The Symetrix 572 SPL Computer is an automatic level controller designed to maximise intelligibility by adjusting system gain in response to ambient noise levels. Unlike conventional systems, the Symetrix 572 uses the sound system’s own loudspeakers as ambient noise sensors, eliminating the need for external sensing microphones.
It periodically switches the speaker line from the amplifier output to its internal sensing input, measures the ambient noise within a second, then reconnects the line to the amplifier. This process uses specialised impedance matching, frequency shaping, and level shifting circuits to ensure accurate noise readings from virtually any speaker configuration, whether transformer-coupled or direct-coupled, at 25V or 70V.
The Symetrix 572’s operating functions are managed by a microprocessor running proprietary Symetrix software, significantly reducing calibration time and allowing the installer to optimise system performance for different environments. During setup, the 572 stores key information without requiring external test equipment.
Inputs include separate connections for paging and music, as well as a direct paging microphone input. Both speakers and amplifiers connect directly to the Symetrix 572. Its front panel includes a page-over-music function, providing up to 14 dB of attenuation during announcements. Multiple option switches allow the installer to define how the system responds to changes in the acoustic environment. A front panel LED meter displays gain changes, assists with calibration, and identifies system errors.
Once calibrated, the Symetrix 572 smoothly adjusts system gain to maintain consistent levels. To use the loudspeakers as sensors, it requires moments of silence in the audio signal. The unit can take advantage of naturally occurring silent periods or enforce sample times by momentarily fading out the music, taking a measurement, and fading it back in within seconds. Importantly, the 572 will not interrupt an active page signal to take a reading.
The Symetrix 572 offers reliable, automated system level control suitable for environments such as shopping centres, restaurants, and industrial facilities, providing effective performance without the need for manual operation or additional equipment costs.
Both the Symetrix 571 and 572 SPL Computers perform similar functions but differ in application and design. The Symetrix 571 uses one or more microphones to sense ambient noise, allowing continuous adjustment without interrupting the audio signal—ideal for situations requiring constant paging.
The Symetrix 572, a cost-effective alternative, uses the loudspeaker system itself as a sensor, eliminating the need for external microphones and cabling. However, it requires periodic silence to take measurements.
Features
- Uses speakers as noise sensing “microphones”
- Separate Page and Music inputs
- Works with direct coupled and distributed systems
- Fast, simple calibration
