bluuebunny/crossref_metadata_2025 huggingface dataset:
Amplitude and Phase Effects of Middle-Ear-Muscle Activity
Authors: Nieder Philip C.
Published: September 2005

Round-window and middle-ear-muscle responses were recorded bilaterally from unanesthetized and unrestrained cats, using implanted electrodes. Amplitude and phase of round-window response to variable rise-time freefield tone pips were measured. Phase as well as amplitude alterations in the acoustic input were correlated with middle-ear-muscle reflex responses. Significant effects were observed over a wide frequency-intensity domain. Effects were usually, but not always, symmetrical in the two ears; sometimes reflex responses were associated with alteration of inputs to the two ears of magnitudes, which could be significant to the spatial localization of the sound source. Also, phase shifts were observed of sufficient magnitude to suggest the possibility of the existence of a peripheral mechanism involved in the process of selective listening to freefield sources. While reflex attenuation effects were variable, results were consistent with the hypothesis that middle-ear-muscles may function to extend the dynamic range of the auditory system by acting as components of an automatic volume-control system with predictive and memory capacities.
Musical Character of Tones as Related to Speed of Tonal Processing in the Nervous System
Authors: Boomsliter Paul C. , Creel Warren
Published: September 2005

Normal subjects hear complex or vibratoed musical tones as “brighter” than steady pure tones. The reasons that underlie these subjective judgments are difficult to assess. Human patients with stenotic lesions of a vertebral artery, which may impair the blood supply to the brain stem and cochlea, have been found to require unusually long stimuli to achieve a sensation of tone rather than noise from short pure tones. The use of various complex and vibratoed stimuli with these patients supports the data found with pure tones but also shows measureable differences in the speed of tonal processing, and especially suggests improvement in tonal projection. Thus, the data suggest that musical phenomena of “brightness,” “extension,” and the like are linked to the neural efficiency of the hearing process.
Detectability of the Deletion of a Tone from a Tone-Plus-Noise Background
Authors: Schulman Arthur I. , Mitchell Rhoda R.
Published: September 2005

Listeners in yes-no detection experiments must distinguish between intervals that contain a signal and intervals that do not. Usually, the signal is an augmented stimulus, as when a brief tone is inserted into a noisy background. But the signal may also be a diminished stimulus, as when a tone is briefly deleted from at noisy background in which it is normally present. This study compared signal detectability under these conditions of insertion and deletion. A 1000-cps tone and white noise were used with E/N0's ranging from 12.6–31.6. A signal of 100 msec duration—tone plus noise in insertion, noise alone in deletion—occurred with probability 0.5 within a welldefined observation interval. Operating characteristics obtained for naive listeners revealed that a tone's deletion was harder to detect than its insertion. With E/N0 = 20.0, ds = 1.67 for insertion and ds = 0.73 for deletion were obtained. For deletion, the mean value of ds increased linearly with E/N0, but the obtained slope of 0.036 was less than half as great as the characteristic slope of similar insertion functions. Possible reasons for such poor deletion detection are discussed, in view of the fact that an ideal observer performs equally well at insertion and deletion.
Auditory Sensitivity of the Chinchilla in Quiet and in Noise
Authors: Miller James D.
Published: September 2005

The results of repeated determinations of the audibility curve of chinchilla confirm onr previous findings. The masked thresholds for tones were determined as functions of the level of a broad-band noise at three frequencies: 360, 1000, and 4000 cps. For masking greater than 15 dB, these functions were linear with slope near 1. The critical ratio at masked threshold was determined at 17 frequencies over the range from 90 to 22 800 cps. The critical ratio increases with frequency and is greater than those measures for cat and man. These results are consistent with the chinchilla's range of hearing and the length of its basilar membrane. [Work supported by Public Health Service Prograin-Project grant No. B-3856 from the National Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Flexural Vibrations of Bilaminar Ceramic Plates
Authors: Schenck Harry A.
Published: September 2005

The differential equation and boundary conditions that govern the electrically forced flexural vibrations bilaminar ceramic plates are developed from linear piezoelectric equations of state. A general formula for the electrical-input admittance of a bilaminar plate is given. The differential equation can be cast in the classical form for thin plates by defining a “modified flexural rigidity” and a “modified ratio.” The applied voltage does not appear in the differential equation as a forcing term; instead, it enters the problem through the boundary conditions as a uniform applied bending moment at any nonclamped edge of the plate. The effects electromechanical coupling are illustrated by solving the equation in the case of a free-edge disk. The resonance frequencies (for constant applied current) and the vibration patterns at these frequencies vary with electromechanical coupling; hence, the coupling coefficient of the plate material can be inferred from simple careful measurements of resonance frequencies. The effects of rotary inertia and shear on the properties of these plates are indicated. [Work supported in part by U. S. Office of Naval Research.]
Broad-Band Excitation of Microwave Ultrasonic Waves
Authors: Hemphill R. B. , Claytor R. N.
Published: September 2005

The conventional techniques for generation and detection of microwave acoustic waves employ resonant cavities and are thus unsuited to applications that require a broad bandwidth. Microwave structures, made from coaxial transmission line or from microstrip, that operate in the TEM mode have the advantage of being broad-bandwidth devices, and the rf electric and magnetic fields in these structures may be used with both piezoelectric and magnetostrictive transducers to generate acoustic waves. The design and performance of microstrip structures are presented. The tranducer loss (defined as the sum of the losses incurred in the generation and detection of acoustic waves) was found to be 116±6 dB at frequencies between 300 and 1000 Mc/sec for a microstrip structure that generates transverse waves along the x axis in quartz. The dimensions of the quartz crystal were N = 0.100, Y = 0.050, and Z = 0.500 in. Measurements on other structures are discussed as well.
Performance Characteristics of a 160 000-W Acoustic Siren
Authors: Polly Robert C.
Published: September 2005

A series of tests was conducted by the Acoustics Section of Test Laboratory at MSFC to determine the performance characteristics of a large acoustic siren. This siren will be used to study long-range sound propagation and is capable of generating either random noise or discrete frequencies. The measurement program and the methods used to analyze the data collected during these tests are briefly discussed. From these tests, it was found that the directivity of the siren was independent of the operating conditions in the frequency range between 31 and 125 cps. A maximum power oulput of 161 000 W was calculated while the siren was being operated at 125 cps. The basic limitation of the present system is its inability to efficiently propagate low-frequeucy sounds (below 31 cps). However, this is a characteristic of the exponential horn and not of the siren. The efficiency of a catenoidal horn at low frequencies is briefly discussed to illustrate the advantage of using this type of horn with the siren.
Improved Broad-Band Random Siren
Authors: Rader W. P.
Published: September 2005

Recent improvements of the design of rotor-drive systems and siren configurations for the broad-band random sirens at the Martin Company's Acoustics Laboratory are discussed. Siren output levels are compared with supply air parameters for single- and multiple-siren configurations. Specifically, spectrum-shaping capabilities are greatly improved by use of variable-speed drive systems. Typical spectrum plots and probability-density curves for siren acoustic output are presented.
Effect of Humidity on Sound-Transmission Loss
Authors: Shiner Allen H.
Published: September 2005

A test program was recently instituted by the United States Gypsum Company Research Center with the cooperation of the Riverbank Acoustical Laboratories to determine the effect of ambient humidity on the sound-transmission loss of a double-leaf gypsum-board partition system. The results of this test series were quite explicit. As the humidity was increased, a degree of freedom that allowed for lateral movement of the gypsum core and paper was introduced. These two skins were then able to perform independently of each other, causing the eventual shift of control frequency from 2800 to 350 cps, i.e., from coincidence to resonance control. In addition, these test data reveal that at some frequencies a difference of as much as 6 dB occurs between the high and low humidity levels, while at others the differential is 0 dB. These differences clearly indicate the need for standardization of the humidity conditions at the present commercial testing laboratories.
Spectrum-Envelope Method for Synthesis of Clarinet Tones
Authors: Strong William J.
Published: September 2005

Clarinet tones ranging in fundamental frequency from 186 to 996 cps were synthesized with an IBM-7090 computer. Each clarinet tone was synthesized by using up to 30 harmonics separated into three groups. Each group was controlled independently of the other two groups with respect to its amplitude as a function of time. For synthesis purposes, the relative amplitudes of the harmonics were obtained from two idealized spectrum envelopes for the clarinet—one for the odd harmonics and another for the even harmonics. In forced-choice testing, the synthetic clarinet tones were identified as clarinet tones 87% of the time, but were confused with oboe, trumpet, flute, and English-horn tones 13% of the time. The spectrum envelopes and the relative amplitudes of odd and even harmonics are discussed in terms of how they affect the identifiability and naturalness of clarinet tones. [Work performed with support from the National Association of Music Merchants.]
Analysis of School Instrumental Music-Room Acoustics
Authors: Patrick Nelson G. , Boner Charles R.
Published: September 2005

The purpose of this investigation was to study the acoustical characteristics of the school instrumental music rooms that have been adjudged satisfactory by the music teachers who use them. Public-school band and orchestra directors long have realized that special acoustical considerations must be given to the rehearsal space assigned to them for teaching purposes if they are to teach critical listening, intonation, musical balance, tone production, and dynamic control of tonal intensity. These attributes cannot be taught within the same acoustical conditions as that of the normal classroom or performance situation. This study located six rehearsal rooms that were reported as being satisfactory acoustically for teaching purposes. These rooms were analyzed for their acoustical characteristics. The study revealed that the several common factors existing among the six rooms differ considerably from the present standards of school musicroom construction.
Effect of Steady Air Flow on the Resonance Frequencies and Q's of the Clarinet
Authors: Backus John
Published: September 2005

A previously published theory of the clarinet [J. Backus, J. Acoust. Soc. Am. 35, 305–313 (i963)] assumed the instrument to be a tube open at one end. On applying the theory to the instrument as usually operated, with side holes determining the operating frequency, discrepancies were found. These were traced to the observation that both the resonance frequencies and the Q's for the vibration modes of the instrument are considerably affected by the steady airflow through it. Quantitative measurements were made on a brass tube provided with holes of varying sizes at one end and excited into vibration at the other end by means of an external sound source. With a hole the order of 13 the tube diameter, the Q of the system could be lowered by a factor of 5 and the resonance frequency increased by as much as 50 cents (3%) with a relatively small flow of air through the tube. By altering the steady airflow through a clarinet blown on an artificial embouchure, changes of the order of 25 cents in the sounding frequency could be obtained. Apparently, the intonation characteristics of the clarinet (and, perhaps, the other woodwinds) depend on more than just the geometry of the instrument.
Determination of Bandpass-Filter Corrections
Authors: Engstrom J. R.
Published: September 2005

Filter corrections for practical bandpass filters are usually obtained by using the point-by-point method. If several filters must be checked, this process can be quite time consuming. This paper discusses a method for directly integrating the area under the filter curve, thus obtaining the necessary filter correction in a comparatively short time. Comparisons of results obtained using both methods are presented.
Optimum Detection of Random Phase Modulation with Phase-Lock Loops
Authors: Clapham R. G. , Moose P. H.
Published: September 2005

A study was conducted to determine the optimum design for a second-order phase-lock loop when used to detect a randomly phase-modulated sine wave of unknown average frequency in a white-noise background. The optimum physically realizable loop was also found for the case when the average frequency is known a priori. A quasilinear model was used to account for the nonlinear characteristic of the phaselock loop and to predict the threshold effect. The results of the study give formulas for calculating the root-mean-square loop-phase error and detector-output signal-to-noise ratio as a function of the input signal-to-noise ratio and the power and bandwidth of the assumed modulating function. The results show a strong dependence of the loop threshold on the characteristics of the modulating function. Careful consideration must be given these parameters in system designs employing phase-lock loops for the processing of this class of signal.
Development of a Missile-Impact Acoustic Transponder
Authors: Pasonski George E.
Published: September 2005

Requirements exist at the Air Force Eastern Test Range (AFETR) to provide missile-impact data at increased ranges from Cape Kennedy. Geography of the AFETR beyond Ascension Island is such that the placement of standard hydrophone target arrays cabled to land sites would be prohibitively costly. Also, with the advent of more-complex missile systems, it has become necessary to increase the bandwidth of the recorded data beyond that which can be effectively handled by cabled arrays. This has necessitated the development of sophisticated, ship-tended acoustic transponders for reception and retransmission of this data. Field tests of the Ship Tended Acoustic Relay (STAR) system were conducted in early 1963, that verified the system feasibility. A total of five transponders were fabricated for the AFETR and tested in 15 600 ft of water, 35 miles northeast of Eleuthera Island. Data in a bandwidth of 50–450 cps was relayed acoustically to an attendant vessel at ranges in excess of 15 nm (nautical miles).
Pertinent Acoustic Characteristics of Cylindrical Wooden Tanks
Authors: DeChico R. A. , Lewis R. C.
Published: September 2005

Measurements of acoustic characteristics of the cylindrical wooden tanks used for sonar calibrations at the NAVAIRDEVCEX have been performed. Characteristics measured include reverberation time for pulsed CW signals, reverberation time for random-noise signals, and the lowest frequency at which these tanks could reasonably be excited. The results of the CW reverberation-time measurements were analyzed to derive attenuation coefficients of the unlined, waterfilled wooden tanks as a function of frequency. Graphs were constructed to permit the determination of useable pulse-repetition rates for desired signal to reverberation levels while using pulsed CW signals. The results of reverberational times for various bandwidths of noise were compared with the CW results. Agreement was found to exist between the CW and noise measurements with regard to the lowest frequency at which the tank could be excited. This frequency corresponded with a quarter-wavelength for the major dimension of the tank being measured. The data obtained are presented graphically and discussed in relation to the capabilities aud the limitations of the tanks for the calibrations of transducers.
Criteria for Noise Exposure
Authors: Rudmose Wayne
Published: September 2005

This presentation is intended to supply information primarily to the individual who has recently become involved with the many problems of “what are acceptable noise levels” and who has not necessarily been involved in the day-to-day business of noise control. Guidelines and criteria describing acceptable noise levels are presented in terms of the following areas of interest: (1) industrial hearing loss, (2) airport levels, (3) industrial levels, (4) residential levels, (5) office levels, (6) auditorium levels, and (7) speech. All terms such as perceived noise level, loudness, noisiness, SIL, etc., that are involved in the interpretation of guidelines and criteria are defined.
TESTEAR—An Electronic Dummy for the Physical Measurement of Sound Attenuation of Hearing Protectors
Authors: Beguin Fred P.
Published: September 2005

The psychophysical testing and evaluation of conventional and communication-type hearing protectors continues to present a major problem in industry, engineering, and Government procurement. Testing is time-consuming, costly, impractical, and not always reliable for routine engineering applications where outcome of such tests cannot be awaited. TESTEAR provides an objective testing method by which the attenuation characteristic of hearing protectors or microphone noise shields can be plotted automatically in a few minutes from a high intensity sound source generating pure tones, bands of noise, or even from actual noise in any given environment. Because the test signals are at high sound-pressure levels, TESTEAR does not require expensive anechoic test rooms. For the same reason, the recorded data are more representative of the performance of hearing protectors under actual field conditions. Comparative tests conducted with 30 subjects with the threshold-shift method and with TESTEAR physical method produced attenuation curves showing close correlation between methods. TESTEAR does not require instrumentation other than that normally found in the acoustics laboratory.
Real Ear Response of Earphones in Relation to Audiometry
Authors: Shaw E. A. G.
Published: September 2005

Real-ear-response curves of representative circumaural and supra-aural earphones have been measured with a probe-tube microphone, the orifice of which is located 1 mm beyond the edge of the tragus. At each sitting, hearing thresholds have also been determined at 9 accurately tuned audiometric frequencies from 125 to 8000 cps. Preliminary data for 3 subjects indicate that the SPL at threshold is virtually independent of the earphone used. However, the earphone response at constant input voltage varies greatly from subject to subject, particularly at high frequencies. Typical earphones show intersubject differences of 10–20 dB in the 8-kc/sec region. Furthermore, a 5% change in frequency may change the response for a given subject by 10 dB. With some subjects, the effort of ear-canal resonance is clearly evident in the response curves.
Loudness from a Mechanistic Standpoint
Authors: Corliss Edith L. R.
Published: September 2005

Fletcher's definition of loudness units (LU) implies a direct relationship between the sensation of loudness and the difference limen for perception of a change in sound intensity. This property of the ear can be derived from the behavior of a mechanistic model. The equations describing the model applied to experimental data on the difference limen for intensity perception in the ear permit calculation of equal-loudness contours and the diffuse-field threshold for the ear, which, in turn, can be compared with experimental data.
Study of Methods for Estimating Loudness
Authors: Corliss Edith L. R. , Winzer George E.
Published: September 2005

The methods for computing loudness developed by K. E. Zwicker and S. S. Stevens were applied to several complex sounds encountered in our work on architectural acoustics. The loudnesses computed on the basis of Stevens' method did not agree closely with the loudnesses computed by Zwicker's method, and the results obtained by using the two methods were not related to one another in any consistent way. Further, studies with subjects showed that both sets of computations gave results at variance with the responses of the subjects. Investigation of the loudness vs frequency contours for our subjects showed closer conformity to the Fletcher and Munson data than to the more recent equal-loudness contours reported by the National Physical Laboratory, the functions reported by Zwicker, or the band-pressure levels that form the basis for the loudness weighting Stevens' method. However, this feature does not suffice to account for the discrepancies observed.
Loudness as a Function of Duration
Authors: Wright H. N.
Published: September 2005

Loudness is measured for 500-, 300-, 100-, 30-, and 10-msec tones at 1000 cps in 5 subjects with clinically normal hearing to determine the nature of temporal summation above the threshold of audibility. The results from numerical-magnitude-balance experiments showed that the form and slope of the loudness function at 1000 cps does not change as a function of duration, at least between 500 and 10 msec. The absolute difference among the numerical-magnitude-balance functions was determined by magnitude production. These results showed that the intensity increase required for equal loudness as a function of duration is the same as that required for the detection of identical tones at the threshold of audibility. The combined results of the foregoing experiments indicate that the growth of loudness as a function of duration is constant for sensation levels greater than 40 dB; and, at sensation levels less than 40 dB, there is a progressive increase in the rate of growth of loudness with a decrease in sensation level. [This research was performed at the Laboratory of Sensory Communication, Syracuse University, Syracuse, New York 13210.]
Is There a Standard Loudness?
Authors: Wright H. N.
Published: September 2005

In the investigation of loudness as a function of duration, the slope of the loudness function was 0.43, considerably different from the slope of 0.54 obtained by numerous other investigations of loudness at 1000 cps. To explain this difference in slope, the hypothesis was made that, when loudness is measured in the absence of a standard presented at a constant sensation level and assigned a fixed number, an implicit loudness-assigned number combination is used as the standard, and that this standard is the comfortable listening level. The comfortable listening level for the subjects used previously was determined as well as the number assigned to this level. By applying appropriate transformations to the results of prior experiments concerned with the slope of the loudness function as a function of the relation between the sensation level at which the standard is presented and the number assigned to that level, it is possible to show that when a standard is not presented the most likely candidate for an implicit reference loudness is the comfortable listening level. [This research was performed at the Laboratory of Sensory Communication, Syracuse University, Syracuse, New York 13210.]
Judged Noisiness of a Band of Random Noise Containing an Audible Pure Tone
Authors: Kryter K. D. , Pearsons K. S.
Published: September 2005

The experiments reported were designed to obtain further data on the perceived noisiness complex sounds consisting of a steady-state pure tone imbedded in a background of random noise. From these data, a method for including a “pure-tone correction factor” in calculation of perceived noisiness in PNdB is derived. The proposed procedure should have practical application for the evaluation of sounds from modern-day jet aircraft or other broad-band sounds that may contain relatively intense, audible pure-tone components. Various problems involved in the measurement and interpretation of band spectra for the location of steady-state pure-tone components in broad-band random noise are discussed.
Transient Vibration of Thin Elastic Shells
Authors: Kraus H. , Kalnins A.
Published: September 2005

A complete solution for the transient response produced by time-dependent surface loads on a thin elastic shell of arbitrary shape is derived by means of the classical method of spectral representation. The solution is expanded in terms of the normal modes of free vibration, and their orthogonality is proved for an arbitrary shell. This method of solution is applicable to any shell for which the free-vibration characteristics (natural frequencies and mode shapes) are known. For application, the response of a hemispherical and a shallow spherical shell to a suddenly applied uniform pressure is calculated and the convergence of the solution is studied in detail. By introducing mode-participation factors, the contribution of each mode to the solution is determined. It is shown that for the shallow shell about four modes are necessary in the solution, while for the hemispherical shell the number of required modes is about fifteen. In either case, when coupled with some available free-vibration analysis, the calculation of the transient response by the method of this paper is well within the practical range of a digital computer.
Some Theoretical Results on Diffraction of Short Waves by Thin Obstacles
Authors: Tuck E. O.
Published: September 2005

Diffraction of short acoustic waves (plane or otherwise) may be treated by methods akin to geometrical optics provided that the lateral dimensions of the diffracting obstacle are large as compared with a wavelength. On the other hand, it is possible to construct thin- or slender-body theories that are directly analogous to corresponding aerodynamic theories only if the wavelength is large as compared with the lateral dimensions. The present theory is an attempt to explore the hazy middle ground where the wavelength and lateral dimensions are comparably small. Diffraction of a plane wave by a two-dimensional thin wing at zero incidence to the oncoming wave is considered as a model for this class of problems, and a method is given for finding the scattering into the region near the plane of the wing. In particular, we find a 45° phase shift and an asymptotic “x−3/2” decay of the scattered disturbance in the shadow region directly behind the wing. A corresponding result for a slender, sharply pointed, three-dimensional obstacle indicates a 90° phase shift and an “x−2” decay with distance.
Industrial Noise-Control Procedures
Authors: Beranek Leo L.
Published: September 2005

Each noise problem must be separated into three parts: source, transmission path, and receiver (listener). This paper gives systematic procedures for dealing with each part in relation to the other two parts. Among the topics discussed are structure and airborne sound, sound from fans, isolation, insulation and absorption, machine design, purchasing specifications, and personnel protection. References to specific “fixes” and the state of the art are given.
Ground-Vehicle Noise Control
Authors: Potter Stannard M. , Newton Thomas J.
Published: September 2005

This paper discusses noise-control criteria by vehicle classification. Vehicle operations are related to noise sources and their effect on the auditor. Procedures in design of quieter components, i.e., engine intake and exhaust systems, body suspensions, new tire treads, etc., are reviewed. Test techniques and performance data are presented for typical noise sources at various operating conditions.
Survey of the Traffic-Noise Problem
Authors: Thiessen George J.
Published: September 2005

Except for cuttings, which are feasible to only a limited extent, the various elements of practical highway design cannot greatly reduce traffic noise. Landscaping and similar forms of barriers can be quite effective but distance is an intimate part of this approach and thus involves the control of substantial land areas. An effective solution can be found in an integrated legislative approach involving land development, zoning, road planning and layout, and noise bylaws. In the latter field, a great deal of experience, in many states and countries, covering several years, is now available. A study of this, by many groups. indicates that performance bylaws, specifying the use of simple instruments, can be made to work and to reduce the noise nuisance.
Threshold Shifts Produced by Pulsed and Continuous Maskers at Equal Sound Pressure and Effective Masking Levels
Authors: Dirks Donald D. , Chandler Jane
Published: September 2005

The effectiveness of pulsed and continuous masking was investigated as a function of frequency, with the masker presented at equal sound-pressure levels and then at equal effective-masking levels. Thresholds at 250, 1000, and 4000 cps were recorded by 10 subjects via a graphic attenuator while a wide-band random noise was delivered either to the test ear (monotic) or the contralateral ear (dichotic). Three methods of presentation were used: (1) pulsed tone and pulsed noise, simultaneous; (2) pulsed tone and continuous noise; and (3) continuous tone and continuous noise. In both the monotic and dichotic conditions, the effectiveness of the pulsed masker, whether presented at equal sound-pressure levels or at effective levels, increased with signal frequency. The threshold shifts in the monotic and dichotic conditions also increased with frequency but the changes were slightly less than for the pulsed-pulsed condition. When noise was present, changes in the variability around threshold as estimated by frequency of excursions over time were observed under certain conditions. This finding was related to the theoretical interpretation of the results. [This work was supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Masking of White Noise by Pure Tones
Authors: Young I. M. , Wenner Claude
Published: September 2005

Pure tones at intensity levels of 80–120 dB re 0.0002 dyn/cm2 were used to mask white noise in steps of 10 dB. The frequency of the pure tones ranged from 200 to 4000 cps in intervals of 100 cycles below 1000 cps and intervals of 1000 cycles above 1000 cps. Pure tones caused maximal masking in the range of 700 to 1000 cps, with the masking effect decreasing on either side of this range. Distortion of the pure tone had a large effect on the masking. When the masking tone had a high distortion factor (13 dB below that of the fundamental), the masking effect was about 25 dB greater and was centered between 300 and 400 cps. With tones having a distortion factor of −30 to −50 dB relative to that of the fundamental, there was no change in the masking effect. [Work supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Measure of the Critical Band for Clicks
Authors: Hafter Ervin R. , Henderson Donald , Deatherage Bruce H.
Published: September 2005

Clicks are often used in studies of binaural interaction because the auditory system responds so well to interaural time differences between them, regardless of their frequency content. Recent data have suggested that the neural “timing” signals generated by clicks may arise at both the basal end of the cochlea and at the place of maximum displacement on the membrane. This spatial response of the cochlear partition is unknown and must be determined to understand fully the psychophysical results from the use of clicks. One measure of this spatial response is the critical band. Utilizing a band-narrowing, masking paradigm, we ascertained the critical band for numerous commonly used clicks. These critical bands are related to the power spectra of the clicks. [Work supported in part under a contract with the U. S. Office of Naval Research.]
Masker Level and Sinusoidal-Signal Detection
Authors: Campbell Richard A.
Published: September 2005

Threshold signal-to-masker ratios (S/M's) for three sinusoids (250, 1000, or 4000 cps) presented in an identical frequency-masker set to from about 0 to 85 dB sensation level (SL) were gathered in this preliminary study. A two-interval, forced-choice procedure was used. The masker was either “continuous” (a signal-detection paradigm) or “pulsed,” i.e., gated ON only during both two-signal intervals (a paired-comparison paradigm). Results agree with previous reports in that the “continuous” masker resulted in considerably lower threshold S/M's than did the “pulsed” masker and the size of the thresholds were generally inversely related to the masker SL. However, plateaus were visible in the functions relating threshold S/M's to masker SL. These plateaus, between 35 and 50 and between 75 and 85 dB SL in the “continuous” masker, appear to coincide with the two negatively sloped portions of the frequency distributions of auditory neuron thresholds as a function of stimulus level reported in 1962 by Katsuki, Suga, and Kanno. Some possible implications of these observations, with regard to the auditory neural-coding scheme for stimulus intensity, are discussed. [Work supported in part by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Contribution to the Theory of Finite-Amplitude Acoustic Fields
Authors: Welsby V. G.
Published: September 2005

Some of the nonlinear aspects of finite-amplitude acoustic waves can be studied, both theoretically and practically, by making use of an electrical transmission-line analog in which the inductance and capacitance per unit length are functions of the current and voltage, respectively. As an illustration, the method is used to confirm the result obtained by Westervelt for an ideal, perfectly collimated beam. It is then extended to deal with other field configurations, e.g., a beam with cylindrical or spherical spreading. The importance of the impedance concept is discussed and it is shown how boundary-wall reflections can be taken into account—for example, when the finite-amplitude field is contained within an open resonant cavity. The transmission line is also useful in studying the conditions under which parametric amplification may take place.
Lifetimes of Empty Cavities Moving through a Liquid
Authors: Eller Anthony , Flynn H. G.
Published: September 2005

An analysis of the motion of an empty, spherical cavity in an infinite, incompressible liquid predicts a strong coupling between radial pulsations of the cavity and translation of the cavity through the liquid. A result of this coupling is that, in the absence of dissipation, a cavity with translational motion does not collapse to zero radius, but oscillates about an equilibrium radius determined by the momentum associated with the translational motion. When viscous dissipation is included, a cavity oscillates about an equilibrium radius that slowly decreases in time. This study indicates that the lifetimes of such cavities may be as much as three orders of magnitude greater than the corresponding Rayleigh collapse times for cavities with no translational motion. Further, the analysis predicts that diffusion of gas into an initially empty cavity may increase its lifetime by three more orders of magnitude. These results are in agreement with recent observations of acoustic cavitation. [Work supported by Acoustics Programs (Code 468), U. S. Office of Naval Research.]
Airblasts from Underwater Explosions at Various Depths
Authors: Malme Charles I. , Carbonell Jaime R. , Dyer Ira
Published: September 2005

The pressure-time pattern of airblasts from underwater explosions depends on the charge-observer geometry and on the charge depth. For deep explosions, the airblast is characterized by a fast-rising peak (P1), a broader second peak (P2), and a subsequent rarefaction phase (P3). P1 is associated with the least-time propagation path. P2 and P3 are produced by the integration of pressure radiation from a large region surrounding surface zero. As the charge depth is increased, the effective area producing P2 becomes smaller until it is essentially reduced to the area of the dome and plume at surface zero. Also, P1 becomes less important as the charge depth decreases and essentially disappears for shallow explosions. The dominant feature in this case is the shock wave produced in air by the supersonically rising dome and plume. An experimental study of these effects was conducted using 0.8-g lead azide charges. Pressure-time traces and high-speed photographic sequences obtained from this study are shown. [Research supported by the U. S. Naval Ordnance Laboratory.]
Role of Acoustic Transients in the Radiation Loading of Pulsed CW Transducer Arrays
Authors: Junger M. C. , Thompson William
Published: September 2005

For an array of identical, uniformly driven transducers, all elements are proved, by mathematical analysis, to experience initially identical radiation loads, whatever the pulse shape. The initial response is therefore uniform over the array. The difference between the initial, uniform radiation loading and the subsequent (spatially) fluctuating loading characteristic of large CW sources results from decaying and sometimes oscillatory acoustic transients. Their periods and decay times are proportional to the envelopment time of the array by a diffracting wave. After the transient subsides, the fluctuating CW radiation loading causes nonuniform element response, and hence the familiar performance anomaly. If uniform response is achieved by tuning or adjusting the excitation of individual elements to compensate for CW impedance fluctuations, the uniform impedance of the pulse beginning causes, paradoxically, initially nonuniform element response. While the transient lasts, certain elements may experience fatigue or cavitation. In brief, uncompensated arrays deteriorate towards stable configurations; compensated arrays, improve. [Work sponsored by U. S. Office of Naval Research, Acoustics Programs.]
Application of the Tchebyshev Polynomial to Element Reduction of Linear Arrays
Authors: Dence D. F. , Spence J. E.
Published: September 2005

There are several methods available for synthesizing a linear array: Bernstein polynomial, LaGrange interpolation, and trigonometric interpolation, to name a few. Associated with each method and the number of elements chosen is an error that, in many cases, is sufficiently less than the allowable error to warrant an attempt to reduce the number of elements. It is the object of this paper to present one possible element-reduction method. Once a polynomial representation for a given array is obtained, the element-reduction method may be employed and makes use of the properties of the Tchebyshev polynomial. It, of all the polynomials that oscillate between ±1 in the range (−1,1), has the largest coefficient 2n−1 of xn and, although xn is algebraically independent of lower powers, it can be expressed as a combination of lower powers in such a manner as to keep the resulting maximum error a minimum. Thus, once an element is eliminated, the amplitude of the remaining elements is used as a degree of freedom.
Optimum-Array Gain for Directional Noise
Authors: Becker C. J. , Cron Benjamin F.
Published: September 2005

From the definition of array gain, the gain of a linear array of point receivers is given in terms of the spatial correlation of the noise. The theoretical methods of obtaining spatial correlation for directional noise and results are given. Experimental verification of the theory is presented. An 8-element equispaced vertical array of elements perpendicular to the surface of the ocean is considered. The gain for the cases of single frequency, narrow-band and wide-band frequencies are computed. Both broadside and endfire steering are analyzed. The gain is computed as a function of the spacing between elements for the case of uniform shading. For each configuration, the gain for optimum shading is obtained. For the case of isotropic noise, narrow-band frequency, the gain is on the order of 10 log 8 or about 9 dB. For directional noise, narrow-band frequency (750–850 cps), broadside steering, and uniform shading, the gain is on the order of 17 dB for optimum spacing. An additional 2 dB is obtained for the case of optimum shading at the optimum-spacing configuration.
Scattering by n-Element Arrays of Identical Rigid Spheres
Authors: Harbold Mary L. , Steinberg Bruce
Published: September 2005

Diffracted fields caused by a number of identical rigid spherical objects arranged in 1-dimensional and 2-dimensional arrays in the path of a plane acoustic pressure wave have been extensively studied for the special case where object dimensions and spacings are comparable to wavelength. A complex experimental measuring system allowed for the simultaneous recording of both amplitude and phase angle for every point in the region of interest, the near-field. Various methods of representing data, including the 3-dimensional method reported at a previous meeting [J. Acoust. Soc. Am. 36, 1010(A) (1964)], were employed to interpret results. Analysis of the composite fields produced by varying n, the number of elements, the spacing between elements, and the angle of incidence, clearly defines the regions and degree of interaction between the individual elements of the array and allows for generalizations to be made concerning arrays consisting of elements of arbitrary shape and arbitrary geometry. [This work was supported by the U. S. Office of Naval Research.]
Acoustic Signal Fluctuations in a Simulated Random Medium
Authors: Knollman G. C. , Hartog J. J.
Published: September 2005

A statistical study has been conducted under controlled laboratory conditions of sound-wave fluctuations inherent in underwater acoustic propagation through a random (in space) medium. Large (with respect to acoustic wavelength) inhomogeneities of equal volume were formulated, using spherical, liquid-filled neoprene balloons, and the refractive indices (relative to water) of the fluid spheres were arranged on the order of unity with deviations up to 1%. (Such weak, large-scale refractive variations are representative, in part, of circumstances in the ocean.) A large number of these balloon inhomogeneities were suspended underwater at random in an experimental acoustic chamber. Signal fluctuations were measured at four different acoustic frequencies and transmitter-to-receiver ranges within the simulated random medium. For each range frequency combination, numerous ensembles were obtained by rotating the fixed transmitter-to-receiver line of sight about its midpoint. The experimental arrangement and procedures involved in the study are discussed, and a comparison is made between laboratory results and extant theoretical treatments. [Work supported by the Lockheed Independent Research Program.]
Coherence in Multiple Random Processes
Authors: Cox Henry
Published: September 2005

A multivariate coherence function is described that gives a quantitative measure of the degree of linear dependence of a random process on a set of n other random processes. The properties of this function are discussed in relation to familiar properties of the coherence function for two random processes. This bivariate case constitutes a special case of the more general problem. The effect of transmission of signals through linear systems both with and without noise and the role of coherence in optimum multivariate linear filtering are discussed.
Technique for Objective Speech-Level Measurement
Authors: Bricker Peter D.
Published: September 2005

The technique described here provides a measure of speech level that is free of the subjectivity inherent in meter reading. A speech-envelope detector remains operated during intervals over which measurement is to be made (“speech spurts”) and gates two counters. One of these accumulates speech-spurt durations and the other accumulates a measure of the energy in each spurt. The ratio of the latter reading to the former, after any desired number of spurts, is the average absolute voltage over speech spurts. This technique is similar in form to the procedure used by a VU-meter reader, but is entirely objective. The resulting measure has a simple physical meaning and is highly reliable. Data presented include the relation to VU readings, performance in predicting loudness matches and loudness estimates, and comparisons of absolute voltage with other measures of the waveform taken by the same procedure.
Parametric Phonetics
Authors: Lawrence Walter
Published: September 2005

“Phonetics” has been defined as the study of the medium of spoken language in all its forms and varieties. The word parameter is here used to designate any attribute of a spoken sound (as, for instance. pitch, formant frequency, or intensity) that can be expressed as an analog quantity. The subject of parametric phonetics embraces all phonetic studies in which speech utterances are expressed as variations of a finite number of specific parameters. Parameters may be defined at the articulatory level in terms of spatial and temporal measurements of the organs of speech, at the acoustic level in terms of computations and instrumental procedures applied to a speech wave form, and at the auditory level in terms of the signals that must be used to control a speech synthesizer to produce a sensation equivalent to an utterance. The paper reviews the instrumentation available for measuring parameters in speech and discusses the possibility of establishing a complete system of parameters valid at all levels, thereby enabling observations at each level to be used to augment information obtained at other levels.
Effect of Filter Bandwidth and Attenuation Characteristics on Sound-Transmission-Loss Measurements
Authors: Sepmeyer L. W. , Oliphant K. S.
Published: September 2005

The effect of filter bandwidth and attenuation characteristics on sound-transmission-loss measurements was investigated by measuring the noise reduction of the same wall system with both 12- and 13-oct filters.
Stage-to-Auditorium Coupling for Variable Reverberation Time
Authors: Christoff Jerry P. , Veneklasen Paul S. , Mann Myron
Published: September 2005

An auditorium for both music and speech requires either a compromise in reverberation time or a scheme to vary the reverberation characteristics. A new approach utilizing the acoustical properties of the stagehouse has been explored in a model and an existing auditorium. The stagehouse, which often contains more volume than the auditorium and far less absorption, is coupled to the auditorium through openings above the proscenium or electroacoustically. Examples from the model and full-scale measurements illustrate the following major advantages: with maximum coupling from auditorium to stagehouse, reverberation times for music as high as 2.5 sec at 500 cps are practical with auditorium volume per person of only 200 ft3; with the coupling eliminated, the reverberation time can be reduced to 1.5 sec, suitable for speech without the addition of absorbing surfaces. Detailed results from model studies illustrate the coupling area required, variation in reverberation time possible, and departure from linear reverberation decays.