Buttenheim, April 2019: It is one of the most impressive and longest underwater road tunnels in the world: the “Neue Elbtunnel” in Hamburg. The tunnel has been taken into service in 1975. With almost 120,000 vehicles passing through the 3.3-kilometer tunnel every day the structure must meet the highest standards of safety. The audio distribution system installed by SALZBRENNER media ensures that in an emergency drivers are alerted quickly and clearly by loudspeaker announcements.

In the first three tubes of the four-core tunnel, the flexible CAS 300 control system from SALZBRENNER media has proven its worth for announcements. Therefore, the Free and Hanseatic City of Hamburg also commissioned the service provider to equip the fourth tube with a version adapted to the customer’s requirements: In this case, announcements can be made either live or alternatively via pre-recorded announcement messages. The Franconian full-service provider scored as a long-standing and reliable partner with its comprehensive system knowledge following conversion of the first three tubes.

Conversion in the shortest possible time

Since the Elbtunnel is only closed to traffic at night, the existing installations were replaced in just one night: The individual steps of the project, which was completed in November 2018, were defined at an early stage and coordinated with the planner, Oliver Reimann’s Sprech-Fabrik company. In addition to audio distribution, SALZBRENNER media also installed loudspeaker and amplifier monitoring. They ensure that all signal paths work properly in an emergency. A special feature: The loudspeakers are monitored by impedance measurement at 20 kHz and thus in the inaudible range. The announcements come from two custom microphone units.

A wave ride through the tunnel

The audio specialists from SALZBRENNER media rely on a very special means of sound distribution for the loudspeaker system: “The Elbtunnel is acoustically challenging because no sound-absorbing surfaces have been incorporated,” explains project manager Kay Rothe from SALZBRENNER media. “The solution was synchronised longitudinal sound reinforcement according to the SLASS concept (Synchronised Longitudinal Announcement Speaker System).” Special software from R&E Kommunikationstechnik GmbH for sequential signal transmission was used.

While the previous loudspeaker system had to deal with the typical tunnel sound overlaps, the SLASS method takes advantage of the acoustic characteristics of the tunnel: The sound is transmitted in wave fronts that move through the tunnel synchronised in time like a single sound wave: The individual loudspeaker signals are delayed in such a way that the loudspeakers transmit them in the correct phase as soon as the corresponding sound waves arrive from the previous loudspeaker. The result: the announcements are much clearer and easier to understand – and instead of around 800, just 46 loudspeakers are needed.