Optimizing spherical loudspeaker array for voice directivity using the spherical cap model

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master_Palakkal_Raghunath_Midhun_2026.pdf (5.85 MB)

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School of Electrical Engineering | Master's thesis
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Date

2025-12-31

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Acoustics and Audio Technology

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Degree programme

Master's Programme in Computer, Communication and Information Sciences
Tieto-, tietoliikenne- ja informaatiotekniikan maisteriohjelma
Magisterprogrammet i data-, informations- och kommunikationsteknik

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en

Pages

44

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Abstract

Conventional mouth simulators are limited by fixed radiation patterns, low power and high self-noise, failing to capture the complex spatial characteristics of real speech, such as the downward tilt of the main radiation lobe. To overcome these limitations, a simulation-driven approach is developed using the analytical spherical cap model, which was implemented and validated against known reference from the work of Aarts and Jansen [ 1 ]. This thesis investigates the optimization of a spherical loudspeaker array to accurately reproduce the dynamic and articulation-dependent directivity patterns of the human voice. A grid-search optimization method is applied to evaluate physical parameters, including array radius , driver radius , for different layouts (1, 4, 9, and 16 drivers), using a magnitude-weighted energy error metric. The single-driver configuration served as baseline proving the existence of optimal points, whereas they were found to be acoustically insufficient for replicating the asymmetric and time-varying nature of human speech. In contrast, by utilizing a frequency-dependent regularized least-squares control strategy (Tikhonov regularization) the multi-driver arrays successfully reproduce the higher-order spatial modes required to match measured phoneme patterns. The results indicate that a 16 driver configuration provides a critical threshold of perceptual authenticity, effectively reproducing the downward-tilted radiation lobes of vowels and the unique spatial signatures of fricatives and nasals. This work establishes a robust framework for developing physical prototypes.

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Supervisor

Arend, Johannes M.

Thesis advisor

Meyer-Kahlen, Nils

Keywords

spherical loudspeaker array, voice directivity, spherical cap model, regularization, phoneme-dependent radiation, ambisonics

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https://urn.fi/URN:NBN:fi:aalto-202601191458

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[dipl] Sähkötekniikan korkeakoulu / ELEC