HOLOPLOT Implements Intelligible Yet Invisible Sound System for St Hedwig's Cathedral, Berlin

	"Having spoken word coming from the center of the space, with the audience 'in-the-round' and no possibility of adding localized loudspeakers, created a unique situation we had to try and solve," says Greif.

St. Hedwig's is a beautiful cathedral in the heart of Berlin. Modeled after the Pantheon in Rome, construction work began in 1747, finally opening its doors to worshipers in 1773. To preserve its rich history, it has just undergone an extensive renovation period that's seen the entire interior transformed. HOLOPLOT has been chosen to supply the audio solution, delivering its X2 Matrix array system for seamless, unobtrusive spoken word reinforcement.

The nave sees big changes, while the original interior layout returns, but now with seating in the round. The aesthetic is clean and simple with white walls, clean lines, and minimal internal details -- with strictly no option for visible loudspeakers.

Circular in shape, with a 30m diameter, the central space rises to a dome that peaks at a total height of 33m. The huge parabolic space has renowned acoustics for music and is well-suited for performances from the Klais Opus organ. For spoken word, however, the reverb times negatively impact intelligibility and the echo bouncing back to the altar in the center posed a considerable challenge.

Sichau & Walter Architects, who won the redesign contract back in 2014, required an invisible solution that would solve these issues while being flexible enough to adapt to the variety of choral, concert, and spoken word content as their founding partner, Peter Sichau, expands, "Worship architecture fundamentally differs from secular architecture, because its primary purpose is to create a framework, so that the celebrant, in this case the priest, can deliver mass in a way that offers worshipers a religious experience. Our methodology required the architecture and the space to be recognizable solely by the atmosphere and the acoustic of the space, which is very complex and challenging in this case."

The HOLOPLOT team modeled various design options that could meet this exacting brief. As Jakob Greif, HOLOPLOT applications engineer and technical lead for the project, explains, the final system design is a true example of working with a building to achieve the very best for the whole community.

"Circular buildings are not new to HOLOPLOT, but the difference here was the position of the altar and therefore main microphone positions. Having spoken word coming from the center of the space, with the audience 'in-the-round' and no possibility of adding localized loudspeakers, created a unique situation we had to try and solve."

To address the space's positional challenges and 6.5-second reverberation time, Greif and the HOLOPLOT team designed a system based on the X2 Matrix array.

X2 is HOLOPLOT's compact Matrix array loudspeaker, equipped with power over ethernet, enabling it to receive audio and control signals, and power through a single cable, simplifying installation and, in combination with the unit's slim profile, enabling flush mounting. These features allow the arrays to disappear behind custom screens, in narrow, recessed wall cavities, so as to not interfere with the building's smooth, mute colored lines, something that was very important to the project.

X2's size and rotation flexibility enabled the team to utilize the modules in a variety of positions, including fixed in portrait orientation behind the main columns. 3D audio-beamforning then solved the positional issues created by having the altar located centrally, as Greif continues.

"We have hidden 22 MD30 units behind perforated panels," he says. "The arrays are fixed in only three locations and deliver unique coverage zones that disregard the highly reflective surfaces of the cathedral. 3D audio-beamforming and our optimization algorithms not only allow us to create a circular, rounded beam but also to split the direct throw, avoiding the altar microphone in the center of the nave and raising the gain before feedback threshold."

"Our priests will finally be able to speak comfortably at the altar and that is possible thanks to the way HOLOPLOT has designed the active beams," notes Johannes Rogge, technical and media integration lead for the St. Hedwig project. "I am really impressed by how that works; to be able to hear the difference just by moving a few meters, is amazing."

Thanks to increased sound control in both the horizontal and vertical axes, ensuring that sound energy does not hit the highly reverberant walls, diluting the clarity of speech, the team was able to build on these positive results to offer the cathedral committee a range of functions, increasing flexibility, usability, and, importantly, promoting creativity in the space.

"The technical team for the cathedral is staffed by volunteers, so it was essential to provide a system that was not intimidating to use," says Greif. "We have created a range of different presets that can be accessed to support any type of performance, as well as supporting the priest delivering mass or sermons. We also included a preset for exciting the nave's natural acoustic which will give a much more musical result, elevating the spiritual feel of a choral performance. The result is something we are really proud of, and we hope the community of Berlin will be proud of it, too."

"Based on this experience, HOLOPLOT is the only system that can be used for such tasks in the future," Sichau says. "No other system that I know allows for massive spatial impression or the specific adjustment of acoustic subtleties."