Volume 29, Issue 5, May 1957
Index of content:
29(1957); http://dx.doi.org/10.1121/1.1908961View Description Hide Description
Suggestions are made pertaining to standard methods of measuring the sound absorption of acoustical materials and the sound transmission loss (STL) of partitions. (1) Concerning the reverberation chamber method of measuring the sound absorption of materials, it is shown that the absorption varies with the position of the sample in the chamber, owing to interference patterns. An estimate is made of the difference in absorption of a sample on the floor (a) centrally and (b) touching one side wall. It is suggested that sample position should be specified as distant at least half a wavelength (λ/2) from walls and reflecting surfaces other than the one backing the sample. (2) Regarding the measurement of STL it is suggested that microphone position be specified as at least λ/2 from walls and the corresponding distances from edges and corners of reverberation chambers. The technique in which the microphone is placed near a wall is not recommended. (3) As a single figure for the over‐all sound insulation value of a partition, the arithmetic mean of the decibel STL figures at various frequencies is often used. It is suggested that a better average figure is obtained if the linear ratios corresponding to these decibel figures are averaged instead of the decibel figures themselves. This removes the logarithmic weighting of the latter average, for which there is no physical justification.
29(1957); http://dx.doi.org/10.1121/1.1908963View Description Hide Description
The concept of the critical band, or Frequenzgruppe, is shown to apply to loudness summation. When the spacing between a group of pure tones is increased, the loudness remains constant until a critical point is reached, after which the loudness increases. The same effect occurs when the width of a band of noise of constant SPL is made larger. The critical band width at which loudness summation begins to depend on the spread of energy is approximately the same as the critical band width determined previously by methods involving thresholds, masking, and phase. The critical band as measured directly by these three methods (plus the method of loudness summation) is about two‐and‐a‐half times as wide as the critical band derived from the assumptions made by Fletcher, but its dependence on frequency is approximately the same. The relation of the critical band to other functions is noted.
29(1957); http://dx.doi.org/10.1121/1.1908965View Description Hide Description
Békésy‐type, transparent models of the cochlea were used in the present study. Suspensions of aluminum dust in glycerin‐water solutions provided frequency responses sufficiently high so as to improve the display of Békésy's “eddies” and to allow demonstration of particle motion within the “perilymphatic” fluid. The membrane displacement was found to vary with frequency, whereas the revolving velocity of the dc eddy currents varied with the square of frequency. The “bed” of each eddy was narrowest along the membrane and much wider elsewhere, as evidenced by a reciprocal variation in speed, ac particle motion (in response to pure‐tone signals) was longitudinal proximal to and trochoidal (elliptical) alongside the membrane. In general, the elliptical orbits flattened out with distance from the membrane or from the eddy's mainstream upon which particle motion was superimposed. Along the membrane, the trochoidal pattern conformed to the changes of the traveling wave, while in the rebound portion of the eddy it became almost longitudinal. No ac particle motion was seen to occur beyond the eddy. A phase lag of ac particle motion, totalling 360°, accumulated gradually throughout the eddy so that particles in the inbound and rebound portions of the eddy were in phase opposition to each other. Orbits of ac particle motion resulting from stimulation by complex tones were observed also and analyzed as Lissajou figures. A given phase relation between the partials of complex orbits remained unchanged throughout the eddy, although their relative magnitude did alter. In the case of beats, two separate patterns were observed in response to the beat frequency and to the intermediate frequency. This indicated that the model reacted nonlinearly to such stimulation.
29(1957); http://dx.doi.org/10.1121/1.1908967View Description Hide Description
A brief history of the finding and development of aluminum‐iron alloy introduces the description of our industrial specification as finally decided upon by the organized group. The description covers the specification for the melting and rolling processes, both of which are main factors affecting the magnetostriction characteristics. Improvement of transduction efficiency is then discussed in general, and it is concluded that no other material which has larger coupling factor than that of nickel, or “Alfer,” (i.e., the 13.5% aluminum‐iron alloy), is necessary, in so far as the transducers to be used at their resonance are concerned. Improvement in the efficiency can be attained only by the considerable elimination of the eddy current, and this is accomplished by our several magnetostrictive transducers made of Ni‐Cu ferrites which are shown to be excellent for generating underwater ultrasound. Electroacoustic efficiency is as high as 90% even at such higher frequencies as 70 and 100 kc. Intense generation of ultrasonic waves is successfully carried on up to the rate of 3 w/cm2 of the radiation surface.
29(1957); http://dx.doi.org/10.1121/1.1908969View Description Hide Description
The structure and operation of the Hartmann air‐jet ultrasonic generator has been reviewed critically, and modifications are described which substantially increase the efficiency and available power output of the original device. Experimental results are presented in confirmation of the theoretical analysis.
An important part of the development has been the employment of a secondary resonator and projecting exponential horn. A novel design using a large number of whistles in a single horn (Multiwhistle R.B.) is described. This unit has a wide frequency and power range, and has been employed in France for agglomeration of aerosols,ultrasonic drying, fog dispersal, and other interesting applications.
Measurements with Ordinary Sound and Ultrasonics Carried Out in the Physical Laboratory of the University of Louvain29(1957); http://dx.doi.org/10.1121/1.1908971View Description Hide Description
29(1957); http://dx.doi.org/10.1121/1.1908973View Description Hide Description
The object of this investigation was to determine the effect of ultrasonic energy on 0.07 and 1.05% carbon steels during transformation from austenite to ferrite under controlled cooling. The ultrasonic energy was produced by means of a bowl‐shaped crystal of bariumtitanate and was coupled to the steel samples through distilled water. Ultrasonic frequencies of 400 and 1000 kc were used.
It was found that the ultrasonic treated samples of 0.07% carbon hypo‐eutectoid steel had finer grain size and greater hardness than the reference samples which had undergone the same heat‐treating cycle but with no ultrasonic treatment. When either the intensity or the frequency of the ultrasonic energy was increased, the grain size was further decreased.
For the 1.05% carbon hyper‐eutectoid, it was found that the lamellar layers of ferrite and iron carbide making up the pearlite crystals were definitely thicker in the ultrasonic treated samples than in the untreated ones. Hardness tests made on the pearlite crystals substantiated the above results.
Absorption and Dispersion of Forced Spherical and Cylindrical Sound Waves According to the Navier‐Stokes Equations29(1957); http://dx.doi.org/10.1121/1.1908975View Description Hide Description
In his classical paper on infinitesimal sound waves in perfect gases endowed with shear viscosity, bulk viscosity, and heat conduction, Kirchhoff [Ann. Phys. 136, 177–193 (1868)] considered not only plane waves but also a certain class of curved waves. He showed that the absorption and dispersion of these waves is determined by the solution of a biquadratic equation for the complex frequencies, but in discussing the behavior of particular waves he employed only one of the two pairs of roots, and this he linearized with respect to the driving frequency. The biquadratic itself, as extended by Langevin so as to hold for fluids obeying an arbitrary equation of state, has been solved exactly and generally by C. A. Truesdell [J. Rational Mech. Anal. 2, 693–762 (1953)]. In his comprehensive analysis and interpretation of the solutions, however, Truesdell considered only forced plane waves.
In the present article I give a new version of Kirchhoff's approach to curved waves of expansion (an arbitrary motion may be regarded as the vector sum of an isochoric irrotational motion, a set of vorticitywaves, and a set of expansion waves.Vorticitywaves are not considered in this note. As has been remarked in varying degrees of generality by M. Lessen [J. Aero. Sci. 21, 849–850 (1954)]; Lagerstrom, Cole, and Trilling, [“Problems in the theory of viscous compressible fluids,” GALCIT (1949)]; S. Jarvis, Jr., J. Acoust. Soc. Am. 27, 70–73 (1954)]; and U. Yao‐Tsu Wu [J. Math. Phys. 35, 13–27 (1956)] the propagation of linearized vorticitywaves is independent of bunk viscosity and heat conduction) and show how Truesdell's results on plane waves may be adjusted so as to apply to the class of curved waves considered. Spherical and cylindrical waves are analyzed in some detail.
Proper treatment of this problem requires dimensionless variables and hence some reference standard of length. Two alternatives are considered: (1) the unit of length is a linear dimension of a given oscillator, (2) the unit of length is the wavelength corresponding to the driving frequency according to the theory of nondissipative fluids. In the brief remarks of Kirchhoff, apparently only the first possibility was noticed.
For the second class of spherical waves, the absorption coefficient per cm is shown always to be much less than that for the first class. There is a frequency‐dependent factor which tends to increase the amplitude with the frequency.
Similar analysis is carried out for cylindrical waves, which me shown to behave in a fashion intermediate between plane and spherical waves.
In principle, the results are contained in Kirchhoff's paper. However, the analysis there, expecially as given in the expository work of Rayleigh [Theory of Sound (Dover Publications, New York, 1945), Vol. II, pp. 319–323] does not make clear how much depends on linearization with respect to frequency and how much does not. The purpose of Sec. 1 of this note is to show that Kirchhoff's method of reducing the analysis of certain curved waves to that of plane waves is valid exactly, at all frequencies.
29(1957); http://dx.doi.org/10.1121/1.1908977View Description Hide Description
Shock impulses have not as yet yielded to any practical method of spectral analysis that would permit convenient exact calculation of all the peak internal responses of hardware subject to such accelerations, and also permit comparison of shock severities by inspection. The shock spectrum with a few supplementary techniques, provides adequate insight into the responses of a one degree of freedom resonator. As an indication of the responses of a system with several coupled degrees of freedom, a second‐order shock spectrum is defined. An oscillatory constituent of the spectrum is also defined in such a way as to be applicable to any order of spectrum. Investigation of these two concepts leads to the conclusion that if the first‐order shock spectrum technique is to be used as a basis for comparison of the severity of a laboratory test shock with that of a service shock, spectra should be plotted for both positive and negative directions. Moreover, when feasible, such spectra should ordinarily be plotted as distinct curves for the intervals during and after the test shock, and the oscillatory constituent for the interval during the shock should be estimated.
29(1957); http://dx.doi.org/10.1121/1.1908979View Description Hide Description
In order to examine certain possible irregularities in the loudness function, the method of adjustment was used to halve and double the loudness of a 1000‐cy tone at the levels 30, 60, 90, and 120 db re 0.0002 μbar. The results tend partially to confirm some of the irregularities found by Robinson. The results also indicate that a reasonable approximation to the loudness function is the rule that a change of 10 db corresponds to a loudness ratio of 2:1. This means that loudness grows approximately as a power function of intensity. It is noted that the power function also describes the relation between psychological magnitude and stimulus magnitude on a dozen other perceptual continua.
Effect of Time on Pitch Discrimination Thresholds under Several Psychophysical Procedures; Comparison with Intensity Discrimination Thresholds29(1957); http://dx.doi.org/10.1121/1.1908981View Description Hide Description
This paper presents a study of the effect of the interstimulus interval on pitchdiscrimination the cases of five different psychophysical procedures. These procedures were approximately analogous to those employed by Pollack for intensity discrimination. All the experiments described here for pitchdiscrimination were carried out at a constant sound level of about 40 db above threshold, the mean reference frequency being 1000 cps. The listeners examined were five young men with normal hearingacuity between the ages of 20 and 30. From the experimental data it appears that, irrespective of the method used, the mean over‐all performance of the subjects in pitchdiscrimination deteriorates only slightly as the interstimulus interval increases from 1.25 to 5 sec. In order to stress the large discrepancies among the performance of the listeners, the data for each subject were reported with special care. The effect of stimulus duration on pitchdiscrimination is briefly discussed.
29(1957); http://dx.doi.org/10.1121/1.1908983View Description Hide Description
The perception of vowels heard in noises of various spectra is analyzed by means of stimulus‐response matrices. The stimulus vowels were spoken in PB‐word lists and in syllable lists in which the vowels were equally probable. The matrices show shifts in vowel confusions depending on how different noise spectra mask the vowelformants.Vowel duration and intensity are measured and related to vowel perception. Vowel guessing is related to past training.
29(1957); http://dx.doi.org/10.1121/1.1908985View Description Hide Description
Subjects spoke /s/‐vowel‐/s/ monosyllables at two syllabic levels which required a large contrast in effort without extreme departure from average conversational effort. At the higher level the median within‐syllable consonant‐vowel ratio was approximately −14 db; at the lower level (vowel 18 db down) it was approximately −7 db. The ratio also varied with position of the consonant within the syllable, with vowel and with sex of speaker; effort, vowel, and sex interacted. The variations were systematic and large enough to have implications for intelligibility.
29(1957); http://dx.doi.org/10.1121/1.1908987View Description Hide Description
A model of the larynx has been constructed, and measurements of air resistance for this model have been made. The dc resistance R was measured for diameter d of the glottis from 0.1 to 3.2 mm, for subglottic pressuresPs up to 64 cm water and/or volume velocities v up to 2 liters/sec. To a good approximation, the resistance was equal to the sum of a frictional term, proportional to d −3, and a turbulence term, proportional to vd −2. The frictional term dominates at small diameters and/or small volume velocities, with v proportional to Psd 3 and the differential resistance Rd=R. The turbulence term dominates at large diameters and/or large volume velocities, with v proportional to and Rd = 2R. Over the major region the pressure at the outlet of the glottis was about , where PB is the kinetic pressure in the glottis, and the pressure over the entry of the glottis was about 1.37PB . The applicability and the implications of the results to various problems of normal voice production are discussed.
29(1957); http://dx.doi.org/10.1121/1.1908989View Description Hide Description
Two experiments, employing a total of 388 subjects, were conducted to further study factors influencing performance on the delayed speech feedback task. The rate of presenting reading material, the intensity, and length of delay of speech feedback served as independent variables. A linear relation was found between performance on the feedback task and intensity of the delayed signal. There was an interaction between intensity and delay time of the speech feedback, clearly demonstrating that various delays are differentially effective only at high intensity levels. That the role of delay is more than a simple interference factor produced by background noise was also demonstrated.
29(1957); http://dx.doi.org/10.1121/1.1908992View Description Hide Description
An experiment is described in which words were automatically compressed in duration and presented to observers for identification. The effects of time compression and of time sampling are assessed, and compared with those of periodic interruption. The results of an analogous nonauditory study of the effects of phonemic sampling are presented.
29(1957); http://dx.doi.org/10.1121/1.1908994View Description Hide Description
The dependence of the ultrasonicabsorption coefficient on the intensity was measured indifferent liquids (water, ethyl and methyl ethers, toluene, transformer oil, and glycerine) by means of the thermal method (thermocouples). The measurements were made at 1.5 Mc/sec with intensities of 0.3–9 w/cm2. There was found a considerable increase of nearly two orders of magnitude in the absorption.Measurement at higher static pressures, up to 15 kg/cm2, gives results which coincide, within the range of error, with the results of the measurements at atmospheric pressure, suggesting that the influence of cavitation is small.
Direct experimental observation of the harmonics in a traveling wave of finite amplitude was accomplished. The receivers were quartz plates with their fundamental frequencies equal to the frequencies of the harmonics; to remove standing waves between the receiver and the transducer, an acoustic filter was used, consisting of a thin plate “transparent” for the appropriate harmonic and opaque for the fundamental at a certain angle. Absolute measurement of the harmonic intensity was obtained by a radiometer which was placed behind the acoustic filter.
29(1957); http://dx.doi.org/10.1121/1.1908996View Description Hide Description
The limitations in the use of the Debye relation for relating the nuclear relaxation time,T 1, to the shear viscosity, η, are emphasized. The possible connection between the correlation time, τ c , and the shear and volume relaxation times as measured by ultrasonics is investigated. It is shown that τ c and the average shear relaxation time in glycerol are very close in value. Furthermore, the value of τ c found for water is very close to the volume relaxation time as calculated from ultrasonic absorption data. By assuming that τ c is proportional to the shear relaxation time a reasonable explanation of the pressure dependence of T 1 is obtained.
- LETTERS TO THE EDITOR
29(1957); http://dx.doi.org/10.1121/1.1908998View Description Hide Description
29(1957); http://dx.doi.org/10.1121/1.1908999View Description Hide Description