bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Analysis of the Scattering of Short Acoustic Pulses by a Thin-Walled Metallic Cylinder in Water
Authors: Horton C. W. , King W. R. , Diercks K. J.
Published: September 2005

A theoretical analysis given of the scattering of plane acoustic waves by a thin-walled metallic cylinder in water. It is shown that a surface wave of low attenuation is propagated around the cylinder as a flexural vibration and that this wave acts as the “creeping” wave discussed by Franz. The phase velocity of this wave depends on frequency so that one must use group velocity for short pulses. Theoretical calculations are compared with experimental measurements made on an aluminum and a brass cylinder of wall thickness 0.094 in. and o.d. 5.475 in. over a frequency range of 70 to 130 kc/sec. The theoretical curve of the velocity of pulses around the aluminum cylinder shows a frequency dependence that agrees with the experimental curve, but the magnitude of the theoretical value of the velocity is 10% too low. It is not possible to excite these waves in the brass cylinder with the present experimental arrangement.
Minimizing Feedback in Sound Systems and Room-Ring Modes with Passive Networks
Authors: Boner C. P. , Boner Charles R.
Published: September 2005

A procedure for reducing feedback in sound systems and controlling room-ring modes is described. Narrow-band antiresonant passive filters are introduced in the link circuit(s) (LC) of the amplifier, each LC being tuned to the frequency of the particular mode to be controlled. Depth of notch is regulated by taps on the high-Q inductor of the filter. Usable system gain before feedback is increased and smoothness of the house curve of SPL versus frequency is improved. Experimental observations in some fifty large rooms with sound systems indicate that, in highly reverberant rooms such as churches, the number of self-oscillatory modes and ring modes that interfere with speech intelligibility is limited. If a room-ring mode has the same frequency as a feedback mode, narrow-band insertion losses of as much as 30 dB may be required. Otherwise, notch depths of 3–10 dB or so are normal. Observations are reported on the priority order of the modes, effect of microphone position, beating modes, and other phenomena that have been encountered.
Central Periodicity Pitch
Authors: Nieder Philip C. , Creelman C. Douglas
Published: September 2005

Perceptual phenomena are reported that are observed when interrupted noise is presented to one ear and either correlated or uncorrelated continuous noise is presented contralaterally. Also described are effects observed when the contralateral stimulus is also interrupted noise. These and related results support the conclusion that there exists a central mechanism for the perception of periodicity pitch and require that existing models of central neutral processes of pitch perception and binaural fusion be modified.
Relationship of Measured Vibration Data to Specification Criteria
Authors: Kroeger R. C. , Hasslacher G. J.
Published: September 2005

The highlights of a successful vibration-data measurement program—from sensor selection and evaluation to data processing—are reviewed. Time-sampled data from missile flights are analyzed and various errors attendant to spectral analysis are considered. Unique methods of data presentation are discussed also. Finally, the respective accuracies of the data analyses are compared, and the impact of these data on design specifications is noted.
Propagation of Acoustic-Gravity Waves in a Temperature- and Wind-Stratified Atmosphere
Authors: Pierce Allan D.
Published: September 2005

A theory is presented that permits the study of the effects of horizontal winds on the dispersion and amplitudes of acoustic-gravity waves in the atmosphere. It is shown that the effective horizontal group velocity for a given frequency in a given normal mode depends on direction of propagation as well as on frequency and that it is not necessarily in the same direction as the horizontal-wavenumber vector. A number of useful integral theorems are derived from a variational principle and one is subsequently applied to the development of a perturbation method for the computation of wind effects on dispersion. Application of the method to a realistic example indicates that winds can appreciably alter the dispersion of the normal modes and that they should be considered in any quantitative interpretation of experimental microbarograms.
Approximation to the Diffraction of Sound by a Circular Aperture in a Rigid Wall of Finite Thickness
Authors: Wilson George P. , Soroka Walter W.
Published: September 2005

An approximate solution for the diffraction of a plane sound wave indicent normally on a circular aperture in a plane rigid wall of finite thickness is obtained by postulating rigid, massless, infinitely thin plane pistons in each end of the aperture, whose motions simulate the movement of the air particles at these positions under acoustic excitation. Plane longitudinal waves are assumed inside the aperture. Numerical solutions obtained on an IBM-7090 computer very closely coincide over a wide range of frequencies with those of much more complicated existing exact solutions. Furthermore, extensive experiments were conducted on the transmission of reverberant sound through steel pipes of various lengths and diameters inserted individually into a heavy wall between two concrete chambers of 1750 ft3 each. Measured values of reverberant sound-transmission loss through these apertures were found to agree within experimental error with those calculated from the approximate theory. Experimental results indicated that the assumption of plane-wave propagation in the aperture was valid up to values of d/λ exceeding unity, where d is the pipe diameter and λ is the wavelength of incident sound.
Velocity of Sound in Distilled Water for the Temperature Range 20°–75° C
Authors: McSkimin H. J.
Published: September 2005

The velocity of sound in distilled water has been measured over the temperature range 20°–75°C at frequencies near 60 Mc/sec, using a technique described in J. Acoust. Soc. Am. 29, 1185–1192 (1957). Additional measurements near 25°C and at 100 Mc/sec were also made. The weighted-mean velocity obtained at 25.00°C is 1496.65±0.10 m/sec and for 74.00°C is 1555.10±0.10 m/sec (maximum value). Comparisons with the literature are made.
New Method of Measuring Reverberation Time
Authors: Schroeder M. R.
Published: September 2005

A new method of measuring reverberation time is described. The method uses tone bursts (or filtered pistol shots) to excite the enclosure. A simple integral over the tone-burst response of the enclosure yields, in a single measurement, the ensemble average of the decay curves that would be obtained with bandpass-filtered noise as an excitation signal. The smooth decay curves resulting from the new method improve the accuracy of reverberation-time measurements and facilitate the detection of nonexponential decays.
Some Experimental Observations on the dc Resting Potentials in the Guinea-Pig Cochlea
Authors: Butler Robert A.
Published: September 2005

The dc gradient across the reticular lamina, which can be as large as 185 mV, represents the algebraic difference between the endocochlear potential (EP) and the negative resting potential found within the organ of Corti. During asphyxia, the decline in CM paralleled closely the decline in this dc gradient. These data suggest strongly that CM represents a modulation of both dc resting potentials. The negative resting potential was examined further. Like EP, it is most probably extracellular, since it can be recorded with glass pipettes having a tip diameter of 25 μ. It decreases as a linear function of log K+ concentration in scala tympani, and it appears to be much more resistant than EP to cochlear temperature reduction.
Localization of High-Frequency Tones
Authors: Feddersen W. E. , Sandel T. T. , Teas D. C. , Jeffress L. A.
Published: September 2005

In an earlier study, [Sandel, Teas, Fedderson, and Jeffress, J. Acoust. Soc. Am. 27, 842 (1955)] the writers attempted to correlate interaural intensity and time differences with the subject's localization response. The present paper is an extension of that work. It includes physical measurements of interaural time differences and intensity differences, and attempts to relate these differences to the localization response at a variety of frequencies. The stimuli to be localized were provided through earphones, and the subject was required to match the position (in his head) of a noise and a tone. The noise to one ear was delayed, and the tone presented with no time or phase difference. The subject adjusted the interaural level of the tone until it and the noise appeared to be in the same place. The two were presented alternately by means of a gate having a 150-msec rise and decay time.

Data from the localization judgments were then compared with the findings from the acoustical measurements of time and intensity. Several systematic trends were found and compared with results of the previous study.
Surface and Volume Sound from Boundary Layers
Authors: Meecham William C.
Published: September 2005

It is made plausible for turbulent boundary layers that surface, dipole sound is in general very much less than volume, quadrupole sound. This is so for two reasons. Firstly, the relative volume sound is increased by several orders of magnitude because of shear-flow enhancement within the boundary layer. Secondly, through the use of an image argument similar to that used in the discussion of flat layers, it is indicated that the dipole sound is reduced by a factor of (L/R)2, where L is the boundary layer thickness and R is the surface radius of curvature. A discussion of irregular, surface bumps shows that such imperfections may be the source of significantly large dipole sound. A calculation is given of low-Mach-number surface and volume sound from a rotating cylinder.
Output of a Sound Source in a Reverberation Chamber and Other Reflecting Environments
Authors: Waterhouse Richard V.
Published: September 2005

It is important to know the output of a source as a function of position in a reverberation chamber. Expressions are given for the sound power output of simple monopole and dipole sources as functions of source position in various reflecting environments. They are obtained by the use of the method of images and a general formula due to Rayleigh for the output of a number of simple sources. The cases of a dipole source near a reflecting plane and a simple source near a reflecting edge and corner are treated, and the effect of the band width of the source is considered. The results apply when the reflectors enclose the source, as in a reverberation chamber, unless the distance in wavelengths between parallel walls is small and the absorption in the enclosure is low. Some experimental data are given, and the reverberation chamber method of measuring the power output of sources is discussed. In the general case of an extended source emitting nonspherical waves near reflecting surfaces, it may be more convenient to find the variation of power output with position by experiment than by calculation.
Temporal Effects in Simultaneous Masking by White-Noise Bursts
Authors: Zwicker Eberhard
Published: September 2005

The motivation of the research described was to investigate the behavior of a masking transient that indicates that masking of a short signal pulse by a longer white-noise burst is stronger at the beginning of the masker burst than later. The threshold of signal pulses masked by masker bursts was measured as a function of different variables such as bandwidth and center frequency of the signal, delay between onset of masker and onset of signal, duration of signal and masker, level of masker, and repetition rate. The results reveal very little “overshoot” of the threshold of short pulses as a function of the ON time of the masker if the signal and the masker have the same or similar broad spectra. The overshoot increases up to 13 dB as the bandwidth of the signal decreases down to that of a tone. The size of the “overshoot” and the prior excitation seem to be related to each other. Taking this in account, the thresholds under different conditions can be calculated on the basis of detection models. The measured and the calculated values are in good agreement.
Monaural Temporary Threshold Shift following Monaural and Binaural Exposures
Authors: Hirsh Ira J.
Published: September 2005

The monaural temporary threshold shift (TTS) was measured under several experimental conditions to ascertain whether or not it depended upon whether one ear or both ears were exposed to sound. The TTS for 1000 cps is the same whether the tested ear alone or both ears simultaneously are exposed to a 1000-cps tone at 20, 80, or 100 db sensation level. There is also no difference in the initial part of the recovery curve for 1400 cps after exposure to 1000 cps at 100 db SL, but the diphasic recovery curve or “bounce” is clear only after monaural exposure, not after binaural. The TTS for 4000 cps after a 3-min exposure to white noise at 110 db SPL also shows little or no difference between monaural and binaural exposure. Somewhat different conclusions are reached if one separates the TTS for the less susceptible ear of all listeners from the more susceptible ear. The less susceptible ear shows more TTS after binaural exposure than after monaural, while the more susceptible ear shows less TTS after the binaural exposure.
What is Masking?
Authors: Tanner Wilson P.
Published: September 2005

Three experiments are presented and analyzed in terms of a conventional definition of masking and a masking index conforming to this definition. It is demonstrated that, even though all of these experiments yield data permitting calculation of the masking index, at least three distinct processes lead to these data: signal masking, distortion of the sound wave form, and listener distraction. Either masking theories should take these three processes into account, or masking should be redefined.
Comparison of Hearing Thresholds in Air and in Water
Authors: Wainwright Walter N.
Published: September 2005

Hearing thresholds were measured for two subjects over a frequency range of 250 cps to 4000 cps. These measurements were made both in air and in water. When threshold intensity levels are compared, it is shown that the greatest loss in hearing acuity in water occurred over the frequency range from 500 cps to 2000 cps and amounted to approximately 20 db, while below 300 cps the threshold intensity in water was lower than that in air. Measured intensity levels for an underwater swimmer speaking into a face mask are also presented.
Binaural Summation of the Acoustic Reflex
Authors: Simmons F. Blair
Published: September 2005

The gain in sensitivity of the middle-ear-muscle acoustic reflex with binaural, as opposed to monaural, exaltation was studied in awake cats. Measurements were obtained with electrodes permanently implanted on the round-window membrane and in the muscles themselves. Summation at reflex threshold occurred only with tones of similar frequency and was most marked at low frequencies. For binaural tones considerably above reflex threshold, summation was most marked for the most dissimilar frequencies measured—1 and 8 kc/sec.
Effect of Auditory Cue on Discrimination of Auditory Stimuli
Authors: Veniar Florence A.
Published: September 2005

This report presents the results of an investigation dealing with (1) signal discrimination as a function of frequency range of the stimulus ensemble, and (2) the effect of auditory cue on discrimination of auditory stimuli as a function of frequency differences between cues and subsequent stimuli.

Data are presented for three observers. The results obtained are compared with predictions based upon the null hypothesis and a narrow-band scanning model.
Variations of the Ultrasonic Pulse-Superposition Method for Increasing the Sensitivity of Delay-Time Measurements
Authors: McSkimin H. J.
Published: September 2005

A number of methods are described for increasing the sensitivity of a measuring technique that has proven to be particularly useful for determining 3rd-order moduli and other quantities from measured changes in ultrasonic delay times [J. Acoust. Soc. Am. 33, 12 16(1961)]. Pulse cancellation, phase comparison, and methods involving either pulse position or frequency modulation have been examined. Two of the circuits developed are amenable to automatic frequency control, with precisions better than one part in 106.
Studies on the Near Fields of Monopole and Dipole Acoustic Sources
Authors: Horton C. W. , Sobey A. E.
Published: September 2005

It is shown that when an observer is not farther than one wavelength from an acoustic source, he can determine the distance to the source from measurements of the pressure and of the particle velocity of the medium. The expressions are developed using integrals of the power so that they are relatively insensitive to the pulse shape. Exact expressions are obtainable only in the case of a monopole source. However, a ratio R2 is introduced which shows a monotonic dependence on distance in the near field and which is surprisingly insensitive to the nature of the source and to the shape of the wave. Experimental measurements are carried out for a dipole source. Agreement between the theory and the experiment is only moderate because of the difficulty in making sufficiently accurate acoustic measurements.
Acoustic Absorption Coefficients of the Surface of Laboratory Animals
Authors: Ackerman Eugene , Farwell Robert W. , Oda Fujio , Anthony Adam
Published: September 2005

Sound absorption measurements on haired mice, hairless mice, rats, and guinea pigs have been made using reverberation chambers. The initial reverberation-time experiments on haired and hairless mice were conducted in a cylindrical chamber using a Brüel and Kjaer recorder. Later measurements on all types of animals were made in an asymmetrical chamber using an oscilloscope and an electronic counter. The absorption coefficients were measured in the frequency band from 1 to 20 kc. All experiments showed that the absorption coefficients rise between 6 and 20 kc. Those for the haired animals approach 100%. Hairless mice had lower absorption coefficients approaching 20% at 20 kc.
On the Dynamics of a Bull Whip
Authors: Bernstein B. , Hall D. A. , Trent H. M.
Published: September 2005

The production of a cracking sound by a bull whip is discussed. Photographic evidence shows that the crack is produced by the tip of the whip exceeding the speed of sound and giving off shock waves rather than by the whip slapping itself. This evidence includes motion pictures as well as still shadow pictures which show the tip shedding shock waves. There follows a mathematical discussion of an idealized bull whip with a view to the problem of how the free end of this mechanism achieves a high velocity while the end held in the hand moves relatively slowly. A mathematical solution is given in which it is assumed that a discontinuity in tension propagates down the whip.
Contour Vibrations of Thin Rectangular Plates
Authors: Onoe Morio
Published: September 2005

An approximate theory based on an energy principle has been applied for contour vibrations of rectangular plates and compared with experimental data of ADP Z-45° cuts with a satisfactory agreement.

The existence of a special mode, which has attracted little attention heretofore, is shown and its connection with the complex branches of the dispersion equation is discussed.
Effect of Third-Formant Transitions on the Perception of the Voiced Stop Consonants
Authors: Harris Katherine Safford , Hoffman Howard S. , Liberman Alvin M. , Delattre Pierre C. , Cooper Franklin S.
Published: September 2005

Experiments using synthetic speech show that third-formant transitions are cues for the perception of /b,d,g/. Detailed results are presented for a variety of third-formant transitions paired with each of a number of second-formant transitions in initial position before the vowels, /i/ and /æ/.

The results obtained with various third-formant transitions depend in part on the steady-state level of the third formant, implying the existence of third-formant loci analogous to those previously found for the first and second formants. The data of the present experiment are not sufficient to permit a specification of these loci.

The effects of third-formant cues are independent of the two-formant patterns to which they are added. When a third-formant cue enhances the perception of a particular phoneme, it typically does not do so equally at the expense of the other response alternatives.
Masking of Speech by Noise at High Sound Levels
Authors: Pollack Irwin , Pickett J. M.
Published: September 2005

Speech intelligibility was examined at high noise levels for a range of speech and noise spectra. Over a wide range of conditions, deterioration of speech intelligibility was observed with a constant speech-to-noise (S/N) ratio at high noise levels. Little change in intelligibility was observed for over-all speech levels to 130 db in the absence of background noise. Control tests ruled out distortion within the equipment as the factor associated with the loss of speech intelligibility.
Frequency Dependence of Echoes from Bodies of Different Shapes
Authors: Hickling R.
Published: September 2005

The echo returned by a body is known to be frequency dependent if the incident sound has wavelengths greater than or comparable with the over-all dimensions of the body. Unfortunately, a theoretical investigation into such a dependence involves lengthy computation since exact mathematical solutions are required. In this paper the results are presented of calculations which determine the echoes from the end-on aspect of a rigid prolate spheroid of fineness ratio 5/3 and from the beam-on aspect of an infinite circular cylinder, the incident sound consisting of plane monochromatic waves. These are compared with similar known results for a sphere. It is shown for these particular examples that the frequency dependence of the echo varies significantly with the shape of the body which returns the echo. It is suggested that bats use such properties in determining the form of their surroundings.
Variational Method for the Vibrations of the Indian Drums
Authors: Sarojini T. , Rahman A.
Published: September 2005

The frequencies of the lower modes of vibration of the Indian drums, the right- and left-hand thabalas which have circular drumheads loaded concentrically in the former and eccentrically in the latter have been computed by the method of variation of parameters incorporating the variation of the surface density of the drumheads in the normalizing integral. The boundary value problem is first formulated in terms of a modified form of bipolar coordinates suitable for the eccentrically loaded left-hand thabala, the boundary value problem of the right-hand thabala being obtained as a special case when the eccentricity parameter vanishes. It is then shown that the harmonic character of the modes of vibration is primarily determined by the ratio of the radii of the loaded and unloaded regions, the eccentric placement of the loaded region in the left-hand thabala merely bringing about a small separation between the frequencies of the even and odd modes.

The computed frequencies are compared with previous calculations. In the case of the right-hand thabala where exact values are known the agreement is as good as 1% and in the case of the left-hand thabala where only approximate values are known the agreement is about 10%.
Endolymphatic Oxygen Tension in the Cochlea of the Guinea Pig
Authors: Misrahy George A. , Hildreth Kenneth M. , Shinabarger Edward W. , Clark Leland C. , Rice Edward A.
Published: September 2005

Oxygen tension of the endolymph in the scala media of the guinea pig cochlea was measured using a micro-polarographic technique. Near the stria vascular is the oxygen tension was 55 to 70 mm Hg. Deeper in the scala media it decreased gradually to 16 to 25 mm Hg. Effects of sound, hypoxia, hyperoxia, and hypercapnea were studied. Oxygen tension decreased with hypoxia and sound, and it increased with hyperoxia and hypercapnea. A technique to check the integrity of a metallic-plated microelectrode is described.
Confidence Ratings, Message Reception, and the Receiver Operating Characteristic
Authors: Pollack Irwin , Decker Louis R.
Published: September 2005

A rating scale was added to the standard articulation test procedure in order to obtain independent information about a listener's criterion for message acceptance or rejection. We find that assignment of confidence ratings does not interfere with the accuracy of message reception. The form of the receiver operating characteristic—the relationship between correct confirmations and false alarms—yielded by the rating procedure is similar to that yielded by a binary decision of message acceptance or rejection. In addition, the confidence rating is directly related to the average accuracy of message reception. This relationship is relatively invariant over a range of speech-to-noise ratios.
Temporary Threshold Shifts following Monaural and Binaural Exposure
Authors: Ward W. Dixon
Published: September 2005

The temporary threshold shifts (TTS) following monaural and binaural exposure to three different high-intensity stimuli were compared in 49 listeners. In all cases, the binaural exposures produced less TTS than the monaural, though the difference was greatest at lower frequencies. Results are interpreted to indicate that the middle-ear muscles contract more vigorously for binaural exposure than for monaural, thus producing more reduction of the effective intensity of lower-frequency stimulus components. However, the possibility of influences exerted by efferent or cochleo-cochlear systems cannot be ruled out. The relation of these results to the fact that industrial hearing loss first develops at 4000 cps is discussed.
Funneling in the Nervous System and its Role in Loudness and Sensation Intensity on the Skin
Authors: v. Békésy G.
Published: September 2005

The relation between the subjective intensity of a vibration on the skin and the physical amplitude of the vibration is different for the different parts of the skin, for example, the finger tip and the shoulder. The reason for this is that the sensation of vibration “loudness” is a complex interaction of summation and inhibition along the stimulated skin surface. Both summation and inhibition vary with the amplitude of the vibration, the distance between the stimulated areas, the slope of the spatial distribution of the stimulus along the surface of the skin, its time pattern, and the density of the innervation. I have tried to describe these relations as variations in “funneling action” of the nervous tissues in the hope that this terminology will lead to a better understanding of the various phenomena.

A series of experiments was designed to establish rules for the estimation of the funneling action. For this purpose (1) the vibration loudness produced by a point vibrator was compared with the loudness produced by stimulation of a large area of skin (which may serve to explain why the curves of equal loudness for pure tones in hearing are compressed at the low frequencies); (2) the difference limen for amplitude variations was investigated under different conditions; (3) the lateral spread of the skin sensations was determined; and (4) all these phenomena were compared with analogous sensations in hearing. Through the concept of funneling, rotating skin sensations are brought into very close relation with rotating tones (Drehtön), and Mach's law of contrast in vision with a similar phenomenon of the “funneling” action observed on the skin. Finally, it is demonstrated by experiments that once a funneling action is established on the skin, there is a certain period of time during which it inhibits all other sensation, exactly as in hearing. It is very similar to the refractory period of the nerves. These refractory times are considerably longer when the funneling action takes place at the higher levels of the brain.
Creation of Pitch through Binaural Interaction
Authors: Cramer Elliot M. , Huggins W. H.
Published: September 2005

This paper is an investigation of the phenomenon which was observed by Huggins in 1953. Huggins found that a binaural stimulus gives a fairly clear perception of pitch although the separate stimuli to the two ears give no such perception. The basic stimulus consists of white noise introduced into one ear while the same white noise, phase transformed in a narrow band of frequencies, is introduced into the other ear. A practiced subject listening to this stimulus reports a faint pitch quality which is judged to sound about the same as narrow-band filtered noise. A forced-choice technique was used in which six subjects were asked to judge the direction of the pitch change when the frequency band over which the phase shift occurs was changed. The control consisted of the same stimulus presented to the two ears. Data are presented indicating the relationship between the percent of correct judgments and the three experimental variables, frequency, band width, and intensity level.
Confidence Ratings and Message Reception for Filtered Speech
Authors: Decker Louis , Pollack Irwin
Published: September 2005

The statistical decision model, which has achieved outstanding success in describing the detection of signals in noise was applied to the reception of filtered speech. A confidence rating was added to the articulation test procedure in order to obtain additional information about the listener's criterion of message acceptance and message rejection of filtered speech. The relation between correct confirmations and false alarms—the Receiver Operating Characteristic—obtained with filtered speech corresponds with that typically obtained with noise interference. It is suggested that the “noise” of the decision model may be extended to a wide range of operations which perturb the signal.
Effect of High Pressure on Sound Absorption and Chemical Equilibrium
Authors: Fisher F. H.
Published: September 2005

Interest in acquiring more definite knowledge of the mechanism of sound absorption in electrolytic solutions led to this experimental investigation of the pressure dependence of this phenomenon. A technique was evolved to measure sound absorption in liquids as a function of pressure at frequencies of 100–600 kc. The following properties of a 0.5-molar solution of MgSO4 were measured up to 20 000 psi at 26°C: absorption, relaxation frequency and velocity. The absorption at 20 000 psi is less than one quarter that at atmospheric pressure and the relaxation frequency remains constant at 1.2×106 rad/sec over this pressure interval within the estimated experimental error of ±10%. The velocity increases linearly with pressure at the rate 0.1588 m/atmos. From these data the chemical and adiabatic compressibilities are computed.

In an effort to secure quantitative agreement with experimental results some new aspects of the dissociation theory are discussed.
Averaging Time and Data-Reduction Time for Random Vibration Spectra. I
Authors: Morrow Charles T.
Published: September 2005

Most narrow-band-width wave analyzers currently available on the market were designed for producing spectra of periodic signals. When they are applied to producing spectra for low-frequency random signals such as occur in vibration, a longer averaging time must be provided on the output side of the detector circuit to average out fluctuations and yield data of satisfactory statistical significance. The application of standard statistical techniques in relation to the band width of the selective circuit provides design data for averaging circuits to be added as modifications to existing analyzers. Proper averaging time carries with it a requirement of a slower sweep rate and hence greatly increases the time required for producing a spectrum. Techniques and apparatus for producing a spectrum in a decreased time interval are discussed.
Experimental Hydrophone-Size Correction Factor for Boundary-Layer Pressure Fluctuations
Authors: Gilchrist Richard B. , Strawderman Wayne A.
Published: September 2005

The results of some experimental measurements, made to determine the hydrophone-size correction factor, are presented and compared with the theoretical results of Corcos. The measurements agree with Corcos' theoretical hydrophone-size correction factors over the range of Strouhal numbers, from 0.01 to 4.0, covered by the experiment. In addition, a practical method of determining effective hydrophone size is presented.
Elastic Strain Produced by Sudden Application of Pressure to One End of a Cylindrical Bar. II. Experimental Observations
Authors: Fox George , Curtis C. W.
Published: September 2005

Measurements are presented which show that the elastic strain produced in a cylindrical bar by step-function end-loading corresponds closely to predictions of the theory presented in Part I. In particular, even at large distances from the end of the bar, there is an observable strain moving faster than the bar velocity determined by Young's modulus. The theoretical shape for the head of the pulse conforms to experiment, and the head is followed by oscillations having the correct periods and amplitudes. Second-mode oscillations appear at the times predicted and with the expected periods and amplitudes.
Temperature- and Wind-Dependent Ambient Noise under Midwinter Pack Ice
Authors: Ganton J. H. , Milne A. R.
Published: September 2005

Measurements of ambient noise under shore fast pack ice during winter revealed two distinct noise-producing mechanisms. One mechanism was the production of tensile cracks at the surface of the sea ice by thermal stresses caused by decreasing air temperatures. The resulting ice-cracking sounds produced impulsive noise. The second mechanism was the interaction of the granular ice surface with the wind, which produced Gaussian noise. Separate pressure spectra are presented for underwater noise generated by each mechanism. The spectra and the statistical properties of the underwater noise appeared to be related to the local meteorology and the temperature changes within the ice cover.
Pitch Ratings of Voiced and Whispered Vowels
Authors: Harbold George J.
Published: September 2005

The problem was to investigate listener judgments of voiced and whispered vowels in an effort to compare relative pitch of voiced and whispered speech. The results indicate, at least for those vowels that showed significant differences, that tonality may not be the sole determinant of listeners' pitch judgments. A comparison of rank orders of the present study and rank order from a previous investigation provided further support to the hypothesis that relative pitch of vowels is not independent of the vowel itself.
Effect of Pressure on Ultrasonic Relaxation in Electrolytes
Authors: Carnevale E. H. , Litovitz T. A.
Published: September 2005

Measurements of the ultrasonic absorption and velocity were made on aqueous solutions of ammonia up to pressures of 2030 kg/cm2. The results show that the absorption decreases and the relaxation frequency increases as the pressure is raised. The data are consistent with the assumptions of Eigen that the excess sound absorption is due to a chemical relaxation effect brought about by the lag in the shift in the equilibrium NH3⋅H2O⇌NH4++OH−, and that the rate of the reaction is diffusion controlled.
Experiments with an Inverted Pendulum Subject to Random Parametric Excitation
Authors: Bogdanoff J. L. , Citron S. J.
Published: September 2005

Experimental results are presented that verify the theoretical conclusion that an inverted pendulum may be stabilized with second-order stationary, random parametric excitation having a discrete-power spectral density. Experiments also verified that the theoretical condition on frequency spacing is critical.
Gravest Contour Vibration of Thin Anisotropic Circular Plates
Authors: Onoe Morio
Published: September 2005

In a previous paper [J. Acoust. Soc. Am. 28, 1158 (1956)], it was shown that the gravest mode of contour vibration of an isotropic thin circular plate has the circumferential order of two and is mostly equivoluminal in nature. Although the exact expression of the displacements includes Bessel functions, it can be reasonably approximated by a simple combination of trigonometric functions, which makes it possible to handle the anisotropic case. Since the mode is the gravest, Rayleigh's principle is applied in a procedure of approximation, taking an angle of rotation and a wave number as adjusting parameters.

The results are compared with experiments of quartz vibrators. Calculated frequencies show agreement better than 1% with an exact value for isotropic plates and an observed value for a rotated Y cut of quartz, which has a limited anisotropy. The accuracy decreases as the degree of anisotropy increases. For the X cut of quartz, the calculated value is 4.7% higher than an observed value.

One of the significant characteristics of the mode of vibration of an anisotropic plate is the fact that the direction of maximum displacement makes a certain angle with a crystallographic axis. The calculated value of this angle agrees exactly with the observed angle for the rotated Y cut of quartz and within a few degrees for the case of the X cut of quartz.

Equivalent electric circuit constants and surface patterns of piezoelectrically induced charges are also calculated and compared with experiments.
Changes in Cochlear Endolymphatic Oxygen Availability, Action Potential, and Microphonics during and following Asphyxia, Hypoxia, and Exposure to Loud Sounds
Authors: Misrahy G. A. , Shinabarger E. W. , Arnold J. E.
Published: September 2005

In order to evaluate the role played by endolymphatic hypoxia on deafness due to exposure to loud sounds, continuous recordings of oxygen availability, action potential, and microphonics were taken during asphyxia, “chronic hypoxia,” and after loud sounds. The curves so obtained are compared and show that hypoxia may play an important contributory role in the temporary losses of heating following loud sounds. Possible mechanisms of auditory trauma are reviewed briefly.
Elastic Wave Scattering at a Cylindrical Discontinuity in a Solid
Authors: White R. M.
Published: September 2005

This study deals with the scattering of plane compressional and shear elastic waves incident obliquely on an infinitely long nondissipative cylindrical elastic discontinuity in an isotropic solid. Equations whose solutions are the coefficients in series expressions for the scattered waves are derived for the case of scattering at an elastic solid cylinder embedded in a different solid medium. From these equations are obtained those governing scattering at a fluid-filled cylindrical bore, and at an empty bore.

In general, when a wave of either the compressional or shear type is incident on an elastic discontinuity, scattered waves of both types are produced, a process known as “mode conversion.” A simple relation is shown to exist between the two far-zone distributions-in-angle, and between the two scattering cross sections for the waves undergoing mode conversion in the scattering of compressional and normally polarized shear waves incident normally upon either a fluid-filled or an empty bore.

For an empty bore whose diameter was comparable with a wavelength in the solid, computed distributions-in-angle for the scattering of normally incident compressional and normally polarized shear waves were verified experimentally. Measurements were also made of the scattering of compressional waves at a fluid-filled bore in a solid, and of the far-zone directivity patterns of some compressional and shear wave piezoelectric source crystals radiating into a solid medium.
Investigation of Structure-Borne Active Vibration Dampers
Authors: Rockwell T. H.
Published: September 2005

The use of active feedback elements to produce damping of multiresonant structures has been extended to include the case in which the damping-force generator is supported by the structure being damped. A theoretical damping equation is developed and experimental verification is obtained for the particular case of a uniform aluminum beam damped at its midpoint. In this structure-borne configuration, the active damper is potentially applicable to a wider variety of vibration problems because external support for the damping-force generator is no longer necessary. When applied to the uniform beam, an experimental structure-borne damper demonstrated damping bandwidth in excess of 10 kc/sec and equivalent loss factors of up to 0.22 for resonant frequencies below 2 kc/sec.
Ultrasonic Energy Generated by Sandblast
Authors: Suckling E. E.
Published: September 2005

A blast of sand on a steel plate produces ultrasonic radiation detected by a quartz crystal.
Measurement of Noise Sources in Ducts
Authors: Dyer Ira
Published: September 2005

Recently Kerka, and earlier Beranek, Reynolds, and Wilson, discussed the measurement of sound power radiated by a fan in a straight duct, by measurements of the sound pressure inside the duct. A difficulty associated with this technique is that above a certain frequency the sound pressure varies markedly across transverse section of the duct and the relation between mean square pressure and power is not simple. The transverse variation can be understood by application of mode theory to propagation of noise in the duct. In the theory it is assumed that the noise source is purely random and of low internal impedance. Propagation in the various duet modes is shown to be statistically independent, and to give rise to equipartition of energy in the limit of high frequencies. The theory agrees well with measurements reported by Kerka. With the use of the theory, it is possible to select measurement positions inside the duct such that the mean square pressure is related to the power flow by the simple plane-wave equation.
Detection of Random Acoustic Signals by Receivers with Distributed Elements: Optimum Receiver Structures for Normal Signal and Noise Fields
Authors: Middleton David , Groginsky Herbert L.
Published: September 2005

This paper deals with the passive detection of noiselike signals in the presence of both external (environmental) noise and self-generated (receiver) noise, using an array of transducers. Starting with the Bayesian formulation of the general detection problem, a set of matrix integral equations is derived whose solution yields the optimum detector function. By regarding the resultant time-varying filters as operators and the defining matrix integral equations as a set of operational equations, it is possible to examine the underlying structure of the optimum detector most easily. It is shown, thereby, that factorization of the space-time operations (i.e., separation of the required filter into two successive operations—the first depending only on the geometry of the array, the second depending only on the statistics of the noise processes) is not, in general, possible in optimum systems. Only in the strong-signal case has it been possible to show that factorization analogous to conventional beam forming can be utilized in optimum array detection. Another interesting conclusion is that an optimum detector is not superdirective in the limiting case of strong external directive noise.
Remote Masking in the Absence of Intra-aural Muscles
Authors: Bilger Robert C.
Published: September 2005

To ascertain the rôle of the stapedial reflex in remote masking, remote and contralateral remote masking were studied on separate groups of listeners who had had their stapedius muscles excised surgically. In addition, separate groups of listeners who had audiometrically and otoscopically normal ears were used to obtain control data. The results of these studies show that neither remote nor contralateral remote masking depends upon the stapedial reflex; both, however, do vary with degree of hearing loss. In the case of remote masking, an orderly relation was found to exist between the amount of remote masking and the sensation level (SL) of the masker [re hearing levels (HL) at 1000 and 1500 cps]. This, along with exaggerated remote masking in cases of sensorineural loss, supports the earlier explanations of remote masking solely in terms of cochlear mechanics. For contralateral remote masking, the relationship between masking and hearing loss was not as orderly as that for remote masking. The absence of a systematic relationship between SL of the masker and onset or amount of contralateral remote masking suggests it to be a central rather than a peripheral phenomenon.
Scattering of Sound by a Rigid Movable Sphere
Authors: Hickling Robert , Wang N. M.
Published: September 2005

The echoes from a rigid, freely movable sphere, due to an incident train of plane waves, are computed, together with the associated rigid-body motions of the sphere. These results are compared with those for a rigid, immovable sphere and it is shown that they differ significantly only for values of ka below about 5. The significance of the results in relation to previous work on sonar echoes from solid, elastic spheres in water is discussed. A particular case of forced motion of the rigid sphere, where the echoes diminish to zero at high frequencies, is also investigated.
Extension to the Theory of Howlback in Reverberant Rooms
Authors: Antman Herbert S.
Published: September 2005

A method of evaluating response time of a public address system is suggested utilizing electrical network feedback theory.
Hazardous Exposure to Intermittent and Steady-State Noise
Authors: Kryter K. D. , Ward W. Dixon , Miller James D. , Eldredge Donald H.
Published: September 2005

The following document was prepared by NAS-NRC CHABA Working Group 46. This group was asked to specify damage-risk criteria for exposure to sound. The paper contains graphs of maximum sound-pressure levels and durations of exposures that the Working Group believes would be tolerable and examples of the use of these graphs in addition to background information and a discussion of the rationale, assumptions, limitations, and general problems pertinent to the development and application of a damage-risk criterion and related exposure contours.
Further Study of the Isopreference Method of Circuit Evaluation
Authors: Tedford W. H. , Frazier T. V.
Published: September 2005

Experimental evidence is presented in support of the isopreference method for evaluating speech-transmission circuits. The method, originally proposed by Munson and Karlin, [J. Acoust. Soc. Am. 34, 762–774 (1962)], derives a one-dimensional scale suitable for use in rating communication circuits. This study is a similar experiment using a larger number of subjects. It demonstrates that the method is reproducible even for circuits of poorer quality than those originally investigated. It also suggests several improvements in technique.
General Reciprocity Parameter
Authors: Bobber Robert J.
Published: September 2005

The reciprocity parameter used in the reciprocity calibration of electroacoustic transducers is derived for the general case of arbitrary boundary conditions and arbitrary definitions of responses. A general reciprocity parameter is defined as the ratio of the volume velocity emanating from a surface defined in the transmitting response to the resulting pressure averaged over a surface defined in the receiving response. It is shown how the general parameter concept leads directly and simply to the various special parameters for the cases of spherical waves, cylindrical waves, plane waves, diffuse sound, couplers, and tubes. Application of the concept to in situ and nearfield conditions is also described.
Linear versus Logarithmic Averaging
Authors: Cox Henry
Published: September 2005

Consider n data samples {x1, ⋯, xn} such that o<L⩽xi⩽U < ∞. Let K = U/L; then it is shown that independent of n a lower bound on the ratio of the geometric mean to the arithmetic mean of the data samples is given by [lnK/(K − 1)]K{(1/lnK)−1/(K−1)}. This bound is useful in acoustic signal processing since it limits the amount of deviation that can be attributed to averaging logarithms vice taking the logarithm of the average of data samples. Both methods are currently in use at facilities specializing the processing of acoustic data. For a K of 10 dB, for example, the geometric mean is less than 1.5 dB below the arithmetic mean.