bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Halving and Doubling of the Loudness of White Noise
Authors: Poulton E. C. , Stevens S. S.
Published: September 2005

The decibel changes required to halve and to double the apparent loudness of a white noise were determined at nine sound pressure levels by 36 subjects. The subjects adjusted the level of the noise by means of an improved control—a “sone potentiometer” whose angular turn is roughly proportional to the loudness produced. An attempt was also made to measure and control some of the biasing factors that affect loudness estimations. Results: the median decibel changes required to produce a 2:1 loudness ratio ranged from 6 to 10 db, approximately.
Masking by a Periodically Interrupted Noise
Authors: Pollack Irwin
Published: September 2005

A scale of noise intermittancy may be represented at one extreme by a continuous noninterrupted noise and, on the other extreme, by an interrupted noise with silent intervals between successive noise bursts. The differential characteristic for various conditions along this scale is the noise level in the interval between successive noise bursts (the inter-burst level). The effects of a wide range of periodically intermittant noise conditions upon the masked threshold of a tone and the intelligibility of speech were examined. The principal result of these tests is that the masked threshold associated with an intermittant noise can be closely described by two functions: (1) the masking produced by an interrupted noise with silent intervals between successive noise bursts, and, (2) the masking produced by a continuous uninterrupted noise at the inter-burst level.
Intelligibility of Peak-Clipped Speech at High Noise Levels
Authors: Pollack Irwin , Pickett J. M.
Published: September 2005

The effect of symmetrical speech peak clipping upon speech intelligibility in noise was examined. Over a wide range of conditions, intelligibility is independent of the level of peak clipping if the postclipping speech power is held constant. Peak clipping thus achieves protection of the ear against painfully loud speech without demanding penalty of intelligibility. Indeed, under restricted ranges of conditions, peak clipping may actually improve intelligibility with a constant speech power.
Diffraction of Light by Ultrasonic Waves Progressing with Finite but Moderate Amplitudes in Liquids
Authors: Zankel K. L. , Hiedemann E. A.
Published: September 2005

The study of the asymmetry of the light diffracted by ultrasonic waves progressing with moderate amplitudes in liquids is used to detect and measure the finite amplitude distortion in water and carbon tetrachloride. A theory is developed which relates the distortion present to available isothermal compressibility measurements. This development includes the presence of absorption.

Measurements of the second harmonic were made in water at 2 Mc and 4 Mc, at distances up to 50 cm, and at peak ultrasonic pressures between zero and 1.5 atmos. More detailed measurements were made in carbon tetrachloride at frequencies of 2 and 3 Mc, at distances up to 21 cm, and at pressures up to 0.7 atmos. For both liquids, good agreement is obtained between the experimentally measured values and the theoretically predicted results.

Small amounts of distortion were easily measured. The second harmonic could be measured when the intensity of the harmonic was less than 0.04% of the intensity of the fundamental. Distortion could be measured when the fundamental was much less than 0.2 atmos.
Cavitation Microstreaming
Authors: Elder Samuel A.
Published: September 2005

In the research reported here an attempt has been made to discover by experiment what physical assumptions and approximations are appropriate in the theory of cavitation microstreaming, especially for cavitation bubbles located near solid boundaries. A systematic investigation of the phenomenon has been made and its dependence on certain parameters (e.g., amplitude of sound) has been determined. The investigation has disclosed that as the sound amplitude is varied, other conditions remaining the same, the streaming changes discontinuously through several stable regimes. It appears that in order to account for the generation of vorticity one needs to assume different conditions at the boundaries for each regime. For at least one regime, a theoretical model due to Nyborg seems to be applicable; comparison made with experimentally determined streaming velocities.
Statistical Evaluation of Near-Field Sound Pressures Generated by the Exhaust of a High-Performance Jet Engine
Authors: Kamps Edwin C.
Published: September 2005

The operation of modern, high-performance turbojet engines creates an environment that promotes rapid structural fatigue in many areas in jet aircraft. To facilitate the simulation of a valid test environment and, therefore, enable fatigue resistant structure to be readily developed, the characteristics of the near-field sound pressures created by the jet stream must be established. This study is concerned with the establishment of the level and the rate of occurrence of peak pressures in relation to the commonly measured rms level. A method is presented which enables the determination of these qualities from rms sound pressures recorded on magnetic tape. Also included are typical results obtained from near-field sound pressures generated by the jet exhaust of a General Electric CJ805 turbojet engine. Noted conclusions: (1) Occurrence of peak pressures does not follow a Rayleigh Distribution. (2) Peak pressure distribution is not altered by the physical position related to the jet stream nor does it appear to be a function of frequency. (3) A maximum ratio of peak to rms pressure is shown to exceed four, but a physical limit is not established.
On the Acoustics of Cocktail Parties
Authors: MacLean William R.
Published: September 2005

Parties are classified as loud or quiet, and the distinction is shown to depend often upon a critical acoustic relationship rather than upon the guests themselves. An explicit formula is found for the maximum number N of well-mannered guests compatible with the quiet party. When this number is exceeded, the party will become a loud one within a calculable time T.
Binaural Communication Systems: Preliminary Examination
Authors: Pollack Irwin
Published: September 2005

The principle of a communication system which purchases additional channels by shifting selective operations from equipments to human operators is examined. For selected conditions, the system may perform adequately for low-priority communications.
Capacitance-Type Displacement Probe
Authors: Shattuck Russell D.
Published: September 2005

A noncontacting displacement probe is described which is linear throughout the audio-frequency range over a wide displacement amplitude range. The instrument employs commercially available condenser microphone circuitry to measure the displacement of any conducting surface. Entirely conventional audio-instrumentation may be employed to analyze test data obtained with the probe. A typical output voltage, with the gauge located 0.1 in. from the vibrating member is 25 mv for a 0.001-in. displacement amplitude. A simple accessory is described for checking the instrumentation sensitivity.
Hydrophone Minor Lobes Produced by Volume Scattering
Authors: Bell Thaddeus G.
Published: September 2005

Volume scattering the ocean determines the lower limit to what can be achieved in a hydrophone's in situ minor lobe response. This paper makes theoretical examination of the magnitude of minor lobes produced by volume scattering. It is concluded that for a directional hydrophone of moderate-to-high directivity, the relative minor lobe response due to volume scattering is given to a close approximation by the product of the scattering cross section and the distance to source divided by the directivity factor. Direction of source has a comparatively small effect. Attenuation constant may be neglected unless the attenuation loss between source and hydrophone is larger than 1 db or so.
Discrimination of Number of Simultaneously Sounding Tones
Authors: Thurlow Willard R. , Rawlings Irving L.
Published: September 2005

The aim of tim present experiments was to investigate the accuracy with which the number of simultaneously sounding tones can be perceived. Various one-, two-, and three-tone stimuli were presented to subjects, who had to judge how many tones were present. Results showed that discrimination of number of different tones sounding was far from perfect (even though Ohm's acoustic law would lead us to expect high accuracy). The discrimination of the average person was not improved even when frequency components were widely spaced. Accuracy of perception was poorer for two- and three-tone combinations than for one-tone stimuli. Number of allowable response categories also affected percent correct responses. Individual differences in performance were found to be large.
Continuity Effects with Alternately Sounding Tones
Authors: Thurlow Willard R. , Elfner Lloyd F.
Published: September 2005

The present experiments investigated the conditions under which one of two alternating tones can be made to sound continuous. When one tone, B, of 21-msec duration, was sounded alternately with a tone, A, 11.3 times per sec, tone A appeared to sound continuous if tone B was made 10 to 20 db higher in sensation level than tone A. The intensity required to produce the “continuity” effect was found to be least when tone B was near to tone A in frequency.

The continuity of tone A could be broken, however, by increasing the off-time of tone A (which also increased the on-time of tone B). To measure this more precisely, duration of interruption (off-time) of tone A was varied, and continuity thresholds were obtained for tone A alternating with tone B, when B was set near in frequency to A and at 15 db higher sensation level. It was found that tone A sounded continuous with longer off-times when tone B was present during the interruptions than when it was absent. Certain of these thresholds varied as a function of the rate at which tones A and B were alternated.
Effect of Ultrasonic Waves on Concentration Gradients
Authors: Penn Robert , Yeager Ernest , Hovorka Frank
Published: September 2005

Schlieren techniques have been used to study the effects of ultrasonic waves on concentration gradients produced by electrochemical methods. With standing waves at intensities below cavitation levels, the zones of depleted electrolyte at the cathode stratify at the displacement nodes of the standing waves while the zones of excess electrolyte at the anode stratify at the displacement loops. These stratification effects provide an explanation for the ripples produced on the surfaces of metals electrodeposited in standing waves.

Microschlieren techniques indicate that ultrasonic waves at cavitation levels reduce the effective thickness of the diffusion layer at an electrode to a value of 10−3 cm or less. The mechanism for the disruption of the gradients is believed to involve the microdisturbances associated with cavitation bubbles at or near the electrode surface.
Application of Counter-Chronograph Technique to Measurement of Sonic Velocities
Authors: Hashmi S. Z. R. , Khan S. A. , Ali I.
Published: September 2005

Counter-chronograph technique, familiar in other fields, is applied to the measurement of sonic velocities. The method can also be utilized for nondestructive testing of concrete and other specimens.
Detection of a Pulsed Sinusoid in Noise as a Function of Frequency
Authors: Green David M. , McKey Mary J. , Licklider J. C. R.
Published: September 2005

The detectability of a pulsed sinusoid (0.1 sec) in white noise was measured at sixteen frequencies ranging from 250 to 4000 cps. The measurements are compared with the results previously obtained from experiments in which continuous sinusoids of indefinite duration were used. The dependence of detectability on frequency appears to be very similar in all the experiments. We also measured the detectability of compound signals, i.e., signals with 12 and 16 sinusoidal components. A comparison of the detectability for the single and combined sinusoids allows us to determine approximately how the auditory system sums energy over frequency.
Second-Order Instrumentation Systems with Frequency-Dependent Stiffness and Damping
Authors: Rule Eric , Suellentrop Fred J. , Perls Thomas A.
Published: September 2005

The theory of the dynamic properties of thin fluid films is reviewed and it is shown how these properties can be used to introduce frequency-dependent damping and stiffness factors into the equations governing the response of second-order instrumentation systems such as transducers for the measurement of dynamic accelerations, vibration, pressure, sound, etc. By proper design, the frequency-dependent nature of these factors can be utilized to provide substantial improvement in the frequency-response characteristics of such systems over the characteristics obtainable with the usual second-order system with constant viscous damping. For the specific case when the fluid is air at normal temperature and pressure, curves are given from which transducers can be designed to have optimum frequency-response characteristics.
Surface and Groove Noise in Disk Recording Media. I
Authors: Howling D. H.
Published: September 2005

A theoretical and experimental investigation into the causes and mechanism of playback surface and groove noise of recorded media has been made. It is shown that such noise can be considered as arising from the random superposition of voltage pulses produced by local changes in the number and size distribution of welded friction junctions or asperities supporting the playback stylus load. A generalized noise equation, involving the physical parameters of the recorded medium and the playback stylus, has been derived and shows reasonable agreement with the measured playback noise spectra for several cold-flowing and rigid plastic surfaces. From the noise equation emerges a concept of modulation noise and prediction of its dependence on modulation velocity. Examination of the playback noise level as a function of recording and playback conditions has also been included. It is also shown that surface noise measurements can be used to give information concerning the n/a ratio associated with the theory of friction.

The measured lower limit of wide band playback noise for most plastic surfaces corresponds to an equivalent rms lateral noise velocity of 10−2 cm/sec or equivalent lateral noise amplitude of 1 μin. peak at a linear velocity of 15 cm/sec. The equivalent roughness is thus half of that associated with an optical flat. Using this information, it is shown that at 1000 lines/in. information density a signal-to-noise ratio of 50 db at a linear velocity of 15 cm/sec should be realized.
Propagation of Band-Limited Noise in a Layered Wave Guide
Authors: Clay C. S.
Published: September 2005

The normal mode solution of the problem of the radiation field of a simple harmonic point source in a layered wave guide is extended to the case of a band-limited noise source. This theory is used to calculate the radiation field of a simple harmonic point source and a point noise source in shallow water over a thick layer of unconsolidated sediments, and the calculations are compared with experimental data. The experimental dependence of the acoustical pressure upon source distance is in agreement with that calculated from the theory.
Results Obtained from a Vowel Recognition Computer Program
Authors: Forgie James W. , Forgie Carma D.
Published: September 2005

As an initial step toward a general speech recognition computer program, program was developed to recognize ten English vowels in isolated words of the form |b| -vowel- |t|. The input to the computer was real-time spectral data. The program first determined the rough location of the first two formants. The remaining confusions were resolved by (1) finer determination of the F1 and F2 locations by the use of slope and/or valley information, (2) the use of pitch information, and (3) in certain cases the determination of the position of F3. The over-all score for 21 subjects (11 male and 10 female) was 88%. By the use of duration information, the score was raised to 93%.
Message Uncertainty and Message Reception
Authors: Pollack Irwin
Published: September 2005

The fundamental principle of language engineering—namely, that the probability of a correct message reception is critically dependent upon the size of the set of messages available for communications—was examined experimentally. Accuracy of message reception was found to be independent of the message-source uncertainty, but critically dependent upon the response uncertainty—or more exactly, upon the size of the set of relevant response categories. Implications for a conceptual model of the listener's behavior are suggested.
Message Repetition and Message Reception
Authors: Pollack Irwin
Published: September 2005

The improvement in word intelligibility associated with successive presentations of a word in noise was examined with recorded and with independent samples of the speech and/or its background noise. The listener's criterion for termination of a trial was shown to be a crucial determinant of the gain of intelligibility with successive presentations. The improvement in intelligibility was greater for independent samples of speech and noise than for successive presentations of a single recorded sample. The observed improvement, however, was less than predicted for the ideal observer with perfect memory by the theory of signal detectability. Indexes of response discriminability and signal discriminability are briefly discussed.
Frequency Response of an Acoustic Air-Jet Generator
Authors: Gravitt James C.
Published: September 2005

The mechanism which gives rise to the intense vibrations of an acoustic air-jet generator is investigated both experimentally and theoretically. The results indicate that the mechanism for establishing the vibrations in the generator consists of pressure instabilities in the nozzle air stream which act as the source of the forced oscillations of an air plug in the resonator cavity.
Performance of High Frequency Barium Titanate Transducers for Generating Ultrasonic Waves in Liquids
Authors: McSkimin H. J.
Published: September 2005

A study is made of high frequency (10 mc/sec) barium titanate transducers radiating into water, with band width and efficiency being of principal concern. Optimum electrical damping alone is considered; however, it is demonstrated that the introduction of an intermediate 14 wavelength thick composite mechanical element results in superior performance. Of the units constructed, the best exhibited a frequency band width (half-power points) of 44% with 4-db midband loss (equivalent insertion loss on a 2 transducer basis). Focusing radiators, as well as plane, were tested.
Some Ultrasonic Measurements in Normal and Superconducting Aluminum
Authors: Morse R. W. , Bohm H. V.
Published: September 2005

Ultrasonic attenuation measurements in an aluminum single crystal near the superconducting transition temperature are described. These include both longitudinal and shear wave attenuations at frequencies of between 11 and 58 Mc/sec and at temperatures between 1.0 and 4.2°K, as well as attenuation as a function of magnetic field in the normal state. It is found that the attenuation of shear waves at the transition temperature shows a discontinuity of about 25% of the total attenuation, this fraction being relatively independent of frequency. The longitudinal wave attenuation shows a sharp but continuous drop at the transition temperature. It is shown that the electron mean free path l can be estimated from the magnetic field dependence of the attenuation and that the condition kl<1 (k = 2π/λ, λ being the ultrasonic wavelength) holds for the measurements. The possible significance of the shear wave discontinuity is discussed.
Effective Onset Duration of Auditory Stimuli
Authors: Tobias Jerry V. , Schubert Earl D.
Published: September 2005

In analyzing interaural temporal relations, the binaural system may receive information from one or more of three separate stimulus aspects: (1) difference in time of the start of stimulation, (2) difference in time between similar portions of the continuing wave form at the two ears, and (3) difference in time of the end of stimulation. In this study, the first and third kinds of difference were combined for convenience as “transient disparity”; the second was called “ongoing disparity.” The relative effectiveness of these two temporal relations in producing changes in auditory localization was investigated by finding, for various values of transient disparity, a value of ongoing disparity that brought the sound back to center. For a given value of transient disparity, the necessary ongoing disparity value varies as a function of stimulus duration. Transient disparity loses its effectiveness for stimulus durations greater than about 150 msec. For a duration of 100 msec, it takes roughly 35 times as much transient disparity as ongoing disparity to bring the sound to center; for a duration of 30 msec, it takes about 7 times as much; and for a duration of 10 msec, 4 to 5 times as much. From the working hypothesis that the relative values of transient and ongoing disparities are directly proportional to the durations over which each cue is operative, an “effective onset duration” appears to lie between 2 and 4 msec.
On the Influence of the Diffraction of Sound Waves around the Human Head on the Characteristics of Hearing Aids
Authors: Wansdronk C.
Published: September 2005

A small hearing aid, hanging in an anechoic room is made to drive an AVC circuit, the output signal of which is conducted to a power amplifier and loudspeaker and can be recorded on a tape. During playback of this tape, with the output of the recorder connected to the power amplifier, the same sound field as existed around the hearing aid is reproduced. If the apparatus is placed on a person in the position where it is to be worn and that person is situated so that the hearing aid is at the same point as during the recording, the output of the hearing aid during playback of the tape will indicate the influence of the diffraction around the human head.

Three specimens of hearing aid were measured on different people. The results showed that there exists a large difference between the hearing aids but no fundamental differences between the persons. The curves plotted for males and females showed the same trend, and no correlation was found with the hairdress. We did not succeed in an attempt to replace the human head by a simple model, such as a wooden sphere or a wooden box, the agreement of the diffraction phenomena between model and head being too poor.
Surface and Groove Noise in Disk Recording Media. II
Authors: Howling D. H.
Published: September 2005

A theoretical and experimental investigation into the causes and mechanism of playback surface and groove noise of recorded media has been made. It is shown that such noise can be considered as arising from the random superposition of voltage pulses produced by local changes in the number and size distribution of welded friction junctions or asperities supporting the playback stylus load. A generalized noise equation, involving the physical parameters of the recorded medium and the playback stylus, has been derived and shows reasonable agreement with the measured playback noise spectra for several cold-flowing and rigid plastic surfaces. From the noise equation emerges a concept of modulation noise and prediction of its dependence on modulation velocity. Examination of the playback noise level as a function of recording and playback conditions has also been included. It is also shown that surface noise measurements can be used to give information concerning the n/a ratio associated with the theory of friction.

The measured lower limit of wide band playback noise for most plastic surfaces corresponds to an equivalent rms lateral noise velocity of 10−2 cm/sec or equivalent lateral noise amplitude of 1 microinch peak at a linear velocity of 15 cm/sec. The equivalent roughness is thus half of that associated with an optical flat. Using this information, it is shown that at 1000 lines/in. information density a signal/noise ratio of 50 db at a linear velocity of 15 cm/sec should be realized.
Tuning Preferences for Piano Unison Groups
Authors: Kirk Roger E.
Published: September 2005

Unison strings of a concert grand piano were tuned to five “unison” conditions. The conditions were “zero-beat” tuning and the upper string of three string unison groups tuned sharp and the lower string tuned flat by 12, 1, 2, and 3 cents relative to the center string. Magnetic tape recordings were made of the piano tuned under these conditions. These recordings in the form of a paired comparison preference test were presented to musically trained and untrained subjects. The most preferred tuning conditions for three string unison groups as recorded and reproduced from magnetic tape, are 1 and 2 cents maximum deviation among strings. Musically trained subjects prefer less deviation in tuning among unison strings than do untrained subjects. Close agreement was found between the subject's tuning preferences and the way artist tuners actually tune piano unison strings.
Transient Behavior of the Dynamic Absorber
Authors: Snowdon J. C.
Published: September 2005

The ability of a dynamic absorber of optimum design to reduce the transient motion of resiliently mounted equipment is discussed theoretically. The motion of the mounted item is assumed to result from step-like foundation displacements possessing a wide range of rise times. The absorber mass is attached to the mounted item by a viscously damped spring. It is shown that the transient motion of the mounted item is characterized by the rapid manner in which it decays with time.

In general, if the contents of a resiliently mounted item are to receive the greatest possible protection from damage due to shock, the maximum acceleration and the maximum displacement and relative displacement of the mounted item should be simultaneously small. These are conflicting requirements, but they are fulfilled more closely than is possible with a simple mounting when a dynamic absorber of mass comparable to that of the mounted item is utilized.
On Woodwind Instrument Bores
Authors: Benade A. H.
Published: September 2005

The properties of horns that are suitable for use in woodwinds are deduced from first principles. The cylindrical pipe and complete cone are shown to be the only shapes which satisfy these requirements exactly. The behavior of nearly perfect cylinders and almost complete cones is described, the influence of closed finger holes on the effective bore of an instrument is discussed, and the effect of the mouthpiece cavity is analyzed. Damping of the normal modes by the walls of the bore is shown to play a dominant role in the playing behavior and tone color of woodwinds, and various consequences are deduced.
Siren Design for Producing Controlled Wave Forms at High Intensities
Authors: Allen C. H. , Watters B. G.
Published: September 2005

On the assumption of the additivity of steady and acoustic flow characteristics, an equation was developed for the time variation of a siren port area required to produce a sinusoidal wave. If low efficiencies can be tolerated the port opening may be kept small and the operating pressure made large compared with the acoustic pressure; then the equation reveals the well-known fact that the proper port area variation is nearly sinusoidal. For high efficiencies the operating pressure must be made to approach the peak acoustic pressure and the port area variation must depart widely from a sinusoid if a sinusoidal pressure wave is to be generated.

A siren was designed and built to verify the assumptions. The output signal was found to be sinusoidal at the design operating pressure and to depart from sinusoidal as expected at operating pressures either higher or lower. Efficiency at the design pressure was between 35 and 45% which is between 70 and 90% of the theoretical maximum efficiency for a sinusoidal sound generator of the siren type using a dissipative valving mechanism.

The derived equation might be used to determine the port area variation of a siren for generating chosen nonsinusoidal wave form by substituting, within limits, the expression for the desired wave in place of the sine function.
Asymptotic Theory of Diffraction in Inhomogeneous Media
Authors: Seckler Bernard D. , Keller Joseph B.
Published: September 2005

Some boundary value problems are considered for the reduced wave equation in media having planar or cylindrical stratification. They are solved exactly and the solutions are expanded asymptotically for high frequencies by using the method of stationary phase in conjunction with the WKB method and the Watson transformation. The asymptotic expansions are compared with the corresponding diffracted fields found by using the geometrical theory described in the companion article “Geometrical theory of diffraction in inhomogeneous media.” In all cases the asymptotic expansions agree completely with the corresponding results derived by the geometrical theory, thus verifying this theory.
Space Requirements for Equipment Items Subjected to Random Excitation
Authors: Skoog J. A. , Setterlund G. G.
Published: September 2005

If an equipment item is supported on a low-frequency mounting, there must be sufficient space allowance around the item to permit unrestricted vibratory motion. Also, the motion of the equipment item must be within the allocated travel of the mount. If the system is linear, the required space can be computed for random motion by the application of Fourier series. The solution includes motion of the adjacent structure and phase angles. After a review of basic random theory showing the application of random theory to design, an expression is developed for calculating the space required for an equipment item to vibrate. A numerical example is included to illustrate a method for estimating structural response and structural phase.
Flexural Vibration of Thin Laminated Plates
Authors: Pister Karl S.
Published: September 2005

This paper describes a procedure for calculating the frequencies of free vibration of plates composed of bonded, thin elastic laminae. The problem is reduced to the calculation of composite elastic parameters and the transposition of results from corresponding single-layer plate problems. The vibration is assumed to be governed by the Poisson-Kirchhoff theory of flexure, omitting the effects of transverse shear deformation and rotary inertia.
Effect of Background Noise on the Auditory Intensive Difference Limen
Authors: Sherrick Carl E.
Published: September 2005

A study of the effect of random background noise on the intensive difference limen (DL) for pure tones was made by a method similar to that developed by Riesz. Three frequencies (250, 1000, and 4000 cps) at three sensation levels (20, 40, and 60 db) were studied, with signal-to-noise ratios of −15, −10, 0, and 10 db present for each condition. Analysis of the data revealed only signal-to-noise ratio as a significant factor affecting the DL. Repetition of the experiment with the psychophysical method of average error, for a 1000-cps signal at levels of 10, 30, 50, and 70 db, and signal-to-noise ratios of −10, 0, 10, and 20 db resulted in a lack of systematic shift of the difference limen. The curve relating the difference limen obtained by modulation to signal-to-noise ratio appears to parallel that found in quiet when the difference limen is plotted against sensation level. Some hypotheses relating to the differences of psychophysical procedure are stated.
New Theory of Jet-Noise Generation, Directionality, and Spectra
Authors: Ribner H. S.
Published: September 2005

A theory of jet noise is developed from the observation that in low-speed turbulence Lighthill's quadrupoles combine to behave like simple sources ∼∂2p(0)/∂t2, where p(0) is the “incompressible” local pressure in the turbulence. An integral for the far-field intensity involves the space-time pressure covariance ℛ within the turbulent. Choice of ℛ in a worked example shows how pronounced directionality results from pattern “convection” (modified by fluctuation) in conjunction with the time retardation. Further directionality is accounted for in terms of a Green's function (discussed qualitatively but not worked out) for a point source at rest in the mean shear flow, describing the lateral refraction and diffraction.
Effect of Gas Content in Media on Ultrasonic Cleaning
Authors: Larson Larry G. , Berglund Edward D.
Published: September 2005

The measurement of ultrasonic cleaning as a function of the gas content of the media is described. A positive relationship between cleaning and gas content is noted.
Measurements of Thermal Relaxation in CO2 Extended to 300°C
Authors: Shields F. Douglas
Published: September 2005

The tube method has been used to extend measurements of sound absorption in carbon dioxide to 300°C. Results indicate that all of the vibrational specific heat in CO2 relaxes with a single relaxation time. This relaxation time at 305°C was found to be 3.05 ×10−6 sec.
High-Intensity Sound Reverberation Chamber and Loudspeaker Noise Generator
Authors: Fiala W. T. , Hilliard J. K.
Published: September 2005

A high-intensity sound test chamber capable of producing 145 db and having a working area of 6×3×112 ft is described. The chamber uses the principle of reverberant sound to test electronic packages used in aircraft and missiles. Double wall construction and use of Aquaplas for panel damping provides the necessary sound insulation. Complete instrumentation and the loudspeaker generator will be described.
Intelligibility of Known and Unknown Message Sets
Authors: Pollack Irwin , Rubenstein Herbert , Decker Louis
Published: September 2005

The effect of the frequency of occurrence of words upon their intelligibility in noise was examined under two conditions: (1) in unknown message sets where the specific words under test were initially unknown to the listener; and (2) in known message sets where the specific words under test were known to the listener. Substantial effects of word frequency are observed with unknown message sets, but not with known message sets. In known message sets, the prime factor determining intelligibility is the phonemic interconfusability among the words. In unknown message sets, it is suggested that the important determinant of the intelligibility of a word is its frequency of occurrence relative to the frequencies of the words with which it might be confused.
Linguistic Considerations in the Study of Speech Intelligibility
Authors: Lehiste Ilse , Peterson Gordon E.
Published: September 2005

Intelligibility is defined as a property of speech communication involving meaning. Since only meaningful units have normal linguistic distributional properties, only meaningful units have the phonetic properties of actual speech. An auditory intelligibility dialect ratio is defined for a listener relative to a specified message. An analysis is presented of the Harvard PB lists, and a set of 10 lists of 50 monosyllables each is presented having an almost exact first-order phonemic balancing.
Measurement of Ultrasonic Wave Velocities and Elastic Moduli for Small Solid Specimens at High Temperatures
Authors: McSkimin H. J.
Published: September 2005

An improved buffer rod-specimen unit is described for measuring longitudinal wave velocities in solids at temperatures up to 350°C. The method is particularly useful in determining elastic moduli of single crystals since very small path lengths in any prescribed direction can be employed. The use of molten metals to provide coupling at still higher temperatures is discussed.

Two methods involving mode conversion at an impedance discontinuity are described for measuring shear wave velocities. Application to crystals of cubic symmetry is detailed, with a note on possible extension to less symmetrical crystals of any orientation.

Data for fused silica and single crystal germanium are listed for temperatures up to 300°C in illustration of the methods described.
Acoustic Properties of Hemoglobin Solutions
Authors: Carstensen Edwin L. , Schwan Herman P.
Published: September 2005

Absorption and velocity of sound in the range 0.5 to 10 Mc have been measured for solutions of hemoglobin under various conditions of temperature, concentration, and chemical environment. The hemoglobins of several species of mammals and different chemical forms of hemoglobin have been studied.

In the absorption per wavelength only minor variations with frequency have been observed. Dispersion in the velocity of sound of these solutions has been measured. It has been possible to relate quantitatively the magnitude of the absorption and dispersion through relaxation theory by assuming broad distribution of relaxation times.
Piezoelectric Relations and the Radial Deformation of a Polarized Spherical Shell
Authors: Toupin R. A.
Published: September 2005

The piezoelectric relations and equations of equilibrium for an elastic spherical shell permanently polarized in the radial direction are derived. The solution for the radial displacement corresponding to uniform pressures on the inner and outer surfaces of the shell and a given voltage difference between the surfaces is obtained.
Acoustical Damping for Linear Accelerometers
Authors: Stedman C. K.
Published: September 2005

The acoustical damping system described in this paper uses a diaphragm, coupling chamber, and a resistive element in the form of a plug of porous sintered metal. A major feature of the development is the use of pressurization to match the acoustic impedance of the coupling chamber to that of the plug. Critical requirements which must be satisfied by the diaphragm, the chamber, the plug, and its acoustical termination are presented. The theoretical frequency response is presented in dimensionless form, and expressions for the dimensionless parameters are given in terms of physical constants of the instrument. Experience with instruments designed according to these principles and manufactured in quantity by Statham Instruments, Inc., has confirmed the theory.
Synchronism of Neural Discharges and Their Demultiplication in Pitch Perception on the Skin and in Hearing
Authors: von Békésy Georg
Published: September 2005

The role of the volleys in the sensation of “pitch” on the skin was investigated. It was shown that the existence of rotating skin sensations does not insure perfect synchrony between sinusoidal vibrations and the discharges in the neural pathway. Experiments seem rather to indicate that, just as vibration loudness is a complex result of summation and inhibition, so is pitch sensation on the skin also influenced by summation and inhibition of a large group of end organs. One experiment showed that the pulse rate experienced on the skin is much lower than the pulse rate of the stimulus. This suggests a sort of “demultiplication” in the rate of the neural discharges along the neural pathway. This is one possible way in which synchronism may be maintained between the stimulus and the neural discharges, even though the frequencies transmitted are lowered.
Critical Bands and the Loudness of Complex Sounds Near Threshold
Authors: Scharf Bertram
Published: September 2005

The loudness of multitone complexes and bands of white noise was measured as a function of band width at levels between 5 and 35 db above threshold. When account is taken of the changes in the loudness that are due to the nonuniformity of the ear's sensitivity at low levels, the spreading of energy appears to have the same general effect on the loudness of both line spectra and continuous spectra centered at frequencies as low as 400 cps and as high as 5000 cps. At 5 db SL the spreading of energy does not increase the loudness, and may even decrease it. Above about 10 db SL, the spreading of energy in a complex sound over more than a critical band increases the loudness. As the sensation level is raised up to 35 db, the spreading of energy becomes more and more advantageous to loudness. The critical band defines the limits within which the spreading of energy leaves the loudness of a complex sound unchanged. The widths of the critical bands that were measured in these experiments on loudness summation below 35 db are approximately the same as those measured in experiments on loudness summation at higher levels and also in experiments on phase, threshold, and two-tone masking.
Proposed Keyboard Musical Instrument
Authors: Clark Melville
Published: September 2005

A musical instrument is proposed with the following elements: a tone generator capable of reproducing the attack and decay transients and the steady state of the tones of conventional musical instruments with correctly proportioned partials, the frequencies of those associated with one note being integral multiples of a low frequency; keyboards sensitive to the speed with which a key is depressed and the distance to which it is depressed, so that the intensity of each note may be expressively controlled at all times; a unit for the controllable generation of massive choruses from solo voices by producing narrow, complex spectra about each partial; an intensity control unit; environment modification equipment to alter the apparent size of the room within which the music is heard and the apparent size and location of the source, and to distribute and diffuse the sound; a preset unit in which sequences of timbre, vibrato, choral massiveness, environmental characteristics, and other factors may be established before performance and quickly and easily called forth during performance. The features include tones of familiar character and quality, realistic choral effects, expressive touch, environmental control, flexibility, and ease of playing. Numerical results are appended to demonstrate the feasibility of construction.
Shielding Flap Type Jet Engine Noise Suppressor
Authors: Maglieri Domenic J.
Published: September 2005

Far-field noise measurements from model tests of a shielding flap type jet noise suppressor are presented in the form of radiation patterns and frequency spectra. The tests were conducted using a cold air jet issuing from the nozzle in such a manner as to attach to and flow along the surface of a shielding flap. Whereas other proposed noise suppressors provide generally symmetrical noise radiation patterns, the present device skews the pattern in a beneficial way such that large noise reductions are obtained in the downward direction. These large noise reductions are thought to result from both the acoustic shielding of the flap and the benefits of flow attachment.
On the Detection of Signals in Nonstationary Noise by Product Arrays
Authors: Thomas John B. , Williams Thomas R.
Published: September 2005

Two detection systems having multiple inputs each consisting of nonstationary noise and a stationary random signal are analyzed and compared on a signal-to-noise ratio basis. In both systems the inputs are divided into two groups and the sum of each group is formed. In the first system the resulting two wave forms are multiplied directly and the product averaged. In the second system the two wave forms are strongly clipped prior to multiplication, forming a polarity-coincidence correlator. Previous studies have shown the latter system to be slightly inferior for stationary noise. The results of this paper show that the latter system may be quite superior in certain types of nonstationary noise.
Auditory Localization of Clicks
Authors: Deatherage Bruce H. , Hirsh Ira J.
Published: September 2005

Previous investigations on the auditory localization of sounds have established that interaural differences in time and in intensity are both important. There have also been attempts to set temporal and intensive differences against each other, so that a lead in time at one ear accompanied by an increase in intensity at the other ear would cause a sound to be localized in the midline. On the basis of hypotheses suggested by physiological observations, two experiments were carried out. The first showed that the intensive difference required to offset a difference in time at the two ears depends upon the level of the sounds. Clicks at low level require smaller differences in intensity to offset a given temporal difference than do clicks at a high level. The relation between intensive differences (decibels) and temporal differences (microseconds) is not linear at any of the levels studied. In the second experiment, high-frequency masking noise interfered with reception in the basal turn of the cochlea. Although this noise did not mask the clicks, it produced a temporal lag that required compensation by a time delay at the opposite ear. The relations between these psychophysical results and physiological findings are discussed.
Indices of Signal Detectability Obtained with Various Psychophysical Procedures
Authors: Swets John A.
Published: September 2005

The index of detectability d′ was estimated from data collected with various psychophysical procedures, specifically, the forced-choice method with different numbers of alternatives, and the yes-no method. The estimates were, in all instances, quite comparable. This result is comforting in view of the fact that none of the other indices extant provide a unification of data collected with different procedures. This result is also somewhat surprising view of the fact that the calculation of d′ assumes perfect memory, and forced-choice experiments were conducted with as many as eight temporal alternatives.
Multiple Observations of Signals in Noise
Authors: Swets John A. , Shipley Elizabeth F. , McKey Molly J. , Green David M.
Published: September 2005

The use of repeated presentations of a given signal event as an experimental technique in psychoacoustic studies provides information about several general properties of the hearing process. From the relationship between the gain in detectability that results from additional observations and the type of signal and noise employed, inferences can be made about: (1) the observer's ability to integrate over time, (2) the amount of noise generated by the auditory system, (3) the nature of the process of frequency analysis, and (4) the observer's mode of dealing with uncertainty as to signal frequency. The first set of experiments permitted five observations of each signal where the signal consisted of a pulsed tone, of known frequency, in noise. Both variable noise, i.e., noise that is statistically independent from one presentation to another, and constant noise, i.e., noise that is exactly the same on each of the five presentations, were used. With variable noise, the detectability index d′ improves, as predicted, as the square root of the number of observations. The use of constant noise, which results in less improvement, provides an estimate of the portion of the total noise affecting detection that is of internal origin. The results under different levels of external noise indicate that internal noise is proportional to external noise. A second set of experiments employed signals whose frequencies were unknown to the observers, and signals comprised of several widely spaced frequencies. Their results are discussed in relation to three alternative models of the process of frequency analysis.
Noise-Reducing Line Microphone for Frequencies below 1 cps
Authors: Daniels Fred B.
Published: September 2005

A novel type of line microphone is described that utilizes a distributed input primarily for the purpose of improving signal-to-wind-noise ratio. The input to the transducer takes place through a tapered pipe that is coupled to the atmosphere by means of acoustical resistances uniformly spaced along the length of the pipe. The relationship between the resistances of the openings and the longitudinal variation in the characteristic impedance of the pipe is so adjusted as to make the system nonreflecting. Microphones of this type have been constructed for use in the frequency range below 1 cps for the purpose of studying atmospheric pressure oscillations in this range. A prototype, 1980 ft long with 100 openings, which gives an improvement in the signal-to-noise ratio of as much as 20 db under severe wind conditions, is described.