The core of evacuation solution is formed by interconnected Dynacord Promatrix 8000 systems
Over 24 substations equipped with Dynacord DPC 8015 call stations are linked to the main control rooms

The Rennsteig Tunnel in the Thuringian Forest is, with a length of 7,916 meters, Germany’s longest road tunnel and the fourth longest in Europe. A construction project of this magnitude imposes tremendous demands on all the components and materials involved. The voice alarm and evacuation equipment is of particular importance as, in an emergency, a reliable, high-quality system could save lives. Responsible for the design and implementation of the installation here was the German Ingenieurbuero Hoffmann (Hoffmann engineering office), which was commissioned by tunnel project specialists Goldfunk of Erfurt.

The core of the evacuation solution is formed by two interconnected Promatrix 8000 systems – one in each of the control rooms in the service building. A total of 24 substations equipped with Dynacord DPC 8015 call stations are linked to the main control rooms. Spaced at intervals of around 600 meters, Dynacord P 64 digital audio matrix managers control and supervise 16 each of the 300 loudspeakers.

The P64 controllers form a Dante network linked by two fiber-optic rings. “In a network of this size, a clean network structure is of critical importance,” says Frank Roßa, the project’s technical director. “You have to work very closely from the outset with the responsible network administrators; the requirements must be clearly defined and information on structures exchanged. Since the Dante system in the Rennsteig Tunnel will be used redundantly, this exchange was essential.” Both the primary and secondary Dante ports were utilised, so that it will remain functional. “In fact here, even if parts of the system were to go down, the life-saving announcements would still be transmitted,” affirms Roßa.

“Tunnels have very peculiar acoustics due to their hard concrete walls and cylindrical shape,” continues Roßa. “These are quite different from both outdoor and hall acoustics. In tunnels, reflections are legion, which is why special loudspeakers, GF-TH1 ‘tunnel horns’ from Goldfunk, were used.”

Just as important here as the reliability of the solution is its intelligibility. For this reason, Roßa and his team, for years now when working on tunnel projects, have opted for a longitudinal speaker configuration. In other words, all the horn loudspeakers point in the same direction, with appropriate delays introduced by the P64 Digital Matrix Manager. Taking advantage of the boundary effect, the loudspeakers in the Rennsteig Tunnel are mounted in the roof at intervals of around 50 meters. “By this means, a uniform wave front is obtained, reflections are kept in check, and the level of intelligibility is enhanced,” Roßa explains.

The loudspeakers were tuned using special measuring techniques, with equalisation and delay added subsequently. The complexity of the installation is revealed by another detail: “The loudspeaker parameters for the main shaft of the tunnel differ from those obtaining in the breakdown bays,” states Roßa. “For this reason they were tuned differently in each case and steps taken to improve the acoustics in the latter. For example, sound-absorbent panels were installed to interrupt the reflections from the smooth concrete walls.” To drive the loudspeakers assigned to it, each substation is armed with two Dynacord DSA 8805 multi-channel power amplifiers. The entire system is controlled and supervised through the use of IRIS-Net software with a custom-tailored graphic user interface.

The meticulous planning here certainly paid off. The independent company IFB Consulting, for example, has visited the site already several times to conduct measurements. “The results were more than satisfactory,” Roß pleased to report. “And not only in terms of intelligibility and acoustic level. The Rennsteig Tunnel recorded a speech transmission index of around 0.5; for a tunnel, that’s an absolutely fantastic STI!” The Rennsteig Tunnel installation, in Roßa’s view, is a suitable reference for comparable projects. “It shows that you can achieve magnificent results with P64 Digital Audio Matrix Managers and audio signal transmission via Dante. These allow you, on the one hand, to build in redundancy and, on the other, to enjoy high-quality transmission on multiple audio channels. For a tunnel of this size, this is a groundbreaking achievement.”