AEM’s AA21-400 Cabin PA and Siren Controller is a single, panel-mounted unit that provides a simple interface to all generations of AEM’s loudspeaker amplifiers and speakers. It maximizes the performance and reliability of your aircraft's PA system with state-of-the-art design, improved frequency response, and an optimized microphone input circuit.
https://www.aem-corp.com/loudspeaker-systems/legacy-pa-systems
https://www.aem-corp.com/loudspeaker-systems/legacy-pa-systems