WSDG has modernised the world’s oldest surviving large-scale planetarium, equipping the space with a modernised acoustic design ahead of its centenary.
The centenary modernisation aimed to improve the visual and acoustic conditions within the existing auditorium, replacing the former inner dome’s perforated metal panels which featured unperforated edges and imperfect joints along the borders which 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, accommodating a concealed loudspeaker system and improving sound distribution within the auditorium’s highly
curved geometry.
The cylindrical lower walls beneath the lower dome also needed to be redesigned to optimise the sound field.
Following an earlier acoustic consultancy at Volkshaus Jena in 2021, the Ernst-Abbe-Stiftung appointed WSDG to the planetarium project in June 2025.
WSDG was taked with covering acoustic inventory measurements, room-acoustic analysis, and modelling, as well as assessment of the new dome-screen material and development of the auditorium treatment concept.
Prof. Dr.-Ing. Wolfgang Ahnert
provided senior acoustic oversight and strategic guidance, while Tobias Behrens took responsibility for acoustic consultancy throughout the project, including the existing condition measurements, evaluation of the acoustic properties of the Endure Screens Micro Pro projection surface, and development of room-acoustic treatments for the dome and walls.
Robin Breitbach supported the creation and detailing of the room-acoustic simulation model, particularly the precise modelling of acoustically effective materials and surfaces.
WSDG measured the existing auditorium before
its interior was completely removed, leaving the protected concrete cupola and internal geodesic structure untouched. The measurements established the room’s reverberation characteristics and identified the acoustic behaviour generated by its concave dome and cylindrical lower walls.
Tobias Behrens commented: “The architecture that makes the planetarium so extraordinary also creates a very particular acoustic challenge. 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 programmes and live events.”
Replacing the formerly segmented inner dome was a key element of the modernisation, overhauling the space with a visually continuous projection field.
The team selected Endure Screens Micro Pro, a surface designed for projection applications. WSDG assessed its perforation and sound-transmission characteristics, confirming its suitability for use in front of
the venue’s 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.
Behrends adds: “The key was to treat the dome as a single architectural, acoustic and technological system. 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 series of quadratic residue diffusers, 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.
Using the acoustic model, WSDG improved the placement and balance of the different treatments to promote an enveloping and evenly distributed sound field. The concept was designed to support the planetarium’s wide-ranging programme, including astronomical presentations, full dome films, educational events, concerts, and immersive audiovisual productions.
The acoustic work formed part of a wider technical overhaul, completed for the venue’s 100th anniversary. Zeiss modernised
the existing Universarium star projector and installed 11 Zeiss Velvet 4K projectors, creating an 8K full dome image.
Behrens closes: “Planetariums bring architecture, image and sound together in a uniquely immersive way. 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.”