Public address systems are often used for both announcements and background music distribution. Volume controls can be used to adjust the level locally. In addition to volume control, program selectors can also be installed to select five different programs locally. In the event of an (emergency) announcement, the built-in relay ensures that the message is broadcast at a preset level, independent of the local volume setting.
The volume controls come in three versions according to power rating: 12 W, 36 W, and 100 W. The total load of the loudspeakers connected to a volume control may not exceed the rated power.
Each of the three versions is also available in two versions. One is a power-saving, 4-wire volume override (/10 models), where the override relay is activated during an emergency call. The other is a failsafe, 4-wire volume override (/20 models), where the override relay is deactivated during an emergency call.