ISEAT 2026

Acoustic Center Localization for Holographic Directivity Measurements of Loudspeakers by Christian Bellmann, Wolfgang Klippel, Yuyang Liu

Abstract: Holographic methods enable high-resolution loudspeaker directivity measurements with accurate low-frequency behavior and reliable high-frequency phase information, while requiring fewer measurement points than traditional turntable-based measurements.

In spherical wave expansion, the sound field is represented by spherical harmonics and Hankel functions around a chosen expansion point. Although small mismatches of the acoustic center are automatically compensated, larger deviations increase the required expansion order and thus measurement effort.

This work presents and evaluates methods for acoustic center localization to achieve more compact representations and reduced measurement time. Two classes of approaches are considered: delay-based methods, which estimate the acoustic center from sound propagation delays, and wave expansion-based methods, which optimize the expansion point based on properties of the spherical harmonic coefficients.

The methods are evaluated using both simulated data and measurements of real loudspeakers. Results demonstrate frequency-dependent trade-offs between accuracy, speed, and robustness, and provide practical guidelines for selecting suitable localization strategies.

Loudspeaker Directivity Measurement by Christian Bellmann
September 13, 2026 | 1:30 pm to 6:00 pm | Hall 5

Abstract: This master class provides an introduction to modern methods for measuring and analyzing loudspeaker directivity and acoustical performance. It covers both traditional far-field directivity measurements and modern near-field holographic techniques. The course explains how spherical wave decomposition, double-layer scanning, and holographic post-processing can be used to reconstruct free-field radiation from near-field measurements.

It further addresses the extraction and interpretation of the spatial transfer function, on-axis response, sound power, and directivity, and discusses their relevance for loudspeaker evaluation, room interaction, and modern 3D audio applications such as beam steering. 

The master class combines theoretical background with practical measurement demonstrations, giving participants both a solid understanding of the underlying principles and hands-on experience with state-of-the-art acoustical measurement techniques.