NEXO system proves reliability in extreme underground environment

A challenging underground environment in southern France has provided the perfect real-world test for NEXO’s ePS-EN54 loudspeakers, installed deep within the vast network of galleries at the Grotte Saint-Marcel cave system.

The project was delivered by French audio-visual integration specialists Atelier du Son et de l’Image (ADSI), known for creating bespoke AV installations in unusual environments and visitor attractions across France. Their previous work includes sound installations in museums and heritage venues, such as the renowned Musée Grévin wax museum in Paris.

Stretching across more than 60 kilometres of galleries, the Grotte Saint-Marcel is one of the largest cave systems in France. Visitors follow a 400-metre circuit through enormous underground chambers carved by a former river, where sound and light installations enhance the experience and help bring the natural environment to life.

Back in 2024, ADSI’s project manager Bertrand Gazi invited NEXO’s engineering support team to demonstrate a proposed sound system to the site operators and their scenography partner Creafactory.

“The team was very impressed with the ePS12 and eLS18 system we demonstrated for far-field sound effects and audio for video projection, along with ID14 speakers for near-field voiceover and tour explanations,” recalls NEXO’s David Hochtstenbach. “What I remember most from that day, though, was the extreme humidity in the cave – it permanently killed my laptop.”

The installation was completed a year later and includes 6 each of NEXO’s EN54-rated ePS12 and ePS10 speakers with 3 x eLS18 subs, and a total of 18 of NEXO’s ultra-compact ID14s positioned along the visitor route.

To preserve the natural environment of the cave, all cabinets were finished in custom RAL colours to blend into the surroundings. Mounting loudspeakers directly to the cave walls was prohibited, so the system has been carefully positioned among the rock formations, where many of the units are continuously exposed to dripping water.

Earlier this year, NEXO Quality Director Cyril Picard visited the site to assess how the system was performing after nearly twelve months of operation in conditions where humidity levels exceed 80 percent.

“During development, the ePS-EN54 loudspeakers were tested extensively, including 800 hours of salt spray testing and 600 hours of UV exposure – although UV clearly isn’t a concern 400 metres underground,” he explains.

“From the use of high-grade A4 stainless steel screws to UV-protected cloth and durable polyurethane coatings, every detail has been carefully engineered. Even so, it was a unique opportunity to inspect the system after almost a year of continuous operation in such extreme conditions.”

Despite the challenging environment, the inspection confirmed the system was performing exactly as intended.