bluuebunny/crossref_metadata_2025 huggingface dataset:
Relative Loudness of Sinusoidal and Square Wave Tones
Authors: Zeitlin Lawrence R.
Published: September 2005

Experiments with acoustically complex tones have shown that, if components are sufficiently separated from one another along the frequency scale, the total loudness is equal to the sum of the component loudnesses presented separately. If the frequency components of the complex tone are not widely separated, however, masking and interference effects occur. In this study consideration is given to complex tones of the type normally encountered, tones in which the frequency components are of unequal strength, and which are close enough to overlap on the cochlea. Utilizing the method of adjustment, subjects equated the loudness of a variable intensity pure tone (sine wave) with a reference standard complex tone (square wave). A loudness match was obtained at 100, 150, 200, 300, 400, 700, 1000, 2000, and 4000 cps. A harmonic analysis of complex wave form was obtained by photographing the cathode ray tube of a panoramic sonic analyzer and measuring the relative intensities of the fundamental and harmonics of the complex wave form on the print. The absolute intensity of the pure tone was considerably greater at the lower frequencies when matched for equal loudness with the complex tone. Methods of obtaining a rough approximation of the complex tone loudness by summating the loudnesses of its harmonics are discussed.
Measurement of the Fluctuating Pressure on the Surface of a Circular Cylinder
Authors: Gerrard J. H.
Published: September 2005

Measurements have been made on a 1-in. diam cylinder spanning a wind tunnel in a range of Reynolds number (104 to 105) in which vortices are shed. Work is progressing on cylinders of other diameters. The pressure fluctuations are predominantly of the fundamental frequency of vortex shedding and the spectrum is a narrow band of randomly fluctuating amplitude. The width of this narrow band increases with velocity of the flow. There is a power law relationship between the fluctuating pressure at the fundamental frequency and the velocity of the stream approaching the cylinder. A similar relationship exists between the velocity and the pressure integrated round the surface over a short length of the cylinder which indicates that the rms lift coefficient increases with Reynolds number like (Re)1.24. The fluctuating drag coefficient (at second harmonic frequency) varies in a similar way but is about one-tenth of the magnitude of the lift coefficient. The three-dimensional character of the flow is illustrated by the marked effect of small changes in the conditions on the wall at the cylinder end, and by measurements of correlation of fluctuating quantities at points separated along this span.
Ultrasonic Emulsification
Authors: Potsis Angelos , Yeager Ernest , Hovorka Frank
Published: September 2005

The ultrasonic emulsification of various liquid pairs has been investigated at several frequencies in the range of 104 to 106 cycles/sec with relatively uniform ultrasonic fields at intensities less than 10 w/cm2 as well as in the nonuniform fields from focused transducers with maximum intensities of the order of 103 w/cm2. Cavitation conditions in the liquids have been modified by varying the static pressure and the percent saturation of the liquids with an inert gas such as N2. Ultrasonic emulsification has been found to be produced by both cavitation and surface waves at the liquid interfaces with the former predominant under ordinary circumstances. Particle sizes as evaluated by optical and electron microscopy are generally of the order of 10−4 cm. The equilibrium particle size distribution shows only minor frequency dependence but significant differences are evident between the distributions obtained with the relatively low-intensity uniform sound fields and the converging sound fields with the high local intensities. These results will be considered in terms of the various second-order forces favoring agglomeration as well as the dispersive factors associated with cavitation and surface waves. [This research has been supported by the Office of Naval Research.]
Reaction of Aqueous Chloroform with Ultrasound
Authors: Karpovich John
Published: September 2005

A study of the reaction of aqueous chloroform under the influence of ultrasound has been made. The reaction was followed by measuring the conductivity of the aqueous phase and the volume of the gases liberated. At the termination of the reaction the chloroform was completely reacted out. All the products were collected and identified. The gases liberated were carbon monoxide and carbon dioxide in the ratio of about 4 to 1 by volume. The main liquid product was tetrachloroethylene with lesser amounts of pentachloroethane and trichloroethylene. The principal solid product was hexachloroethane with traces of higher chlorinated hydrocarbons. Hydrogen chloride was present in the aqueous phase. It is interesting to observe that both the liquid and solid products have low vapor pressures. This observation supports the hypothesis that the reaction takes place in the vapor phase.
Spatial Fluctuations of Steady-State Sound Fields in Rooms
Authors: Schroeder Manfred R.
Published: September 2005

The methods used in solving the problems related to the interpretation of frequency response curves of large rooms [M. R. Schroeder, J. Acoust. Soc. Am. 29, 1258 (1957)] are employed for the computation of the principal parameters of spatial response curves in large rooms at fixed frequencies. The results for the rms response fluctuations and the mean level difference between maxima and minima are the same as for frequency response curves, namely 11 and 10 db, respectively. The mean spacing of adjacent maxima depends upon the dimensionality of the space, the wavelength, λ, and the isotropy of the sound field. The mean spacings are 0.50λ, 0.67λ, and 0.79λ for complete isotropy in one, two, and three dimensions, respectively.
Telemetering System for the Measurement of Boundary Layer Noise
Authors: Kamperman George W. , Noiseux Denis , Jones R. V.
Published: September 2005

This paper describes a telemetering system for measuring boundary layer noise on a supersonic rocket sled. Conventional telemetering components were used for its construction. The acceleration present on a typical supersonic sled during a test period is 10g. The deceleration may reach 100g after the test period. The maximum sound pressure levels vary between 160 db to 170 db re 0.0002 microbar and the frequency range of interest is from 35 to 10 000 cps. The telemetering system is designed to operate from a self-contained power supply. The performance characteristics of the telemetering system are discussed with particular attention given to the selection and evaluation of a microphone for the measurement of boundary layer noise. [The work was sponsored by Air Force Contract No. 33(616)-3938.]
On the Production and Perception of Fricative Consonants
Authors: Heinz J. M. , Stevens K. N.
Published: September 2005

The fricative sounds are produced when the vocal tract is excited by acoustic noise generated from turbulent air flow near a narrow constriction in the tract. The mechanism of the production of fricative consonants is investigated with the aid of an idealized mechanical model of the human vocal organs. Power-density spectra as functions of air flow are calculated from sound pressure measurements around the model. An electrical analog circuit is derived to represent the model for sound radiated on axis. “Source” spectra are inferred from comparisons of the transfer function of this electrical circuit with the measured data. On the basis of the model studies, the constricted vocal tract is approximated by a simple, lumped element circuit excited by appropriate noise sources. A comparison is made between the spectra of the outputs of this system and existing data on the natural fricatives /ζ/, /s/, and /f/. Listening tests performed on the synthetic sounds in isolation and in syllables constructed with synthetic vowels having appropriate formant transitions have demonstrated the adequacy of the analog circuit. In agreement with other studies, distinction between /θ/ and /f/ is made principally on the basis of formant transitions rather than spectrum. [This work was supported in part by the U. S. Air Force (Air Force Cambridge Research Center) and the U. S. Navy (Office of Naval Research).]
Alternate Transmission Channel for Use in High-Level Noise
Authors: Moser Henry M.
Published: September 2005

The underlying purpose of this research was to make a survey of the hand signals currently employed by personnel who work in high level noise around military, commercial, and industrial flight lines, and to test these signals for intelligibility at a school for the deaf with a panel of young deaf adults. Also considered was the possible use of the manual alphabet in spelling critical words. Light, distance, angle of presentation and background were some of the variables considered in this intelligibility study. These are somewhat analogous to those encountered in intelligibility study of oral language. Signals employed by personnel to communicate similar messages, vary considerably from one installation to another. Investigation was made of the effects of distance, manner of sending or coding of the message and receiver variability. [This research was carried out in connection with Contract AF 19(604)-1577, monitored by Operational Applications Laboratory, Air Research and Development Command, Bolling Air Force Base, Washington 25, D. C.]
Phonetic Analysis of Speech Signals Simultaneously Recorded at Ear and Tips
Authors: Oyer Herbert J.
Published: September 2005

Previous study has shown that when speech signals were recorded at lips and left ears of speakers, and fed to headsets of trained listeners at specified S/N ratios, signals, origin ear, were significantly more intelligible than signals, origin lips. A comparative analysis is made of phonetic elements of listener response to speech signals, origins ear and lips elicited in the earlier study. Listener responses totaled 72 000. Listeners highly trained on fifty words tend to restrict substitute responses to words within the list for signals of both origins. Fewer substitutions of words from outside the original list occur as noise in the listening condition becomes more destructive. Substitutions remain relatively constant between origins through ratios. Omissions for stimuli, origin lips, increase more rapidly. Number of sounds in the test stimuli had no differential effect on intelligibility when related to origin. The frequency of occurrence of two, three, four, and five sound word substitutes is in almost complete agreement with frequency of occurrence of two, three, four, and five sound words in the test list. Analysis of intelligibility errors relative to vowels and diphthongs in the test list revealed that words containing (æ, ∧, α, ɔ, aʋ, and ɔl) were less intelligible from origin ear. than origin lips through S/N ratios. [This research was carried out in connection with Contract AF 19(604)-1577, monitored by Operational Applications Laboratory, Air Research and Development Command, Bolling Air Force Base, Washington 25, D. C.]
Application of Corner-Reflectors to Sonar Transducers
Authors: Fitzgerald James W. , Smithson John R.
Published: September 2005

The corner-reflector antenna for electromagnetic radiation has been studied theoretically by J. B. Kraus [Proc. Inst. Radio Engrs. 28, 513 (1940)] and experimentally by E. F. Harris [Proc. Inst. Radio Engrs. 41, 645 (1953)], as well as others. However, little use has been made of analogous reflector for beam pattern formation with sonar transducers. The simple image theory of the corner reflector is reviewed in the light of applications to the acoustic case. Theoretical results for reflected impedance, forward gain, and radiation pattern are in good agreement with experimental results. In order to obtain a narrow-beam, high intensity underwater-sound projector, a corner reflector has been constructed, tested, and used. The transducer element consists of a line of BaT:O cylinders located in the bisectional plane of a 90° corner reflector. Impedance, gain and pattern have been investigated as a function of the distance in wavelengths of the transducer element from the line of intersection of the two reflecting surfaces. To date, only the 90° reflector has been examined. As a means for acoustic-pattern formation, the corner reflector is of simpler construction than the cylindrical parabola and offers the advantage that the beam pattern can be readily changed by altering the reflector position and angle.
Velocity of Sound in Distilled Water
Authors: Wilson W. D.
Published: September 2005

The velocity of sound has been measured in distilled water as a function of temperature and pressure to an accuracy of 1 part in 10 000. An ultrasonic pulse technique similar to that developed by Greenspan at the Bureau of Standards was used to obtain the velocities directly in the temperature range 0.90°C to 90.00°C and for pressures between 14.7 psi and 14000 psi. The increased accuracy achieved in this work shows that the velocity vs pressure curves are linear at 20°C; concave upward at lower temperatures and concave downward at higher temperatures. The velocity maxima of the isobars shift to higher temperature as the pressure is increased. This substantiates the results obtained by A. H. Smith and A. W. Lawson.
Solution of the Wave Equation for a Particular Sound Velocity Variation
Authors: Murphy S. R. , Potter D. S.
Published: September 2005

The solution of the wave equation for a point source in a medium whose velocity of propagation is given by c = c0z/(z2 − a2)1/2 is presented. An integral representation of the solution is obtained paralleling Pekeris [J. Acoust. Soc. Am. 18, 295 (1946)]. An expansion of the integrand into a series of Hankel functions allows the integration to be performed. The solution thus obtained is briefly discussed in the asymptotic limits. (This work was supported by the Bureau of Ordnance, U. S. Navy, under Contract NOrd 12937.)
On the Construction of Schematic Diagrams for Mechanical Systems
Authors: Trent H. M.
Published: September 2005

The role that is played by a schematic diagram in the analysis of a mechanical system is discussed. Having defined the function of these diagrams, it is then possible to collect together those ideas and principles on the basis of which a systematic technique for constructing these diagrams can be evolved. Illustrations of the process are given.
Electrostatic Uniangular Microphone
Authors: Olson Harry F. , Preston John
Published: September 2005

The electrostatic uniangular microphone consists of an electrostatic transducer combined with an acoustical network to provide a uniform response with respect to frequency and a uniangular directivity pattern. The microphone exhibits a high order of directivity. The polar directional pattern is independent of the frequency.
Electroacoustic Phase Shift in Loudspeakers
Authors: Stroh W. Richard
Published: September 2005

A complex transfer function is defined which relates the sound pressure at a point on the principal axis of a loudspeaker to the electrical input of the speaker. The argument of this function consists of an angle representing the phase shift in the speaker itself, plus an angle proportional to frequency representing travel time. By using an electrical delay line to match the travel time, the phase shift in the speaker itself can be measured directly. Typical phase functions for moving-coil and electrostatic loudspeakers are shown; the general behavior of these curves is explained in terms of the known mechanical properties of the speakers. The effect of loudspeaker phase distortion on transients and correlation functions is discussed. Finally, the possibility is explored of using such phase measurements in the phasing of multiple-speaker systems.
The Distributed Transducer
Authors: Wilmotte Raymond M. , Greenspan Martin
Published: September 2005

The distributed transducer is an array of elements separated by inactive material having their common characteristic impedance, z0, and terminated in z0 at one end (absorber). The voltages at the successive inputs are delayed to correspond with the speed of sound in the array. The case of identical elements far below resonance was studied by Rabinow et al.; the principle is due to Hartley. We describe a transducer having elements not necessarily identical: they may or may not be operated near resonance. Any frequency response which can be represented by a sine series can be synthesized; Fourier sine series are of especial interest, in particular that for a flat (i.e., square wave) response. Some methods of minimizing the power dissipated in the absorber will be discussed. In one of these, each element is “duplexed,” i.e., replaced by two identical elements so spaced that the absorber current vanishes at midband and at certain other frequencies. [The work was done for Raymond M. Wilmotte, Inc., under contract AF 30(602)-1361 with the Rome Air Development Center of the Air Force.]
A Microphone Calibration Facility
Authors: Kamperman George W. , Wiener Francis M. , Allen Clayton H.
Published: September 2005

The free-field frequency response of a microphone is conveniently determined in a large anechoic chamber. However, anechoic chambers that are effective below 100 cps are large in size and often prohibitive in cost. This paper discusses an economical microphone calibration facility which consists of (a) a small anechoic chamber approximately 10-ft cube having a useful free-field frequency range from 400 cps to 100 kc, and (b) a long hard wall duct with an 8-ft terminating wedge. This duct has a useful frequency range from 20 to 700 cps and permits achieving a plane progressive wave in this range. The performance characteristics and the cost of this facility are described in this paper.
Shock Wave Propagation in Shallow Water
Authors: Snay Hans G.
Published: September 2005

A short outline will be given on the acoustic theories of wave propagation in a layer (Pekeris, Cagniard, and Rosenbaum). These theories do not adequately describe shock wave phenomena from explosions in shallow water. It will be shown how high-amplitude effects modify the profile and amplitude of the wave and how these effects can be theoretically accounted for. Cavitation is the second factor which affects the shape of the wave. It may considerably reduce the amplitude of the main shock wave and entirely eliminate later pulses.
Profile of an Explosive-Induced Plane Shock in Air
Authors: Fowles G. R.
Published: September 2005

An experimental travel-time curve for the plane shock produced in air at room temperature and atmospheric pressure by a detonation wave from solid explosive is analyzed by a graphical procedure based on the method of characteristics [R. Courant and K. O. Friedrichs, Supersonic Flow and Shock Waves (Interscience Publishers, Inc., New York), Chap. II]. From the observed velocity and attenuation of the shock, profiles of pressure, density, particle velocity, temperature, entropy, and sound velocity have been calculated at fixed times. The calculation is based on the Rankine-Hugoniot jump conditions, the conservation laws for particle-isentropic flow, and the equilibrium equation of state as computed by Gilmore and by Hilsenrath and Beckett. The effects of relaxation and radiation are neglected. The results are compared with those obtained assuming an ideal gas equation of state with γ = 1.4. Preliminary results show that pressure, density, and particle velocity decrease with distance behind the shock as expected, but that temperature, sound velocity, and entropy increase behind the shock. A qualitative argument is presented which indicates that this last result may be expected for sufficiently nonuniform shock waves. [This work supported in part by Office of Chief of Ordnance, U. S. Army.]
Space Requirements for Equipment Items Subjected to Random Excitation
Authors: Skoog J. A. , Setterlund G. G.
Published: September 2005

An equipment item supported on a low frequency mount requires a certain vibratory clearance with adjacent structure. With a random vibration input to an equipment item, the response of the equipment item is random and with the motion of the adjacent support being random, random motion analysis techniques are used. After a review of basic theory, an expression for the root mean square of the required clearance between an equipment item and adjacent structure is developed for a linear system. The solution includes some undetermined resonance characteristics and phase characteristics of complicated missile structure. A typical numerical example is given to illustrate the use of the final expression. These structural factors are discussed.
Some Near- and Far-Field Noise Measurements for Rocket Engines Operating at Different Nozzle Pressure Ratios
Authors: Mayes W. H.
Published: September 2005

Measurements of near- and far-field noise pressures are presented for rocket engines having about 5000-lb thrust, and for which the nozzle exit pressure was changed systematically in order to study its effects on the noise level and spectra. Near-field surveys indicated that the highest noise pressure occurred at about 20 diam distance downstream of the nozzle near the transition from supersonic to subsonic flow. At a radial distance of two diameters the noise pressure levels varied from about 145 db just upstream of the nozzle to about 170 db downstream of the nozzle and no consistent trends were noted as a function of nozzle exit pressure. In general, the spectra at points downstream of the nozzle contained considerably more low-frequency noise than those measured upstream of the nozzle. It was noted that the maximum farfield noise was radiated in the downstream direction at angles of 30° to 45° from the jet axis. The noise energy radiated from all nozzles averaged about 0.5% of the mechanical energy of the exhaust stream, the least noise being radiated by the nozzle having an exit pressure less than atmospheric.
Temporary Auditory Threshold Shift Produced by Exposure to Broad Band Noise
Authors: Glorig Aram , Grings William , Wheeler D. E. , Summerfield Anne
Published: September 2005

In this study of temporary auditory threshold shift (TTS) some 70 normal hearing subjects were exposed to broad-band noise at 100 db SPL. Growth and recovery of TTS were determined from thresholds measured at 30 minute intervals during a four-hour period, two-hour exposure plus two-hour recovery. The exposure-recovery test series was run on each of three different days for each subject to allow estimates of repeat reliability of shifts in groups and in individuals. At all frequencies tested, the growth and recovery of the shift are logarithmic functions of time of the form TTS = const × log exposure (or recovery) time + const. The magnitude of the shift is larger at the higher frequencies. From replication to replication there is no consistent change in the magnitude of the two-hour shift either for the group mean or for individuals. There is no systemic change in individual pre-exposure thresholds with replication. Control group data indicate that practice effects did not affect the results. (This research was supported in part by a grant from the National Institutes of Health.)
Vibration Damping by a Stiffened Damping Layer
Authors: Kerwin Edward M.
Published: September 2005

For a number of years it has been known that bending vibrations in a plate can be damped by the application of a layer of damping (viscoelastic) material that is in turn stiffened or constrained by a backing layer or foil. A common example is the damping tape currently used in aircraft. This paper presents a quantitative analysis of the damping effectiveness of such a stiffened layer. As in the work of H. Oberst (e.g., in Akust. Beth., 1952, 1954, 1956) the damping is characterized by the loss factor, η, which is the normalized imaginary part of the complex bending stiffness of the damped plate. The calculated damping factor depends on the wavelength of bending waves in the damped plate, and on the thicknesses and elastic moduli of the plate, the damping layer, and the stiffener. A complex shear modulus is assigned to the damping layer, where all of the energy dissipation is assumed to take place. Damping factors have been determined experimentally on laboratory test bars for a number of stiffened damping layer applications for frequencies from about 100 cps to 4000 cps over a range of temperatures. Gratifying agreement with calculated damping has been found for variations in frequency, temperature, and damped-bar geometry. Further studies on optimum single-layer applications and on multiple-layer applications will be described at a later date.
Comparison of the Acoustic Performance of Calfskin and Plastic Drum Heads
Authors: Hardy Howard C. , Ancell James E.
Published: September 2005

A recent innovation in the musical field has been the introduction of drum heads made of sheet Mylar plastic. This investigation reports the acoustical differences found in heads made of the two materials. Two types of drums were chosen, the bass drum and the field drum. Two identical drums of each type were fitted with heads, and investigations were made for several tension adjustments. A professional drummer was engaged to adjust and play these drums and a professional quality tape recording was made of their sounds, including single impact beats and steady rolls. These tape recordings were then analyzed in the laboratory. The average acoustical spectra of the drums were determined in half octave bands (similar to the method of Sivian, Dunn, and White), using the quasi-steady-state sound of the roll. The peak sound level spectra were also obtained using the General Radio impact sound analyzer. A further analysis was made of the buildup and decay of the drum sounds in chosen frequency bands using a high speed graphic level recorder. The analysis of the test results shows that under certain operating conditions there are considerable differences in the performance of the two kinds of heads. These differences correlate with subjective reactions. The chief physical differences are: (1) the calfskin drum head is capable of a much larger range of tension adjustment, and (2) under certain conditions it has more damping. When the bass drum is tuned to concert tightness, there is a significant difference in the two spectra and in the time variation of intensity. In the field drum there is little spectral difference, but the calfskin gives a more staccato beat with less “metallic” ringing.
Vibration of Rods between 20 and 200 000 Cycles
Authors: Biesterfeldt H. J.
Published: September 2005

The specimen to be investigated carries one or more turns of wire at each end and vibrates between the pole shoes of a permanent magnet. By changing the position of the magnet, longitudinal, torsional or bending vibrations may be excited in the frequency range from 20 to 200 000 cps. The driving force is constant; this constancy makes it possible to study the driving point impedance and the frequency response of a rod over a wide frequency range, including the effect of all its resonances. The resonance curves and the effect of assymetries in the rod on the shape of these curves are discussed. Finally, the values of the Q for bending, torsional, and longitudinal modes for plastics and for wood are given and compared with one another.
Vocoder and its Application to the Transmission of High-Quality Speech over Narrow-Band Channels
Authors: Schroeder Manfred R. , David E. E.
Published: September 2005

A vocoder for frequencies between 3 kc and 10 kc is described. It requires a transmission band width of 300 cps. This covoder is used with a 3-kc uncoded speech band to which the compressed frequency components are added by standard multiplexing methods. Thus, high-quality speech may be transmitted over conventional 3.5-kc voice channels. As a result of this technique, the reproduced speech for the same transmission band width not only appreciates in quality but is more intelligible. The simple spectra[ structure of many speech sounds above 3 kc permits a particularly effective application of voice coding principles. A description by as few as 2 to 6 parameters, depending on the kind of encoding, is sufficient. On the other hand, in order to insure a faithful reproduction of the plosive sounds the band width necessary in the individual channels is approximately twice as great as in vocoders with more modest quality requirements. The frequency compression ratio is approximately 20:1 for a channel-type coding and 70:1 for resonance coding. In developing a vocoder for the transmission of high-quality speech a number of details must be considered which may be neglected in vocoders for intelligible speech. Among these we mention the mixed quasi-periodic and aperiodic excitation as it occurs in voiced fricatives, the exact reproduction of individual pitch period lengths, and a reasonable preservation of the peak factor of the synthesized speech. The techniques employed to solve these problems will be discussed. A magnetic tape recording demonstrating the quality of this vocoder will be played.
Evaluation of Time-Frequency Scanning for Narrow-Band Speech Transmission
Authors: Peterson Gordon E. , Subrahmanyam D. L.
Published: September 2005

Two basic sampling methods for the transmission of intelligible speech with reduced channel capacity have previously been studied. The channel vocoder developed by Dudley is based on frequency separation or band analysis, and Schiesser and Fairbanks, Everitt, and Jaeger have developed a basic technique of time sampling. The possibility of sampling in both time and frequency offers a third major possibility which should be investigated. For this study a narrow-band speech transmission system was constructed which scans the time-frequency plane. The system scans in either a sinusoidal or in a saw-tooth manner over a frequency range of 200 to 7000 cps. In order to achieve the scanning, a variable carrier frequency oscillator, having a frequency shift of ±30% of the carrier frequency and an amplitude modulation of ±2 db, has been developed. The process of scanning leaves empty spaces in the time-frequency plane, and a four-channel time-delay system which employs an electrostatic method of recording has been used to fill the gaps in the plane by repeating the signal samples. When signal reiteration is employed with this system, a score of 75% of monosyllabic phonetically balanced word lists was obtained with a scanning filter of 1000 cps band width and a sinusoidal scanning rate of 30 times per sec. This intelligibility is appreciably higher than that which can be achieved with a fixed 1000-cy filter located in the frequency region of maximum intelligibility.
Supplementing the Formoder with Fixed Vocoder-Like Bands
Authors: Sukys R. , Bach R. E. , Chang S. H.
Published: September 2005

The Formoder is a speech compression system using parametric signals. The most important parameters are those used to control the average pitch frequency; the central frequencies and intensities of (1) two damped oscillations for nonturbulent sounds tunable in the first (F1) and second (F2) formant region, and (2) two noise spectra for turbulent sounds, one tunable in the second formant region (C2), and the other in the higher frequency region (C3) from 2500 to 6000 cps. Assuming time sharing of channels for parameters of (1) and (2) there are five parametric channels. To improve the performance of the Formoder a scheme is proposed in which the original Formoder parameters describing the average pitch, F1, F2, and C2 are retained while vocoderlike fixed bands (one parameter per band} are used in the upper frequency range 2500–6000 cps. Four such bands are used for turbulent sounds to replace C3 and two bands are added for nonturbulent sounds with central frequencies set at 2500 and 3500 cps. The total number of parametric channels is thus increased from five to seven. Preliminary experiments show some promise and the detailed results will be reported. [This research is sponsored by the Air Force Cambridge Research Center under Contract No. AF19 (604)-3465.]
Response of Nonlinear Strings to Random Force Fields
Authors: Lyon Richard H.
Published: September 2005

The response of a perfectly flexible string with longitudinal deformation to random excitation is studied in some detail. The equations of motion are essentially those of Carrier (Quart. Appl. Math. 3, 157–165). The modified mean square response for the “plastic” and “elastic” strings is discussed and it is shown that the mean square deflection is increased in the former and diminished in the latter. It is also shown that the probability distributions are altered, the response to Gaussian noise being in general non-Gaussian. [Work supported by Air Force Contract AF33 (616-5426).]
Experiments on Scattering of Sound by Turbulence
Authors: Mintz Michael D. , Ingard Uno
Published: September 2005

At the Fifty-fifth Meeting of the Acoustical Society of America [.J. Acoust. Soc. Am. 30, 670 (1958)], some results from field measurements on the scattering of sound were presented. In the present paper, results from laboratory experiments are reported. Pulses of 100 kc/sec sound, transmitted through a region of turbulence, are analyzed by means of a pulse height analyzer and counter. The pulse height distribution is determined for various scattering angles and the corresponding scattered sound energy is evaluated. In addition to these results on scattering of a collimated beam of sound, some preliminary results on the scattering of a cylindrical wave are presented. [This work was supported in part by the U. S. Army (Signal Corps), the U. S. Air Force (Air Research and Development Command), and the U. S. Navy (Office of Naval Research).]
Acoustic Siren for Generating Wide-Band Noise
Authors: von Gierke H. E. , Cole John N. , Oestreicher Hans L.
Published: September 2005

A new type siren capable of simulating wide-band noise environments like those produced by turbojets, rocket engines, and aerodynamic flow is described. The siren uses the principle of a series of overlapping, slotted rotors, rotating at different and “irrationally related” speeds, to produce a nonperiodic modulation of a gas jet. The wide-band noise spectrum radiated by the jet can, mathematically, best be approximated by an “almost periodic” function; that is, the spectrum is a line spectrum but with infinitely many lines in each interval of frequency. A series for the power spectrum can be derived and used to guide the design of a siren for a specified spectrum. Experimental results obtained with different configurations of a model siren with a one-quarter inch air jet are presented. These results indicate that the continuous spectrum fluctuates only plus or minus 3 db over the frequency range from 200 to 10 000 cps and a narrow-band analysis of the noise (2% band width) reveals no discrete frequencies above 200 cps and only some relatively small amplitude discrete frequencies below 200 cps. For all practical purposes the noise appears to have random character. Large models built on this siren principle should produce wide-band noise at the high sound pressure levels required for sonic fatigue and environmental testing.
Evaluation of the Use of Swivel-Mass Vibrators as Sonic Generators
Authors: Gibbs N. E. , Miller G. E.
Published: September 2005

A mathematical analysis of an air driven swivel-mass vibrator is presented. An analysis of energy transfer and the forces developed explains the ability of the device to lock in at a resonant frequency of the structure to which it is attached. The phenomenon of “mode jumping” is also explained on the basis of this analysis. The results of measurements made to determine the efficiency of an air driven swivel-mass vibrator are given. It is shown that the efficiency is greatly dependent on the type of resonant structure (pipe, bar, diaphragm, etc.) being considered.
Electronic Equipment and Transducers for Pulse Measurements in the Frequency Range 500 cps to 10 Mc
Authors: Skudrzyk Eugen J.
Published: September 2005

The electronic equipment is built up as simple and efficient as possible. A thyratron furnishes the time sweep (1 to 10 000 times a second) for a cathode-ray tube and the pulse obtained by differentiating its plate voltage triggers a heavily biased blocking oscillator. The blocking oscillator generates a sinusoidally modulated pulse of a width adjustable between one and about 100 oscillations at frequencies between 5000 cps and 10 Mc. The amplifier has an amplification of about one million; it can be used aperiodically or can be tuned. Short and adjustable time constants, and peak clipping germanium diodes in the grid circuits make it possible to connect pulse generator, amplifier, and transducer in parallel without any noticeable disturbance due to oversaturation of the amplifier, the same transducer may thus be used as a generator and a microphone simultaneously. The electronic circuits will be discussed in detail. The high-frequency transducers are barium titanate disks driven at one of their subresonances below their fundamental thickness resonance, to minimize the transients. The need for absolute calibration is avoided by working simultaneously between a standard and test pieces of various length. For the low frequencies a simple and very powerful transducer has been developed that is suitable for sending acoustic pulses into the ground.
Acoustics of Severance Hall
Authors: Shankland R. S.
Published: September 2005

Severance Hall has several acoustical problems introduced by its shape, which have seriously limited its effectiveness for performances of the Cleveland Orchestra during the years 1930–1958. The auditorium volume is small relative to the size of the audience, and this basic limitation makes it difficult to achieve the optimum reverberation time for orchestral music. Severance Hall was originally built with a theater stage to make possible the presentation of plays and operas. This has seriously limited its effective use by the orchestra, since a large fraction of the orchestral sound was lost through the thin stage ceiling and walls, and furthermore, the shapes of these surfaces were not good for projecting sound to the audience. The stage and auditorium were joined by an elaborate proscenium and a very heavy curtain which further reduced the sound transfer between stage and auditorium. Another major defect as regards shape in Severance Hall is the almost complete lack of wall or ceiling surfaces that could reflect sound to seats on the main floor. As a result, the sound reaching these areas has been low in intensity and lacks the effect produced by reflected sound mixed with direct sound. Another serious limitation is that on both sides and rear of the main floor there are coupled promenade spaces of such shape that sound entering them is almost entirely lost to the audience. The disposition of the boxes in Severance Hall is such that at either side they do not receive a balanced sound from the orchestra, and all boxes suffer from the fact that practically no reflected sound reaches them. This shape defect also affects a number of seats at the sides of the balcony. During 1958 a number of corrections were made in the acoustics of Severance Hall designed to rectify as much as possible the above conditions. An entirely new stage shell has been constructed of heavy wood and is tightly enclosed so that a large fraction of the orchestral sound is now projected to the audience. Furthermore, the shape of the stage shell provides a considerable amount of mixing and blending of the sound, which is a great advantage for the conductor and orchestra. This feature will also be important for the numerous recordings made by the Cleveland Orchestra. The material and design of the heavy wood shell, floor, and risers for the stage, were chosen to achieve a large measure of resonance. Another important modification is the complete removal of the proscenium and heavy curtain which in effect brings the orchestra out into the auditorium to a much greater degree. Finally, the heavy lined carpeting which was present throughout Severance Hall on all aisles, promenades, and under the seats, has been removed and replaced with an attractive vinyl the covering of low acoustical absorption. These modifications have made an enormous improvement in the quality and loudness of orchestral music in Severance Hall and are highly approved by the concert audience.
Area under the EEG Trace as a Measure of Changes Evoked by Auditory Stimuli
Authors: Mills Peter J. , Derbyshire Arthur J. , Carter Richard C.
Published: September 2005

Evaluation of hearing in sleeping children by the EEG method has depended upon inspection of the trace by an expert who must have the capacity to detect subtle variations of the EEG pattern. He also finds it difficult to quantify his decisions. We are presenting a more objective method which uses area, as measured by a planimeter, as an alternative to inspection by an expert. The difference between the areas under the EEG trace before and after stimulation may be defined as the EEG response. The “area” method has allowed us to study the effects of intensity and temporal pattern of stimulation on the EEG response. We have observed progressive increase in area with increase in intensity of stimulus. Stimulation rates faster than four per minute produce adaption indicated by progressive reduction in area. A complex relationship exists between temporal pattern of stimulation and difference of area (response). When presenting a series of stimuli at fixed intervals of time, a response, as evidenced by change of area, often precedes the stimulus showing “expectancy” by the subject. We accept this as evidence of time conditioning or learning by the sleeping subject.
Pitch of Periodic Pulses
Authors: Flanagan James L. , Guttman Newman
Published: September 2005

An exploratory experiment is described in which subjects adjusted the frequency of one periodic pulse-train to match the pitch of a different train. The stimuli consisted of four combinations of plus and minus pulses per fundamental period: (a) +; (b) +, −; (c) +, +, −, −; (d) +, +, −, +, −, −. The pulses were of equal amplitude and 0.1 msec duration. The interpulse interval was always an integral divisor of the fundamental period. Listening was accomplished in quiet, at a sensation level of approximately 45 db, with headphones connected binaurally in phase. For low fundamental frequencies where the interpulse interval is greater than six msec, the pitch match is made to equate the number of pulses per second, regardless of pulse polarity. At high fundamental frequencies where the interpulse interval is less than 1 msec, the fundamental frequencies are equated. The matches for interpulse intervals between 1 and 6 msec may be difficult and uncertain, and depend upon the configurations of pulse trains. The amplitude and phase spectra of the stimuli are calculated. An electrical analog of the basilar membrane is used in an effort to relate the results to patterns of membrane displacement.
Progression of Hearing Loss as a Function of Industrial Noise Exposure
Authors: Glorig Aram , Summerfield Anne
Published: September 2005

Hearing tests were made on selected persons in three differently located plants of a large United States industry. Rate of job turnover for these employees is very low, and their noise exposure is constant and continuous. Consequently, we were able to test some 100 men, retest them five years later, and know accurately what their intervening noise exposure had been. Changes in hearing level have been plotted as a function of age, initial threshold, and various parameters of noise exposure. Noise levels of interest in the plants have not changed appreciably in the last few decades and years of employment are equivalent to years of known noise exposure. Hearing thresholds of men who have worked in this noise from one to fifty years were used for an analysis of hearing level as a function of age and of various parameters of noise exposure. The results of this analysis will be reported and discussed in conjunction with the results of the five-year study.
Simulation of Airborne Noise and Its Effect on Components
Authors: Fricke Werner , Kaminski R. K.
Published: September 2005

The spatial and spectral sound pressure distribution of a near noise field as produced by a jet or rocket engine is surveyed. The noise inside compartments can be estimated from the noise reduction through the walls. Best simulation of the inside noise field is obtained by reverberant chambers with random noise excitation. Random noise test facilities, designed by Bell Aircraft Corporation, are described. They are able to produce any desired aircraft or missile spectrum, with an over-all SPL up to 150 db and were applied to testing of airborne components or complete systems. Also resonant tubes, using sinusoidal excitation, were used for analytical investigations of small components. Test results will be discussed.
Comparison of the Receiver Operating Characteristic for Messages Received by Ear and by Eye
Authors: Carterette Edward C. , Cole Michael
Published: September 2005

Receivers were presented with equal-length words under two conditions of difficult reception: (1) by ear, against a background of white noise; and (2) by eye, for a brief period in a tachistoscope. For each word presented, the receiver recorded a message and, immediately following, gave a confidence rating with respect to his accuracy of reception. The similarities between the functions for the auditory and visual modes of reception are remarkable. It is found that for both auditory and visual presentation the accuracy of reception is (1) directly related to the confidence rating, (2) relatively invariant over a range of signal-to-noise ratios, (3) is not impaired by the task of rating, and (4) changes very little with successive repetitions. Furthermore (5) the distributions of rating categories change very little with successive repetitions. These results support and extend the generality of the statistical decision-making theory of the receiver [see especially W. P. Tanner and J. A. Swets, Psychol. Rev. 61, 401–409 (1954); and J. P. Egan, Tech. Rept., AFCRC TR 57-50, AD 110064 (1957)]. (This work was supported by the Research Committee of the University of California.)
Some Experiments on Frequency Recognition
Authors: Tanner Wilson P.
Published: September 2005

Four frequencies in two configurations were presented separately to four observers in a random order. In one configuration the signals were separated by steps of 5 cy. In the other there were two pairs of frequencies; the members of each pair were separated by five cycles, but the pairs were separated by 500 cy. In each case the observers' task was to state which one of the four possible tones had been presented on any one trial. Frequency recognition error rates for the two configurations were nearly the same, although the patterns of errors were quite different. In the first configuration, there were frequent confusions between the two middle frequencies. In the second, there were few confusions between pairs but more confusions within the pairs. The experiment was repeated with ten cycle separations. Again there were two groups, four closely grouped frequencies, and two pairs of frequencies 10 cy apart with 500 cy separation between pairs. Again the percentages of errors were nearly the same, while the patterns were different. The results are considered in terms of a scanning model, a multiplex model, a threshold model, and variable band model. (This work was carried out under sponsorship of the Operational Applications Laboratory, Air Force Cambridge Research Center, and Evans Signal Laboratory, Signal Corps Engineering Laboratories, Fort Monmouth, New Jersey.