The Influence of CVT Metal and Density on Voice Directivity Patterns Across Two Octaves: A Double-Case Study

The spatial characteristics of voice radiation represent an important yet still insufficiently explored dimension of vocal performance and pedagogy. While previous studies have focused on spectral and glottal correlates of vocal modes, less attention has been given to how these modes shape the directional distribution of sound energy in space. Building on prior work on complete vocal technique (CVT), this study explores how the perceptual parameters of metal and density may influence voice directivity patterns across vocal modes and stylistic contexts.

A double-case study was conducted involving two professional singers (M1-AMAB, F1-AFAB) performing sustained phonation across four CVT vocal modes, each modified in terms of metal (neutral, reduced, and full) and density (reduced, full) for Neutral, Overdrive, and Edge. A total of 1088 samples were recorded using a hemispherical microphone array in an anechoic chamber. Directional sound radiation was analyzed across absolute and relative domains and evaluated using front-back ratios, spectral tilt, and directivity indices. Factor analysis was employed to reduce spatial dimensionality and explore consistent radiation patterns. Correlations were tested between radiation factor scores and directivity and acoustic.

Across the two singers, we observed singer-specific differences in spatial radiation patterns that appeared to relate to variations in metal and density. Full metallic and full density for Overdrive and Edge conditions tended to show more forward-focused radiation, particularly in the 2-5-kHz band. Classical productions showed a tendency toward broader radiation patterns in the 0-2-kHz band, whereas contemporary conditions appeared more directional. Factor scores suggested the presence of structured directional components, and correlations with directivity parameters indicated recurring tendencies across metal levels and, in some cases, density. In these two singers, differences in radiation could not be attributed solely to sound pressure level or fundamental frequency, which may point to the contribution of coordinated vocal tract shaping.

In this double-case study, variations in metal-and to some extent density in Overdrive and Edge-were associated with singer-specific changes in three-dimensional radiation, beyond what could be explained by pitch and loudness alone. These preliminary observations suggest that spatial acoustics may provide a useful extension of the CVT framework and may hold relevance for pedagogical and technological relevance of controlling vocal directivity. The study introduces novel parameters for quantifying radiation and proposes their integration into applied settings such as voice training, performance acoustics, and immersive audio systems.