摘要:

Tracings from cine x ray of the vowels of four speakers of Twi clearly demonstrated that vowels from harmony set 1 [/i,e,o,u/] systematically differed from vowels of harmony set 2 [ι,ε,(a),ɔ,ο/]by different vocal tract shapes: set 1 vowels had a wider pharynx and an advanced tongue root, while set 2 vowels had a narrower pharynx and a retracted tongue root. In spite of their different vocal tract shapes the two vowels /ι/ and /e/ have very similar formant frequencies. The difference in the vocal tract shapes is that /e/ has a wider pharynx and also a wider mouth cavity than /ι/. The fact that these vocal tract shapes produce similar formant frequencies can be explained with reference to perturbation theory: the area functions of these two vowels are approximately symmetric about the midpoint. Similar acoustic and articulatory data were found for one speaker of Ijo.

ISSN:0001-4966    

DOI:10.1121/1.3437138

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The basic principles of cross‐correlation and cross‐spectral density functions, along with the correlation coefficient and coherence functions derived from them, are briefly reviewed and discussed in the context of noise control problems. Although theoretically related (correlation and spectral density functions are Fourier transform pairs), one form of analysis is often preferred over the other for specific applications. For example, the frequency domain format of the coherence function is generally more convenient for evaluating the simple linear dependence between a source and receiver, while broad‐band cross‐correlation functions are usually more desirable for applications involving the determination of transmission paths. In practice, usuallya combination of the techniques, obtained by Derforming cross‐correlation analyses in contiguous narrow frequency increments, is commonly required to obtain meaningful results. These various considerations are outlined and illustrated with physical examples. The limitations of the variousanalysis considerationstechniques are emphasized throughout.

ISSN:0001-4966    

DOI:10.1121/1.3437146

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Complicated noise generators such as turbomachines can be represented by a geometrically fixed array of localized dipole sources whose distribution when integrated over the surfaces of the machine sum to the net surface dipole contribution to the farfield sound. Experiments were carried out on an off‐the‐shelf axial flow fan wherein blade surface pressures were detected with an embedded miniature pressure transducer, and motor support strut pressure fluctuations with an embedded quarter‐inch microphone. These pressures were cross‐correlated against the farfield sound, with time delay. Both the source and the farfield signals were bandpass filtered at the blade passage frequency of the fan, before being correlated. Results gave information revealing causes of the on‐axis noise radiation from the fan at the blade passage frequency. The contribution of pure‐tone radiation from the struts was compared to that from the fan blades. The effect on the overall sound pressure level of variations in phase of the sources, both on the gtruts and on the blades, was determined. Details of the experimental approach are presented, and the interpretation and usefulness of the data is discussed. [Work supported by Canadian DRB Grant No. 9611‐03.]

ISSN:0001-4966    

DOI:10.1121/1.3437151

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Internal sources of flow unsteadiness can contribute substantially to the airfield noise from jet engine exhausts. Since this noise contribution often takes an indirect path to the farfield observer, it is not always clear that the source is inside the duct and not in the jet, as a directional microphone might suggest. Direct cross correlations, between in‐duct and farfield microphones can be used to demonstrate the relationship between the source region and the observed signal. In addition to knowing that the two are related, it is of interest to know how much of the farfield noise is due to sources inside the duct. Experiments in which a source in the duct is driven by sine waves, narrow‐band noise, and broad‐band noise are used to demonstrate the use of the normalized cross correlation to show a quantitative relationship between the source region and observer. Aerodynamic sources are added and the method of determining their relative importance is discussed. The technique is then applied to the evaluation of the contribution to overall exhaust noise made by unsteady combustion and/or flow over struts inside an engine. [Supported by NASA Grant NGR 31‐001‐241.]

ISSN:0001-4966    

DOI:10.1121/1.3437152

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

We reported earlier [J. Acoust. Soc. Am.54, 310 (A) (1973)] that the time‐intensity trade for the residue is comparable to that of a low‐frequency tone equal in pitch to the residue, and different from the function for a signal of the carrier frequency. Consequently, the question arises as to whether the more central processing of the residue and a low‐frequency signal are sufficiently similar that they form a fused image when the residue is sent to one ear and a low‐frequency signal to the other. An experiment was conducted in which a 200‐Hz tone and a residue were presented simultaneously to opposite ears at various interaural phase relationships. Under such conditions, the subjects perceived the 200‐Hz tone in one ear and the residue in the contralateral ear, irrespective of the interaural phase relationship. Thus, it is suggested that the lateralization of the low‐pitched residue is mediated by a neurological mechanism substantially different from that activated by the 200‐Hz tone, even though both incorporate time‐intensity trading. This result is in keeping with other dissimilarities between psychoacoustic responses to the residue and to low‐frequency tones.

ISSN:0001-4966    

DOI:10.1121/1.3437156

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A three‐alternative forced‐choice procedure was employed to measure monaurally the phase and amplitude of the cubic combination tone, 2f1−f2. To measure phase, two primariesf1andf2were presented simultaneously with a third tone at frequency 2f1−f2. The third tone had phase θ in two intervals and phase θ + 180° in the third interval. A plot of percent correct discrimination as a function of θ was used to determine the phase of the combination tone. The phase of the combination tone was calculated to be ±90° from the value of θ which resulted in minimum discrimination. A “mirroring” technique was then employed to determine the amplitude of the combination tone. In the odd interval a cancellation tone was added 180° out of phase from the combination tone. Percent correct discrimination was measured as a function of the level of the cancellation tone. It was assumed the minimum in the function occurred at a level 6 dB greater than the combination tone. The results obtained from various objective and adjustment procedures will be compared. [This research was supported by an NIH grant.]

ISSN:0001-4966    

DOI:10.1121/1.3437163

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Ultrasonic vibration potentials (uvp) are alternating potential differences which arise when sound waves are propagated through electrolytic solutions. The amplitude of the uvp depends on the masses of the hydrated ions which in turn are related to their partial molal volumes. 200‐kHz pulse‐modulated ultrasonic waves were used for the measurement of the uvp's of uni‐univalent electrolytes in methanol, ethanol, and dimethylformamide (DMF). Uvp's were found to depend little on concentration in the range 3.10−4‐3.10−2Mfor nitrates and chlorides, but showed small decreases for bromides and large decreases for iodides. The amplitudes of the measured uvp's were strongly dependent on the nature of the electrolyte and of the solvent. The uvp data were combined to data of partial molal volume of electrolytes to yield the partial molal volumes V̄10of monovalent ions in methanol, ethanol, and DMF. Hepler's equation was used to split the V̄10's into their geometric and electrostrictive contributions. It was found that the geometric contribution depends essentially on the packing of the solvent molecules about ions. The electrostrictive contribution appeared to be mostly dependent on the nature of the content of the layer of atoms, 3–4 Å thick, in contact with the ion.

ISSN:0001-4966    

DOI:10.1121/1.3437169

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The propagation of transient scalar waves in a three‐dimensional random medium is considered. The analysis is based on the smoothing method, which is equivalent to a second‐order scattering theory. An integro‐differential equation for the coherent (or average) wave is solved for the case of a statistically homogeneous and isotropic medium and a delta‐function source. This yields the coherent Green's function of the medium. It is found that, in general, the randomness of the medium causes a gradual smoothing and broadening of the waveform with propagation distance, as well as a reduction in propagation speed of the wave. Depending on the distance from the source measured in terms of a certain dimensionless parameter, three propagation zones can be identified. In the near zone the waveform is determined primarily by attenuation of the high‐frequency components of the wave, whereas in the far zone it is determined mainly by dispersion of the low‐frequency components. The intermediate zone is a region of transition between the near and far zones. The theory yields order‐of‐magnitude estimates of sonic boom rise times which show good agreement with measured values.

ISSN:0001-4966    

DOI:10.1121/1.3437178

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Experimental studies of an ultrasonic beam incident onto a liquid‐solid interface have been reported [J. A. Smith, R. L. Smith, and M. A. Breazeale, J. Acoust. Soc. Am. 50, 105 (1971)]. The reflected beam was found to exhibit an energy redistribution (rather than a simple lateral displacement as predicted by Schoch and Brekhovskikh). In an attempt to find a theoretical model to describe this experimental observation, an expression for the “internal structure” of the reflected beam as given by Brekhovskikh was modified. By using a Gaussian distribution for the incident beam and including the second derivative of the phase shift in the reflection coefficient, the intensity of the reflected beam is expressed in terms of the distance along the interface. The expression for the intensity distribution of the reflected beam is given in terms of complex error functions of finite argument (suggested by Larry Flax of NRL). The calculated intensity distribution agrees reasonably well with the experimental data for four samples. [Research supported in part by the U. S. Office of Naval Research.]

ISSN:0001-4966    

DOI:10.1121/1.3437180

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The Optacon is a direct‐translation reading aid for the blind. In operation, material that has been hand scanned by the small pickup camera is reproduced in vibratory form upon the 144‐element vibratory stimulator array. The present array configuration is the result of extensive psychophysical, engineering, and manufacturing effort. The array utilizes piezoelectric “bimorphs,” driven at 250 Hz, for electromechanical energy conversion. Custom integrated circuit driving circuits enable compact packaging. The 24 rows are spaced 45 mils apart and the six columns 90 mils apart, enabling the entire display to be presented on the fingertip of the blind user.

ISSN:0001-4966    

DOI:10.1121/1.3437186

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP