat less attenuation than the Zwislocki resonant plug; the Gentex helmet and Telephonics sonibar muffs (with sound-powered phone and without) were the least effective attenuators of noise. Only in the frequency range from 60 to 300 cps were plugs better than the better muffs. All devices gave more attenuation as the frequency region increased from low (60 300 cps), to medium low (300 1000 cps), to medium high (1000–2900 cps), to high (2400–8000 cps), except for the Zwislocki resonant plug in the high-frequency region. The effect of sealing ring, headband pressure, and volume was experimentally studied independently of the actual devices tested. Flow-resistance measurements were made to explain the combined effects of headband pressure and seal around the ear.
Muffler Theory Considering Flow
Authors: Eichler Ewald
Published: September 2005

The effect of a steady subsonic flow component upon the acoustical properties of pipes and of laminar and turbulent flow resistances is accounted for in an elementary fashion. The effect of the alternating or acoustic component upon the steady-flow properties is treated likewise. Acoustic transmission loss referred to the end radiation from a pipe is related to back pressure (increase in steady pressure due to the muffler). Equivalent circuits and diagrams of transmission loss vs back pressure are presented for some simple arrangements of pipes, volumes, irises, and flow resistances.
Intra-Aural Muscle Reflex in Man
Authors: Weiss Howard S. , Shinabarger Edward W. , Mundie J. R.
Published: September 2005

The intra-aural muscle reflex was studied in human subjects using the method of tympanomanometry previously reported (4th International Conference on Medical Electronics, New York, July 16–21, 1961). Little attention has been given to the particular characteristics of the reflex itself, i.e., which muscles are involved, latency, amplitude, or duration of contraction. Instead, interest was focused on the relative ease or difficulty with which various acoustic stimuli were capable of eliciting a just-demonstrable reflex. Thus, seven different stimuli, whose amplitude envelope varied as a function of time, were presented at five different frequencies to a panel of subjects. Reflex “thresholds” were determined for each stimulus and compared to the detection-level threshold for the same signal. Results of these and other observations are reviewed, and the possible theoretic and practical implications are discussed.
Temporary Threshold Shift and Contralateral Threshold Shift: Reliability and Temporal Course
Authors: Loeb M. , Fletcher J. L.
Published: September 2005

In a previous study, negligible correlations were found between two presumed indices of acoustic reflex action—threshold increase in the ear contralateral to a stimulated ear and temporary threshold-shift reduction by presentation of an activating tone before each of a series of impulsive stimuli. One possible explanation is that the reliability of each index—or perhaps that of acoustic reflex activity itself—is sufficiently low so that the hypothesized relationship would be masked. Reliabilities of temporary threshold shift (TTS) and of contralateral threshold shift (CTS) were measured, therefore, at various intervals after initiation or production by click or noise stimuli. CTS reliabilities ranged from low to moderate. TTS reliability was higher, especially immediately after exposure, but TTS reduction reliability would presumably be lower. While the magnitudes of the reliabilities were such as to explain lack of relationship of the indices, the use of either index as a diagnostic sign is not precluded.
High-Quality Speech Compression - Expansion Method
Authors: Johnson Oliver
Published: September 2005

A new and more sophisticated method of speech compression and its evaluation are presented in this paper. Original waveforms are segmented according to the developed criteria. The resulting segments are used to construct new waveforms which are continuous and which retain the original speech qualities. Under this new method, exact control is achieved in the generation of fixed-length speech passages from variable-length passages. The quality of machine-constructed speech from prerecorded words is appreciably improved through the control described. Also, the method potentially provides a means for increasing the speech throughput over communication channels. Listening tests were conducted to evaluate the intelligibility of the new compression method and to compare it with two existing methods of compression. Curves of intelligibility as a function of compression ratio are included for each method.
Voiceprint Identification
Authors: Kersta L. G.
Published: September 2005

Initial successes indicated that a voiceprint identification system analogous to existing fingerprint identification is a possibility. Subjective matching of voiceprints has resulted in success scores of better than 97%. For the purposes of voiceprint identification, a library tape was recorded containing the voices of 15 male and 10 female, essentially normal American voices. The recording consisted of 10 cue words chosen for the high frequency with which they appear in telephone conversation. The cue words were uttered four times by each speaker, first singly, then in two five-word sentences, and finally in narrative during which each cue word appeared at least two times. Spectrograms were made from the above recordings and prepared for subjective testing. The voiceprints were randomly arranged for presentation in groups of 20, each group comprising four different utterances of a cue word by five different speakers. Upon initial presentation of five groups of 20 voiceprints to seven experienced subjects, four recorded perfect scores, two recorded one error, and one subject recorded two errors. A panel of naive female students under 18 years of age was chosen next and given five days of voiceprint reading experience. Upon presentation of the first voiceprint identification problem, the panel recorded only two errors in seven groups of 20 voiceprints In successive experiments, the matrices were expanded to 9 and then 12 talkers. Identification success scores exceeded 98% for over 5000 decisions. In a later series of experiments, simulated identification problems were investigated resulting in success scores exceeding 97%.
Subway-Vibration Measurements at the New Lincoln Center Philharmonic Hall
Authors: Miller Laymon N.
Published: September 2005

The design of the new Philharmonic Hall at the Lincoln Center for the Performing Arts in New York has incorporated certain provisions for the reduction of earth-borne and structure-borne noise and vibration into the building from the nearby subway running beneath Broadway. Vibration levels due to subway passages were measured at several positions within the building following completion of the main structure. The vibration-isolation treatments and the results of the vibration measurements are described.
Lead as an Architectural Sound Barrier
Authors: Goodfriend Lewis S. , Ostergaard Paul B.
Published: September 2005

Very high values of sound-transmission loss can be provided by lead-backed building materials at moderate costs. To achieve this requires optimizing the thickness of the building material—gypsum board, plywood, hardboard, or sheet metal—in relation to panel weight. Some practical examples are shown, along with a low-cost laminating technique. (This work was supported by the Lead Industries Association Expanded Research Program.)
Architect's Search for Acoustical Truth
Authors: McQuade Walter
Published: September 2005

The papers will be followed by an open discussion led by all the session speakers on the platform.
Optimization of a Crosscorrelator for the Case of a Linear Delay
Authors: Remley Winslow R.
Published: September 2005

An omnidirectional noise source can be detected and its asymptotic bearing determined by crosscorrelating the outputs of spatially separated sensors and detecting the peaks in the correlation curves. In general, however, if the geometry is time-varying, the statistical relationships of the signals are not stationary, and the correlation between the received signals can be seriously degraded. This problem may be obviated by employing a short integration time in the conventional correlation operation and by assuming the delay is a constant during this time interval. However, the output noise of the correlator is inversely proportional to the integration time and, consequently, to maximize the output signal-to-noise ratio, one must compromise between signal correlation and noise suppression. In this report, the output threshold signal-to-noise ratio of a crosscorrelation detector is calculated for a general signal spectrum and integration time under the assumption of a constant delay rate but of otherwise ideal conditions. It is shown that the delay-rate degradation of the output signal is equivalent to introducing a factor which is obtained by smoothing the autocorrelation function of the input signals. Subsequently, low-pass, rectangular-signal spectra are assumed, and the output signal-to-noise ratio of the crosscorrelator is numerically evaluated for various delay rates and time-bandwidth products. For zero delay rate, the output signal-to-noise is a linear function of the time-bandwidth product, but, for nonzero delay rates, optimum points exist.
Detectability of Pure Transmission Delay in Telephonic Conversation
Authors: Bricker Peter D.
Published: September 2005

Telephonic communication via satellites in stationary orbit will impose transmission times of several tenths of a second on both the original signal and on any echoes that may occur. If the eventual achievement of perfect echo suppression is assumed, there remains the question of whether transmission delay alone will seriously impair the utility of satellite circuits for conversation. Attempts to answer this question using special echo-free circuits in the laboratory have been plagued by lack of realism in the conversations, while currently feasible suppression of echo in the field produces undesirable side effects. The laboratory experiment reported here incorporated two novel features: (1) Seven preselected pairs of subjects conversed on matters on which they felt strongly, so that no puzzles, check lists, or the like were necessary. (2) The conversers were able to remove delay from the circuit whenever they detected it. A delay equivalent to that encountered in a double satellite bounce (1.2 sec roundtrip) was abruptly but quietly introduced 22 times in the course of a total of two hours of conversation. This change so often went undetected for a minute or more that it could hardly be considered seriously disruptive. This finding, however, cannot be generalized to all types of conversations. Ancillary findings and suggestions for further research on conversations are discussed.
Discrimination of Missing Pitch Pulses
Authors: Michaels Sheldon B. , Lieberman Philip
Published: September 2005

The object of this experiment was to determine the discriminability of missing pitch pulses in synthesized vowel-like sounds. Pitch pulses were derived from samples of real speech. Individual pitch pulses were removed from certain parts of these pulse trains. A fixed vowel POVO-type synthesizer was then excited by these pulse trains, and listeners were asked, in an A–B test, to discriminate between the POVO excited by complete pulse trains and the POVO excited by pulse trains having missing pitch pulses. It was found that a single missing pulse in the middle of a sustained monotone could be easily discriminated. However, stimuli having missing pitch pulses near the onset of the utterance could not be discriminated from stimuli generated from complete pulse trains. Discriminability depended on the position of the missing pulse in the pulse train. Discriminability of missing pitch pulses also depended on the average pitch period, the rate of change of pitch periodicity, and the total stimulus duration.
Sonic Load History Recorder. I. Feasibility Study
Authors: Doelling N. , Noiseux D.
Published: September 2005

The acoustic loads to which an aircraft is subjected during its lifetime must be known for structural-fatigue analysis in aircraft design. The Sonic Load History Recorder senses, filters, smooths, and records some measure of the length of time the sound pressure has spent in a given level band. Sound-pressure-level distributions over long periods of time are calculated for a present-day aircraft from engine-operating parameters, operational characteristics of the aircraft, and from ambient atmospheric conditions. The requirements for a device which is designed to provide a useful description of acoustic loads at a point on an operational aircraft are developed on the basis of the SPL histories and fatigue criteria. [This work was supported under U. S. Air Force Contract AF 33(616)-7789.]
Dynamic-Photostress Analysis of Velocity Transformers
Authors: Hornett Henry , Sun Frank W.
Published: September 2005

Certain transparent materials and certain strained plastics demonstrate the phenomenon of double refraction or birefringence. They divide an incident ray of light into two beams which travel at different speeds through the material. This means that one beam will be retarded in relation to the other while traveling through the plastic. In addition, the two beams transmitted through the doubly refractive materials are polarized at right angles to each other. The direction of polarization corresponds to the direction of principal strains or stress in the materials. These materials make the stress visible as colored fringe patterns. With the aid of this technique, the stress distribution and particle amplitude on four types of help wavelength velocity transformers (namely stepped, conical, exponential, and calenoidal) were observed and photographed. These experimental results were compared to those calculated from theory.
Vibrations of Rods, Plates, Shells, and Composite Homogeneous and Inhomogeneous Vibratory Systems
Authors: Skudrzyk E. J.
Published: September 2005

The theory of electrical lines and filters is based on the concept of a characteristic impedance. Similar concepts are permissible for mechanical systems. It thus becomes possible to derive a generalized theory that is free from insignificant details such as the exact nature of the boundary conditions or the exact shape of the vibrator. The resulting formulas are unexpectedly simple and lead to accurate agreement with the experimental results. The theory can be generalized for inhomogeneous systems, such as shells with joints and coupled systems. The most interesting characteristics of vibrators such as rods, plates, plates with joints, and shells, with joints and stiffening rings, are discussed in detail. (This work was sponsored by the U. S. Atomic Energy Commission and the Bureau Naval Weapons.)
Response of Beams to Noise Fields
Authors: Lambert R. F. , Tack D. H. , Fang G. T.
Published: September 2005

Modal response characteristics of distributed parameter systems under random forcing can be viewed in the complex frequency domain from a singularity diagram. Such diagrams displaying the source and the system response poles and zeros associated with a given mode of vibration often are capable of portraying the interaction between source and system singularities in a comparatively simple manner. This technique is very helpful when predicting response to random forcing such as encountered in moving noise fields which exhibit simple source poles. Interpretation of results of several experiments on turbulent forcing of beams and ribbons is given from this viewpoint in the light of new information about the statistical properties of boundary-layer turbulence. Good agreement is obtained if both velocity-dependent and frequency-dependent eddy lifetimes are allowed. Certain inherent limitations in the technique are mentioned. Some recent work on the influence of boundary impedance on the location of the system response poles also is discussed. (This work was sponsored by the WADD, U. S. Air Force.)
Compact, Cartridge-Actuated Shock Exciter for Small Components
Authors: Holloway R. A. , Sutherland W. W. , Mintz Fred
Published: September 2005

In the course of a program to develop a convenient method for transient calibration of accelerometers, a compact shock exciter of fairly novel design was developed. This unit, built around a modified “captive-bolt” cartridge-actuated cattle stunner, is useful for applying shock pulses to accelerometers and other small components. The shape of the acceleration curve is approximately a distorted half-sine pulse with a duration between one and two milliseconds. By varying the powder charge in the cartridge and the mass load on the moving assembly, the peak acceleration can be varied over about a 10:1 range, peak values ranging from about 400 to 4000 g. The corresponding velocity changes range from about 10 to about 50 ft/sec.
Summating and Cortical-Evoked Potentials in Guinea Pigs
Authors: Misrahy G. A. , Dzinovic S. , Spradley J. , Garwood V. P.
Published: September 2005

Small amounts of glucose-glucose oxidase injected into scala media 1 may reduce the summating potential in normal guinea pigs greatly without producing any change in the endocochlear dc potential. This was not possible in guinea pigs deafened with Kantrex. The fraction of summating potential unaffected by the injection of glucose-glucose oxidase was affected by asphyxia. These results support Davis' thesis that most of the summating potential derives from hair cells. The smaller fraction of summating potential unaffected by glucose-glucose oxidase appears closely related to endocochlear dc potential. Cortical evoked responses to tones of high, medium, and low frequency were mapped on the surface of the cortex of curarized guinea pigs. Stimulation of the eighth nerve with electrodes placed in scala media 1 and scala tympani 1, across the basilar partition, evoked cortical responses only with pulses of long duration and very large current flow. These data are in accord with an hypothesis of chemical initiation of impulses in the eighth nerve. (This work was supported by National Institutes of Health Grant No. B-3453.)
Anatomy of the Otic Capsule of the Bullfrog and Its Role as an Auditory Transducer
Authors: Geisler C. Daniel , Frishkopf Lawrence S. , van Bergeijk Willem A.
Published: September 2005

In order to interpret single-unit responses to auditory stimuli recorded from the eighth nerve of the bullfrog, it was judged necessary to investigate the structure and innervation of the various sensory organs within the otic capsule. The otic capsule is known to contain eight sensory organs: 3 semicircular canals, saccule, utricle, lagena, and the basilar and amphibian papillae. The first six of these structures have been found by other investigators who used behavioral or physiological methods to transduce information about the spatial position and vibrational state of the animal. The remaining organs, the basilar and amphibian papillae, are thought to be auditory in function, both because of their structures and because of their connection to the perilymphatic system. The anatomy and innervation of these two organs are discussed, particularly in relation to their possible function as auditory transducers.
Theorem Concerning the Aerodynamic Sound of a Free Inviscid Flow
Authors: Powell Alan
Published: September 2005

A theorem is presented which is a direct consequence of the Lighthill theory of aerodynamic noise generation when expressed in the equivalent point-source approximation; the same theorem also follows from the vortex theory of sound generation. It states that the sum of the sound pressures at points located at equal distances on each of three mutually perpendicular axes, with the origin in the flow, is zero. This is based on the incompressible-flow approximation and applies to a flow which is inviscid and unconvected. There is also an analogous form of the theorem for two-dimensional systems, concerning the sum of the sound on any two mutually perpendicular axes. The value of the theorem is demonstrated by showing how there can be no net longitudinal quadrupole strength for an inviscid noise-generating flow. This is illustrated by considering the sound radiators of a plane shear layer undergoing a small two-dimensional disturbance. (This work has received partial support of the Office of Naval Research, under contract.)
Theoretical Efficiency of Circular Sources
Authors: Embleton T. F. W. , Thiessen G. J.
Published: September 2005

The intensity and power radiated from continuous circular sources and circular arrays of point sources are derived from first principles. For the first-mentioned source, the final analytical expressions are extremely simple—that for intensity being CJμ2(ka sinθ), where C is a constant and θ the angle between the field point and the normal to the source plane. The radiation pattern depends on the product of the source radius a and the wave number k; the direction of its maximum is determined primarily by the phase parameter μ. No minor lobes exist on the axial side of the major lobe. The expression for power predicts an anomaly wherein the power—for most ka>1.9—is greater for a source “dephased” by a small amount than for one having all elements radiating in phase. These expressions are applicable to the reduction of noise from centrifugal and axial blowers and aircraft propellers. In particular, it can be shown to be impossible to reduce the noise appreciably from a single section of an open compressor by using different numbers of blades in the rotor and stator unless the difference in number exceeds the value of ka. This is usually precluded by considerations of “solidity.”
Perception of Coloration in Filtered Gaussian Noise—Short-Time Spectral Analysis by the Ear
Authors: Schroeder M. R. , Atal B. S. , Kuttruff K. H.
Published: September 2005

Frequency-response irregularities of electroacoustic components (loudspeakers, microphones, etc.) are usually well audible when the response irregularity exceeds several decibels. In contrast, the considerable frequency irregularity of rooms (10 db or more) is generally not perceived when listening in rooms to speech or noise. To resolve this paradox, the following hypothesis has been made: The ear is not directly sensitive to the frequency irregularity of a “filter” inserted between it and the sound source, but rather to a smoothed version of its frequency response, corresponding to the ear's inability to resolve fine detail of irregular frequency responses. (The limited frequency resolution is a necessary consequence of the short-time spectral analysis performed by the ear.)—Experiments with filtered Gaussian noise have confirmed this hypothesis for a variety of periodic frequency responses with different frequency irregularities and peak spacings. Investigations with aperiodic (more roomlike) frequency responses are in progress. Test tapes for the subjective tests were prepared by a digital computer. (The filtering by digital computer is particularly convenient because of the difficulty of instrumenting filters with the precision required in these experiments.)—The most interesting result of the subjective tests is the time-weighting function (“time window”) employed by the ear model in its short-time spectral analysis. Whether the time-weighting function obtained in noise-coloration experiments is applicable to other experiments involving temporal summations is not yet known.
Pitch of Double Pulse Trains
Authors: Small Arnold M. , McClellan Max E.
Published: September 2005

Several investigators have reported that listeners presented with a periodic series of dc pulses of constant amplitude, deviation, and polarity judge the pitch of this pulse train to correspond to the pulse-repetition rate. If a second pulse train identical to the first is added, a new pitch appears which is related to the temporal displacement between adjacent pulses of the two pulse trains. This study investigated the precision with which 10 listeners were able to match the pitch of a sinusoid to “that pitch which changed when the time separation between adjacent pulses changed.” Six pulse delays at each of three repetition rates were employed. Results indicate that, for a pitch match, the frequency of the sinusoid was adjusted to almost exactly 1/Δt, where Δt is the time in seconds between proximal pulses. Matching precision was greatest at 100 pps and less precise at 25 and 400 pps. For a given pulse rate, precision also decreases as pulse separation decreases. Although listeners differed in their ability to perform the task, under optimum conditions over 90% of the judgments of all listeners fell within one semitone of 1/Δt. (Some listeners had all of their matches within 20 cents of 1/Δt.) It is suggested that, because of this “accuracy” and precision and because of the lack of any obvious spectral correlates, these data may represent an instance in which pitch is based on a temporal analysis of the signal.
Scattering Cross Section of Arrays of Rigid Pressure-Release and Resonant Elements
Authors: Junger M. C. , Thompson W.
Published: September 2005

The scattering cross section of orderly arrays of identical elements is discussed. Emphasis is placed on spherical scattering elements which are small in terms of wavelengths. In this range, pressure-release elements exhibit a relatively large, frequency-independent, omnidirectional scattering cross section which makes it necessary to consider cross coupling between elements, i.e., to account for the contributions to the wave incident on one element by the waves scattered by other elements. Cross-coupling need not be taken into account in an array of rigid elements because of their much smaller scattering cross section, which stands as (ka)4: 1 to the cross section of a pressure-release element. The two scatterers differ further in that the scattered field of the rigid element comprises a dipole component comparable in magnitude to the omnidirectional component. Finally, the effect of resonances of spherical scatterers is explored. If the resonance occurs at small ka, and in the absence of structural damping, a resonant mode raises the scattering cross section to a value proportional to (ka)−2. In practice, radiation damping is the limiting factor for the breathing mode only. In this case, it can be so large as to exclude resonant amplification. The directivity pattern of 20 equidistant spherical elements arranged in a spherical surface array was computed for pressure-release and rigid scatterers. In contrast to the single spherical scatterer, arrays are markedly directive, and become more so as the radius of the scattering elements is decreased. (This work was supported by BuShips under direction of U. S. Navy Underwater Sound Laboratory.)
Measurement of Acoustic Coherence
Authors: Shapiro A.
Published: September 2005

At the 1961 Spring Meeting of the Acoustical Society of America, the author suggested the adoption of the definition of coherence that is now prevalent in the field of multidimensional stochastic processes. At that time, some theoretical work was presented that led to an interpretation of the definition in terms of phase-difference variability. In this paper, the practical aspects involved in the measurement of acoustic coherence are presented. Criteria for the design of experimental procedures are given, and questions concerning sampling variability and the determination of sample values are discussed. [This work was supported by the Office of Naval Research under Contract Nonr-2461 (00).]