Volume 31, Issue 6, June 1959
Index of content:
31(1959); http://dx.doi.org/10.1121/1.1907770View Description Hide Description
The generation of nasal consonants can be simulated approximately by a cascade connection of simple electrical tuned circuits excited by a quasi‐periodic electrical buzz source. The lowest resonance for nasal consonants is in the vicinity of 200 to 300 cps, and the damping of this resonance is greater than that for the first resonance of vowels. A terminal‐analog synthesizer and control device have been used to generate a number of synthetic syllables, each consisting of a nasal consonant followed by a vowel, with smooth formant transitions between consonant and vowel portions. Systematic listening tests have shown that the identification of the nasal consonant is determined largely by the frequency position of the second resonance of the nasal portion of the syllable, and thus by the direction and extent of the second formant transition of the vowel, as noted in other studies. The identification of the nasal consonant is also dependent to some extent on the duration of the consonant and transition portions of the syllable. Isolated nasal consonants generated by this procedure can also be identified with reasonable consistency.
31(1959); http://dx.doi.org/10.1121/1.1907771View Description Hide Description
The shape of the vocal cord wave is an important parameter in a true analog representation of the vocal mechanism, since the final speech wave is a function of both the generator wave shape and the transfer impedance of the vocal tract. The shape of this wave has been determined by two independent methods: (1) by the derivation and use of a network having a characteristic which is the inverse of the first vocal resonance, and (2) by measuring the area of the vocal cord opening as a function of time through the use of motion picture studies. Harmonic analysis of some of the typical shapes obtained indicate that a uniform distribution of harmonic amplitudes is a rarity; instead there is a tendency for the distribution to have a cyclical variation of the form (sinkn/kn 2). The results obtained through the use of the inverse network indicate that the main excitation of the higher resonances occurs at the point of vocal cord closure and that the magnitude of this excitation can be controlled by the talker over wide ranges.
31(1959); http://dx.doi.org/10.1121/1.1907772View Description Hide Description
The author is working towards the development of an ultrasonic viewing system which is an analog in ultrasound of conventional light photography. In the present paper it is shown that a sonic lens is able to resolve two sources of ultrasound whose spacing is about equal to the length of one wave of the sonic energy in use. It is also shown that at the frequency being used (3 Mc) uniform illumination of an object for sonic viewing is very difficult because Fresnel near field and other diffraction and interference effects occur very readily and that these effects are frequently themselves not stable.
31(1959); http://dx.doi.org/10.1121/1.1907773View Description Hide Description
The molecular basis for ultrasonicabsorption in liquids is reviewed. The various loss mechanisms are all relaxation processes which include such phenomena as vibrational, isomeric, structural and shear relaxation effects. The relation between such factors as the relaxation time and the properties of the liquid are considered.
31(1959); http://dx.doi.org/10.1121/1.1907774View Description Hide Description
The problem of propagation of traveling waves in a right circular cylinder having hexagonal elastic symmetry is considered here. Exact expressions for the displacements produced by both the compressional and torsional modes are obtained. A conclusion of importance in ultrasonic methods is the result that the compressional and torsional modes propagate independently without coupling either through the equations of motion or the boundary conditions. A condition relating the frequency and wave number of the torsional wave is derived.
31(1959); http://dx.doi.org/10.1121/1.1907775View Description Hide Description
A general method is developed for the solution of the linearized equations of elasticity for both homogeneous and inhomogeneous media. This method yields solutions which describe propagating waves which may be pulses, rapidly changing wave forms, or periodic waves. It is not restricted by the usual considerations which depend upon separation of variables. The solution consists of a series of terms, the first of which describes the wave motion predicted by geometrical optics. Subsequent terms account for certain types of diffraction effects. The series is not necessarily convergent but is presumably asymptotic to the solution.
31(1959); http://dx.doi.org/10.1121/1.1907776View Description Hide Description
Special arrangements are used to produce small‐scale eddying near surfaces at which reactions are taking place. Experiments in which the reaction involves a photographic emulsion acted upon by developer show that the development process is considerably accelerated in small areas where the near‐surface flow is concentrated. Resonant gas bubbles appear to be by far the most efficient sources of sonically induced micro‐eddying. When such a bubble rests on an emulsion surface the development reaction in its neighborhood is significantly affected, evidently because of the local “microstirring,” at ambient pressure amplitudes much less than are typically used in sonic and ultrasonic applications. Sonic microstreaming, especially as induced near resonant bubbles at boundaries, appears to be an important mechanism in accounting for certain well‐known effects of ultrasound. Continued development may lead to means for applying microstreaming to surface processes in a controlled and specifiable manner.
31(1959); http://dx.doi.org/10.1121/1.1907777View Description Hide Description
The operation of the human heart together with the sounds resulting from normal operation are discussed. Examples of the diagnostic, intracardiac sounds due to several of the common congenital lesions are cited and analyzed. Transmission and magnitude of heartsounds within the heart have been measured and are reported.
31(1959); http://dx.doi.org/10.1121/1.1907778View Description Hide Description
The attenuation of sound propagated out‐of‐doors is conveniently separated into attenuation due to spherical divergence and excess attenuation due to atmospheric and terrain effects. This excess attenuation is principally caused by sound absorption in the air, the refractive effects of temperature and wind gradients, by turbulence and the effects of terrain and ground cover. To investigate these effects the propagation of sound over open, level ground, through dense evergreen forests, and between hilltops was studied experimentally in the frequency range between about 300 cps and 5000 cps. Extensive micrometeorological instrumentation was utilized to measure and record the relevant micrometeorological parameters simultaneously with the acoustic data for a wide variety of weather conditions. Data on the attenuation of the mean received sound pressure level as well as on the fluctuations about the mean were obtained and correlated with the state of the atmosphere.
Over open level terrain, the excess attenuation upwind was found to exceed that for downwind propagation by as much as 25–30 db for source and receiver heights of 12 and 5 ft, respectively. Temperature and wind gradients near the ground‐air interface largely account for this difference. In hilltop‐to‐hilltop propagation, wind direction is of secondary importance, and in dense woods absorption and scattering control. Empirical functions were derived for the purpose of estimating the mean excess attenuation as a function of frequency and distance, for a given set of micrometeorological conditions. These charts have been found useful in many practical problems involving the propagation of sound over open level ground.
31(1959); http://dx.doi.org/10.1121/1.1907779View Description Hide Description
Exact general solutions of the three‐dimensional elasticityequations of motion in polar cylindrical coordinates are obtained for axisymmetric and antisymmetric thickness‐shear vibrations. These solutions are applied in solving five solid and hollow circular bar problems. Natural frequencies are tabulated.
31(1959); http://dx.doi.org/10.1121/1.1907780View Description Hide Description
A typical single wall is characterized by a free flexural wave speed, cB , which increases with . When cB approaches c 0 (the speed of soundwaves in the surrounding medium) the impedance of the wall to incident soundwave ceases to be mass‐like because of the coincidence effect and the transmission loss will be less than that given by mass law. Since for homogeneous walls, the deleterious effects of the coincidence of the flexural wave speed with the phase velocity of sound in the medium can be avoided for homogeneous walls by reducing the ratio of B/M. (B is the dynamic bending stiffness of the wall; M is the mass per unit area of the wall.) Thus the problem of good acoustical performance in homogeneous walls is seen to be in essential conflict with the need for structural rigidity.
A new wall design has been found in which the ratio of the static to the dynamic stiffness can be in excess of 1000:1 and where the stiffness changes from the static to the dynamic value in such a way that the acoustical behavior is nearly that of a perfectly limp wall. If desired, the loss tangent of the wall can be made large and nearly constant over a wide range of frequencies.
31(1959); http://dx.doi.org/10.1121/1.1907781View Description Hide Description
This paper deals with some measurements concerning the threshold versus duration for tone pulses. A new hypothesis introduced: Switching on a tone pulse of intensity I results in an effect s somewhere in the hearing pathway, that approaches its final value asymptotically according to an exponential function; this final value is proportional to I; perception occurs when s exceeds a critical value s 0. The experiments show that this hypothesis gives a better description than the hypotheses thus far used. The time constant varies from ca 375 msec at 250 cps to ca 150 msec at 8000 cps. For short pulse durations the data deviate from the hypothesis. This deviation can be explained by the assumption that energy integration around each frequency is restricted to a fixed band width. A formula is derived which gives a correction to the mentioned relationship for short durations. In this way the band width at the different test frequencies could be determined. The general course of this band width as a function of frequency agrees with the “Kopplungsbreite” after Gässler.
31(1959); http://dx.doi.org/10.1121/1.1907782View Description Hide Description
Whereas temporal intervals as short as a few milliseconds are sufficient to separate two brief sounds so that a listener will report that there are two (instead of only one) sounds, a longer separation time of between 15 and 20 msec is required for the listener to report correctly which of the two sounds preceded the other. This minimum temporal interval appears to be independent of the kinds of sounds used: whether short or long, of high or low frequency, of narrow or wide band width. There is some suggestion that rise‐time and duration may change this minimum interval, but these somewhat secondary relations are not investigated in detail here. The length of the required temporal interval suggests that the judgment of order requires other mechanisms than those associated with the peripheral auditory system.
31(1959); http://dx.doi.org/10.1121/1.1907783View Description Hide Description
With the theory of signal detectability as a framework, two psychophysical experiments were conducted in which each observation interval was well defined for the listener. Each interval contained noise, and it either did or did not (p=0.5) contain a signal (1000 cps, 0.5 sec in duration). In separate sessions of the first experiment, either the listener gave a yes‐no decision or he responded with a rating (1–4) after each observation interval. Operating characteristics were obtained with E/N 0 equal to 15.8. It is clear from the data that the trained listener can perform as well when he adopts the multiple criteria necessary for the rating method as when he adopts the single criterion required by the binary‐decision procedure. In the second experiment, only the rating method was used to determine the relation between d′ and E/N 0. The resulting function, for d′ ⩽ 3.0, approximates straight line which passes through the origin and which has nearly the same slope as that obtained in other laboratories.
31(1959); http://dx.doi.org/10.1121/1.1907784View Description Hide Description
An experiment is described in which time and intensity differences of 2‐kc high‐pass clicks were mutually offset to produce sound images centered in the head. Binaurally correlated and uncorrelated clicks were used, and the trade was tested at 10–70 db SL. The results show that generally the two types of clicks behave similarly, and that up to 60 db SL, at least, as over‐all intensity increases, the time difference compensating a given intensity difference (in db) decreases. A function is derived describing what is interpreted as a physiological intensity‐to‐time conversion. The place of such a conversion in lateralization is discussed.
31(1959); http://dx.doi.org/10.1121/1.1907785View Description Hide Description
The loudness of complex sounds was studied as a function of the number of components. Complexes of two, three, four, and eight tones, and a band of white noise were matched in loudness to a 1500‐cy tone. The over‐all spacing, ΔF, between the lowest and highest components of these stimuli was held constant at either 175, 1600, or 3400 cps. All the complexes were centered around 1500 cps when ΔF was either 175 or 1600 cps. At each of the four levels tested (25, 50, 75, and 90 db SPL),loudness remained essentially unchanged when only the number of components within a complex was varied. This invariance of loudness occurs even though inhibition may be greater within the complexes that contain a larger number of components. It is suggested that the increased inhibition may be offset by greater loudness summation when the energy is more evenly distributed within the complexes.
31(1959); http://dx.doi.org/10.1121/1.1907786View Description Hide Description
There is psychophysical evidence that both spectrum and periodicity of acoustic signals may be cues for pitch judgments. At the level of the auditory nerve, these stimulus characteristics seem to be coded in terms of place and time pattern. Very little is known of their representation higher levels of the nervous system. Tonotopic organization of the auditory cortex has been demonstrated in anesthetized cats by the evoked strychnine potential technique. In these demonstrations only tonal stimuli were used. We use similar physiological preparations but employ acoustic stimuli that permit independent manipulation of spectrum and periodicity. The results show that the previously reported tonotopic organization is based only upon spectral characteristics of the stimulus.
31(1959); http://dx.doi.org/10.1121/1.1907787View Description Hide Description
The TTS at 4 kc was measured 2 and 17 min after successive 12‐min exposures to broad‐band noise at 106 db SPL separated by 18 min of silence. The results indicate that the TTS existing at the beginning of a particular exposure can be treated as additional time of exposure. Thus, if the residual TTS has a value that would be produced by R min of exposure, then the total TTS at the end of an M‐min exposure will be given by solving the equation for growth of TTS with exposure time set equal to M+R.
31(1959); http://dx.doi.org/10.1121/1.1907788View Description Hide Description
As part of an over‐all evaluation of the USNEL Flight Deck Communications System, an RCA modulated air‐flow loudspeaker (air speaker) was tried out as a speech and alarm signaling transducer on the flight deck of an aircraft carrier. Tests with 200‐ to 6000‐cps noise showed that the air speaker produced 130 db SPL at optimum points on the deck, as compared to 110 db for the present system.Speech intelligibility and alarm detection tests showed the air speaker to be usable with jet aircraft at idle (30%) power while the present loudspeakers could not be heard. Neither loudspeakersystem was adequate with jets at full power.
31(1959); http://dx.doi.org/10.1121/1.1907789View Description Hide Description
An apparatus is described that applies the frequency components of speech, as spoken into a microphone, to the fingers of one hand with the purpose of enabling a deaf person to comprehend speech. Frequency is indicated by position along the fingers. The sense of touch is not called upon to make any direct frequency discrimination by distinguishing vibrational sensations of different frequencies as in previous attempts of this nature [R. H. Gault, J. Franklin Institute 204, 329–358 (1927)]. The frequency analysis is done partly electrically and partly mechanically. Small tuned steel reeds are used for the final frequency analysis. These steel reeds also serve as transducers by operating directly against the fingers.
The results of a short series of experiments on a deaf person are promising but the recognition of individual consonants is difficult.