bluuebunny/crossref_metadata_2025 huggingface dataset:
Auditory Tests with Synthetic Vowels
Authors: Miller R. L.
Published: September 2005

The results are given for a series of phonetic evaluation tests which were made by means of synthetically produced vowel sounds. By emploment of synthetically produced sounds, a number of the significant parameters could be varied in an independent and systematic manner without encountering the uncertainties and limitations of the human speech mechanism. The types of parameter changes which were investigated by this means were those of fundamental frequency or pitch, formant frequency and amplitude, and, finally, the number of formants important to a sound. The results of the tests indicate that all of these parameters are important in the evaluation of the sound. In particular, there is a shift in the phonetic evaluation which can be attributed to pitch alone.
Further Electrophysiological Observations on Auditory Masking and Fatigue
Authors: Rosenblith W. A. , Rosenzweig M. R.
Published: September 2005

Electrical responses to supra-threshold acoustic clicks are easily observed at the two extreme stations of the auditory nervous system of anesthetized cats: the round window and the auditory cortex. The neural components of the round window response and the cortical potentials have been shown to be particularly sensitive, amplitudewise, to masking noises and to previous exposure to loud sounds. The effects of repeated exposures and the effects of the intensity and duration parameters for given exposures have been investigated. We have also collected data regarding central factors in masking and fatigue. Present results indicate: (1) that the cortical response to supra-threshold clicks delivered to the left ear remains essentially unaffected after the right ear has been exposed to loud sounds; (2) that the cortical response to a click delivered to the left ear is unaffected by a masking noise delivered to the right ear, even if the noise is sufficient to reduce (mask) the neural response to a right ear click stimulus. These results are valid only as long as there is no appreciable acoustic leakage from ear to ear.
The Aural Recognition of Pulsed Signals in Very Narrow-Band Noise Backgrounds
Authors: Dieter C. L. , Lieberman G. , Peterson H. L. , Finney W. J.
Published: September 2005

Experimental studies of the aural recognition of pulsed sinusoidal signals in noise backgrounds have been extended to include masking by bands of random noise less than 1 cycle per second in width. The results of these narrow-band masking experiments are of particular value in establishing more accurate electrical circuit representations for the human hearing mechanism as a pulsed-signal detector.
Relation between Vortex Sound Generation and Wind Resistance
Authors: von Wittern Wolf W.
Published: September 2005

The vortex sound generation of rods rotating like propeller blades of different profiles was investigated up to tip speeds Mach No. 1.0. It was found that the rotating blade, as far as the vortex sound field is concerned, represents a sound source of first order moving on a circle. Out of the periodic variations of the sound pressure at different points of the sound field, the directivity pattern rotating with the blade was determined and found in good agreement with the calculated directivity pattern of a dipole rotating on a circle (see Oestreicher, Abstract J4). The radiated acoustic power was found to increase with the 6th–10th power of the tip speed of the blade. Out of the radiated acoustic power and the driving power of the rod, the acoustic mechanical efficiency was determined. This efficiency as a function of tip speed showed a characteristic relation to the aerodynamic qualities of the investigated profiles. The frequency analysis of the vortex sound showed that aerodynamically poor profiles generate a relatively small band of frequencies around the frequency of the Karman street, but aerodynamically good profiles generate a broad spectrum.
A Consideration of the Moment 〈F(t)|F(t)|n〉Av in the Detection Problem
Authors: Westervelt Peter J.
Published: September 2005

The recognition of a signal having asymmetric wave form or harmonically related line structure will be discussed. A general consideration will be given to the average 〈F(t)|F(t)|n〉Av when F(t) consists of a signal plus noise. A simple circuit for taking the average when n − 1 consists of two square law rectifiers connected in parallel. The application of this circuit to the recognition of a signal consisting of fundamental and second harmonic terms will be treated in detail.
The Dynamics of the Cochlea
Authors: Fletcher Harvey
Published: September 2005

Since Békésy's excellent experimental measurements of the mechanical constants and movement of the basilar membrane, two major papers have become available which give theoretical discussions of the subject discussed in this paper, one by Peterson and Bogart and one by Zwislocke. In the former the frictional force was neglected and a solution was obtained which throws considerable light on the mechanism, but the calculated curves of amplitude at various positions along the basilar membrane are far from those observed by Békésy. In the latter paper the frictional term is considered the all-important one, and the vibrating mass is neglected, and the author claims that his calculated amplitude curves fit those observed except for the phases; however, all of the details of this calculation are not given. In the present paper all three terms in the mechanical impedance of the basilar membrane are taken into account, and calculated amplitudes are obtained which agree approximately with those observed in amplitude and phase and time of travel of the wave from the stapes to any point on the membrane.
Some Statistical Aspects of Half-Loudness Judgments
Authors: Garner W. R.
Published: September 2005

Fairly complete data have been obtained for half-loudness judgments of a 1000-cps tone, from 18 observers, at ten intensities (10 to 100 db SPL), with two methods (adjusting either the first or second tone of a two-tone sequence). Ten settings were made by each observer, with each method, at each intensity level. An analysis of variance was carried out with the entire set of data, with the following conclusions: (1) The variance of repeated observations by one observer with the same method accounts for 22 percent of the total. (2) That due to consistent differences between observers accounts for 35 percent of the total. (3) That due to differences in intensity accounts for 26 percent of the total. This variance reflects the extent to which the half-loudness function is not parallel to the equal intensity function. (4) The interaction variance between observers and intensity accounts for 11 percent of the total, indicating that the shape of the half-loudness function is different for different observers. (5) Variances involving method were consistently small, although statistically significant. (6) The absolute attenuation necessary for half-loudness is somewhat larger than previously reported.
A New Procedure for the Investigation of Experimentally Induced Acoustic Trauma in Man
Authors: Reger Scott N.
Published: September 2005

A procedure is described by means of which the time interval during which a given temporary threshold shift produced by a high level traumatizing noise and the time required for the threshold to recover to near normal threshold values can be determined with useful accuracy. Initially, the subject's threshold values are ascertained for the noise and for the “test” tone. The levels of the two sounds are then raised to the desired intensity levels, e.g., the noise to 110 db and the test tone to 40 db above their respective threshold values. The two sounds are then presented alternately, the noise for ten seconds, the test tone for one second, this cycle being repeated until the subject reports inaudibility of the test tone. By instructing the subject to depress “yes” or “no” switches when the test tone is or is not heard and by connecting the switches to an appropriate recording mechanism, the time (in terms of ten-second intervals) over which 10-, 20-, 30-, and 40-db threshold shifts result are readily obtained. Also, by discontinuing the traumatic tone and attenuating the test tone (now presented continuously) in, e.g., 10-db steps whenever the subject responds with the “yes” button, the acceleration of the recovery curve is obtained. An almost infinite number of parameters result from varying the duration, intensity level, and frequency composition of the noise and the test tone. The procedure, with reasonable care, eliminates the possibility of producing permanent traumatic damage to the ear. Experimental results reveal marked individual differences in the length of time over which a given temporary threshold shift for the tone occurs. Curves of experimental data will be presented. It is anticipated that this procedure will constitute a significant noise susceptibility test by means of which “tender” ears can be differentiated from “tough” ears.
Interaural Pitch Disparities Induced Near Discontinuities in Thermal Noise Spectra
Authors: Webster J. C. , Davenport E. W. , Thompson P. O.
Published: September 2005

The shift in pitch of a pure tone due to thermal masking noise has recently been reported by Schubert, by Watson and Frazier, and by Egan and Meyer. The present paper deals with the kind and the amount of such a shift in the presence of noises with abruptly changing spectrum. Using the method of adjustment, subjects varied the frequency of a tone in the left ear until it matched in pitch a tone alternately presented in the right ear. In addition to the tone, a continuous noise condition was also induced in the right ear. These noise conditions varied in random order to include flat spectrum noise, low passed noise, high passed noise, and a combination low pass, high pass noise. Pitch matches without noise preceded and followed the matches involving noise. It was found that even though the masking was less for pure tones on a sloped portion of the low passed noise spectrum, the pitch rise was greater than the rise in pitch due to flat noise. Conversely, the shift of pitch on the sloped portion of a high passed noise was either negligible, approaching the no-noise condition, or in some cases was even shifted downward. These data seem to indicate that the shift in pitch is not only a function of the amount (spectrum level) of the noise, and the signal to noise level, but also depends upon the shape of the masking noise spectrum.
Instantaneous Frequency Band Multiplication, Division, and Analysis
Authors: Vilbig Friedrich
Published: September 2005

In the replay apparatus for visible speech films, it was first necessary to make the film. Then the film was passed by a slot and the emanating modulated light was inverted into frequencies by the aid of a modulation disk. Phono recordings of music pieces that were first recorded on replay film have a good quality when played back through the replay apparatus at normal, multiplied, and divided modulation disk speed. It was also found possible to pass negative as well as positive picture film patterns through the device. However, a disadvantage of such a system is the time delay and associated work of producing the speech film. It will be shown in this paper that it is possible to replay immediately spoken information by using special apparatus in conjunction with the replay device. For this, it is not necessary to pre-analyze the speech band on film. It may be done, for example, by a set of 100 magnetostriction filters, utilizing 30 cps band widths for each filter element for a total band width of 3000 cps. For frequency band analyzing purposes the outputs of the single filter elements are connected to 100 elongated neon tubes. The spectrum distribution is immediately seen by the envelope of the lengths of light portrayed by the 100 adjacent neon tubes. For frequency band compression or expansion, by similarly portraying 100 small neon tubes which are positioned in a small light wave guide, 100 light points are produced along a thin line. Each light point is varied in intensity by one of the elementary filters. Now, instead of a speech film, it is possible to project these 100 speech-controlled light points to the modulation disk. Thus, the output may be an instantaneously divided, multiplied, or normal speech spectrum. It is noteworthy that instead of the neon bulb array a smaller special multigrid oscilloscope tube may be used.
A High Frequency, Wide Range Acoustic Interferometer for Biological Work
Authors: Richards J. R. , Goldman D. E.
Published: September 2005

In biological work, rapid measurements with small samples are often necessary. A two-crystal interferometer has been built for liquid or semi-solid samples of 30 to 100 cc. Sound velocities can be determined to within one part in 500 with a travel of less than 3 mm using a crystal output voltage of about 200 microvolts. Provision has been made for temperature control and for rapid change of crystals to permit measurement at 1, 2, 4, 12, and 36 mc. A phase comparison method has been used for wavelength determinations incorporating a dual heterodyne reduction to audiofrequencies with Lissajous' figures on an oscilloscope. A sonic delay line has been included for absorption measurements using pulsed sound and a calibrated attenuator.
New Methods of Indirect Ultrasonoscopy and Ultrasonography
Authors: Ernst Paul J. , Hoffman Charles W.
Published: September 2005

In a previous paper a method of direct ultrasonography was developed. This paper deals with recent experiments on indirect ultrasonoscopy and ultrasonography mainly using special phosphors. The actual technique involved in the new methods is discussed and their results illustrated by lantern slides.
Study of One Factor in the Perception of the Unvoiced Stop Consonants
Authors: Liberman Alvin M. , Delattre Pierre , Cooper Franklin S.
Published: September 2005

Work reported previously on synthetic speech produced from hand-drawn and highly schematized spectrograms has suggested an experimental test of the role of a single acoustic (spectrographic) variable in determining the identifiability of the voiceless stops p, t, and k. Schematized syllables consisting of a stop-like sound followed by a two-formant vowel were presented for identification of the consonant. The schematic stop consisted of a brief burst of tones confined to a narrow frequency range. The center frequency of this burst was varied in 12 equal steps from 360 to 4320 cps. Each schematic stop was paired with each of 7 two-formant cardinal vowels. The results show close agreement between subjects on the choice of certain frequency positions for p, t, and k; a systematic variation of this position from vowel to vowel; and, in certain cases, so marked an interdependence of the stop and vowel components of the schematic syllable that the same schematic stop was judged by a large majority of the subjects to be p when paired with i and u, but to be k when paired with a. Hence, it appears that the syllable rather than the phoneme may, at times, be the irreducible acoustic stimulus.
Sound-Level Meter and Sound-Survey Meter
Authors: Peterson Arnold , Gross Ervin E.
Published: September 2005

For some time, engineers making noise measurements have required increasingly versatile equipment. The sound-level meter has been supplemented by accessories to meet this need, but it has frequently been a limiting factor in the over-all performance. To remedy this condition a new sound-level meter has been developed. It not only meets the standard specifications but also has the high fidelity range from 20 c to 20 kc necessary for utilization of modern microphones. The stabilized amplifier with wide dynamic range and separate output system supplies a signal suitable for frequency analyzers, high fidelity tape recorders, or level recorders. Miniaturization has led to a compact, light instrument. Many applications, however, can be handled by a simple noise meter and are economically feasible only if a low cost instrument is available. To meet this need a companion instrument, the sound-survey meter, has been developed, whose performance closely approximates that of standard sound-level meters but with simplified operating features. Its diminutive size and good characteristics make it ideal for many tests and survey measurements. With this low cost instrument available, more people will make acoustic measurements, which result should ultimately lead to more widespread understanding and better handling of acoustic problems.
Shift of the Transition Points in Barium Titanate by Partial Substitution
Authors: Brajer E. J. , Jaffe Hans , Kulcsar Frank
Published: September 2005

We have found that the second transition point occurring near 10°C in barium titanate (BaTiO3) is raised by the incorporation of zirconium oxide at the rate of about 5°C per mole percent ZrO2. This makes it practical to utilize the high values of piezoelectric voltage output found in polarized barium titanate ceramic at temperatures below the second transition. The Curie point is lowered about 3°C per mole ZrO2. Barium zirconate (BaZrO2) addition causes the same shift in both transition points, but does not give as high a voltage output coefficient as ZrO2. Stannic oxide and barium stannate cause a larger downward shift of the Curie point but a smaller upward shift of the second transition than zirconium oxide. Other additions, including lead titanate, lower the second transition point. This effect is desirable for piezoelectric ceramics where large variations of capacitance with temperature in the operating range are to be avoided.
Resonant Effects of Mammalian Erythrocytes in Ultrasonic Fields
Authors: Ackerman Eugene
Published: September 2005

The exponential breakdown rate of erythrocytes in intense acoustic fields does not depend on the frequency for sonic fields of constant velocity amplitude. At higher frequencies, the errors in commonly used measuring instruments obscure the effects of varying frequency. Instead of physically measuring the ultrasonic field, we have observed the relative breakdown rates of beef, rabbit, sheep, and human erythrocytes. The ultrasonic energy was applied directly to the suspension from ceramic transducer elements. To compare breakdown rates from one experiment to the next, we held constant the plate voltage, the oscillator frequency, and the transducer current. An additional check was provided by the output from a small ceramic probe inserted into a fixed position in the suspension. No differential frequency effects were observed below 250 kc. Between 300 and 600 kc, optimum frequencies were found at which relative breakdown rates increased markedly. These frequencies are characteristic of the donor species; they represent cellular resonances. The possible interpretations of these resonances in terms of cell structure will be discussed.
The Modes of Vibration of Semi-Flexible Rod under Tension
Authors: Kenworthy Ray W. , Jennings Vernon A.
Published: September 2005

The possible modes of vibration of a rod under conditions which are intermediate between a perfectly flexible string and a stiff bar have been calculated from existing general theory. An experimental investigation of the first ten modes yields results in agreement with the theory with in approximately 0.5 percent Deviation from a harmonic series increases with the number of the mode of vibration.
Spherical Wave Radiation in Solid Media
Authors: Blake F. G.
Published: September 2005

Divergent compressional waves in solids differ from similar waves in fluids, even though the particle displacement be parallel to the direction of propagation in both media. Perhaps the simplest example is the wave propagating from a radially oscillating spherical cavity in an infinite solid medium. When a sinusoidally varying pressure is generated in such a cavity, the normalized acoustic radiation impedance is a function of σ, the Poisson's ratio of the medium, as well as of the ratio of cavity radius to wavelength. As σ increases from zero to one-third, the radiation reactance varies in magnitude, but remains a negative or stiffness reactance at all frequencies. When σ becomes greater than one-third, a resonance frequency of zero radiation reactance appears, above which the reactance is positive or inertial. Then as σ approaches its limiting value of one-half, the resonance frequency decreases to zero and the familiar accession to inertia of fluid medium acoustics is obtained. When an impulsive pressure is generated in the cavity, as by an explosion, the form of the radiated pulse is a damped wave train which does not closely reproduce the original pressure pulse.
Noise Characteristics from Axial Flow Compressors
Authors: Mawardi Osman K.
Published: September 2005

The conventional methods of design of axial flow compressors usually consider the losses introduced by the generation of noise to be of negligible magnitudes and therefore ignore them entirely in a study of compressors. As a result, there is scant information on the relation between the noise level and the performance properties of compressors. In the present paper an attempt is made at working out the basis of a method of evaluation of the noise characteristics from compressors. The method makes considerable use of the experimental findings of Beranek and Rudmose on noise due to airplane propellers. The analysis presented here considers the noise to be generated by a number of point sources of equal magnitudes but of random phase. The resultant intensity level of these point sources (presumed to be located at the tip of the compressor blades) is calculated on a statistical basis. The expected noise level is given as a function of blade tip speed, clearance between blades and stator case, number of blades and the power expended in driving the compressor.
Propagation of Sound in a Water Spray Muffler
Authors: Mawardi Osman , Hemond Conrad
Published: September 2005

In many jet engine testing facilities, water sprays are installed in the exhaust piping to cool the exhaust gases to temperatures which will not damage the walls of the pipe. The water sprays appreciably alter the character of the sound propagation through the piping. The present paper discusses the dependence of the attenuation of sound on such characteristic parameters of the water-spray muffler as its geometry, the amount of air circulated, the quantity of water sprayed, and the average sizes of the water droplets in the air stream. The attenuation of sound in the muffler is found to be due mainly to viscous losses in the boundary layer between water droplets and air. The theory discussed demonstrates that in order to achieve maximum sound attenuation through such a muffler there are optimum conditions as to quantity of water used and the method of its injection into the air stream. The relative velocity of the air stream to that of the injected water must lie within a critical range in order to fix the average size of the water droplets.
Some Data on the Performance of Sound Attenuating Treatments
Authors: Labate Samuel
Published: September 2005

An attempt has been made to obtain reliable information on the intrinsic performance of sound attenuating treatments used in the air flow passages (stacks, ducts, tunnels) of test cells and other aircraft engine test facilities. The apparent performance in a particular installation may be influenced by flanking transmission through the surrounding structure, by standing waves within the cell, by reflections at the ends of the treated section, by the radiation pattern at the exit, and by the spectral characteristics of the noise source for the measurements. These effects must be assessed separately if one is to obtain valid data on the attenuation value of the treatment itself. One can then correlate measurements from many installations and from laboratory experiments to yield generalized performance characteristics. Some results so obtained are given for (a) uniformly spaced absorptive baffles within and parallel to the air stream over a range of baffle thicknesses and separations, (b) absorptively lined sections of ducts, and (c) right-angle bends with absorptive lining facing the incident sound. Illustrative of the generalization, the data on bends are fitted to a single curve plotted against the ratio of duct width to wavelength with good agreement where the absorptive lining satisfies certain scaling restrictions.
Noise Control for Eight- by Six-Foot Supersonic Wind Tunnel
Authors: Beranek L. L. , Labate S. , Bolt R. H. , Newman R. B. , Ingard U. , Marsh E. T. , Mull H. R. , Evvard J. C.
Published: September 2005

The noise produced by a large experimental supersonic windtunnel in which a shock wave was employed to produce high wind velocities and in which a jet engine was operating was sufficient to disturb residents of Cleveland within five miles during after-midnight operations early in 1950. The disturbing noise extended from 5 cps to 8000 cps. Components between 4 and 20 cps were reduced by a series of resonators. Components between 20 and 700 cps were reduced by a set of six parallel lined ducts properly chosen in size and lined according to charts of P. M. Morse. Above 700 cps, the reduction was provided by a series of parallel absorbent baffles and two lined bends. The resultant acoustic muffler renders the noise unobjectionable even in nearby office buildings, without affecting significantly the aerodynamic performance of the windtunnel.
Effect of Different Types of Electrodes in Electrophonic Hearing
Authors: Flottorp Gordon
Published: September 2005

What Stevens has called the electrophonic effect, i.e., the sensation of hearing due to an electric current passed through the head, was first observed by Volta in 1800, and for many years it was thought to be a single phenomenon having a single cause. Jones, Stevens, and Lurie showed that at least three different kinds of sensation, involving three separate mechanisms, may result from electric currents applied to the head, but it now appears that electrophonic hearing is even more complicated than they supposed. Depending upon the kind of electrode system employed, a sinusoidal electric current gives rise to at least five phenomena. (1) Electrode immersed in salt solution in the ear (the most common method). The subject hears a complex tone, containing mostly second harmonic, suggesting the action of a square-law transducer. (2) Electrode in contact with the epidermis of the meatus. The subject hears the first harmonic, and at low frequencies he may also hear a noise. (3) Electrode on the mucous tissue inside the middle ear (with the eardrum removed). The subject hears the first harmonic and/or a noise. (4) Large-area electrode on the skin, any place on the head. Provided the skin is dry the subject hears the second harmonic; if it is wet, he hears nothing. (5) Moving electrode on the skin or on the roof of the mouth (fricative effect). This gives the strongest sensation of hearing. The subject hears either the first harmonic or the first and second harmonics, or the second harmonic alone, depending upon the applied voltage and upon the placement and the properties of the electrode. The experimental results seem to indicate that the hearing of a tone under any of these five conditions is probably due to vibrations set up outside the cochlea, although there appears to be at least four different transducing mechanisms. Contrary to earlier hypotheses the tympanic membrane is apparently not involved in the conversion of the electrical energy into mechanical vibration.
Antibiotics and the Cochlea
Authors: Hawkins Joseph E.
Published: September 2005

Electrophysiological study of the ototoxic effects of streptomycin in the cat has shown that prolonged treatment with large doses of the antibiotic may cause varying degrees of depression of the microphonic response of the cochlea, with or without comparable reduction in the amplitude of the response of the auditory nerve. Hydroxystreptomycin exhibits this specific toxicity in a much higher degree, while certain preparations of neomycin cause rapid and complete loss of the functions of both the microphonic mechanism and of the nerve. Commercial dihydrostreptomycin, on the other hand, usually causes an enhancement of the microphonic response and, at the same time, depression and splintering of the action potential patterns of the nerve. The nature of the ototoxic action and its significance for the study of auditory physiology are discussed.
New Types of Ear Wardens
Authors: Zwislocki J.
Published: September 2005

On the basis of experience with previous models, new ear wardens have been developed in an effort to improve the intelllgibility of speech heard through the wardens and the protection of the hearing of the wearer, and to provide him with maximum comfort. One of these wardens attenuates the whole frequency range important for hearing, one serves as a low pass filter. The choice between them depends upon the characteristics of the noise encountered and the activity of the wearer. Experiments have been carried out to assess the protection afforded under a variety of conditions in both industrial and military situations.
Recent Advances in Hearing Aids
Authors: Hector L. Grant , Pearson Harry A. , Dean Neal J. , Carlisle Richard W.
Published: September 2005

The experience gained in fitting a large number of impaired persons with hearing aids is presented, showing illustrative ranges of impairment between 30 and 100 decibels fitted with three progressively powered hearing aids. General features of each hearing aid are discussed, showing the circuits and arrangements for peak clipping and automatic gain control. The microphone, air and bone receivers are described, considering features developed for providing optimum reliability in service, such as moistureproofing and design arrangements providing miniaturization concomitant with ruggedness.
Perception of Speech by Deafened Listeners and Its Relation to the Design of Hearing Aids
Authors: Fletcher Harvey
Published: September 2005

This paper describes a method of calculating the articulation scores which a talker-listener pair will obtain in terms of the response of the hearing aid, the audiogram (both bone and air) of the listener, and talking level of the talker, and the proficiency factor of the talker-listener pair. This method was used to calculate the articulation scores for all the talker-listener pairs and the six kinds of hearing aids used in the test at Harvard made by Davis and his associates. The calculated and observed results agree within the experimental error. The philosophy underlying the method of calculation is used to predict the ideal type of response to be used by a deafened listener. It leads to the following simple rule. The ideal response R in db gain at any frequency is given by R = βA − 23βB + αI, where βA is the hearing loss by air conduction, βB is hearing loss by bone conduction, and αI is the over-all gain (same for all frequencies) to bring the speech level at the listener's ear to its optimum value. If the values of βA − 23βB at the three frequencies 500, 1000, and 2000 chs are examined and the average of the two highest values called β2, then the maximum value of αI is given by αI(max) = 52 − β2. The optimum gain αI is, in general, less than αI(max), and so a means of lowering the gain in the set must be provided. When αI(max) calculates to be negative, then the optimum gain αI is equal to αI(max). These gains are all with reference to a speaker 100 cm from the listener, and speaking so that his average level at the listener's ear is 66 db. If the speaker moves farther away or talks softer, then it is counted a negative gain or a loss. If he moves closer or talks louder it is counted as a gain.
Signal Detection in Hearing
Authors: Sherwin C. W.
Published: September 2005

A question is raised regarding the operation of the two time constants in hearing. The short-time constant of about 15 milliseconds, due presumably to the cochlear filter system, is a “signal amplitude integrator.” The long-time constant of about 0.5 second, due presumably to the central nervous system, is a “signal power integrator.” Under some conditions not yet understood, the short-time constant can be directly observed by signal duration experiments without interference from the long-time constant. Some experiments were performed on the detection of pure tones in white noise in which both “signal detections” and “false alarms” were recorded. It was found that the listener does not treat errors of the “signal miss” type in the same manner as he treats errors of the “false alarm” type. For signal detectabilitles ranging from 30 to 90 percent a typical observer will have an almost imperceptable false alarm probability, usually much less than 1 percent. This result will be discussed in the light of the theoretical behavior of the two integration mechanisms mentioned above.
In Search of the Missing 6 Db
Authors: Munson W. A. , Wiener Francis M.
Published: September 2005

The unexplained difference in sound pressure in the ear canal which appears to exist when equally loud low frequency tones are presented alternately from an earphone and from a loudspeaker has bedeviled acousticians for many years and, unfortunately, still continues to do so. There are presented here the results of some of the measurements carried out at the Bell Telephone Laboratories which show the magnitude of the effect and various attempts at explaining it. While no satisfactory explanation has been found, it is hoped that publication of these results will stimulate interest in the problem.
Ultrasonic Attenuation in Human Skull Bone
Authors: Hueter T. F. , Ballantine H. T. , Kyrazis D.
Published: September 2005

Some measurements have been made on attenuation in bone in order to provide basic information needed in certain medical applications of ultrasonics. Valid data are difficult to obtain because of inherent variability in bone thickness and structure, and because adequately fresh bone samples are not easy to obtain. A special “bone gun” was used to obtain disks from cadaver skulls, and measurements were made on some 35 of these disks within a few hours after death. Attenuation coefficients (in db/cm) were determined by measuring the insertion loss of samples of different thickness. The attenuation increases by more than 60 db/cm over the range from 0.26 to 3.5 megacycles, but the function is not linear. A possible mechanism for the nonlinear behavior is suggested.
A Method for Studying Speech Communication Systems
Authors: Corliss E. L. R.
Published: September 2005

Because of the statistical nature of speech sounds, time-exposure photographs of the display on a Panoramic Analyzer can be used as high speed acoustic spectrograms of impulsive sounds. For speech systems, the analyzer is modified to sweep at the syllable articulation rate. The photographs can be interpreted to show quantitatively a number of characteristics of speech communication systems. So far, this process has been applied to the study of the characteristics of speech recordings and in the calibration of speech audiometers.
The Information of Elementary Auditory Displays
Authors: Pollack Irwin
Published: September 2005

Whereas the ear's sensitivity for detecting a difference in frequency between two tones is remarkably acute, the ability of listeners to identify (and name) tones presented in isolation is relatively poor. When the frequency of a single tone (in the frequency range 100–8000 cps) is varied in equal logarithmic steps (and when the sound level is arbitrarily varied to reduce loudness cues), the amount of information transferred is about 2.3 bits. (The equivalent proficiency of response for an informational transfer of 2.3 bits is perfect identification among only 5 tones.) The amount of information that can be transferred is, within rather wide limits, independent of the number of tones and the range of frequencies employed.
A High Intelligibility Interphone System for Use in Military Aircraft
Authors: Kettler A. H. , Flodman L. J. , Martin D. W. , Graham M. L.
Published: September 2005

At the end of World War II the introduction of a wide variety of extremely noisy aircraft flying very long missions at high altitudes had placed demands on interphone communications that the old system could not meet. Beginning in 1947 an entirely new system was developed with the close and active cooperation of the Air Materiel Command (now Wright Air Development Center). The criterion of performance is the word articulation of the entire system. New microphones, headsets, loudspeakers, amplifiers, control panels, and power supplies were developed. The resulting system has a frequency range of 200–6000 cps. It is very flexible, extremely comfortable, and provides high word articulation scores in 120-db sound fields at altitudes up to 35,000 feet.
Performance Characteristics under Water of Plane Arrays of Barium Titanate Transducers
Authors: Camp Leon
Published: September 2005

Plane arrays of barium titanate transducers are described. Their polar intensity patterns are shown with the results of calibration tests. The quantity of data presented is offered as proof that these are unquestionably excellent instruments.
Measurements of the Tonal Characteristics of Carillon Bells
Authors: Slaymaker Frank H. , Meeker Willard F.
Published: September 2005

High quality magnetic tape recordings were made of individual bells at the carillon location, including bells cast by Meneely and Company, Watervliet, New York; Van Aerschodt, Louvain, Belgium; John Taylor and Company, Loughborough, England; Franz Schilling Söhne, Apolda, Germany. Measurements made on the tapes with a sound analyzer, Stroboconn, and an automatic level recorder gave the relative tuning, the relative amplitudes at the microphone position, and the decay rates of the various components in the bell tone. The hum tone, strike tone, minor third, perfect fifth, octave of the strike tone, octave plus a major third and octave plus a perfect fifth, as well as other higher components, will be demonstrated audibly with the aid of a sound analyzer.
Mechanical Sound Sources for Obstacle Perception by Audition
Authors: Twersky Vic
Published: September 2005

Two simple devices of the type mentioned in the title will be discussed. Each consists essentially of a cup-sized parabaloidal plastic reflector with a vibrator in the focal plane. The first type, similar to one developed by D. R. Griffin at Cornell, employs a dented flat steel spring and produces loud broad-band high frequency clicks when triggered. The second employs a miniature reed whistle and produces several different high frequency squeaks (depending on how a rubber bulb built into the horn is manipulated). Preliminary tests with four subjects indicate the following: The first type produces sufficient sound for distinct echoes to be returned from distant objects outdoors but is too loud for indoor use; the second type is useful indoors up to a far point of 5–20 feet (depending on ambient noise), giving rise to essentially the same sort of cues obtained with the continuous wave electronic models employed previously.
Acoustic Instrumentation for High Intensities
Authors: Leonard R. W. , Rudnick I.
Published: September 2005

This paper will describe a 100-kilowatt audiofrequency siren and associated measuring equipment. Plane waves are produced in a 10-inch diameter tube at pressure levels in excess of 180 db. The condenser microphone used in these measurements operates at temperatures of the order of 170°F and in air stream velocities of the order of 200 miles per hour.
Duality in Mechanics
Authors: Le Corbeiller P. , Yeung Ying-Wa
Published: September 2005

Given an electric network Ee which has M meshes and P node-pairs, its electric dual Ei will have P meshes and M node-pairs and its classical mechanical analog Mf will have M + 1 nodes, M independent node-pairs and P independent node cycles. A second mechanical system Mv, the classical analog of Ei, will have M cycles and P node-pairs. If, for example, M = 2, P = 3, the system Ee, and Mv, analogs in the Firestone or “mobility” method, will be governed by two mesh equations, expressing that the algebraic sum of the voltages or velocities around any loop is zero; the systems Ei and Mf, also Firestone analogs, will satisfy two node equations, expressing that the algebraic sum of the currents or forces leaving any node is zero. These four sets of equations are identical, interchanging symbols suitably. The consideration of the four systems, Ee, Ei, Mv, Mf, forming a complete set, shows the advantages of the Firestone over the classical system of analogies and suggests a systematic use of duality in mechanical as well as in electrical systems.
Analytical Comparison of Square-Law and Correlation Detectors
Authors: Hills Robert , Faran James J.
Published: September 2005

A mathematical analysis has been made of two methods of using a two-element array for the reception of random signals. In the first method, the signals from the two elements are added and the resultant “sum” signal is measured with a square-law rectifier and an averager; in the second, the instantaneous product of the signals is formed and averaged. A point source of random noise in an isotropic noise background is postulated as providing the input signal to the systems. With the exception of constant terms in the average output of the square-law detector, the “directivity patterns” of the two systems are the same and are simple functions of the autocorrelation function of the signal. With any practical (finite-time) averaging device, unwanted fluctuations (noise) will appear along with the signal in the output of both systems. For small input signal-to-noise ratios, it is found that the output dc-signal-to-ac-noise ratio is never less for the correlator than for the square-law detector, but can be as much as 3 db greater for the correlator, provided the element spacing is sufficiently wide.
Experimental Comparison of Square-Law and Correlation Detectors
Authors: Faran James J. , Hills Robert
Published: September 2005

A semicircular array, 30 ft in diameter, of 41 five-inch loudspeakers has been built in the Harvard anechoic chamber to provide a two-dimensional isotropic noise background. A separate gas-tube noise generator powers each speaker. Signals can be superposed on the noise applied to any speaker. With this array it is possible to study methods of detecting and locating signals in such a background. Included in the instrumentation is circuitry for the measurement of the signal-to-fluctuation-noise ratio at the detector output. Preliminary experiments using a two-element array and a square-law or correlation detector have been carried out. The measured patterns and signal-to-noise ratios are in good agreement with theory.
A Simple Electronic Correlator
Authors: Faran James J.
Published: September 2005

Attention has been drawn in the literature to the possible utility of correlation techniques in the reception of acoustic signals. In applying such techniques, it is often necessary to find the average of the instantaneous product of two electrical signals; the black box which performs this function, which is that of a generalized detector, may be called a correlator. By use of the quarter-squares method of multiplication [AB = 14(A + B)2 − 14(A − B)2], correlators can be constructed using common triodes as the square-law devices. In practice, however, such multiplier-averagers depend strongly upon the vacuum tube characteristics which in turn require, for stability, regulated plate and heater supplies and frequent balance adjustments. If the square-law vacuum tubes in the circuit mentioned above are replaced by linear rectifiers, as many have suggested, it is shown that the resulting circuit is similar in action to a correlator. The output of this “linear rectifier correlator” is a somewhat distorted replica of the un-normalized cross-correlation function of the input signals, but the output signal-to-noise ratio for small input signal-to-noise ratios is not appreciably less than that for a multiplier-averager. The linear rectifier correlator has the practical advantage of being completely independent of power supplies, if contact rectifiers are used, and requires no balance adjustments if care is used in its construction.
A Simplified Audiospectrometer
Authors: Benson R. W. , Hirsh I. J.
Published: September 2005

A relatively small array of equipment is described that permits the measurement of the power spectrum of irregular or discontinuous sounds, including speech. A sample of speech, or any other sound, is recorded on a loop of magnetic tape that can be played back over and over again. Repetitions of the sample are independent of the variability of the talker. The output of the tape playback is fed through a system of cascaded, variable electronic filters; the output of the filters is fed to a square-law integrator circuit, which has been adapted from Rudmose et al.; and the output pulses of the integrator activate an electronic scaler. Scaler counts are proportional to the energy and an absolute value of energy is obtained from a calibration in counts per second. Flexibility is enhanced by the fact that the number and the width of frequency bands measured may be determined or changed at will. From an apparatus point of view it is shown that spectral analysis of speech need not require special components, which must be purchased for that purpose alone, but rather mostly employs equipment that is standard in most experimental laboratories. Increase in the time required for measurement is offset by a reduction in the size and complexity of equipment. Preliminary measurements in which both octave and equal-mel bands were used yield results that are in substantial agreement with those of previous workers.
Measurement of the Ultrasonic Absorption Coefficient by a Modified Radiation Pressure Method
Authors: McNamara F. L. , Beyer R. T.
Published: September 2005

A technique reported by Barone and Nuovo has been adapted to the measurement of ultrasonic absorption in liquids. The output of an rf transmitter is 100 percent modulated at an audiofrequency and applied to a crystal. This results in a periodic variation of the radiation pressure in the acoustic beam. A condenser microphone has been constructed, employing a front face consisting of a thin sheet of plastic, coated with silver paint. The microphone responds to the audiofrequency variation radiation pressure, and its output is preamplified and then detected on a harmonic analyzer. The apparatus has been tested in water in the frequency range 9 to 30 mc, and the measured values of the absorption coefficient agree with the accepted values within a few percent. Measurements of the absorption coefficient have been carried out in a number of uni-univalent electrolytic solutions.
The Ultrasonic Absorption in Acetate Solutions
Authors: Barrett R. E. , Dill M. W. , Beyer R. T. , McNamara F. L.
Published: September 2005

The measurements of the ultrasonic absorption coefficient in aqueous solutions of sodium acetate, reported previously, have been extended. The results indicate a value of the absorption coefficient below that for pure water at frequencies above 20 mc. Measurements have also been made of the sound velocity and kinematic viscosity of the solution, and the classical absorption coefficient computed. These values for the solution are slightly higher than the corresponding values for water. It appears that the presence of the solute in some way disrupts the structural relaxation which is hypothesized to account for excess absorption in water. Similar measurements are being made in potassium acetate solutions.