The JBL® Commercial CSM-21 offers fixed I/O, pre-configured architecture, full stereo or mono operation, flexible routing and control of multiple audio sources, simple front-panel configuration and control without the need for a computer, compatibility with the CSR wall controllers, compatibility with the CSPM paging microphones, and optional duplication of audio channels to another device via a Cat5 cable.

The CSM-21 features two stereo music inputs with gain control and clip LEDs, and one stereo output with an active crossover and a dedicated subwoofer output.

Two additional inputs are provided for music override. First, a mic input with phantom power and gain control can be routed to the output zone, ducking the music by a user-configurable amount. Second, a line input allows high-priority ducking of all sources, which is ideal for alarms.

Dedicated controls for music EQ and dedicated controls for global mic EQ allow the frequency content of each input type to be customized independently. LevelGuard™ is provided to retain consistent volumes between the various inputs, and AutoWarmth™ is provided to ensure full fidelity at all zone volume levels.

A Zone Remote port facilitates connection of the CSR wall controllers, which can provide source selection and/or volume control. Source select, music level, and mic level can also be controlled on the front panel. For additional control, two logic inputs facilitate page steering and music muting via contact closure.

Two RJ-45 Link ports allow multiple CSM devices to be linked to increase the number of output zones. Linking CSM devices shares the inputs from the main devices over Cat5 cable and eliminates the need for Y-cables.