Volume 35, Issue 4, April 1963
Index of content:
35(1963); http://dx.doi.org/10.1121/1.1918499View Description Hide Description
A real‐time audio‐frequency spectrum analyzer is described which consists of a bank of 54 contiguous bandpass filters of the Gaussian type. Up to 1000 cps, the filters have a constant bandwidth of 70 cps; above this frequency the bandwidths increase at a constant percentage of about 6.5%. The output of each filter is rectified and the resulting dc signals are scanned by a solid‐state multiplexer. Thus, a single output, which is a function of the power spectrum, is made available for visual display and/or computer processing. Practical advantages of Gaussian filters are described for the analysis of transients of noise, music, or speech, and examples of the analyzer output are presented.
35(1963); http://dx.doi.org/10.1121/1.1918501View Description Hide Description
Speech distortion is defined broadly as any operation that evokes inappropriate behavior by a listener in response to speech. Two categories of distorting operations are distinguished: (1) response‐independent, in which the transfer function applied to the original speech signal is not determined by the probable response of the listener (e.g., masking, filtering); and (2) response‐dependent, in which the distorting operation is related to the probable response of the listener during undistorted transmission and therefore may be specified in linguistic terms (e.g., foreign accent). Two experiments examine the effects and interactions of these two types of distortion. Twenty‐four Midwest Americans listened to recorded articulation lists rendered by one American and three foreign‐born speakers under eight conditions of masking and filtering. Reducing the speech to noise ratio to 20 dB or the transmission bandwidth to 500 cps yields approximately 50% reduction in word articulation for both native and foreign accent speech. The latter was approximately 40% less intelligible than native speech under all experimental conditions.
35(1963); http://dx.doi.org/10.1121/1.1918503View Description Hide Description
Three experiments using one speaker and 30 listeners provided correlated data on subglottal pressure, average volume velocity through the glottis, fundamental frequency, effective sound pressure in front of the speaker, and judgments of loudness. Experiment 1: In 12 repetitions each of bee, bay, bar, bore, and boo spoken at various loudnesses, it was found that in the middle range (subglottal pressure) ∝ (effective sound pressure)0.6; and the level of the vowel in bar was about 5 dB greater than in bee or boo produced with the same subglottal pressure. Experiment 2: In 32 repetitions of the vowel /ɑ/ uttered at various loudnesses with the pitch uncontrolled, it was found that an increase of subglottal pressure of about 6.5 cm aq accompanied an increase in frequency of half an octave; and to a first approximation (rate of flow) ∝ (subglottal pressure). It follows that (rate of work done on the air) ∝ (subglottal pressure)2 ∝ (effective sound pressure)1.2. The exponent 1.2 compares well with the exponent 1.1 found by Lane, Catania, and Stevens for the autophonic response. Experiment 3: Thirty subjects judged the loudness of each word taken from Experiment 1 relative to the reference token in the frame Compare the words: bar and …. It was found that for any one vowel in the middle range, (loudness) ∝ (effective sound pressure)1.2, suggesting that subjects assessed the work done and not the auditory sensation in the usual way as found by Lane, Catania, and Stevens.
35(1963); http://dx.doi.org/10.1121/1.1918505View Description Hide Description
The possibility that speech may be perceived with reference to articulation prompted this preliminary study of muscle action during speech production. The question investigated was: what is the difference, if any, in the acoustic and articulatory characteristics of /f/ in utterance final position and /f/ embedded in final consonant clusters. The acoustic duration of /f/ friction,measured spectographically, was about twice as great in final position as in any other position. On the other hand, electromyograms were similar for all positions of /f/. The change in /f/ friction duration from final to prefinal position is therefore a contextual effect on acoustical properties of production alone. The motor gesture is more independent of context.
35(1963); http://dx.doi.org/10.1121/1.1918507View Description Hide Description
A continuous speech sample of six seconds' duration is pitch synchronously analyzed and resynthesized in terms of a series of orthonormal functions. The series used is obtained from a set of sixteen exponentially damped sinusoidal base functions with fixed frequencies and fixed damping at each frequency. Both the computations of the orthonormal function set and the speechanalysis‐synthesis operations were carried out using digital computers. The results are compared by means of listening tests, curve plots, and sound spectrograms. The major difference between the input and resynthesized speech that is evidenced in all three comparisons due to discontinuities in the resynthesized waveform at the boundaries between pitch periods.
35(1963); http://dx.doi.org/10.1121/1.1918509View Description Hide Description
Experiments are described which suggest that, for human perception, the information concerning the location of a formantlike complex sound is contained in the two most prominent harmonics. This result is limited to the condition where adjacent harmonics are more widely separated than the width of a critical band.
35(1963); http://dx.doi.org/10.1121/1.1918511View Description Hide Description
Ultrasonic measurements of relaxation phenomena in the 30‐ to 270‐Mc/sec range have been obtained in 10 homogeneous linear polysiloxane liquids (commonly called silicones) and in a number of heterogeneous mixtures of them. Absorption and velocity data for both instances are presented. In the former case, an analysis is presented on the basis of single‐relaxation theory. Special emphasis here is placed on the 6‐ and 10‐atom fluids. The discussion of the results in the heterogeneous liquids is given in terms of a “dynamic viscosity.”
35(1963); http://dx.doi.org/10.1121/1.1918513View Description Hide Description
Ultrasonic diffraction in NaCl and KCl single crystals, as well as in steel, has been studied by the pulse‐echo method from 8–45 Mc/sec with disk transducers. The diffraction is of the Fresnel type, so that the curves of loss due to diffraction can be plotted with a normalized abscissa , where z is the path length in the specimen, a the transducer radius, and λ, the ultrasonic wavelength. In general, the loss curve is not monotonic in S. The shape of the curve is dependent upon the specimen material, the crystallographic direction of ultrasonic propagation, and the transducer plating configuration. The position of the last local maximum in the loss curve is a function of the anisotropy of the specimen. In particular, its position in steel (isotropic case) agrees with the theoretical position for isotropic materials.
35(1963); http://dx.doi.org/10.1121/1.1918515View Description Hide Description
An experimental investigation of the acoustic properties of grade 00 and 000 steel wool has been carried out over a wide frequency range from zero to 10 kcps. Packing densities ranged from 0.063–0.489 gm/cm3. Various gases have been used, with ratios of specific heats ranging from 1.11–1.41, and kinematic coefficients of viscosity ranging from 0.0318–1.056 cm2/sec. The results indicate that the work of Zwikker and Kosten for a porous material made of cylinders may be generalized. The pore radius of these authors becomes a characteristic length to be associated with the fibrous material.
35(1963); http://dx.doi.org/10.1121/1.1918517View Description Hide Description
Viscous and thermal losses of acoustic energy at a metal wall are calculated for the condition in which there is a low Mach number flow sustaining a temperature difference between the gas and the wall. The acoustic loss is found to decrease as the walls are cooled below the temperature of the main body of the gas. The results of the study are relevant to experiments on acoustic amplification by solid rocket propellants and to at least some cases of liquid propellant rocket acoustic instability.
35(1963); http://dx.doi.org/10.1121/1.1918519View Description Hide Description
The theory of vibrations of longitudinally polarized, thin‐wall ferroelectric ceramic tubes is derived including the lateral influence on the longitudinal vibrations. Tenors are utilized throughout the derivation, but a summary of the results is presented in the commonly used matrix forms.
The equations of motion and the equations of state for materials possessing transverse isotropy are transformed to cylindrical coordinates. A new electromechanical equivalent circuit is obtained which is similar to that of Mason, except that the latter ignores lateral effects. The new theory explains experimental results which would be considered anomolous in the older one‐dimensional theory.
35(1963); http://dx.doi.org/10.1121/1.1918521View Description Hide Description
The elastic moduli of pyrolytic graphite, a polycrystalline material exhibiting large elasticanisotropy, have been measured by the ultrasonic pulse‐echo method. In units of 1011 dyn/cm2, they are c 11 = 5.21, c 12 = 1.88, c 13 = 1.80, c 33 = 2.58, and c 44 = 0.15.
35(1963); http://dx.doi.org/10.1121/1.1918523View Description Hide Description
The equations of motion for a hydrodynamicsolid are studied for a pressure‐density relation appropriate to pulse propagation in solid and compactible media. After collapse of the compactible material, the pressure‐density relation is assumed to have the form . A semianalytical method of solution is used on the resulting one‐dimensional set of nonlinear partial differential equations. By using characteristic variables, the nonlinear differential equations are transformed to a set of linear partial differential equations whose solution is then obtained numerically. Applications are made to aluminum, for which the constants A and γ are known, and to compactible materials using an assumed value for γ. This investigation serves to define the various types of phenomena that can occur in a semi‐infinite compactible material that is shocked by a rectangular pressure pulse. In particular, the analysis shows that the shock‐wave penetration depth at the end of the first shock‐rarefaction interaction has a minimum when regarded as a function of the material porosity.
35(1963); http://dx.doi.org/10.1121/1.1918527View Description Hide Description
Experimental procedures and techniques are described for measuring, in an oceanographic tank, the scattering of underwater acoustical radiation from submerged, isolated liquid‐filled spheres. Of interest are sphere diameters of the order of or larger than the acoustic wavelength and acoustic impedance contrasts of as much as 20%. A novel dual‐hydrophone detecting scheme is presented which enables extraction of the scattered signal from the total (incident plus scattered) signal arriving at the receiver. Since the scattering sphere is mobile, azimuthal radiation patterns can be determined. A few typical scattering diagrams are displayed and are found to agree favorably with those derived from theoreticaltreatments available in the standard literature. Density and speed of sound variations (between the liquid within the sphere and the surrounding water medium) are obtained by employing various mixtures of liquids as the internal constituent. A brief survey is given of the results derived from scattering measurements with liquid spheres of various diameters and impedance contrasts.
35(1963); http://dx.doi.org/10.1121/1.1918529View Description Hide Description
Dispersion characteristics of underwater sound on the Arctic continental shelf north of Alaska were investigated at ranges between 2 and 250 km and for frequencies between 3 and 250 cps. Explosive charges were used as sources, and geophones were used as detectors. Observations were interpreted in terms of normal‐mode theory, and good agreement between theory and experiment was found for both phase and group velocity. Portions of the first and second modes were recognized at all ranges, and, at short ranges, “leaking modes,” associated with the ice layer, were also noted. For long ranges, the water wave amplitude varied as the −1.85 power of range.
35(1963); http://dx.doi.org/10.1121/1.1918531View Description Hide Description
Some results of a four‐year experimental study of sound propagation in the Arctic are presented and interpreted. The duration, form, and intensity of waves received at distances up to 1400 km are explained using ray theory and modes, in which source characteristics, refraction, scattering at the ice surface, and bottom effects are important.
35(1963); http://dx.doi.org/10.1121/1.1918533View Description Hide Description
The scattering of a plane wave by an elastic prolate spheroid at arbitrary angle of incidence is formulated by means of an expansion in spheroidal wave functions. The structural response of the spheroid is expressed in terms of a surface impedance operator. Even for a homogeneous elasticsolid or shell, the impedance operator generally couples the spheroidal modes of the acoustic medium, and hence numerical solutions involve the inversion of an infinite set of linear equations. However, a number of special cases are considered here for which direct solutions can be obtained. These include resonant mode scattering and low‐frequency scattering.
When one of the structural modes is excited by the incident wave at its resonant frequency, it may radiate with such intensity as to mask radiation by other modes. The conditions under which this type of scattering can take place are shown to be very restrictive.
When the acoustic wavelength is large and the frequency is small compared to the lowest natural frequency of the structure, the scattered field can be analyzed into uncoupled monopole and dipole fields. Simply asymptotic expressions, not involving spheroidal functions, are presented for a spheroid with finite compressibility and inertia as well as for the limiting cases of rigid and fixed boundary and pressure‐release boundary.
35(1963); http://dx.doi.org/10.1121/1.1918535View Description Hide Description
The sound‐absorption coefficient for a small area of an acoustical material is much greater than for a very large (or infinite) area. Measurements of the distribution of sound pressure at the surface for diffusely incident sound suggest that the additional absorption should be proportional to , where A is the area of the material. Experimental data on absorption coefficients are presented which confirm this deduction.
35(1963); http://dx.doi.org/10.1121/1.1918537View Description Hide Description
The effect of a loudness cue on the perception of the temporal order of dichotically presented clicks was investigated. It was shown that one can find a range of temporal intervals between dichotically presented clicks for which increasing temporal separation results in a decrease in the correct judgment of temporal order.