The effect of vocal-tract wall compliance on tongue-tip trills is to create a favorable pressure-flow relation at the tongue tip for sustained vibration. The governing equations are derived for a model based on this mechanism, and data on unvoiced trills are used to help set parameters for a numerical simulation of the model.

No abstract

No abstract

An analysis is made of sound generation by aerodynamic sources near an acoustically compact body (or compact surface feature on a large boundary) that can deform in an arbitrary manner. It is shown how such problems can be investigated by simple extension of the compact Green's function used in the treatment of compact rigid bodies. It is known that this method can furnish rapid and accurate predictions of sound generated by flows with extensive, non-compact distributions of sources in cases where a numerical treatment requires at best tens or hundreds of hours of CPU time. Illustrative applications are made to study (i) the sound generated by a nominally rigid circular lamina of time-dependent radius held in an irrotational mean stream, and (ii) the production of voiced speech by vorticity interacting with a simple model of the vocal folds. In case (ii), it appears that predictions are represented well by a quasi-static approximation that permits the particular results of this paper and previous investigations to be generalized to arbitrarily configured folds.

Beginning at the age of about 14 months, eight children who lived in a rhotic dialect region of the United States were recorded approximately every 2 months interacting with their parents. All were recorded until at least the age of 26 months, and some until the age of 31 months. Acoustic analyses of speech samples indicated that these young children acquired [inverted r] production ability at different ages for [inverted r]'s in different syllable positions. The children, as a group, had started to produce postvocalic and syllabic [inverted r] in an adult-like manner by the end of the recording sessions, but were not yet showing evidence of having acquired prevocalic [inverted r]. Articulatory limitations of young children are posited as a cause for the difference in development of [inverted r] according to syllable position. Specifically, it is speculated that adult-like prevocalic [inverted r] production requires two lingual constrictions: one in the mouth, and the other in the pharynx, while postvocalic and syllabic [inverted r] requires only one oral constriction. Two lingual constrictions could be difficult for young children to produce.

The theory of the sibilant fricative [s] is formulated and solved as a mathematical problem of aeroacoustics. Air is forced through the constriction between the tongue blade and the hard palate by intra-oral pressure, forming a jet that strikes the upper incisors and leaves the mouth through a gap between the upper and lower incisors. The principal source of sound is the ‘diffraction’ of jet turbulence pressure fluctuations by the incisors. The spectrum of these pressure fluctuations incident on the teeth is modelled analytically using an empirical formula adapted from turbulent boundary-layer theory. Predictions are made about the far field acoustic pressure spectrum with reference to measured and estimated values of vocal tract dimensions and intra-oral pressure. Predicted spectra compare well with observations. The principal spectral peaks are determined by vocal tract physiology anterior to the tongue–palate constriction. The theory furnishes the first correct prediction of the dependence of the overall sound pressure level on the intra-oral pressure.

Speech samples of 12 speakers (8 children and 4 adults) producing the fricatives /s/ and/sh/ followed by the vowels /i/ and /u/ were analyzed to locate the major spectral prominences. Results showed that the fricative low-frequency prominences for children's samples differed from those of adults in three important ways: (1) They were generally higher in frequency; (2) they were greater in amplitude relative to higher frequency regions; and (3) they showed greater effects of vowel context. The first finding can be explained by a simple scaling of adult models of fricative production to accommodate children's smaller vocal tracts. The other two findings suggest, however, that there are other anatomical and articulatory differences between children and adults affecting fricative production. The data presented here suggest that one important difference may be the relative sizes of the fricative constriction and the glottal opening.

A fluid mechanical, or aeroacoustic, point of view is followed to study possible sources of sound during phonation. Concentration is on two features of the vocal tract during phonation: abrupt area change from the glottis to the vocal tract and the finite length of the vocal tract. With these features, a source of sound distinct from the volume velocity source can be identified and a preliminary account of its effect on the acoustic field given. This source of sound is an oscillating force resulting from an interaction of rotational fluid motion with itself. Because of the schematic nature of the geometry of the model used here, this source may be considerably modified in actual phonation. It is concluded that specification of volume velocity is not enough to specify the source during phonation, even neglecting source-tract interaction.