A room-combining setup

A common arrangement for hotels and conference facilities is to have one or more large rooms that may be subdivided by flexible partitions. Sound reinforcement
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A room-combining setup

Jan 1, 1998 12:00 PM, Mike Sims

A common arrangement for hotels and conference facilities is to have one ormore large rooms that may be subdivided by flexible partitions. Soundreinforcement for any configuration of these sub-rooms is usually providedby a room combining system. Room combining refers to the management ofaudio signal mixing and routing to interconnect sub-room sound systems whenthose sub-rooms are combined into larger rooms. There are custom (aeuphemism for painful) ways to perform this function; these methods involvemany relays, matrix mixers, logic and a tangle of wire.-Severalmanufacturers, however, have integrated solutions for room-combiningapplications. These products offer simplified system wiring (relative to acustom installation) and straightforward interfaces for the end user.

Room combining: Basic structureFigure A shows a block diagram of a generic four-room combining system.Although the actual implementation will vary depending on the type ofequipment used, the elements shown give a good conceptual picture of anyroom combining system. Note that although equalization and other signalprocessing may also be used in a room combining system, these blocks areomitted for clarity.

Here's a rundown of how these elements work together in a typicalroom-combining system:

System microphones: A number of microphone drops are located in eachsub-room, usually on wall panels or floor boxes. Line-level inputs forrecorded audio or audio from video sources may be provided if such sourcesare needed.

Remote volume control: The end user will often need some control over thesound system volume. For example, the number of people in the room mightrequire minor level adjustments. Volume controls in sub-rooms that havebeen combined may be linked by the system such that all volume controls inthe combined rooms control volume for the entire combined sound system. Itis usually wise to limit the range of user level control to prevent grossmisadjustment. Some type of lock-out mechanism for any in-room controlswill also protect the system. In addition to the volume control function, aroom source select option may be included. This feature allows the user toselect either room audio or background music to feed the room sound system.

Microphone mixer: A microphone mixer function must be provided for eachsub-room to generate a summed output from the microphone and line-levelinputs in each sub-room. Either automatic or manual mixers may be used,depending on the specific requirements of the installation.-In rooms wheretwo or more microphones can be used simultaneously, an automatic mixer canhelp prevent the possibility of feedback. Preventing feedback isparticularly important if the system is reconfigured by non-technicalpeople.-If automatic mixers are used, it's important that the roomcombining system also combines the auto-mixer NOM (number of openmicrophone) attenuation signals to preserve correct NOM function as roomsare combined.

Audio matrix controller: The audio matrix controller is the heart of aroom-combining system. The matrix controller takes the audio output fromeach sub-room and generates the audio feeds to the sub-room poweramplifiers. For example, if rooms 1 and 2 are combined, then the audio feedto the amplifiers for rooms 1 and 2 would consist of the sum of theindividual audio outputs from rooms 1 and 2. The matrix controller may alsoperform auxiliary tasks, such as paging control and head-table speakermuting control. Different systems implement the paging function indifferent ways. For example, some systems may allow paging to all sub-roomstogether as well as to any sub-room individually. Others may allow only ageneral page to all sub-rooms together.

Central control panel: The central control panel may or may not be presentin the system. Again, the operational requirements of the user will dictatethis choice. One option is a custom fabricated panel with the actualfloorplan of the facility shown. Pushbuttons, used to reconfigure the roomand their indicators are part of the panel. Another option might be agraphic touch panel, either provided by the system manufacturer or by athird-party vendor. The programmable graphic touch panel has advantagesover the more common custom panel approach if future changes in the layoutor operation of the facility might necessitate changes in the userinterface. Touch panels can also help minimize user errors by limiting usersetup choices. The control panel (or another panel) may also provide thecapability to monitor the audio in each room.

Power amplifiers and loudspeakers: A power amplifier must be provided foreach sub-room in the system. Amplifiers in room-combining applications haveno particular requirements. Most loudspeaker systems for theseinstallations will be distributed 25 V or 70 V systems. The amplifiers mustbe capable of driving a 25 V or 70 V network of distributed loudspeakers tothe required sound pressure levels. Head table speaker control is oftenimplemented if a system loudspeaker contributes significant energy to anactive microphone to cause a feedback.-In this case, a relay or other meansof muting the loudspeaker selectively would be provided.