Summary:
- The room-acoustic strategy integrates the protected dome, Endure Screens Micro Pro projection surface and concealed HOLOPLOT immersive audio into one cohesive environment.
- To prevent sound energy from concentrating in problematic focal points caused by the venue's concave dome and cylindrical lower walls, WSDG deployed behind-the-screen absorption along with lower-wall quadratic residue diffusers (QRDs).
- This balanced treatment controls reverberation while maintaining clarity for diverse programming—from astronomical shows to live concerts—without altering the venue's protected historical concrete structure.
WSDG has completed the acoustic design for the modernization of the Zeiss-Planetarium Jena ahead of its centenary. WSDG developed an acoustic strategy integrating the venue’s protected dome structure, new projection surface, and HOLOPLOT immersive sound system.
[Cosm: Take Me Into the Ballgame]
The centenary modernization aimed to comprehensively improve the visual and acoustic conditions within the existing auditorium. The former inner dome was assembled from perforated metal panels whose borders, unperforated edges, and imperfect joints remained visible during star shows and film projections, interrupting the intended continuous image. The replacement therefore needed to create a uniform white field for fulldome content, accommodate the concealed loudspeaker system and improve sound distribution within the auditorium’s highly curved geometry. Additionally, the cylindrical lower walls beneath the dome needed to be redesigned to optimise the sound field.
Opened on July 19, 1926, the Zeiss-Planetarium Jena traces its origins to the pioneering work of ZEISS engineer Dr. Walter Bauersfeld, who developed the fundamental form of the planetarium projector in early 1919. Following an earlier acoustic consultancy at Volkshaus Jena in 2021, the Ernst-Abbe-Stiftung appointed WSDG to the planetarium project in June 2025. The scope covered acoustic inventory measurements, room-acoustic analysis and modelling, assessment of the new dome-screen material, and development of the auditorium treatment concept.
In October 2025, WSDG measured the existing auditorium before its interior was completely removed. The protected concrete cupola and internal geodesic structure remained untouched. The measurements established the room’s reverberation characteristics and identified the acoustic behaviour generated by its concave dome and cylindrical lower walls.
“The architecture that makes the planetarium so extraordinary also creates a very particular acoustic challenge,” said acoustic consultant Tobias Behrens. “In concave spaces, reflections can be directed towards focal points and sound energy can become concentrated in particular areas. Our task was to control those geometric effects while retaining a reverberation time appropriate for planetarium shows, film screenings, educational programs, and live events.”
A central element of the modernization was the replacement of the former segmented inner dome lining with a visually continuous projection field. The project team selected Endure Screens Micro Pro, a surface developed for high-end projection applications. WSDG assessed its perforation and sound-transmission characteristics, confirming its suitability for use in front of the concealed HOLOPLOT X1 and X2 Matrix Arrays.
Behind the Micro Pro surface, a sound-absorptive overlay controls both reverberation time and problematic acoustic focusing. This allows the dome to function as a broadband absorptive area while maintaining the uninterrupted white surface required for full-dome projection.
“The key was to treat the dome as a single architectural, acoustic and technological system,” Behrens explained. “The screen had to deliver a seamless image, the treatment behind it had to control the room, and the loudspeakers had to remain effective through the surface. None of those requirements could be resolved in isolation.”
For the cylindrical lower walls, WSDG developed a combination of quadratic residue diffusers (QRDs), broadband absorbers ,and reflective surfaces. The QRD elements scatter incident sound in multiple directions, helping to disrupt the focusing patterns produced by the curved geometry. Broadband absorptive areas control reverberant energy, while strategically retained reflective surfaces prevent the room from becoming excessively damped.
The acoustic work formed part of a wider technical renewal completed for the venue’s 100th anniversary. ZEISS modernized the existing UNIVERSARIUM star projector and installed eleven ZEISS VELVET 4K projectors, providing an 8K full-dome image. Together with the HOLOPLOT system, the new technology significantly expands the auditorium’s capabilities for immersive audiovisual programming.
The planetarium’s own assessment of the completed modernization is also positive. Stefan Harnisch, technical manager at the Zeiss-Planetarium Jena, summed up his satisfaction with a touch of understated but telling reaction, commenting, “There is a certain sense of satisfaction within me.”
“Planetariums bring architecture, image and sound together in a uniquely immersive way,” Behrens concluded. “At Jena, the aim was to respect a landmark that helped define modern planetarium design while creating the acoustic conditions required for the next generation of planetarium experiences. It is a very special project because its historic engineering and contemporary technology are inseparable.”
