bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavior of Microphones at Elevated Temperatures
Authors: Mercer D. M. A.
Published: September 2005

The behavior of Altec condenser microphones, and their associated preamplifiers, has been examined up to 500 degrees F. In general, considerable cycling from room temperature up to working temperature, or aging, or both, are needed before a microphone has a stable response at such temperatures. Marked irregularities in response often appear at higher frequencies, which might be attributed to resonances in the microphone. Calibration curves are presented, and a discussion of suitable tubes.
A Probe Microphone Development
Authors: Goff Kenneth , Watters Bill G.
Published: September 2005

The probe microphone first reported by R. W. Leonard [J. Acoust. Soc. Am. 24, 113(A) 1952] has been modified for use in aircraft engine test cell measurements. Tests have been run to define the range of application of the microphone in terms of pressure, temperature, wind velocity, and level. The results of these tests indicate possible wide application to aircraft noise fields in engine test facilities, wind tunnels, and ventilation systems. The probe, designed to be mounted flush in the wall of a duct or an air foil produces a generally negligible aerodynamic disturbance. Designed for operation to 900°F, the probe microphone requires no additional cooling system. The pressure equalizer system permits its use as a probe through the walls of altitude test chambers as well as at sea level.
Instrumentation for the Measurement of Sound Power
Authors: Schultz Theodore John
Published: September 2005

A pair of pressure-sensitive condenser microphones, mounted back-to-back in a space roughly the size of a dime, forms the basis of an instrument for the measurement of acoustic intensity. The sum of the microphone outputs represents the pressure, while their difference represents the pressure-gradient in the sound field, and each is referred to the same point located midway between the two microphones. The gradient signal is converted to a particle-velocity signal in an integrating circuit and the pressure and velocity signals are multipled and averaged in a moving coil dynamometer which has been made to respond uniformly over a wide frequency range by supplying currents to the coils from a pair of amplifiers having a generous amount of negative current feedback. The completed instrument gives pointer indications of acoustic intensity over a 50-db range at any frequency between 90 and 10 000 cps. The equipment is described and examples of applications are discussed. This research has been aided by funds made available under a contract with the U.S. Office of Naval Research.
Measured Absorption Characteristics of Resonant Absorbers Employing Perforated Panel Facings
Authors: Mikeska E. E. , Lane R. N.
Published: September 2005

Interest in the low-frequency absorption characteristics obtainable with resonator-type panel absorbers stimulated reverberation chamber measurements on a group of absorber designs covering a considerable range of resonant frequencies, using commercially available panel materials of 2 to 11 percent open area. One series of absorbers investigated consisted of three panels of different perforation covering three different porous materials and backed by a hard wall. Absorption peaks in the frequency range from 500 to 160 cps were found with depth of 2 to 412 inches behind the panels, partially or completely filled with the porous material. A further series of absorber designs consisted of perforated panels covered with cloth of suitable resistance and mounted with air-space backing, after the manner of Ingard and Bolt. With air-space depths of 312 to 1412 inches, absorption peaks in the frequency range from 700 to 85 cps were found. Measurements showing the effect of cloth resistance and of partitioning of the air space into small cells will be presented.
How a Communications Booth is Developed
Authors: Baran J. G.
Published: September 2005

The development of the Burgess-Manning line of Acousti-Booths has closely paralleled the growth in interest and acceptance of the concept of acoustical treatment for living and working space. As steady progress has marked the acoustical art and science, in like manner has the design and increased functional detail of the communications booth been pushed forward. This paper outlines a brief history of the field of applied acoustical theory as it applies to telephone communications booths. A story of the role which cooperative research plays in adding to the literature as well as in producing a series of Acousti-Booths of successively increased performance and utility is covered. How performance is achieved in this type of consumer product and what questions need be answered to implement advances in theory is outlined. A result of this continuing program of investigation is the new Model 45 Acousti-Booth. The Booth is analyzed as to physical dimensions, shape, comfort in use, and acoustical effectiveness, showing why the specific details were incorporated into the design and, in so doing, attains a 50 percent reduction in loudness.
Simplified Optical Modeling for Auditoriums
Authors: Leonard R. W.
Published: September 2005

The use of light rays in observing reflections from the surfaces of auditorium models is at least as old as the Acoustical Society itself. The adaptation to be described is a reduction of the three-dimensional modeling technique of Vermeulen to a two-dimensional model which is adequate in many cases. The equipment outlay is nominal, and the model may be set up on a blueprint or ozalid showing the section under study. When the optimal profiles have been selected these may be traced directly on the print. In a few minutes results may be obtained which would require hours by the conventional ray drawing technique.
Reverberation Measurements on Thick Absorbers with Variable Slit Facings
Authors: Leonard R. W. , Sepmeyer L. W.
Published: September 2005

The results of absorption measurements on 1-in. Fiberglass backed by large air spaces and faced by a variable slit structure will be presented. The flexibility of these composite absorbers in the correction of low-frequency reverberation will be indicated.
Design of the New Aula Magna, Ciudad Universitaria, Caracas
Authors: Newman Robert B. , Purcell Jack B. C. , Williams Keith
Published: September 2005

Although the basic shape of this new hall was set by the architect, many opportunities were presented for unusual design collaboration between architect, engineer, and sculptor in this project. The provision of random sound reflecting and diffusing panels on walls and ceiling and the canopy over the stage give excellent sound distribution in the basically difficult fan-shaped plan, and at the same time give reason for an unusual architectural treatment of the interior. A number of echo problems were encountered in the finished building, and the study and control of these, together with the final adjustments of the reverberation characteristic are discussed.
On the Propagation of Noise in Pipes. I
Authors: Mawardi O. K. , Young J. E.
Published: September 2005

The theory of a noise field inside a pipe is worked out in detail. An expression is found for an equivalent Green's function for the domain of the pipe. Relations are determined for the extension of the results to higher-order sources. Averaging is carried out according to standard statistical procedures. It is hoped that the present work can be employed in derivations relating to the field due to noise sources inside the pipe.
An Explosive Noise Source
Authors: Watters Bill G. , Baruch Jordan J. , Galloway William J.
Published: September 2005

An explosive noise source which uses a 10-ga blank shotgun shell has been used for measuring the acoustical performance of sound attenuating passages such as those used in jet engine test facilities and large ventilation systems. The source has a peak power output of the order of 10 000 watts, is portable, and has a high degree of repeatability. The frequency spectrum on an octave band basis closely simulates that of a typical jet engine. Instrumentation has been developed for analyzing the results of shot tests and close agreement between these and pure tone and random noise test techniques has been obtained.
On the Shielding of Noise Outdoors
Authors: Stevens K. N. , Bolt R. H.
Published: September 2005

Shielding of noise by buildings and walls can serve very usefully in the control of noise in communities. Fehr has reported a method, derived from diffraction theory, for computing the insertion loss of an impervious wall of infinite length and arbitrary height, placed between a point source and point receiver at arbitrary distances from the wall. Hayhurst has reported measurements on shielding by walls up to forty feet high, using stationary aircraft as noise sources. This paper presents further measurements on shielding by structures outdoors and attempts to correlate the available results with theory. In practice one must take into account, in addition to the idealized diffraction from an infinite shield, several factors including (a) finite size and detailed geometry of the shielding structure; (b) radiation from the ground image of the noise source; (c) attenuation contributed by the terrain, with and without the shield interposed; (d) refraction, scattering, and shadow effects caused by wind and temperature gradients and by turbulence. Studies of these effects have been made and procedures for estimating the amount of shielding obtainable in certain practical cases will be reported.
Behavior of Engine Test Cell Structures
Authors: Labate Samuel , Beranek Leo L. , Watters Bill G.
Published: September 2005

Recent data are presented on the directivity of hot and cold vertical stacks, on the effects of adding linings to right-angle bends, on the attenuation due to added cooling water, and on the behavior of various types of Soundstream absorber installations.
Measuring the Sound Attenuation of Space Absorbers for Jet-Engine Test Cells
Authors: Waterhouse Richard V. , Cook Richard K. , Berendt Raymond D.
Published: September 2005

The space absorbers were long hollow cylinders of perforated metal, filled with glass fiber; their profile was streamlined for airflow parallel to the axis of the cylinders. The absorbers were placed in a hollow concrete pipe which was then used like an impedance tube except that it was rigidly terminated at the end, and the variable measured was the absorption of sound waves in passing along the tube. The direction of propagation of sound was parallel to the axis of the cylinders so that absorption occurred at grazing incidence. For octave bands of noise, the interference pattern given by theory for the mean squared pressure is 〈P2〉Av = cosh 2ax + (cos3kxsinkx)/kx, where k is the wave number and x distance along the pipe measured from the reflecting end. Experimental results were obtained which followed this pattern, and the required sound attenuation factor a was then obtained by a graphical method. Results of reverberation room absorption measurements on some of the cylinders will also be presented.
Apparatus for Measuring Noise of Vortical Origin
Authors: Gifford G. D. , Goldman R. B. , Mawardi O. K.
Published: September 2005

The apparatus used for the measurement of noise from the shedding of vortices off an obstacle consists of a long square tube 3 in. on the side terminated at both ends by Fiberglas wedges. The noise under investigation is generated by placing obstacles of various geometries inside a test section at the center of the tube. A quiet supply of air is connected to the tube through an opening on one side. The air leaves from a similar opening symmetrically placed with respect to the test section. The microphones used for the measurement of the sound field in the tube are situated beyond the intake or discharge openings, and consequently there are no difficulties with microphone wind noise. The background noise in the test section, when empty, is well below the signal levels under study. Preliminary measurements made on baffles of simple shapes are presented for air velocities of 75 to 150 feet per second.
A Survey of Noise Environments in Industry
Authors: Karplus H. B. , Bonvallet G. L.
Published: September 2005

A survey has been made of steady-state noise in various manufacturing industries. Pressure levels in octave bands and corresponding loudness values are classified according to type of industry. Measurements are further sub-divided into “machine levels” taken close to the principal noise sources, and “area levels” taken at greater distances where a larger number of workers is affected. In the noisiest industries about 50 percent of the machine levels were between 95 and 115 db with a loudness between 50 and 500 sones. The area levels in some of the quiet industries were between 77 and 81 db with a loudness around eight to ten sones. A correlation between over-all level and total loudness indicated a range of about 9 db for noises of different character having the same total loudness. The noise spectra of several typical machines will be presented also. Median, quartile, and extreme values are used to specify the range of values encountered.
Sound Propagation in the Ground
Authors: Morse R. W.
Published: September 2005

Propagation along the ground is governed largely by local stratification which leads to guided propagation along the surface. The ground water table provides a large acoustic contrast so that the top layer can act as a type of wave guide. The problem is reviewed theoretically and comparisons are made with measurements to be found in the literature.
A Study of Temperature-Created Shadow Zones in the Atmosphere
Authors: Pridmore-Brown David C. , Ingard Uno , Oleson Stanley K.
Published: September 2005

The sound field around a spherical source located above ground in an atmosphere with a vertical temperature gradient has been studied experimentally and theoretically. The ground is assumed to be described by a normal impedance, and the temperature to fall off with height over ground so as to give rise to the formation of a shadow zone. Experimental results obtained in a model weather chamber will be presented and compared with theory.
Continuous Tone Underwater Reverberation
Authors: Conley Patrick
Published: September 2005

Continuous tone underwater reverberation is the signal observed when the transmitting and receiving transducers are in linear motion, the transmitter is operating at a single frequency, and no major reflecting bodies are in the beam paths. This reverberation has been measured as a function of frequency for ocean depths of 9.5 to 85.7 meters, at transducer speeds up to 7.5 meters per second, and for various sea states. The techniques for measurement are described, and some typical reverberation spectra are shown. The spectra are shown having maxima at approximately the frequency corresponding to the Doppler shift caused by the transducer motion. The spectra are asymmetrical about the maximum, with the general reverberation level decreasing with increasing depth and decreasing sea state.
Theory of Continuous-Tone Reverberation
Authors: Klotzbaugh G. A.
Published: September 2005

The shape of the reverberation curve described in the previous paper can be explained if the scatterers in the water are assumed to be in motion. The reverberation is assumed to arise from a surface layer and from the main volume of the water. Formulas are given for the two components of reverberation. As an alternative, reverberation may be described in terms of general fluctuations in propagation conditions.
Ultrasonics and Progressive Deafness
Authors: Angeluscheff Zhivko D.
Published: September 2005

The ear of man can receive, and interpret as sound, frequencies from 16 to 20 000 cps. Vibrations above this sonic range are not received subjectively as sound, they are ultrasonics. A sound is composed of fundamentals and harmonics of ever increased number of vibrations that may reach the range of ultrasonics. Although not perceived the ultrasonics can damage the auditory mechanism. Constant exposure to sonic-ultrasonic vibrations impair the bearing perception in man. To compensate for loss of hearing, the modern technology advances amplifying devices (hearing aids, pickups, etc.). Piezoelectric materials being employed ultrasonic energy is put to work. The hearing organ exposed to ultrasonics responds with pathological changes. Sono-chemists have reported H-ion shift in plasma and irreversible alteration in the sol-gel balance. Bone pathologists have demonstrated proliferative changes in the periosteum and endosteum, formation of new bony tissue with bluish discoloration resembling “the blue coats of Manasse” in otosclerosis. Low intensities (0.1 watt/sq cm), (0.03 watt/sq cm), 20 000 cps are disrupting cells and stimulating proliferation in the labyrinth. Ultrasonic frequencies pinpointed by transducers upon organic tissue exert tremendous vibratory force of pathological quality. Constant bombardment by ultrasonics, a result of our complex mechanical civilization, must be considered to be responsible for some of the chronic progressive loss of hearing in our populace.
The Early Detection of Deafness with and without Machines
Authors: Fowler Edmund Prince
Published: September 2005

This paper was written as part of the program of education instituted by the subcommittee on the Hard of Hearing and Deaf. Attention is focused upon the early detection and early diagnosis of deafness, especially in little children. Stress is laid on the importance of checking the hearing of babies in the home. In babies audiograms may be very misleading, and particularly the so-called “psychogalvanic test.” Many children who do not respond to sound are not deaf at all, and many who do respond to sound vibrations have no speech hearing whatsoever. Various emotional and mental disorders and brain injuries may be the determining factors. The physician, with or without the aid of machines, must make the diagnosis and institute treatment. The otologist needs the cooperation of the acoustic scientists to solve some of the problems involved in the early detection of deafness in preschool children.
The Propagation Velocity of Surface Waves over the Human Body
Authors: von Gierke H. E. , Franke E. K. , Oestreicher H. L.
Published: September 2005

Mechanical excitation of the body surface with periodical forces or impulses results in waves propagated over the surface in addition to shear waves and compressional waves in the tissue. The waves have been made visible for periodic vibrations up to 150 cps by stroboscopic illumination, and their phase velocity has been measured. Theoretical treatment of the propagation of this wave type in a viscous elastic medium with the properties of body tissue indicated that the propagation velocity undergoes increasing dispersion as, with increasing frequency, the waves change from elastically controlled to viscously controlled waves. In addition, the group velocity is always larger (up to the factor 2) than the phase velocity. New measurements of the group velocity of short wave trains (4 full cycles with a sin2 envelope) substantiated the theory: the group velocity increased from about 2 m/sec at 20 cps to 40 m/sec at 500 cps. This strong dispersion explains the scattering of data reported elsewhere for the propagation velocity of single impacts, the spectra of which were not constant and not well defined.
Effects of High Intensity Sound on Electrical Conduction in Muscle
Authors: Welkowitz W. , Fry W. J.
Published: September 2005

Studies carried out on the curarized, excised biceps muscle of the hind leg of frog (Rana Pipiens) demonstrate that under appropriate ultrasonic dosage (frequency of one megacycle) the action potential response of the muscle can be permanently reduced or completely blocked. This can be accomplished in the absence of a temperature level sufficient in itself to cause permanent suppression. Quantitative determination of the minimum dosage curve (reciprocal of exposure time vs acoustic pressure amplitude) required for a ten percent reduction of the action potential indicates that the shape of this curve is the same as the curve given by Fry for paralysis of the hind legs of frogs irradiated in the lumbar enlargement region of the spinal cord. Histological examination of stained tissue sections shows no gross tearing or vacuolization. Probe measurements made within the muscle also indicate that cavitation is absent.
Some Applications of Time Delayed Signals in Acoustical Environment Control
Authors: Knowles Hugh S.
Published: September 2005

The quality of reinforced or reproduced speech and music can be enhanced in many instances by the use of supplementary loudspeakers which are supplied with suitably delayed and spectrally modified signals. This paper deals with the use of systems in which the spatial distribution of the loudspeakers and the temporal control of the electrical signal energy serve both to control the ratio of direct to reflected sound and smooth the statistical decay of the sound energy and alter the fine structure of the decay so that flutter and echo are reduced. High or low ratios of direct to reflected and delayed sound are used depending on whether speech or music is to be reproduced. Supplementary loudspeakers have also been used in outdoor music systems to provide an artificial acoustical environment which simulates an environment normally preferred for indoor listening. Preliminary reports on listener preferences on abnormal and relatively normal environmental effects are discussed. Some analytical and experimental aspects of the sound ray or geometric and the statistical approach are given.
The Measurement of Human Channel Transmission Characteristics
Authors: Munson W. A. , Karlin J. E.
Published: September 2005

This paper uses concepts in information theory and psychophysics to provide a basis for the quantitative measurement of certain communication properties of the human being. The responses of an observer in a threshold of hearing test were found to be similar to the transmission of a noise and a noise plus a signal over a physical circuit having a bistable element with a variable operating point. With this analogy, the results of threshold tests are used to compute the noise level of human circuits and the operating points of the hypothetical bistable mechanisms in human channels. The noise level is the practical lower limit for the transmission of information. The operating point usually changes systematically with signal level. For many observers it decreases as the signal level is lowered but again increases when the signal approaches the noise level.
Cumulative Effects of Repeated Bursts of White Noise on Threshold for 4000-cps Tone-Pips
Authors: Lightfoot Charles , Jerger James F.
Published: September 2005

An experimental study was made of transient auditory effects occurring in normal ears on a number of occasions during each of which they were exposed to a. series of 100 2-second bursts of noise. Post-burst thresholds for a 35-millisecond pip of 4000-cps tone were determined repeatedly during and following each of several such exposures. Level of burst, burst-pip interval, and rate of repeating each burst-pip sequence were systematically varied. Bursts as low as 90 db (SPL) were observed to accumulate increasing threshold-shifting power during a series of presentations at a rate of 6 per minute. The rate of such accumulation, for a single repetition rate, appeared to be primarily a product of burst level. Changing the burst-pip interval from 90 to 1000 milliseconds had little effect on rate of accumulation; however, there were signs of an interacting effect of level and interval. Changing the burst-pip repetition rate from 6 to 3 per minute diminished the rate of accumulation. At four minutes after exposure to 100 bursts as low as 100 db the thresholds of most subjects had failed to return to normal. Tinnitus was commonly experienced during the latter part of a series of 110-db bursts. Subjects differed significantly in their rate of accumulating additional loss in acuity. We conclude that number and rate of burst-pip sequences are important variables to be controlled in studies of “auditory fatigue” and/or “adaptation.” The reaction of an ear to repeated stimuli appears to have possibilities as an index of the ear's susceptibility to stimulation deafness.
Channels of Reception in Pitch Discrimination
Authors: Pikler Andrew G. , Harris J. Donald
Published: September 2005

Pitch discrimination was studied in four normal-hearing subjects monaurally, binaurally, and in a variety of other channels of reception. There was no difference in sensitivity between the two ears of any subject, nor were there differences in sensitivity of the monaural channels and the binaural channel, provided all channels were carefully matched in loudness. All channels were equivalent under conditions of matched loudness, except the successive interaural channels (standard stimulus in right ear, variable stimulus in left, and vice versa). These channels showed some slight deterioration of sensitivity and some increase in variance which can be attributed to momentary fluctuations of diplacusis. Similar fluctuations were also found in a channel utilizing a monaural standard stimulus and a binaural variable stimulus, the stimuli in the two ears being matched for loudness. Under these conditions, furthermore, a third pitch is sensed, a phenomenon we term triplacusis. Triplacusis must arise from interaural interactions, and indeed the data as a whole point toward a heavily nonperipheral explanation of pitch discrimination.
A Recorded Test for Determining Absolute and Masked Thresholds of Clicks, Bands of Noise, and Warble Tones
Authors: Webster J. C. , Nickerson J. F.
Published: September 2005

A test has been constructed to screen out men who cannot hear well in low levels of noise and/or who have absolute hearing losses of 25 db or more. The test signals consist of one-millisecond clicks, or 34-second pulses of various sounds. For low-frequency acuity pulses of 200–800 cps noise and tones warbling at a 5-cps rate for an extent of 62.5 cps around 500 cps are used. For high frequency acuity a 5000-cps click, pulses of 1600–6400-cps noise, and pulses of a warble tone of 4000 ± 125 cps are used. A warble-tone-pulse of 1000 ± 125 cps, and a 1000-cps click are used for testing the middle or working frequency acuity. These signals are always heard in a background of noise shaped to provide approximately equal masking at all frequencies. The levels of noise vary so as to cause zero, 25, or 35 db of masking at various times throughout the test. If the test is given our earphones the ambient room noise (over-all level, flat position) can reach 50 db without invalidating the test results. The mechanics of the test construction and some preliminary results of using the test will be presented.
The Attenuated Modes in Elastic Plates
Authors: Lyon Richard H.
Published: September 2005

This paper deals with the solutions of the classical frequency equations which represent the attenuated modes in an elastic plate. A graphical procedure for obtaining these modes and their use in the case of forced motion will be outlined.
A Study of the Rijke Phenomenon
Authors: Kerwin Edward
Published: September 2005

This paper presents a theoretical and experimental study of the Rijke phenomenon, that in which a heated grid causes sustained oscillations in the air column in a vertical, open-ended tube. The evaluation of the complex natural frequencies (β = σ + jω) of the tube involved the following: the introduction of a small but finite transition region at the heated grid and the assumption of a heat-transfer relation. The complex natural frequencies are interpreted as driving functions (σ) and as frequency shifts. An experimental evaluation of the complex fundamental natural frequency was made and qualitative agreement with theory was observed on several counts. However, the measured values of σ were much smaller than the predicted values. Application of the theoretical results to evaluate the phase relations at the heater shows agreement with Rayleigh's qualitative criterion for heat-driven oscillations.
The Field of a Spatially Extended, Moving Sound Source
Authors: Oestreicher Hans L.
Published: September 2005

If one assumes that the flow around a subsonically moving, spatially extended sound source is a potential flow, the problem of determining its field can be formulated as a boundary value problem of a partial differential equation of the second order with, in general, variable coefficients. The construction of an elementary solution and a generalization of Helmholtz's theorem for this equation allow the discussion of the sound field. The field of “sufficiently” small sound sources of arbitrary shape with boundary conditions appropriate for the acoustic case and its relation to the concept of a moving simple source, dipole, etc., is investigated in detail.
Theory of the Effect of a Thin Air Film on the Displacement of a Stretched Circular Membrane
Authors: Robey Donald H.
Published: September 2005

In the design of condenser microphones it is standard practice to insert holes or furrows into the electrode face. This modification helps to prevent radial air flow through the electrode-membrane interstice which can result in large dissipative and reactive effects provided the separation is small. The theory governing air reactions from an unmodified electrode is presented. An attempt was made to start with general fundamental equations. Only those simplifications which appeared to have a negligible effect on the accuracy of the results were made; for example, body forces and nonlinear terms have been neglected. Air inertia, rotational and irrotational velocity components, and viscous terms have been retained in the theory. Curves showing the effects of air reactions on the amplitude, phase, and impedance of a stretched titanium membrane are shown. The air stiffness, which continuously increased for increasing frequencies in the range 5 to 20 000 cps, caused the amplitude of the membrane to diminish by more than 20 db. In general, air which is trapped behind the membrane will cause the response of the microphone to rise as the frequency is lowered.
Elastic Wave Velocities in Laminated Media
Authors: White J. E. , Angona F. A.
Published: September 2005

The velocity of elastic waves traveling parallel and perpendicular to the layering in a laminated medium has been determined by means of static elasticity. The procedure is to assume the medium to be in static equilibrium and exposed to certain stresses. The stresses are of such a nature as to generate strains similar to those which would exist during the passage of an elastic wave through the medium. From the application of Hooke's law, an effective stiffness constant for the medium is obtained. The ratio of this effective stiffness to the effective density is the square of the velocity of the elastic wave. For a medium consisting of layers of two materials with the same density but with a velocity contrast of two, the velocity of compressional waves traveling parallel to the layering is 20 percent higher than the velocity of the same wave traveling perpendicular to the layers. The SH shear wave has a velocity which is 25 percent higher than the SV shear wave for the same laminated medium.
Ultrasonic Dispersion in 1,1 and 1,2 Dichloroethane Vapors
Authors: Rao T. Seshagiri
Published: September 2005

The ultrasonic resonator interferometer has been used to measure the ultrasonic velocity at 30°C in ethylidene chloride (1,1 dichioroethane CH3CHCl2), and ethylene chloride (1,2 dichlorocthane CH2Cl CH2Cl) vapors, as a function of frequency over pressure. The ranges of f/p employed are 0.9 to 104 Mc sec−1 atmos−1 in the case of the former vapor, and 1.0 to 100 in the latter. There is an indication of double relaxation in both the cases, the principal frequency/pressure ratios being in the neighborhood of 58 ± 5 in ethylidene chloride and 98 ± 5 in ethylene chloride, which are estimated by a superposition of the experimental curves (velocity vs f/p) with the theoretical curves obtained by using the spectroscopic data along with Kneser's formula. There is good agreement between the experimental and theoretical curves, thereby showing that the observed dispersion in ultrasonic velocity is due to the slow rate of energy exchange between translational and vibrational states.
Ultrasonic Absorption in Toluene
Authors: Beyer Robert T.
Published: September 2005

The ultrasonic absorption coefficient has been measured in toluene by means of the spherical resonator method of Leonard. Measurements were made in the temperature range 6–40°C and in the frequency range 50–400 kc. The existence of a relaxation peak in this region, reported by Moen, has been confirmed. The temperature dependence of the maximum absorption per wavelength indicates a ΔH of about 4000 cal/mole, which would appear to be too small for the process to be one of the excitation of the C–H bond stretching vibration to which Andreae and Lamb attribute this absorption. The measurements at the higher temperatures also suggest the existence of a second relaxation process with a lower relaxation frequency.
Study of Rapid Reversible Reactions in Liquids with Ultrasonics
Authors: Karpovich John
Published: September 2005

A resonance-reverberation method for measuring sound absorption in the frequency range of about 20 kc to about 1 Mc has been developed. The measurements are made in a single spherical glass container which has been calibrated with liquids of known absorption to permit the separation of wall losses from the liquid absorption. Over 40 liquids have been studied with this apparatus. Acoustic relaxations were observed in some cyclohexane derivatives, cyclohexene, methyl formate, ethyl acetoacetate, acetic anhydride, and methyl benzoate. Additional measurements have been made in the relaxation regions of formic acid, ethyl formate, methyl acetate, and ethyl acetate. The relaxations observed in the cyclohexane derivatives have been attributed to the perturbation by the sound wave of equilibria between rotational isomers. The restricted rotation occurs about the single bonds in the ring during the conversion from one chair configuration to another. The relaxation in cyclohexene is due to the perturbation of the equilibrium between the pseudo chair and boat configurations. Restricted rotation about the C–O bonds explains the relaxations in the esters of the carboxylic acids. The acoustic relaxations in the formates and the acetates are identified with the infrared absorption bands at about 1160 and 1185 cm−1.
Cues for the Identification of the Fricatives of American English
Authors: Harris Katherine Safford
Published: September 2005

It has sometimes been assumed that the identification of the fricatives of American English depends primarily on the characteristics of the noise (i.e., nonvocalic) portion of the speech sound. A second possibility is that frequency shifts in the formants of the vocalic portion—previously shown to be cues for the perception of the stop and nasal consonants—are important for the fricatives. These alternatives were tested by combining the noise from one spoken fricative-vowel syllable with the voiced portion of another fricative-vowel syllabic. Results indicate that the important cues for the fricatives s and f are indeed given by the noise part of the syllable, but that the differentiation of f and θ is accomplished primarily on the basis of cues contained in the vocalic part of the syllable. The role of formant frequency shifts (transitions) as cues for f and θ was investigated further. Synthetic formants produced by the pattern playback were paired with noise portions from spoken syllables. The results confirm the importance of transitions as cues for f and θ, and permit specification of appropriate transitions for these sounds. Preliminary explorations were made of the frequency-intensity-duration characteristics of the noise portion of syllables beginning with s and ∫. The differentiation between these sounds appears to depend critically on the lower cutoff frequency of the noise spectrum.
An Instantaneous Pitch-Period Indicator
Authors: Dolansky Ladis-Lav O.
Published: September 2005

Instantaneous indication of the beginnings of individual pitch periods of a voiced-sound speech wave is often desirable in speech analysis. With conventional means, such as linear filtering and subsequent wave-form shaping, this instantaneous indication is very hard to achieve because of the considerable time delay involved. In the “instantaneous” pitch-period indicator the problem is solved by using non-linear techniques and a variable time-gating circuit; a pitch-period beginning is indicated by a marker pulse having a maximum delay of the order of five percent of the pitch-period duration. The application of the device to certain problems of speech analysis will be indicated.
An Analysis of the Confusion among English Consonants Heard in the Presence of Random Noise
Authors: Miller George A. , Nicely Patricia
Published: September 2005

The English consonants p, t, k, f, θ (thin), s, ∫ (she), b, d, g, v, ð (they), z, ȝ (beige), m and n were pronounced before the vowel a (father) by female talkers with General American pronunciation. Listeners heard the syllables in the presence of a masking noise and were forced to guess at every syllable. The signal-to-noise ratio, measured between the over-all level of the noise in a band from 20 to 7000 cps and the level of the vowel as read on a VU meter, ranged from −18 to +12 db in steps of 6 db. Five talkers were used with four listeners for each talker. The most obvious aspect of these consonants in noise is the presence or absence of voicing; voiced and voiceless consonants were seldom confused until S/N was about −12 db or worse. The aspect of nasality also seems to disappear at about −12 db. The next most obvious aspect is the difference between stops and continuants; confusions on this aspect did not occur until S/N was about −6 db or worse. These three aspects define five classes of consonants: voiceless non-nasal stops, p, t, k; voiceless non-nasal continuants, f, θ, s, ∫; voiced non-nasal stops, b, d, g; voiced non-nasal continuants, v, ð, z, ȝ; and voiced nasal continuants, m, n. Confusions within these five classes occurred when S/N was Odb or worse. At favorable signal levels the most frequently confused pair is f and θ, closely followed by v and ð, then p and k.
The Intelligibility of Different Speech Materials
Authors: Hirsh I. J. , Reynolds Elizabeth G. , Joseph Maurice
Published: September 2005

Articulation scores for nonsense syllables and for monosyllabic, disyllabic, and polysyllabic words were obtained as a function of the cutoff frequency of low-pass and high-pass filters and also as a function of signal-to-noise ratio at different noise levels. Results indicate that eliminating all frequencies above or below 1600 cps does not impair the intelligibility of words seriously. The intelligibility of a word is a direct function of the number of syllables in the word and monosyllabic words are more intelligible than nonsense syllables. The relation between the intelligibilities of each word type and nonsense syllables is not the same when the system is impaired by filtering as it is when the system is impaired by noise. The implications of the lack of consistency from one experiment to the other for the generality of the concept of articulation index is discussed.
Optical Measurement of the Sound-Pressure Amplitude and Waveform of Ultrasonic Pulses
Authors: Lester W. W. , Hiedemann E. A.
Published: September 2005

The use of light diffraction for the measurement of the sound-pressure amplitude and the waveform of ultrasonic waves has been extended to the case of ultrasonic pulses. The method has been applied to transducer calibration in water at 5 Mc for pulses of 3 to 12 μsec duration, and compared with calibration by means of continuous waves. The distortion of the waveform in ultrasonic pulses of finite amplitude is demonstrated by measurements of the transducer voltage vs light intensity in the first diffraction orders. All measurements made with continuous waves and with pulses give approximately identical results.
Corrected Calculations of Sound Absorption in Nonassociated Liquids
Authors: Nettleton R. E.
Published: September 2005

Bulk viscosity and ultrasonic absorption coefficients for carbon tetrachloride and chloroform at 20°C, 1 atm, have been recalculated in order to correct an earlier result which has been modified more recent work. The changes increase the vibrational relaxation contribution to the absorption by a factor of order unity, while the structural contributions, resulting from relaxation of the distribution of free volume, are left unchanged. New values for tetrachloride and chloroform, respectively, are: for bulk viscosity 0.2729 and 0.2934 poise; for 2α/ν2, the intensity absorption divided by the sound frequency squared, 8.84×10−15 and 7.88×10−15 sec2/cm. This represents an improvement, which is not very significant, in the agreement with experiment.
Precise Determination of Wavelength with an Ultrasonic Interferometer
Authors: Ikeda Ikuo
Published: September 2005

The method of ultrasonic interferometer has often been used in measuring the sound velocity in liquids. The accuracy of this method, however, is not an excellent. The present method will give a good advance in the accuracy and in the upper limit of the applicable frequencies. The writer was able to detect 0.2 μ of the movement in the acoustical path of particular distances. A frequency of 15 Mc was used.
On the Damping of a Multilayer Plate
Authors: Yildiz Asim
Published: September 2005

The two-dimensional equations governing the motion of a three-layer sandwich of plates are derived subject to suitable assumptions.
Noise Control Criteria for Residential Heating and Air Conditioning Systems
Authors: Blazier Warren E.
Published: September 2005

Because of the sensitive nature of the environment, noise control criteria suitable for use in residences, differ from those applicable to commercial or industrial use. The trend to smaller, more compact, residential air conditioning systems has developed a need for noise control criteria which orient new product design in proper relationship with the ultimate environment. A series of products, having various levels of known customer acceptance, have been subjected to comprehensive acoustical analysis using the reverberation room technique to determine the sound power level (PWL) spectrum of each unit. A modified form of the Beranek NC contours has been found to provide an encouraging correlation with field experience. The best correlation is obtained from 1/3 octave band data which show up important changes in spectrum shape in addition to providing resolution of line spectra in terms of adjacent broad band noise. The largest variability in correlation has been found to depend on the pure tone content. In general, a plus 5-db correction for line spectra exceeding the level of adjacent 1/3 octave bands seems to provide a more consistent agreement with field experience. The language barrier which the acoustical engineer must bridge when influencing product design is well known. This barrier can be made less formidable when control criteria can be presented relative to levels of customer acceptance. A moderately successful method of doing this has been found.
Noise Sources and Transmission Paths in Refrigerating Compressors
Authors: Kirschner Francis G.
Published: September 2005

Quieting reciprocating compressors for refrigeration involves all the classical techniques and devices used in high-speed electromechanical machinery—vibration isolation, balancing, mufflers, flexible connectors, etc.—and an important number of special techniques, involving thermodynamics with temperature changes of 200 to 300°F, pressure changes of the order 20 times atmosphere, high flow velocities, and media where only metallic components with very little inherent damping can be used. The working medium must be carried in pipes under pressure and the flow is modulated by complex pulses due to the high-speed pumping and fast valves, which act like fast switches in a transmission line, generating noise. A study of acoustic transients (pulses) in pipes has been made on an analog scale model (linear acoustical pressures up to 100 dyne/cm2 114 db), then on an actual compressor (high nonlinear pressures up to 107 dyne/cm2) with different acoustical components (inductance, capacitance, resistance) in the line, and different input and termination impedances of the line. The influence of these components on pressure pulsation and outside noise, and how the analog helps to identify noise sources, which have same frequency and amplitude noise output (rpm, intake, exhaust) will be described along with structural noise transmission, through flexible “corrugated metallic hose” under different pressures used in refrigerating compressors. Mechanical impedance measurements carried out on compressor shells to find points with high mechanical impedance for optimum locations of exhaust lines will be shown, with vibration modes and resonant amplification of a typical compressor shell.
Field Survey of the Noise Reduction of Folding Partitions
Authors: Hardy Howard C. , Ancell James E.
Published: September 2005

There is considerable confusion in the public mind on the noise reduction efficiency of folding partitions. Some of the reasons for this state of affairs are (1) exaggerated performance claims by some manufacturers, (2) some unrealistic aspects of the method of testing used, (3) the large variation of data reported by the reference testing laboratories, and (4) the paucity of field data. This paper is a report of field measurements on a number of actual installations. The technique used, which has been applied to a large number of field tests of sound transmission, is very convenient and gives consistent data. The sound source consists of a portable playback of successive magnetic tape loops of half-octave bands of random noise. Measurements are made in both source and receiving rooms with a sound level meter and half-octave band filter. Data are usually obtained in the 106–150, 150–212, 212–300 … 3400–4800 cps bands, thus giving essentially the same measurement frequencies (125, 175, 250, … 4000) that are used in the reference laboratories. The most important parameter in the performance of the partitions is the effectiveness of the seals at the top and bottom as provided by sweep strips, if they are used at all. Using the noise reduction in the critical 600–825 cps band as a reference, for example, the figures vary between 7 to 22 db, depending mostly upon the seal. There are no conclusive differences among manufacturers. Acceptable acoustical isolation for meeting spaces can be made with folding partitions, provided (1) extreme privacy is not needed, (2) the spaces on each side are not too large, (3) efficient sweep strips are used with precautions in installation and maintenance, and (4) there is a reasonable background noise for masking.
Perception of Compound Consonants in Noise
Authors: Pickett J. M.
Published: September 2005

The perceptual confusions among English compounds of two consonants were examined. One defined class of syllables, made up of 15 initial compound consonants in conjunction with three vowel sounds (i), (a), and (o), and another class of 15 final compound consonants in conjunction with the same three vowel sounds, were employed. Recorded syllables were played back against a white noise background and against a low-frequency noise background. Confusion patterns among the compound consonants depended upon the articulatory dimensions of the individual consonant members which formed the compound That is to say, there was little evidence of interaction among the members of the compound. The confusion patterns indicated that the low speech frequencies, i.e., those frequencies heard above the white noise, convey the consonant distinctions of nasality, stop vs liquid, and place of articulation of the liquids. On the other hand, the higher speech frequencies, heard above the low-frequency noise, conveyed the distinction of affrication. The different vowels had minor effects on the perception of the consonants adjacent to them.