Jaime R. Carbonell

Speaker Identification by a Matching‐from‐Sample Technique

This study examines the ability of observers to identify the speakers of short test utterance (monosyllabic words, spondee words, and phrases) when sample utterances by the speakers are available to the observers. In one series of experiments, utterances were presented aurally through headphones; in another series, the same utterances were presented visually as intensity‐frequency‐time patterns. The observers task was to identify (or, in some experiments, to authenticate) the speaker of an utterance by making reference, as often as desired, to samples of that utterance by each of 8 known talkers, and to indicate the confidence of each judgment on a 4‐point scale. Identification scores and confidence ratings were consistently higher for the aural than for the visual experiments. Error scores in the aural experiments seemed to be related to the phonetic content of the utterances. In the visual experiments, errors appeared to be dependent on both phonetic content and number of syllables. [Work supported by ...

Dissipation Associated with Gas‐Pumping in Joint Structures

In recent experimental work dealing with the vibratory energy dissipation of plates with beams riveted to them, it was deduced that air‐pumping, in the space between the plate and the beam, may be the mechanism that dominates the damping. A semiphenomenological theory based on this deduction is developed and is shown to predict satisfactorily not only the order of magnitude of the loss factors but also their dependence on frequency and on gas pressure. This theory attributes the damping to viscous forces associated with gas motion tangential to the plate, resulting from the relative flexural motions between the adjacent plate and beam surfaces. The present theory is limited to the high‐frequency range, where a typical plate flexural wavelength is smaller than the rivet spacing. [Research supported by the National Aeronautics and Space Administration.]

Airblasts from Shallow Underwater Explosions

A shallow underwater explosion causes a supersonic plume to rise into the air. The plume shockwave produces the major peak in the ensuing airblast signature. An experimental investigation of the interaction between water motion and gas was conducted, wherein the parameters of the gas above the explosion were varied. Helium and “freon‐114” were substituted for air, giving a variation of 8 to 1 in sound speed and about 1 to 5 in specific acoustic impedance. The dominant parameter in determining whether the explosion is considered shallow or deep proves to be the Mach number of the plume motion with respect to the gas. Plume velocity, though correlated with gas density, is not inversely proportional to it: a 42‐fold increase in density resulted in halving the plume velocity. Some results of a calculation method to predict off‐axis airblasts from shallow explosions are also presented. These calculations, which show good agreement with experimental data, consider the plume as a decelerating supersonic blunt bo...

Physical Model for Airblast Generation by Underwater Explosions

The technique for calculating airblast pressure signatures from deep underwater explosions presented earlier [J. Acoust. Soc. Am. 36, 1033(A) (1964)] requires detailed knowledge of the interface motion. An experimental study recently completed showed disagreement with linear continuous theory—the decay of the interface velocity following its abrupt rise is position‐dependent and of the order of 20 times longer than that of the underwater pulse. A physical model that explains these discrepancies is presented. It is based on the existence of one or more delaminated layers of water just below the interface, originated by reflected negative underwater pressure pulses. Quantitative predictions based on this model are in good agreement with interface‐velocity data, photographic evidence, and airblast pressures recorded from deep explosions. For shallow explosions, a different mechanism applies; the “bow shock wave” originated by the supersonically rising dome and plume is the dominant feature in airblast genera...

Airblasts from Underwater Explosions at Various Depths

The pressure‐time pattern of airblasts from underwater explosions depends on the charge‐observer geometry and on the charge depth. For deep explosions, the airblast is characterized by a fast‐rising peak (P1), a broader second peak (P2), and a subsequent rarefaction phase (P3). P1 is associated with the least‐time propagation path. P2 and P3 are produced by the integration of pressure radiation from a large region surrounding surface zero. As the charge depth is increased, the effective area producing P2 becomes smaller until it is essentially reduced to the area of the dome and plume at surface zero. Also, P1 becomes less important as the charge depth decreases and essentially disappears for shallow explosions. The dominant feature in this case is the shock wave produced in air by the supersonically rising dome and plume. An experimental study of these effects was conducted using 0.8‐g lead azide charges. Pressure‐time traces and high‐speed photographic sequences obtained from this study are shown. [Rese...

Dual‐Phase Damping Material

Small, overlapping platelets of structural material mixed in a matrix of viscoelastic damping material form a dual‐phase damping material. This composite is an excellent extensional damping treatment because the viscoelastic damping material can be chosen for environmental resistance and high damping without regard for stiffness. The high extensional stiffness necessary in a good additive damping treatment can be obtained by incorporating the stiff platelets. Analysis of simplified, regularly oriented platelet configurations shows that, when the composite is deformed in extension, the platelets extend and the damping material between them shears. As a result of this type of deformation, the dual‐phase material combines some of the better features of constrained and extensional damping treatments. The frequency range of the dual‐phase material is broader than that obtained from constrained layer treatments while the damping of the treatment can be designed to be nearly as great as that of the viscoelastic ...

Technique for the Representation of Speech Power‐Spectrum Envelopes

It is usual to plot the short‐term speech power‐spectrum envelope using nonlinear coordinates such as level vs log frequency, or other coordinates related to the way that a signal is perceived. The technique presented here involves the expansion of the spectrum envelope (described by nonlinear coordinates) in terms of a set of convenient orthonormal functions. The method is, related, but not identical, to the one employed by Pirogov in the harmonic vocoder and Schroeder in the autocorrelation vocoder. It can be conveniently incorporated in present speech‐compression and ‐recognition systems. Results of a preliminary computer simulation are presented. Fourier series expansions were tried, but other orthonormal expansions, such as Laguerre and Tchebicheff polynomials, and orthonormal exponentials are also appropriate.

Mechanism of Vibratory‐Energy Dissipation at Joints in Thin Metal Structures

Experimental results are summarized that indicate that the dissipation of vibratory energy at multipoint‐fastened (bolted, riveted, or spot‐welded) joints connecting panels to stiffeners or to other panels, at frequencies considerably above the panel fundamental, is not associated with interface slip or friction. It is shown that this energy dissipation rather is primarily due to the “pumping” of air produced as adjacent surfaces between fasteners move away from and toward each other. Some implications of these results are pointed out; particular reference is made to the fact that tests at ground‐level atmospheric pressures may lead to underestimates of the vibrations of flight structural components at altitude. [Research sponsored by Air Force Flight Dynamics Laboratory, Research and Technology Division, Air Force Systems Command, U. S. Air Force.]

Airblasts Generated by Underwater Explosions

The pressure‐time history of airblasts produced by deep underwater explosions is characterized by a fast‐rising peak (P1), a broader second peak (P2), and a subsequent rarefaction phase (P3). P1 is traditionally associated with the least‐time propagation path. P2 and subsequent events are attributed to propagation through air from the surface zero region. While linear‐continuum theory of airblast generation seemed to predict P1 with moderate success, its inadequacy in dealing with subsequent events signalled an inapt description of the interface reaction. Several experiments were performed to study the pressure contributions of selected portions of the water surface to the total airblast wave. The results indicated that the air‐pressure pulse radiated by a surface element after the passage of an underwater shock was an “N wave” having a short, high‐amplitude, positive phase followed by a longer, low‐amplitude rarefaction. A modified Towne and Arons technique was developed wherein both phases of the elemen...

Volume Per Seat and Variation of the Reverberation Time with the Size of the Audience

A maximum relative variation of the reverberation time according to the size of the audience must be stated as a design condition for a hall together with the value of the reverberation time itself (for instance, 1.3 sec at 500 cps, ±10%). It is interesting and very useful to compute, quantitatively, how a change in the type of seats, the volume of the hall, or the number of seats would affect the relative variation in the reverberation time according to the number of occupied seats. The present work gives, in the form of equations and charts, an easy way to do this.