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Introduction

Chapter 1

The Symetrix 572 SPL Computer is an automatic level controller that maximizes intelligibility by
changing gain in proportion to environmental noise level changes; in essence, controlling the
volume of the background/paging system by measuring the volume of the ambient noise and then
adjusting the system gain accordingly. Unique to the 572 is its ability to utilize the sound system’s
loudspeakers as noise measurement transducers, in place of the usual microphones. The 572
switches the speaker line from the amplifier’s output to its own sensing input. In less than one
second it reads the ambient noise level and switches the speaker line back to the amplifier. Special
impedance matching, frequency shaping, and level shifting circuits allow the 572 to acquire precise
relative noise measurements from virtually any speaker line, with any number of speakers of any
impedance, transformer coupled or direct coupled, 25V or 70V.

The operating characteristics of the SPL computer are controlled by a powerful microprocessor,
running under Symetrix proprietary software. This reduces the 572’s calibration time and allows the
installer to optimize performance for any situation. No test gear is needed because the 572 obtains
and stores the information it needs during calibration.

The 572 has separate inputs for paging and music as well as a direct paging microphone input.
Both the speakers and the amplifiers connect directly to the 572. A front panel page over music
function enables up to 14 dB of music attenuation during announcements. There are multiple
option switches for telling the 572 how to treat the page/music signal as well as how to react to
changes in the acoustic environment. The LED meter on the front not only indicates gain change
but also aids in setup and calibration and identifies errors.

You show the 572 the parameters of the acoustic environment during calibration and then set the
way you want the unit to respond to changes. The 572 then takes the information it has stored in
memory and makes smooth, appropriate changes to keep the levels exactly where you want them.
In order for the speakers to act as loudspeakers and sensors, there must be times when no audio is
passing through the speakers to allow the sample of the ambient noise to be taken. Thus the 572
takes advantage of silent periods in the paging or music to take a sample, or it forces a sample
based on the front panel setting at timed intervals. The 572 will unobtrusively fade out the music,
take a sample, and then fade the music back in, all in a matter of seconds. The 572 will not, how-
ever, interrupt any signal that appears at the page input, thus keeping the unit from forcing a sense
period during a page.

From malls to restaurants to factories, the Symetrix 572 gives you effective, reliable, system level
control without an operator or the normal additional costs.

Feel free to contact us if you have questions, comments, or suggestions:

Phone:

(425) 778-7728

Fax:

(425) 778-7727

Email:

[email protected]

Website:

www.symetrixaudio.com

Front panel

Rear panel

AC INPUT