ARI Guest Talk: 21 February 2024
Long acoustic reverberation is often considered to yield a diffuse sound field, and ideal diffuseness is often a target in reverberation testing chamber design and when designing reverberation algorithms in 3D/immersive audio or cinema.
While ideal diffuse sound fields are considered to be of infinite extent, using loudspeakers to create extended diffuse sound fields is obviously difficult:
Stefan Riedel (JASA-EL 2022) showed in a listening experiment and in a model of the interaural level differences (ILD) that horizontally surrounding loudspeakers playing uncorrelated noises yield imbalanced ear signal levels whenever one of the listener's ears is closer to the surrounding loudspeakers than the other, with loudspeaker that naturally exhibit the typical radiation decay of -6dB per doubling of distance; interestingly, -3dB/dod was shown to be perceptually optimal.
Also the most elaborate 2.5D wave field synthesis of uncorrelated plane waves by a dense loudspeaker ring apparently fails, when interpreting results obtained in a listening experiment by Frank Melchior (2008, 124 AES Conv).
While experimentally explored, there appears to be no theory that anticipates all thinkable requirements and constraints of diffuse sound field synthesis.
This talk explains how statistical expectation of the resulting second-order quantities (sound energy density, sound intensity, directional sound intensity density) actually yields equations resembling potential theory. Using known tools such as Gauß' divergence theorem (electric flux) and Newton's spherical shell theorem (gravity) helps to find the most important constraints and requirements enabling perfect synthesis of the most relevant metrics, but not all of them.
Franz Zotter (Assoc. Prof.) is Electrical and Audio Engineer (joint degree TUGraz/Kunstuni Graz, 2004), holds a PhD (KUG, 2009), was awarded the Lothar-Cremer medal (DEGA, 2012), got tenure and submitted habilitation (tenure track 2019-2022), and he wrote an open-access textbook about Ambisonics (Springer, 2019). He has been with the Institute of Electronic Music and Acoustics (IEM) since 2004, mostly investgating 3D audio technologies using spherical-harmonics. Currently he is principal investigator of envelopment immersive sound reinforcement (EnImSo, FWF P 35254-N). He will be acting deputy head of IEM from March 2024 on, is co-chair of KUG's ethics advisory board, is an active member of ÖGA, DEGA, VDT, AES, associate editor for acta acustca, has been (co-)organizing several audio-related conferences, and organizing Europe’s Student 3D Audio Production Competitions (since 2017).