German to English Tech/Engineering Sports / Fitness / Recreation sound systems

Crops up in one sentence: Das Nahfeldbeschallungssystem (des Berliner Olympiastadions) unterstützte das Soundsystem der Show.

This is the sound system that is not close to the pitch BUT which enables those on or near the pitch to hear what is going on. Ahem, that's how it was explained to me anyway. Any clever ideas out there? Sincerely baffled, Natalie ;-))