Index of content:
Volume 43, Issue 6, June 1968
43(1968); http://dx.doi.org/10.1121/1.1910971View Description Hide Description
Interference with thresholds for spondees and intelligibility of monosyllabic words (at 60 dB SPL) produced by combining modulated white noise (4 mod/sec, − 10 dB interburst ratio) and connected speech as simultaneous maskers was studied under a variety of interaural listening conditions at each of three masker levels (66, 72, and 78 dB sound‐pressure level). Monaural performance in the presence of both maskers (C m N mS m) was 7.8–10.5 dB poorer than with either masker alone (N m S m or C m S m ). Thus, the two maskers produced added interference substantially in excess of the approximately 3‐dB increase to be expected on the basis of the summing of their powers alone. Very little release from masking was achieved in the transition from monaural (C m N m S m ) to homophasic listening (C0N0S0). During antiphasic (CτNπS0) presentation, approximately 5 dB of release from masking occurred (re C0N0S0). A little less than half as much release from masking appeared when the maskers were given 0.8 msec interaural time delays, while the test material remained in phase at the two ears. Performance with opposing interaural delays (C0.8N 0.8S0) was no better than with parallel time delays (C0.8N0.8S0). Since neither of these conditions yielded as large masking‐level difference as did the antiphasic, even though the sources of signals were lateralized (localized) much more sharply by the subject during time‐delay conditions, this study offers further evidence that localization (separation of source azimuths) and the capacity to understand speech against competing sounds are separate capacities. Various implications of the finding are discussed.
43(1968); http://dx.doi.org/10.1121/1.1910972View Description Hide Description
A previously unrecognized anomaly of pitch perception was discovered by H. F. Stimson while testing his hearing. Signals above 3500 Hz did not produce the same pitch in each ear; the right ear's sensation was that of a sound at a lower frequency, for which he also had normal pitch perception. Between 3700 and 5200 Hz, the pitch perceived in the right ear was independent of the frequency of the stimulus. As intensity was raised, additional pitches appeared; and for an intense sound, a chord was heard whose constituents were not harmonically related. Stimson can match these anomalous pitches with sinusoidal stimuli of the appropriate lower frequency within about 2%; part of this variation is a change of pitch with intensity. Tones in his normal pitch range having a pronounced overtone structure are perceived as multiple. Overtones falling in the anomalous range give rise to the anomalous pitch. This would indicate a Fourier type of analysis before pitch recognition. Beats are not excited by interference between the pitches evoked by signals in the anomalous range and those heard normally. Loudness studies show signal powers to be additive. Tone‐masking and loudness summation experiments yield data suggesting that the pitch recognition mechanism lies in that part of the auditory system in which loudness is perceived—i.e., beyond the cochlea.
43(1968); http://dx.doi.org/10.1121/1.1910973View Description Hide Description
Monaural bone‐conduction thresholds at the mastoid process and frontal bone were obtained on several groups of young adults with normal hearing. The results are reported in force thresholds (decibelsre 1.0 dyn rms) from calibrations made on a Beltone artificial mastoid. The data at the mastoid are in close agreement with the HAIC interim norm and the results of Weston et al. (1967). These results confirm the clinical usefulness of the HAIC interim norm. Likewise, the similarity between the current data obtained at the frontal bone and that reported by Weston et al. (1967) provides a basis for an interim norm until the International Organization for Standardization has completed its deliberations.
43(1968); http://dx.doi.org/10.1121/1.1910974View Description Hide Description
When two or more sound sources radiate identical or nearly identical complex signals, the listener hears a single image located at the nearer source, provided that the delay involved is between about 1 and 50 msec. This phenomenon (together with other closely associated aspects) is generally referred to as the “precedence effect” or “Haas effect.” Less frequently, the terms “law of the first wavefront,” “auditory‐suppression effect,” “first‐arrival effect,” and “threshold of extinction” have also been used in describing certain of these characteristics. Perhaps the earliest investigator to leave a clear record of his appreciation of the single‐image aspect of the phenomenon was Joseph Henry who, in 1849, used the term limit of perceptibility in describing what he had observed. The present paper outlines the historical background of the effect from the standpoint of its investigation and its application in electroacoustical systems.
43(1968); http://dx.doi.org/10.1121/1.1910975View Description Hide Description
The just noticeable difference in phase (ΔΘ) was measured for binaural stimulation and for stimulation of the ring and index fingertips of the same hand. At stimulus frequencies of 40, 60, 120, and 240 Hz, differences in phase up to 120° had no effect on cutaneous localization, while the values of binaural ΔΘ were only 3.6° and 3.3° for 120‐ and 240‐Hz tones, respectively. When the vibration frequency was lowered to 20 Hz, a cutaneous ΔΘ of 47° was obtained. At this frequency, the locus of cutaneous stimulation was found to greatly influence ΔΘ. When the index fingertips of the two hands were stimulated, ΔΘ was 90°, and was 45° when the ring and index fingertips of the same hand were stimulated. A relatively low ΔΘ of 12° was obtained when both vibrator contactors were placed on the same fingertip. The results of this study fail to support von Békésy's hypothesis that the same time delays in stimulation are equally effective as cues in auditory localization and its cutaneous analog.
43(1968); http://dx.doi.org/10.1121/1.1910976View Description Hide Description
The ability of listeners to locate sound in the vertical plane was investigated. The results showed that for auditory stimuli to be located accurately (1) the stimulus must be complex, (2) it must include frequencies above 7000 cps, and, (3) the pinna must be present.
43(1968); http://dx.doi.org/10.1121/1.1910977View Description Hide Description
Listeners, when requested to judge the location of tone bursts on the vertical plane, tended to place the stimuli on a vertical scale in accordance with their respective pitch. Higher‐pitched sounds were perceived as originating above lower‐pitched sounds. This phenomenon was also observed in congenitally blind persons and in young children who presumably were unaware of the use of the words high and low in describing differently pitched sounds. In additional tests, visual cues were found to influence the range of the scale within which listeners perceived the sound sources and they could even bias the location judgments of high‐pitched tone bursts despite contrary binaural cues. But the main implication of the data is that tonal stimuli have intrinsic spatial characteristics, which result in the perception of frequencies with shorter periods as being higher in space than those with longer periods.
43(1968); http://dx.doi.org/10.1121/1.1910978View Description Hide Description
Contralateral threshold shift has been investigated as a function of frequency difference between the masking and test tones. The obtained curves of frequency distribution indicate complex underlying processes. Both the masker intensity and the time delay from the masker onset affect the absolute amount as well as the frequency distribution of central masking. The frequency spread of masking appears consistent with the critical‐band measures at medium masker levels but not at high and low levels.
43(1968); http://dx.doi.org/10.1121/1.1910979View Description Hide Description
Equipment has been constructed that will automatically plot on a chart the resonance curve for a clarinet as produced by external excitation with sound of constant pressure amplitude. On the same chart are plotted for comparison the frequencies of the harmonics of the lowest resonance. The harmonic structure of the sound pressure in the mouthpiece of the instrument when sounded by blowing with an artificial embouchure is also plotted for further comparison. It is found for the lowest notes on the clarinets used that the resonances lie at frequencies progressively lower than the harmonic frequencies. Even harmonics are present in the standing wave in the instrument when sounded, although the odd ones predominate out to the fifth harmonic; only the second is completely absent. As the scale is ascended, the resonances get more out of tune with the harmonics and decrease in number until for the (written) note B♭4, before the change to the next register, there are only two strong resonances. In the next register, the resonances appear to bear only a fortuitous relationship to the harmonics, and the second harmonic is present. Comparison of resonance curves for instruments of different manufacture shows them to be remarkably similar.
43(1968); http://dx.doi.org/10.1121/1.1910980View Description Hide Description
A language maybe synthesized by combining, in a suitable way, elementary speech segments that have been extracted from the utterances of a native speaker of that language. The main criteria for the choice of these elements are discussed. The discussion leads to the definition of a new set of physically determinate linguistic elements that can be obtained by experiment. A preliminary list is reported for the Italian language. From experimental tests, it appears that it is possible to synthesize Italian speech with a small number of elements. These elements may form the basis for research in speech recognition.
43(1968); http://dx.doi.org/10.1121/1.1910981View Description Hide Description
Measurements of the attenuation of sound are reported for oxygen containing up to 2.6% of hydrogen, carbon dioxide or water vapour as impurity. The measurements cover the f/p range from 80 to 1700 Hz/atm and were made with a resonance tube system. The least‐squares fits to the results are given below, where 103 h is the mole fraction of the impurity, and f 0 is the frequency of maximum absorption.
Mixture Equation Standard error
The results are compared with those of other workers, and in particular, it is suggested that the results of Harlow and Kitching are probably in error because they ignored the adsorption of water vapor on the walls of the tube.
Ultrasonic Buffer‐Rod Technique for the High‐Temperature Measurement of the Elastic Moduli of Short Specimens43(1968); http://dx.doi.org/10.1121/1.1910982View Description Hide Description
This paper describes a method of measuring the elastic moduli of short specimens to very high temperatures by the use of ultrasonics. A buffer‐rod technique is used, but the sound is transmitted from the buffer rod to the short specimen across an interface without the use of a couplant. The specimen has a machined index region that extends into the uniform hot zone of a vacuum furnace. The required information is taken from the index region. The experimental technique used to achieve a mechanical bond between the buffer and the specimen that is sufficient to transmit a considerable quantity of ultrasound is detailed. This method has been successfully used to 1150°C, and has potential application up to 2500°C.
43(1968); http://dx.doi.org/10.1121/1.1910983View Description Hide Description
A high‐temperature ultrasonicinterferometer for the study of propagation properties of shear waves through molten glasses below 1600°C and between 3 and 23 MHz is described. Techniques for measuringvelocity and absorption of the transmitted echoes are presented with special emphasis on the study of shear waves in the relaxation region of a molten glass. In this case, an absorption per wavelength as high as 5.4 Np/cycle was measured; this is more than twice the capability of previously reported equipment. The use of a lock‐in amplifier in the video circuit made this work possible. This method of handling the transmitted echoes not only suppressed noise by 25 dB, but also permitted measurements of pulse heights to better than 0.1 dB. The video circuit is not sensitive to rf values and can be used with most existing pulsed ultrasonic systems.
43(1968); http://dx.doi.org/10.1121/1.1910984View Description Hide Description
43(1968); http://dx.doi.org/10.1121/1.1910985View Description Hide Description
Experimental vibration characteristics of twin turbine‐generator sets installed on a common bedplate (prototype system) were studied in the laboratory using a scale plastic model. Treating the major components of the machinery arrangement as rigid bodies, acceleration readings were recorded at many locations on the model and prototype while driving the system simultaneously with known sinusoidal forces. Symmetrical and antisymmetrical modes were separated by using two electrodynamic shakers at symmetrical locations. By comparing the response of the model and prototype, a detailed mode‐shape comparison was established for the first nine major flexing modes. The results show that the natural frequencies and mode shapes of heavy machinery can be determined quite accurately from scaled plastic models.
43(1968); http://dx.doi.org/10.1121/1.1910986View Description Hide Description
If the ratio of the length of an electrode strip to the thickness of a partially electroded infinite crystal plate is kept below a certain critical value known as Bechmann's number— which depends on certain geometric and material parameters then, for the crystal vibrating at frequencies in the neighborhood of its fundamental thickness‐shear frequency, there are no anharmonic overtones of the thickness‐shear motion. The concept of the discontinuously platedstructure can be employed to design crystals with large values of Bechmann's number without decreasing the thickness of the electrode and consequently increasing the electrical resistance of the electrode. In this paper, by means of a special approximate theory, an explicit formula for the Bechmann's number of a discontinuously platedstructure is obtained in terms of the dimensions and material properties of the insulating film, the electrode, and the crystal.
43(1968); http://dx.doi.org/10.1121/1.1910987View Description Hide Description
Two methods of predicting response peak statistics (crests, positive maxima, and rises) for linear systems excited by Poisson impulsive noise are developed. One scheme yields good predictions for the statistics of fairly elementary systems. The other scheme extends these results to more complex systems, suggesting a method of approximating the complex system by an elementary one on the basis of basic system parameters. Empirical results obtained on a bimodal system are presented and agree well with the predictions.
43(1968); http://dx.doi.org/10.1121/1.1910988View Description Hide Description
Correction factors are derived that show the effect of thickness on the fundamental resonant‐frequency equations for cylindrical disks and rods and an equation is given that defines a boundary between a thick disk and a thick rod. These corrections are verified for isotropic and planar isotropic materials using the published frequency data of Shaw and McMahon. Direct comparisons are made with the correction factors of Moseley, Rayleigh, Onoe and Tiersten, Bancroft, and Baerwald. Experimental evidence is provided to show that upon substitution of appropriate frequency constants the corrections apply to the antiresonant frequencies of thick disks and thick rods.
43(1968); http://dx.doi.org/10.1121/1.1910989View Description Hide Description
43(1968); http://dx.doi.org/10.1121/1.1910990View Description Hide Description
The time‐average power flow between two linearly coupled oscillators excited by independent white‐noise sources is shown to be proportional to the difference in the time‐average energies of the oscillators. This proportionality is independent of the strength of the coupling if the oscillator energies are correctly defined. Power balance and energy sharing in the two oscillator systems are investigated, and the power‐flow energy‐difference proportionality relation is extended to a group of N linear oscillators, all with the same natural frequencies and damping ratios and each coupled to all the others by identical springs and masses. The coupled‐oscillator results are applied to a simple coupled‐beam example, in which two almost identical Bernoulli‐Euler Beams are lightly coupled together by stiffness terms. Experimental measurements for this system provide verification of the power‐flow equations provided that the coupling loss factor be correctly computed.