bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Sensitivity for Duration with Auditory Stimuli
Authors: Small Arnold M. , Campbell Richard A.
Published: September 2005

This study attempts to gather information regarding the discriminability of short temporal intervals defined by auditory stimuli. In addition to duration, inter-stimulus interval and the frequency characteristics of the stimuli were varied. By using the method of constant stimulus differences it was found for 45 listeners that discrimination deteriorated as duration was shortened. As inter-stimulus interval was shortened, discrimination became poorer; but the influence of the inter-stimulus interval was less marked as duration lengthened. Frequency composition of the stimuli seemed to be an important factor only at the shortest duration. The point of subjective equality generally remained close to the actual value of the standard stimulus, the only exceptions being at short durations and inter-stimulus intervals. For those conditions which were comparable, the results were similar to those of previous investigators. However, previously proposed hypotheses based on the premise that loudness is the primary determinant of temporal discrimination do not in their present form adequately explain the data. (This research was supported in part by the National Science Foundation.)
Effect of Noise in One Ear on the Masked Threshold of the Other
Authors: Blodgett Hugh C. , Whitworth Randolph H. , Jeffress Lloyd A.
Published: September 2005

Hirsh showed several years ago that, when a noise is presented to both ears and a tonal signal to one, the masked threshold is considerably lower than when the signal also is presented to both ears under homophasic conditions. The present study is concerned with the relation between this masked threshold and the level of the noise in the ear which does not receive the tonal signal. At one extreme. with no noise in the “off” ear, we have the monaural masked threshold. At the other extreme, where the noise is equal in the two ears but the signal is applied to only one, we have Hirsh's condition. The present study involves the transition from one to the other. Data will be presented for a 500-cps signal and various levels of the masking noise.
Binaural Studies of Amplitude Modulated Signals
Authors: Tobias Jerry V. , Jeffress Lloyd A.
Published: September 2005

Experiments on the pitch sensations resulting from signals with low-frequency envelopes suggest that such signals might exhibit interaural phase (time) effects—masking level differences and localization displacements—associated with the low frequency of the envelope. In the present study, the principal signals used were a 5000-cps carrier modulated by 250 cps or by 500 cps. Various modulation percentages and various phase relations between the modulator and carrier were tested for binaural interaction both in a masking situation and in localization. In general, the results were negative—the signals showed no more binaural interaction than would occur with the high frequency alone. Other combinations of high-frequency stimuli which do exhibit binaural interaction will be discussed.
Maximum Interaural Intensity and Time Differences for Clicks Inducing Binaural Lateralization
Authors: Guttman Newman
Published: September 2005

This experiment delineates ranges of interaural intensity and time differences for clicks within which lateralization is induced. The stimuli were dichotic, all-pass, 0.1-msec clicks presented at 1 pps. Given control over time of one click relative to another in the opposite ear, subjects reported, among other things, beginnings of image movement toward the center from completely sided lateralization. Principal results at a constant 16 db SL in the reference ear were as follows: In this ear, the temporal range within which movement occurs shrinks from about 15 msec to 3 msec as the contralateral level decreases from 16 db to the minimally effectual −6 db; the concomitant contralateral temporal range does not shrink quite as much. Similar temporal figures are found at 36 db in the reference ear, but the minimally effectual contralateral level rises to about −2 db. These results may be taken as evidence that the apparent “facilitation” reported previously by us is not necessarily only monaural in origin.
Amplitude-Time Envelope as a Cue to Pitch
Authors: Jenkins Robert A.
Published: September 2005

Past studies have indicated that the amplitude-time domain envelope is a cue to pitch. The study by W.R. Thurlow and A. M. Small, Jr. [J. Acoust. Soc. Am. 27, 132–136 (1955)] indicated that the perceived pitch of a narrowly band-limited double pulse train depends on the shortest interval between pulses and not on the center frequency of the passband. They also suggest a temporal shadowing of the delayed pulse. We shall present data on this interval pitch and on the shadowing threshold. We also shall present the results of investigations with amplitude asymmetric wave trains. The relevance of this data to the design of pitch extractors and the distinction between tone pitch and interval pitch will be discussed.
Aural Detection of a Gated Sinusoid as a Function of its Duration
Authors: Licklider J. C. R. , Flanagan G. H.
Published: September 2005

Using the two-interval forced-choice procedure, we conducted detection tests with gated sinusoids of 1000 cps in Gaussian-process noise. The signals varied in duration from 63 msec to 10 sec. We employed four different schedules or patterns of the time intervals within each trial. Duration was a highly significant variable. The temporal pattern was not. The results confirm and extend the findings of Hamilton and of Green, Birdsall, and Tanner [J. Acoust. Soc. Am. 29, 506–511 and 523–531 (1957)]. The ratio of signal energy to noise power density required for 75% correct detection falls from about 12.5 db at 5.0 msec to about 9.5 db at 20 msec (Green), is then constant at 9.5 db out to 160 reset, and then rises to about 13.5 db at 1.0 sec and 24 db at 10 sec. The question, whether or not these results indicate that the auditory parameters are variable and adjust themselves to the task at hand, will be discussed. [This research was supported in part under Air Force Contracts AF 18(600)-1219 and AF 19(604)-2051, monitored by the Operational Applications Laboratory, Air Force Cambridge Research Center, ARDC.]
Detection of a Pulsed Auditory Signal in Noise as a Function of Duration and Frequency
Authors: Green David M.
Published: September 2005

The detectability of a pulsed sinusoidal signal in white noise was studied as a function of frequency for three signal durations (1000, 100, and 10 msec). For the two longer signal durations the data are consistent with results obtained in previous experiments; the results obtained with the shortest duration are not. At the higher frequencies the 10 msec signal is easier to hear than either the 100 or 1000 msec signal. At low frequencies the 10 msec signal is easier to hear than the 1000 msec signal but not the 100 msec signal. This interaction of signal frequency and signal duration somewhat complicates the problem of developing a simple model to account for the influence of signal duration on signal detectability. (This research was conducted at the Electronic Defense Group, University of Michigan, under a U. S. Air Force contract monitored by the Operational Applications Laboratory.)
Detection of Complex Wave Forms: Effects of Signal Band Width and Duration
Authors: Creelman C. Douglas
Published: September 2005

Detection of signals from resonant systems is of interest both for the field of speech perception and for testing the applicability of Signal Detectability Theory to signals of complex wave form. Stimuli were the output of a recurrently-excited, simple resonant circuit. The impulse frequency was fixed at 100 cps, and the resonant frequency was 500 cps. The signal was, then, a train of decaying 500 cycle sinusoids. This signal was gated for various durations and presented binaurally in a background of white noise to three observers. A two-alternative forced-choice technique was used. Five different rates of decay, giving signal band widths of 10, 30, 100, 200, and 375 cps were used. Each signal was presented at five different durations; 0.01, 0.02, 0.05, 0.1, and 0.20 sec, keeping the energy constant by varying the signal power inversely with the duration. The efficiency (η) of each of three observers was estimated for all 25 combinations of band width and duration. Results show that for narrow-band-width signals efficiency remains fairly constant over the durations studied. On the other hand, wider band-width signals produce lower performance at longer durations. The results are considered in relation to various current descriptive models, and the usefulness of “auditory band width” concepts is weighed in the light of the data. (Supported by the Office of Naval Research and Air Force Cambridge Research Center.)
Pure Tone Masking
Authors: Small Arnold M.
Published: September 2005

Rather than having a fixed level, Im, of the masking stimulus (masker) and varying the level, Is, of the masked stimulus {signal) until the signal was just detectable, Is was fixed and Im was varied until the signal was just detectable. In addition, the frequency of the signal, fs, was fixed, but the frequency of the masker, fm, was varied systematically for each given fs. Stimulus interaction was minimized by keeping Is low. Minimum Im for signal threshold was obtained when fm approximated fs. Also in general less Im was required to mask the signal if fm < fs as compared to fm > fs, where |fs − fm| is equal in both cases. Several other results were somewhat unexpected. If the frequency characteristics of masking are regarded as reflecting the “filter” characteristics of the ear then the attenuation vs frequency plot of these filters is quite uniform with center frequencies from 400 to 6400 cps. Using low Is the cutoff on the high frequency side is quite sharp with a 130–140 db per octave slope over at least a 70 db range and an indication that it may be still steeper at higher Is. An interesting irregularity appears on the Im for masking vs fm plots in the form of a notch when 0.8fs < fm < 0.9fs.
Pitch of Periodic Pulses without Fundamental Component
Authors: Flanagan James L. , Guttman Newman
Published: September 2005

The pitch-matching experiment described at the previous meeting was extended to filtered stimuli. Listeners adjusted the frequency of an unfiltered periodic pulse-train to match the pitch of a train which was high-pass filtered to remove the fundamental component. The stimuli were three combinations of plus and minus pulses per fundamental period: (a) +; (b) +, −; (c) +, +, −, −. The interpulse interval was an integral divisor of the fundamental period. Before being filtered, the pulses were rectangular, equal in amplitude, and 0.1 msec in duration. Listening was done in quiet at a sensation level of approximately 45 db with earphones connected binaurally in phase. The results indicate that for fundamental frequencies less than about 50 cps the pitch ascribed to the filtered stimuli is equal the number of pulses per second, regardless of pulse polarity. For fundamental frequencies greater than about 500 cps, the pitch ascribed equals, or approaches, the frequency of the lowest component passing the high-pass filter. Matches in the range 50 to 500 cps tend to equate the fundamental frequencies of the filtered and unfiltered stimuli. Toward explication, the amplitude and phase spectra of the stimuli are considered, and an electrical analog of the basilar membrane is used in an effort to relate the subjective results to patterns of membrane displacement.
Investigation of Shallow Water Ambient Noise
Authors: Dietz Frank T. , Kahn J. Steven , Birch William B.
Published: September 2005

A reconnasiance investigation has been initiated to determine the seasonal variations of shallow water ambient noise and to correlate the ambient noise spectrum with environmental variables such as: wind speed and direction, wave height, rainfall, etc. The sound field is randomly sampled in time using an omnidirectional hydrophone bottomed in approximately 40 ft of water in Narragansett Bay, Rhode Island. Sound pressures are determined for 19 frequencies in the 40–10 000 cps band and are programed with the environmental data for an IBM 650 computer. The preliminary data are summarized and the correlations between the ambient noise spectrum and its associated variables are discussed. [Supported by the Office of Naval Research under contract Nonr-396(04).]
Fluctuations of Low-Frequency Harmonic Signals over Very Long Transmission Paths in the Deep Ocean
Authors: Berman A. , Clay C. S. , Frosch R. A. , Sherry H. B.
Published: September 2005

A 30-cps simple harmonic sound source was operated at a 40-ft depth in the deep ocean and its signal was observed in the SOFAR channel at distances up to 765 miles from the source. The phase fluctuations of the observed signal were measured. Two of the possible sources of those fluctuations which did not occur in a systematic manner were then considered: first, changing acoustic travel times resulting from the changing inhomogeneities in the medium with time; second, ambient noise. Following Mintzer we have assumed the variance of the fluctuations to be directly proportional to the source-receiver distance and inhomogeneous-patch size a and to be inversely proportional to the wavelength squared. The average upper limit of the parameter of fluctuations resulting from changing travel paths, α2a (where α is a proportionality constant), was found to be 3.3×10−3 cm−1. It was not possible to separate phase fluctuations caused by changing travel paths from those caused by ambient noise. Therefore, the results can be considered only an upper limit.
Propagation of Sound Originating in the Water and Detected in the Ground
Authors: Blaik M. , Clay C. S.
Published: September 2005

The propagation of single frequency seismic waves in the ground from a sound source in shallow water has been studied. Frequencies were studied in the interval from 10 to 150 cps. The experiments were made in an area in which the geological section consists of 1900 ft of unconsolidated sediments over basement. The amplitude and relative phase of the seismic waves were observed at many depths down to basement. The effect of horizontal source-to-detector distance was studied. Portions of these data will be presented along with some discussion of their significance.
Tape-Recorder for Creative Use in an Electronic Music Studio
Authors: Le Caine Hugh , Bowsher John M.
Published: September 2005

The existence of sound storage processes, especially tape-recording, has been responsible for a new point of view in realizing music. The authors believe that the philosophy of “Musique Concrete” is not necessarily involved in this approach and that any method of music production would-benefit by it. Conventional tape-recorders are not well suited to creative use, and in this paper a tape-recorder designed for the purpose is discussed. There will be a demonstration.
Electronic Production of Choral Tone
Authors: Wayne William C.
Published: September 2005

An important quality of traditional musical sound is the rich ensemble effect which results in part from the combination of multiple sources that have the same nominal pitch but slightly different frequencies. Organ builders provide celeste ranks of pipes which are intentionally detuned from their neighbors. Electronic organs generally have fewer sources than pipe organs at a given pitch and their oscillators are inherently much more stable in frequency. It is not necessary to provide an extra set of detuned electrical generators for it is possible to translate signal frequencies electronically. This is accomplished by a group of single-side band, suppressed carrier modulators, and associated band-pass filters. The combined modulator outputs are preferably acoustically radiated by a loudspeaker channel which is spatially separated from the unmodulated loudspeaker channel in order that a subjective dimensional impression be achieved. Equipment of this type can be added to any electronic music system to provide a new set of sources of similar timbre yet transposed in frequency either up or down from the corresponding input frequencies. From an economic standpoint, the musician is thereby provided with many more sources for only a modest increment in cost.
Some Factors Affecting the Intonation of a Clarinet
Authors: Young R. W. , Webster J. C.
Published: September 2005

Experimental data are presented showing the characteristic intonation of a soprano clarinet and how it is affected by ambient temperature, stiffness of reed, length of barrel, and gap adjacent to barrel. An increase of ambient temperature of 10°C raises the intonation 0.09 semitone (9 cents). A stiff reed may make the intonation 15 cents higher than does a soft reed. An increase in barrel length of 4 mm lowers the “bell” notes by 10 cents, but notes an octave higher are changed twice as much: the intonation is distorted. The inside gap resulting from pulling the barrel from the upper joint does not lower the intonation uniformly; notes of the transition register are affected much more than others. Flexibility of intonation varies throughout; high notes can be modified markedly; notes produced by greater length of tube are less flexible. There is a tendency for notes near the center of the chalumeau register to be relatively sharp; this tendency is associated with the use of a single register hole for the entire clarion register.
Acoustical Performance of the Stratford (Ontario) Festival Theatre
Authors: Tanner R. H.
Published: September 2005

The acoustical design of the Stratford (Ontario) Festival Theatre, which on account of the unusual shape presented numerous peculiar problems, was described at the Second International Congress on Acoustics at Cambridge, Massachusetts, in June, 1956. Since that date, the theatre has been completed and two very successful seasons of Shakespearean drama have taken place there. This paper described the acoustical performance obtained both for speech from the platform-type of stage and music from the concealed orchestra gallery, as well as reporting the results of measurements made in the theatre.
Propagation of Pressure Waves of Finite Amplitude in Boiling Water
Authors: Karplus Henry B.
Published: September 2005

Pressure pulses were produced in water boiling in a vertical glass pipe by initiating a shock wave in the gas above the liquid. The steepness of the wave front of the shock decays rapidly so that within a few centimeters below the surface the pressure takes several milliseconds to rise to the value of the shock pressure in the gas. For pressures sufficient to condense all the steam bubbles in the water, a very high pressure is observed at the instant at which all the steam is condensed. This large pressure amplification is due to the sudden deceleration when the water hits the end of the pipe. The observations corroborate computations. (This research was supported by the U. S. Atomic Energy Commission.)
Dynamics of Bone Receiver Instruments
Authors: Weiss E.
Published: September 2005

A detailed analysis of the response characteristics of bone receivers used in hearing aid instruments is presented. Steady-state and transient responses are discussed. The paper describes specifically the dependence of frequency response upon such things as the signal source impedance, the magnetic circuit, and mechanical network. The effect of variations in the static force applied to the bone vibrator is discussed. The performances of some artificial mastoids used to specify the response of production units are compared with particular regard to the possibility of designing a reproducible universal standard mastoid.
Frequency Shifts in the EEG as Indication of Response to Auditory Stimulation
Authors: Norkus Frank J. , Derby-Shire A. J. , Mills Peter J.
Published: September 2005

In the EEG patterns of sleeping subjects, some shift in frequency is typically (perhaps invariably) seen as part of a response to sounds. (Davis—K complex). Obviously, the clear identification of any such single component is an aid in the detection of the total response to which it contributes. A method has been developed for simultaneously recording both a single EEG trace (from a pair of electrodes) and the frequency changes of that trace. This method records frequency by counting the number of times per second the EEG activity crosses its own baseline and of course is independent of amplitude. The inkwriter of the frequency recorder rises and falls as the EEG frequency rises and falls. The cortex is considered to have demonstrated an acoustic response whenever the recorder produces a rise or fall significantly different from the shifts occurring prior to stimulation. The method for this analysis will be discussed.
Vibration as a Quantitative Measuring Tool of Liquid Density
Authors: Thiessen G. J. , Dagg I. R.
Published: September 2005

The vibratious resulting from an unbalanced rotor need not always be unwanted and may be used as a sensitive measure of the density of a liquid. The accurate determination of volume which is usually necessary in density measurements may be eliminated with this method. An L-shaped sample container is mounted on a vertical rotatable shaft so that some liquid remains in the vertical portion of the container during the rotation. Excess volume is thus distributed so that it makes no contribution to the off-balance. The vibration resulting from the off-balance is picked up from one flexibly mounted bearing and is a measure of fluid density. This is applied to the measurement of pulp content in dilute pulp suspensions (less than 1%) occurring in the paper making process.
New Graphic Level Recorder for Acoustic Measurements
Authors: Fitzmorris M. J. , Faran J. J. , Basch M. W.
Published: September 2005

A new level recorder based on the SL-4 has been developed. The driving element of this recorder is a coil suspended in a magnetic field and controlled by a closed-loop servo system. The moving coil travels in a straight line and carries a pen which writes on a paper chart 4 in. wide. The circuits for this recorder have been completely transistorized, and a new magnetic structure has been used. As a result, the size, weight, and power consumption of the instrument have been reduced. Sensitivity has been increased 20 db. A “quasi-rms” detector circuit with adequate dynamic range for noise signals is used. A new, simplified method of construction for the logarithmic potentiometers has been developed and their resolution has been improved. The band width of the servo system which positions the pen is adjustable over a wide range. The effect of the servo band width, damping, and maximum writing speed on the transient response will be described. The corresponding effects upon the recording of reverberation and frequency-response curves will be discussed.
New Artificial Larynx
Authors: Barney H. L. , Haworth F. E. , Dunn H. K.
Published: September 2005

Since the development of the Western Electric reed type artificial larynx (Model 2) about thirty years ago, there has been a number of developments in the general fields of acoustics and electronic circuitry which are applicable to the design of an improved artificial larynx. An experimental model using some of these developments will be described and demonstrated. This new model is inconspicuous in use, and, as indicated by sound spectrographic analyses and articulation tests, has improved speech quality.
Identification of Filtered Vowels
Authors: Peterson Gordon E. , Lehiste Ilse
Published: September 2005

In sustained vowels the formants are essentially fixed in frequency position, so that the various formant frequencies can be eliminated by means of high-pass and low-pass filtering. A filtering technique was employed in order to determine the relative influence of the various formant frequencies upon vowel identification. The endings were removed from the vowels by means of a gate circuit, and the vowels all had essentially the same fundamental voice frequency. Subjects trained in phonetics served as listeners for the experiment. The data show that the contributions of the various formants to vowel recognition differ with various vowels. When the high-pass filter admitted only formants above the third, vowel identification dropped below 5%. Vowel substitutions are highly predictable under certain conditions of filtering. The data thus do not support the thesis that any major section of the vowel pattern is adequate for the identification of all vowels. Rather, they indicate that certain particular aspects of each vowel pattern are primary, or may be considered as essential information bearing vowel parameters.
Automatic Resolution of Speech Spectra into Elemental Spectra
Authors: Stevens K. N. , Bell C. G. , Brady P. T. , Heinz J. M. , Rosen G.
Published: September 2005

The acoustic output for a given configuration and excitation of the vocal tract during speech production can be described in a relatively compact manner by a transfer function characterized by a reasonably small number of poles and zeros. Thus the spectrum of a speech sound (log amplitude vs frequency) may be considered to be the sum of several elemental spectra, each associated with one pole or zero. The spectrum envelope of any vowel, for example, could be approximated reasonably accurately by combinations of spectra drawn from a catalog of 30 to 40 curves that represent simple resonances at a number of different frequencies. A digital computer has been programed to perform such an approximation on spectra of vowel and some consonant sounds sampled periodically in time. Successive comparisons are made between a particular speech spectrum and spectra constructed from a catalog of elementary curves that are stored in the memory. The computer is programed to converge rapidly from a first approximation of the spectrum based on previous examinations of adjacent samples towards the synthesized spectrum that yields the best fit with the input spectrum, and reads out numbers that identify the particular elemental spectra that are finally selected. [Supported by U. S. Army (S.C.), U. S. Air Force (O.S.R., A.R.D.C.), and U. S. Navy (Office of Naval Research), and by Air Force Cambridge Research Center Contract AF 19(604)-2061.]
Investigation of the Shadow Zone for a Particular Sound Velocity Variation
Authors: Potter D. S. , Murphy S. R.
Published: September 2005

In a previous paper [J. Acoust. Soc. Am. 30, 684(A) (1958)] an exact solution was presented for wave propagation in an inhomogeneous medium characterized by a sound velocity variation, c = c0z/(z2−a2)12, for a point source at z0, z0>a. In this paper specific properties of this solution are investigated for real values of a. In this case a shadow zone is produced with a caustic as a boundary. It is shown that the above solution is greatly simplified for a coordinate system in which the caustic is a coordinate line. A general expression for the sound intensity is derived and numerical results for regions on both sides are presented. Frequency as a parameter is discussed and a comparison is made with the results derived by Brekhovskikh [Soviet Phys.-Acoustics 2, 124 (1956)] in the high-frequency limit for regions about the caustic. (This work was supported by the Bureau of Ordnance, U. S. Navy, under Contract NOrd 12937.)
Grain Boundary Scattering in Copper and Brass
Authors: Krautkopf David W.
Published: September 2005

Measurements of attenuation due to scattering have been performed in polycrystalline copper and brass, using the standard pulse technique. Specimens are in the form of cylindrical rods of varying grain size. Frequencies employed range from 100 kc to 100 Mc. The aim of this investigation has been to study the dependence of scattering upon frequency and grain size by direct observation of the scattered radiation. Complications due to mode dispersion restrict the observations to backscattered radiation. Results are of interest in material testing, since many metals and alloys exhibit considerable scattering at high frequencies, thus restricting testing to relatively low frequencies. (This work has been supported in part by the U. S. Atomic Energy Commission.)
Small Scale Acoustic Streaming near a Vibrating Piston Opposite a Rigid Boundary
Authors: Jackson Francis J. , Nyborg Wesley L.
Published: September 2005

In studying effects of acoustic streaming on surface processes it is important to specify the flow as well as possible. One arrangement for generating localized streaming consists, in essence, of a piston of circular cross section placed in liquid a short distance above a rigid boundary. When the piston oscillates along its axis of symmetry (perpendicular to the boundary) eddying motions are observed near the tip periphery—where sharp velocity gradients exist. To permit detailed observation of the flow we have constructed a large-scale low-frequency model which operates at 2 kc. Using dark field illumination and small indicator particles, it is possible to record photographically sonically generated eddying in this case and thus determine velocity distributions. Photographs of the motion for various values of such parameters as viscosity, vibration amplitude, and piston-boundary separation will be shown. Relevant theory will be discussed. [Supported in part by U. S. Air Force Office of Scientific Research, Contract AF 18(603)-54.]
Acoustic Impedance of a Viscoelastic Fluid Confined between Parallel Planes
Authors: Thurston George B.
Published: September 2005

From a general relation between stress and strain and their time rates of change for a viscoelastic medium, special equations are obtained for sinusoidal motion. The medium is described as a viscoelastic fluid and is considered to be incompressible. The general equation for sinusoidal flow of such a viscoelastic fluid is then developed. A solution to this equation is obtained for rectilinear motion of the fluid confined between two infinite rigid parallel planes. From this solution the acoustic impedance per unit area of plane is determined. Functions from which this impedance can be directly determined have been computed and are presented in graphical form. Viscoelastic media which range from a perfect viscous fluid to a perfect elastic solid are treated. It is found that the acoustic reactance of a given fluid will vary from spring-like to mass-like as the frequency passes a certain critical value.
Ideal Spaced Damping Treatments for Flexural Waves
Authors: Kerwin Edward M.
Published: September 2005

Layers of viscoelastic material are useful in the damping of flexural waves in plates. Two basic damping treatments using such layers are the homogeneous damping layer analyzed by Oberst [Akust. Beih. 4 (1952)] and the constrained damping layer analyzed by the author [J. Acoust. Soc. Am. 30, 698 (1958)]. In these treatments the viscoelastic layer is distorted in extension and shear, respectively. In the present paper we show that with both basic treatments, the insertion of a “spacer” layer between the plate and the damping treatment serves to magnify the distortion of the damping material, thus increasing the damping factor. The ideal spacer should be incompressible and infinitely stiff in shear. Its extensional stiffness in a plane parallel to the plane of the plate should be negligible. We treat the case of spaced damping treatments with ideal spacers, showing the increase in damping as a function of spacer thickness. Significant increases in damping factor are found, amounting to a factor of 10 or more in some cases. Some measured damping factors are presented for treatments with and without spacers.
Dependence of Acoustic Velocity in Some Aqueous Hydroxide Solutions on Temperature and Concentration
Authors: Marks Graham W.
Published: September 2005

Much can be learned about the molecular properties of liquids and solutions from investigations concerning acoustic velocity and attenuation. Systematic studies are needed. The present work concerning acoustic velocity in aqueous solutions of LiOH, NaOH, KOH, and NH4OH follows that which was recently done on solutions of Li2SO4, Na2SO4, KHSO4, K2SO4, (NH4)2SO4, and MgSO4. A precision ultrasonic interferometer was employed. Measurements were made over wide ranges of concentration and over the temperature range 0° to 80°C except in the case of solutions of NH4OH. It has been found that the acoustic velocity versus temperature curves rise and are displaced toward lower temperatures just as was found for the sulfate solutions investigated. The specific acoustic impedance varies linearly with concentration at 20°C. Adiabatic compressibilities are represented by the 32 power law. Solutions of NH4OH are at variance with the other hydroxides. The relative association declines with increase in concentration whereas for the others it increases. From the data the apparent molal compressibilities were computed for the temperature range 15° to 35°C. Based on values of the apparent molal compressibilities at infinite dilution, the solvation appears to be about six water molecules per ion.
Ultrasonic Vibration Potentials in Non-Ionic Liquids
Authors: Yeager Ernest , Booker Jonathan , Hovorka Frank
Published: September 2005

Recently Hunter [Proc. Phys. Soc. (London) 71, 857 (1958)] has called attention to ultrasonically produced alternating potential differences in conductivity water. Rutgers and Rigole [Trans. Faraday Soc. 54, 139 (1958)] also have reported ultrasonic vibration potentials in distilled water and several pure organic liquids including n-heptane. A satisfactory explanation was not advanced by these authors but they suggest that such effects in pure liquids seriously complicate the interpretation of previous work in ionic solutions [e.g., J. Acoust. Soc. Am. 25, 456 (1953)]. Further research at Western Reserve University with pulse-modulated ultrasonic waves indicates that these apparent effects in non-ionic liquids are associated with the glass or plastic mountings for the metal electrodes and that a condenser-microphone mechanism probably is involved. Since the internal impedance associated with such a source of alternating potentials is high, it does not appear to cause any appreciable difficulties in the measurements in ionic solutions where the internal impedance is much lower. (This research has been supported by the Office of Naval Research.)
Separation of Temperature and Pressure Effects in Ultrasonic Relaxations in Liquids by Solution Measurements
Authors: Piercy J. E.
Published: September 2005

In investigations of ultrasonic relaxations caused by two state processes—such as monomer-dimer association or the interconversion of rotational isomers—the energy difference between states is usually calculated from experimental results on the assumption that the difference in molecular volume is zero, meaning that only the temperature variation in a sound wave affects the molecular equilibrium. However the pressure variation in a sound wave in a liquid is so large with respect to the temperature variation (∼50 atmos/°C) that significant errors or even castatrophes can be introduced by the rather small changes in molecular volume (⩽5%) that are likely for these processes. The additional experimental variable needed to separate these effects may be provided by measuring solutions of the relaxing substance in inert solvents which possess different ratios of pressure to temperature variation for sound waves. This separation is illustrated by measurements of the ultrasonic absorption of methyl cyclohexane in xylene and nitrobenzene. The difference in free energy and enthalpy between the two chair isomers of methyl cyclohexane in these solutions is found to be 2.2±0.4 and 3.5±0.8 kcal/mole, respectively, and a difference in molecular volume of less than 1% is indicated.
Effects of Progressive Ultrasonic Waves on a Narrow Light Beam Theoretical
Authors: Zankel K. L.
Published: September 2005

The effects of an ultrasonic wave on a light beam that is very much narrower than the sound wavelength, but wide enough that diffraction of the light by the limiting aperture can be neglected, have been theoretically understood for some time. For most of the experiments attempted, these conditions are not simultaneously realized. Expressions for the effect of ultrasound on light beams of arbitrary width are derived. Diffraction of the light by the limiting aperture is included. The expressions do not contain the limitations of the previous theories mentioned above and are valid for arbitrary wave forms. The results are compared with previous experiments. Applications of the results are suggested. (This research was supported by the Office of Naval Research.)
Traffic Noise Problems in Germany
Authors: Grützmacher M.
Published: September 2005

West Germany has recently enacted legislation designed to keep a tight control of traffic noise with the police force properly equipped to enforce it. This paper will discuss this legislation, noise measuring instruments, experiences of the last years, statistical results, subjective measurements of the loudness of traffic noise, and apparatus for the driver's control of car noise.
Preliminary Report on Noise in Hospitals
Authors: Goodfriend Lewis S. , Cardinell R. L.
Published: September 2005

An ideal hospital environment for patients is a quiet one. The conventional attitude towards hospital operation is to insist on a quiet outdoor environment. Actually there are four basic noise source groups creating hospital noise. These are: 1, exterior sources; 2, mechanical operating facilities; 3, patient service personnel; and 4, patient service facilities. A twenty-four-hour picture of noise levels in a modern hospital is shown as well as spectra of the noise measured in private rooms. (This work was supported by the U. S. Public Health Service.)
Upgrading of Acceptability Criteria for Noise in Business Machine Offices
Authors: Embleton T. F. W. , Dagg I. R. , Thiessen G. J.
Published: September 2005

Following a noise survey of twenty-one offices devoted to card processing with business machines it is suggested that the criteria determining whether a given background noise level is acceptable or not may be upgraded in locations which meet certain specific acoustic requirements. The offices surveyed had been selected by a “nonacoustical” authority from those in which personnel had made complaints; in some only noise had been a specific complaint. The survey included both physical measurements (tape recordings) and public opinoin polls (questionnaires). In most cases the results are in very good agreement with Beranek [J. Acoust. Soc. Am. 28, 833 (1956) and Noise Control 3, 19 (January, 1957)]. In a few locations levels of NC-60 and even NC-65 are found to be acceptable. These are distinguished from those requiring a criterion of NC-50 to NC-55 by (i) very good acoustic absorption on both walls and ceiling, (ii) comparative absence of scattering objects such as filing cabinets, (iii) a ceiling height no greater than about 12 ft, (iv) a floor plan which has its principal dimensions in a ratio lying between 1.2:1 and 1.6:1 and which has its maximum dimension less than about 50 ft.
On the Presentation of Data on Fan Noise
Authors: Fitzpatrick H. M.
Published: September 2005

The form of the relation among: speed of rotation, size of fan, flow rate, spectral density of radiated sound power, and sound frequency is derivable from simple considerations of dimensions and acoustic theory. Examples are given.
Source of Noise in Fans
Authors: Hardy Howard C.
Published: September 2005

Many of the phenomena of noise of fans can be predicted from the simple assumption that the source of noise power is a pressure pulse created by the motion of the blade or impellor. From this assumption the well known fan sound laws can be derived: (1) the sound power varies as the fifth power of the blade tip speed, and (2) the sound power is approximately proportional to the product of the brake horsepower and the static pressure. The sound power spectrum is the resultant of the combination of a coherent and incoherent spectrum. The coherent or “harmonic” spectrum is characterized by a series of pure tones whose magnitudes are predicted from the magnitude of the Fourier coefficients of the Fourier series which describes the pressure pulse. The incoherent or “pulse” spectrum has a broad-band characteristic which can be derived from the Fourier integral of the pressure-time curve of the pulse. It appears that the spectrum follows closely what would be predicted for an exponential pulse. The octave, or other proportional band plots, show a rate of increase of three decibels per octave to a broad maximum frequency, and thence a decrease of approximately six decibels per octave.
Method for the Measurement and Analysis of the Near Noise Field of Jet Aircraft
Authors: Tolhurst G. C. , Morrill S. N.
Published: September 2005

Due to the limitations of area available during the operational launching of carrier-based aircraft, the near noise field (12.5, 25, 50, 100 and 200 foot radii) of new or experimental engines needs accurate definition. A system was designed to obtain two simultaneous noise sampling channels, an annotation facility, and two continuous graphic sound pressure level records. An intercommunication network was also provided between the microphone carriers and the recording engineer. The noise analysis was accomplished by employing loops of magnetic recording tape and one-third octave filters. All of the recording and analyzing equipment was housed in a mobile trailer unit fitted with reels for microphone and power cables. Noise profiles of two aircraft will be presented, abstracted from data obtained by the unit described.
Jet Noise Generation and Suppression
Authors: Mollö-Christensen Erik
Published: September 2005

On the basis of similarity laws obtained from controlled experiment, a theory of the generation of the sound emitted to the far field frown a jet is presented. The sound is generated in the high shear region immediately downstream of the nozzle exit, and is scattered by the remainder of the flow. The scattering is partly coherent, partly omnidirectional. The principal features of the far field spectra can be explained in terms of these processes. On the basis of this theory, the mechanisms involved in sound suppressors are discussed, and suggestions are made for a systematic approach to sound suppressor analysis.
Follow-Up Report on Audio Analgesia
Authors: Gardner Wallace J. , Licklider J. C. R.
Published: September 2005

The procedure described at the Fall Meeting—the procedure in which music and noise under the control of the dental patient are used to mask the sound of the dental drill and the pain produced by drilling or extraction—has now been employed on over 500 patients with approximately 90% success. It is now considered definite on the basis of more than 50 extractions (in which the drill did not enter the picture) that the masking noise actually masks pain. The device used to present the acoustic signals to the patient (“Audio Analgesiac”) has been considerably improved, and it is now being used on an experimental basis by several dentists, whose reports are beginning to come in. The use of noise signals more pleasing to the ear than filtered random noise is being explored. The experience to date will be summarized and preferred music and noise signals will be demonstrated.
Optimized Absorption of Sound by a Flexible, Porous Medium
Authors: Lang William W.
Published: September 2005

At the 56th meeting of the Acoustical Society of America [J. Acoust. Soc. Am. 31, 115 (1959)], some results were presented of a study of a flexible, porous medium represented by a simple equivalent circuit. The lumped circuit elements of the analog corresponded to the significant physical constants which characterize the medium. Physically realizable flexible porous materials have widely varying properties. To select media with physical properties which are optimum for the absorption of sound, a program for an IBM 704 computer has been written. This program selects combinations of properties which yield absorptive behavior meeting specified requirements. Results of an analysis covering wide ranges of physical properties of flexible, porous materials are presented.
Improvement of Acoustic Feedback Stability in Public Address Systems
Authors: Schroeder M. R.
Published: September 2005

It has been shown previously that the frequency response of a large room has fluctuations of an average magnitude of 10 db. A related result which has been obtained recently is that the highest peak of the response in the audio band is typically about 12 db above the (constant) mean gain. Since a public address system can become instable when the maximum loop gain exceeds 0 db, the gain could be increased accordingly if the fluctuations of the room response could be eliminated. Unfortunately, this cannot be done. It has been demonstrated both theoretically and experimentally that the response fluctuations in large rooms are an inherent property of the multiple path transmission and result from their statistical interference. However, by inserting suitable electronic circuits into the feedback loop (between microphone and loudspeaker) the effect of the response fluctuations can be eliminated. With the help of such a circuit, we have been able to increase the gain by up to 14 db above the “singing” point before instability occurred. The technique will be described in detail. A demonstration of this method is planned.
Stability of Western Electric Microphones
Authors: Embleton T. F. W. , Dagg I. R.
Published: September 2005

The absolute sensitivities of several Western Electric 640 AA condenser microphones have been measured using reciprocity techniques. All readings are made in terms of the settings of a precision potentiometer. By taking six different pairs of readings instead of the minimum number of three which the reciprocity technique requires, each calibration was checked for self-consistency and any erroneous reading detected immediately. Changes in sensitivity may be measured to ±0.03 db; all measurements have been made at 400 cps. The temperature coefficients of sensitivity varied from one microphone to another; from as little as −0.0025 db/°C to +0.022 db/°C. When measurements were first commenced the microphones showed considerable scatter, as much as ±0.2 db, but after a large number of measurements they settled down to much more steady values. In all cases it was found that the microphone sensitivities were a function of the ambient pressure, thus indicating that the stiffness of the air cavity behind the diaphragm contributes to the total stiffness. In most cases this contribution was of the order of 10%.
Basic Speech Factors
Authors: Veneklasen Paul S. , Christoff Jerry
Published: September 2005

Certain spectral and spacial characteristics of voice output which are basically essential to voice communication studies are presented.