Symetrix 572 SPL User manual

572
572 SPL Computer
User’s Guide

i
Table of Contents
Rev A.00, 24 February, 1999
Symetrix part number 53572-0A00
Subject to change without notice.
©1999, Symetrix, Inc. All right reserved.
Symetrix is a registered trademark of Symetrix, Inc.
Mention of third-party products is for informational
purposes only and constitutes neither an endorsement nor
a recommendation. Symetrix assumes no responsibility
with regard to the performance or use of these products.
Under copyright laws, no part of this manual may be
reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying,
scanning, recording or by any information storage and
retrieval system, without permission, in writing, from
Symetrix, Inc.
572
6408 216th St. SW
Mountlake Terrace,WA 98043 USA
Tel [phone]
Fax [phone]
Email [e-mail]
Chapter 1 Introduction 1
Chapter 2 Operator Safety Summary 3
Chapter 3 Setup 4
Calibration Checklist 6
Chapter 4 Front & Rear Panel Overview 7
Chapter 5 572 Basics 10
Chapter 6 Technical Tutorial 12
Chapter 7 Using the 572 15
Chapter 8 Applications 23
Chapter 9 Troubleshooting 25
Chapter 10 Specifications 26
Chapter 11 Warranty & Service 27
Appendix A External Sensing & Multi-Unit Installations 29
Appendix B Connections 31

572
1
IntroductionChapter 1
TheSymetrix572SPLComputerisanautomaticlevelcontrollerthatmaximizesintelligibilityby
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,transformercoupledordirectcoupled,25Vor70V.
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:[phone]
Fax:[phone]
Email: [email protected]
Website: www.symetrixaudio.com
Front panel
Rear panel
AC INPUT
18W MAXIMUM
POWER
MIC
PAGE
MUSIC
PAGE
LINE INPUTS
OUTPUT
LINE
SPARE
TRIG
SENSE
EXT
CNTRL
RELAY
EXT
AMP
FROM
SPEAKER
TO
123456789011BT123456789012BT
Vc
THIS UNIT CONTAINS NO USER SERVICABLE PARTS.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
UNITED STATES OF AMERICA
LYNNWOOD WASHINGTON,
MANUFACTURED IN
FUSE
PRESS
OPTIONS
NORM
BYPASS LOW
HIGH
SAMPLE
INTERVAL (MIN)
014
PAGE OVER
MUSIC (dB)
2:1 1:2
STTPOUE:ENS
RATIO (dB) U
GAIN (dB)
BYPASS
4030915202625
PAGE/MUSIC
INPUT ERROR
10
15
200
MAX
MODE
-10
-5
0
-15
-20
MIN
5
LEVEL SET (dB)
CALIBRATE
SPL COMPUTER
572
ABCD
1234
PAGE
MIC
GAIN
BYPASS SENSE
GAIN
SENSE MUSIC/
PAGE
5
10 15
20
126

572
2
Do You Have The Right Unit?
Symetrix makes two different SPL computers: the 571 and the 572. Although both units perform
essentially the same task, they are different.
The 571 requires an external sensing microphone(s) to monitor ambient conditions. The 571 works
in real time; adjustments are made continuously, regardless of music, paging, or silence. The 571
does not interrupt the signal path at any time.
The 572 uses the sound system loudspeaker(s) to monitor ambient conditions. Doing this requires
the 572 to monitor the incoming program material for silent sections. Once the 572 detects silence,
it switches to sense mode, switching the loudspeaker(s) from the amplifier output to its sense
input. Sensing takes one to two seconds. Any signal applied to the paging inputs during this time
immediately terminates the sense period. If a silent period never occurs, the 572 forces one. A
front-panel control determines the length of time that elapses before a forced sense occurs.
Sensing may also be triggered externally. The 572 interrupts the signal path during sensing. Table
1-1 provides a tabular comparison of the two units.
Feature 571 572
Uses dedicated microphone for ambient sensing............................. Y N
Uses sound system speakers for ambient sensing ............................ N Y
Sound system loudness controlled by ambient noise conditions..... Y Y
Continuous, real time operation ....................................................... Y N
Program silence sensing triggers ambient sense period .................. N Y
Mic and line level paging inputs ...................................................... Y Y
Page over music (ducking)............................................................... Y Y
Music + page mixing........................................................................ Y Y
Calibration required ......................................................................... Y Y
Timed ambient sensing .................................................................... N Y
Interrupts signal path during sensing ............................................... N Y
Table 1-1. 571 - 572 Feature comparison.

572
3
Operator Safety SummaryChapter 2
Terms
Several notational conventions are used in this
manual. Some paragraphs may use Note, Caution,
or Warning as a heading. Certain typefaces and
capitalization are used to identify certain words.
These are:
Note Identifies information that needs
extra emphasis. A Note generally
supplies extra information to help
you to better use the 572.
Caution Identifiesinformation that, if not
heeded, may cause damage to the
572 or other equipment in your
system.
Warning Identifies information that, if
ignored, may be hazardous to your
health or that of others.
CAPITALS Controls, switches or other markings
on the 572’s chassis.
Boldface Strong emphasis.
Equipment Markings
AVIS:
NE PAS OUVRIR
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.
S’adresser a un reparateur compétent.
RISQUE DE CHOC ELECTRIQUE
N
o user serviceable parts inside. Refer servicing to qualified service personnel.
CAUTION
WARNING:
TO REDUCE THE RISK OF FIRE OR
ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE
DO NOT OPEN
RISK OF ELECTRIC SHOCK
The lightning flash with arrowhead symbol within an
equilateral triangle is intended to alert the user of the
presence of uninsulated “dangerous voltage” within
the product’s enclosure that may be of sufficient
magnitude to constitute a risk of electric shock to
persons. The exclamation point within an equilateral
triangle is intended to alert the user of the presence of
importantoperating and maintenance (servicing)
instructions in the literature accompanying the
product (i.e. this manual).
Caution To prevent electric shock, do not use the
polarized plug supplied with the unit with
any extension cord, receptacle, or other
outlet unless the blades can be fully
inserted.
ImportantSafetyInstructions
Please read and keep these instructions. Heed
and follow all warnings and instructions.
Install in accordance with the manufacturer’s
instructions.
Power Source This product is intended to
operate from a power source that does not apply
more than 250V rms between the power supply
conductors or between either power supply
conductor and ground. A protective ground
connection, by way of the grounding conductor
in the power cord, is essential for safe operation.
Grounding The chassis of this product is
grounded through the grounding conductor of
the power cord. To avoid electric shock, plug the
power cord into a properly wired receptacle
before making any connections to the product. A
protective ground connection, by way of the
grounding conductor in the power cord, is
essentialforsafeoperation.Donotdefeatthe
safetypurposeofthegroundingplug.The
grounding plug has two blades and a third
grounding prong. The third prong is provided for
your safety. When the provided plug does not fit
your outlet, consult an electrician for replacement
of the obsolete outlet.
DangerfromLossofGround Iftheprotective
ground connection is lost, all accessible conduc-
tive parts, including knobs and controls that may
appear to be insulated, can render an electric
shock.
ProperPowerCord Useonlythe powercordand
connector specified for the product and your
operating locale. Use only a cord that is in good
condition.Protectthepowercordfrombeing
walked on or pinched, particularly at plugs,
convenience receptacles, and the point where
they exit from the apparatus.
Proper Fuse The user accessible fuse is a part of
the attached AC connector. The fuseholder
accepts5x20mmdiameterfuses.For117VAC
operation,thecorrectvalueis0.5A,250VAC,
standard.For 230VAC operation, thecorrect
valueis0.25A,250VAC,standard.
OperatingLocation Donotoperatethisequip-
mentunderanyofthefollowingconditions:
explosive atmospheres, in wet locations, in
inclementweather,improperorunknownAC
mainsvoltage, or if improperlyfused.Do not
install near any heat source such as radiators,
heat registers, stoves, or other apparatus
(including amplifiers) that produce heat. Unplug
this apparatus during lightning storms or when
unused for long periods of time.
StayOutoftheBox Toavoidpersonal injury(or
worse), do not remove the product covers or
panels. Do not operate the product without the
covers and panels properly installed. Only use
accessories specified by the manufacturer. Clean
only with a damp cloth.
User-serviceableparts Therearenouser
serviceable parts inside the 572. In case of failure,
refer all servicing to the factory. Servicing is
required when the 572 has been damaged in any
way, such as when a power supply cord or plug
is damaged, liquid has been spilled or objects
have fallen into the apparatus, the apparatus has
been exposed to rain or moisture, does not
operate normally, or has been dropped.

572
4
Setup Chapter 3
What You’ll Need
Toinstall a572, you’llneed the followingitems:
1. The572.
2. Accesstothepoweramplifierinput(linelevel),mixeroutput(linelevel),poweramplifier
output (speaker level), speaker line connections.
3. Background musicfeed(usually themixer line output).
4. Paging feed (line or mic level or both) preferably separate from the background music feed.
5. A time where the ambient noise level in the loudspeaker coverage area is at its normal
minimum. This is the level at which the 572 begins raising the level. Thus, it should NOT
be when the space is dead quiet, unless that is the normal minimum.
6. Program audio and paging signals during calibration.
Overview
The following points of information must be considered during system design and installation.
Placethe 572inthe signalchainas thefinal levelcontrollingdevice.
Equalizers following the 572 are acceptable IF their controls (both EQ and level) will not be
changed after calibration. It is imperative that any gain or level controls used in the signal chain
after the 572 remain unchanged once the unit has been calibrated. This includes wall mounted
autoformer and L-pad speaker-level controls used for zone balancing. Level controls in the signal
chain before the SPL Computer are acceptable, because the unit “reads” input level changes.
Calibratethe572whenthecoveragezone’sambientnoiselevelisit’snominalminimum.
“Nominalminimum”meanswhateverambientnoiselevelistheminimumforthatparticularenviron-
ment, no matter what the actual level may be. It should not be dead silent unless that is normal.
The ambient noise level measured by the 571 during the calibration procedure is used by the
microprocessor to calculate gain changes. As a result, the unit doesn’t care what the actual
ambient noise level is during calibration. However, the overall control range may be inadequate if
the noise level is too high during calibration.
Duringcalibration,runnormalprogramsignalsthroughthesystem.
This allows the SPL Computer to develop an acoustical performance history of the environment
based upon the type of material that will ordinarily be run through the system. No extra test
equipment is required for normal calibration. However, to set the system up for specific operating
levels, a noise source and SPL meter are needed.
Pre-installationConsiderations
Before installing the 572, be sure that you’ve considered the following items:
1. Ambient noise sources in the loudspeaker coverage area. Are there any noise sources
near any of the speakers used for sensing?
2. It is not necessary to use all speakers for sensing.
3. If the speakers are wired using the “home run” method1, then you’ll have extra flexibility in
excluding specific speakers from the speakers used for ambient sensing (if needed).
4. The speaker wiring should be separate from any AC or other EMI-noisy wiring. Neither
side of the wiring can be grounded, except at the amplifier.
5. Hornspeakers mayrequire modification ofthe 572,especiallyif theambient noise levelis high.
6. There can be no user adjustable level controls in the speaker lines.
7. Once calibrated, it is not permissible to alter the settings of any level controls that are
electricallylocatedafterthe572.
1 The home run method of wiring brings each speaker (or sometimes a subgroup of speakers) to the
amplifier on its own pair of wires. The usual method is to wire from speaker to speaker, which saves
wireattheexpenseofflexibility.

572
5
8. If there are multiple loudspeaker zones, there probably ought to be a separate 572 for each
zone.
9. If the poweramplifier is larger than300 watts (70-voltsystems),200 watts (8-ohmsystems),
or 100 watts (4-ohm systems), then the internal 5-amp relay can’t handle the load current.
You must use an external relay.
10. Itis good to knowthe minimum and maximumambient levels (dB SPL) thatthe system is
expected to handle. Of course, the sound system should be able to exceed the maximum
ambient by 3-6 dB (unless it’s in the design that the system can’t out-shout the crowd).
11. It’s preferable that the 572 mix the paging signals with the background music or other
signals internally through its separate paging and music inputs (as opposed to supplying
the572with a mix ofeverything). The 572 monitors itspaging inputs and immediately
terminates a sense period when a paging signal is present. This is not true for the music
input.
12. Loudspeakers from “alien” systems (sound systems located within the sensing zone of the
572, but not under control of the 572) can cause unwanted gain changes.
Connections
A drawing of a typical music with paging system is shown in below. Make all of the following
connections:
1. Pagingmicrophone(ormic-levelmixeroutput)tothe PAGE MIC XLRconnector.Remember
that mic or line paging sources duck the signal connected to the MUSIC input.
2. Line-level paging source (or other source) to the PAGE terminals on TB1. Remember that
mic or line paging sources duck the signal connected to the MUSIC input.
3. Background or foreground music source to the MUSIC terminals on TB1. Signals connected
to this input are ducked (attenuated) by signals present on either of the PAGE inputs.
4. SPL Computer output from TB1 to your sound system’s amplifier(s).
5. Your sound system’s amplifier output to the 572’s FROM AMP terminals on TB2.
6. The speaker output of the 572 to the sound system speakers in the controlled zone.
Figure 3-1. 572 generic hookup diagram.
Caution Failure to connect the 572 to the proper ac mains voltage may cause fire and/
or internal damage. There are no user serviceable parts inside the chassis. Refer all
service to qualified service personnel or to the factory.
Warning Lethalvoltagesarepresentinsidethechassis.Therearenouserserviceableparts
insidethechassis.Referallservicetoqualifiedservicepersonnelortothefactory.
TO/FROM HOUSE
SPEAKER SYSTEM
SPEAKER USED FOR
P.A AND SENSE
SPEAKER USED
FOR P.A.
DOES NOT SENSE
HOUSE
AMPLIFIER
TELEPHONE
SYSTEM BACKGROUND
MUSIC
PAGE
MICROPHONE
AC INPUT
18W MAXIMUM
POWER MIC
PAGE
MUSIC
PAGE
LINE INPUTS
OUTPUT
LINE
SPARE
TRIG
SENSE
EXT
CNTRL
RELAY
EXT
AMP
FROM
SPEAKER
TO
123456789011BT123456789012BT
Vc
THIS UNIT CONTAINS NO USER SERVICABLE PARTS.
FABRIQU AUX E.-U. PAR SYMETRIX INC., LYNNWOOD,WASHINGTON. É
R F REZ TOUTE R PARATION UNTECHNICIEN QUALIFI . ÉÉ É ÉÀ
UNITED STATES OF AMERICA
LYNNWOODWASHINGTON,
MANUFACTURED IN
FUSE
PRESS

572
6
Calibration Settings Table
Set the controls and switches on the front and rear panel as shown below.
FrontPanelControl Setting RearPanel Setting
BYPASSswitch out(NORM) OUTPUT Connectto poweramplifiers.
PAGE MIC gain 12:00o’clock PAGE MIC Connectbalanced, low-impedance
page microphone here.
SENSE GAIN switch out(HIGH) MUSICINConnectline-level musicsource here.
SAMPLEINTERVAL 8:00o’clock PAGE INConnect line-level paging source here.
PAGE OVER MUSIC 8:00o’clock
RATIO 12:00o’clock
LEVELSET MIN 9:00o’clock
LEVELSETMAX 8:00o’clock
OPTION switches Alldown
CalibrationChecklist
You initiate the calibration procedure by pressing the MODE switch once (from OPERATE mode).
Complete the following checklist before beginning the calibration procedure.
•Complete all input and output connections.
•Apply power to the 572.
•Verify that the unit passes signal in the BYPASS mode. Enter BYPASS mode by depressing the
BYPASS switch. Return the BYPASS switch to the OUT position. You should still have audio.
•Set Option switch B to the UP position (sense view). Observe the LED bargraph. There should
be at one LED on, up to a maximum of 7 LEDs on. If no LEDs are on, depress the SENSE GAIN
switch. Leave the switch in whatever position results in a reading between the first and last
LEDs in the bargraph.
•Set the front and rear panel controls as shown in Calibration Settings Table (previous page).
Caution The 572 resistively mixes its line inputs in Bypass mode. This can cause attenuation
whose amount depends upon the actual source devices as well as the amplifier(s)
connected to the unit’s outputs.
The 572 delivers unity gain when the output is operated unbalanced, and the gain
is +6 dB when the output is operated balanced.
Calibration Procedure
1. Apply program or paging signals to the 572’s input(s).
2. Press the MODE switch once to enter CALibration mode.
3. Using the 572’s LEVEL SET MIN control, adjust the control for the minimum desired
operating level when the LED bargraph indicator marked SET MIN flashes.
4. Using the 572’s LEVEL SET MAX control, adjust the control for the maximum desired
operating level when the LED bargraph indicator marked SET MAX flashes.
The 572 “listens” to the sound system for about 8 seconds at the minimum level (after it detects the last
adjustment of the MIN control), and then for about 8 seconds at the maximum level (after the last
adjustment of the MAX control). Then the microprocessor returns the unit to OPERATE mode under the
new calibration values.
When the calibration procedure is completed, the acoustic performance record of the room is placed in
nonvolatilememoryalongwiththeminimumandmaximumlevelsettings.Theunitwilloperateunder
these calibration settings until the calibration procedure is run again.
The calibration procedure may be run as many times as necessary. If for any reason the procedure is
interrupted before completion, the unit returns to operate mode under the previously stored values. If
the procedure is run to completion with no changes, the unit calculates the same values as it did under
the previous calibration procedure, and puts those new values into nonvolatile memory. Only when the
level set max or LEVEL SET MIN setting is changed does the unit put new operating values into memory.
You can force sensing by turning the sample interval control to 1 and then quickly returning it to 5.
You can also force sensing by using option switch D and TB2-3.

572
7
Front & Rear Panel OverviewChapter 4
Front Panel Overview
Feature Description
BYPASSswitch When depressed, resistively mixes the line level music and page inputs
and hardwires them to the output terminals. The 572 will pass signal
regardless of it’s operational status.
PAGE MIC GAIN trimpot Screwdriver adjust level control provides up to 26 dB attenuation of
signals from the page mic input.
SENSE GAIN switch Determines the gain of the sense preamp. When the switch has been
depressed, the sense preamp’s gain is 40dB higher. Use option switch B
to help you determine the correct setting for this switch.
SENSELED Indicates that the 572 is sensing the ambient conditions in the
controlledarea.
MUSIC/PAGELED Indicates that the 572 is in its music/page mode.
SAMPLEINTERVAL This control sets the time period between forced samples to compute
sound pressure level changes. If the 572 takes a silence-caused sample
during this time period, the sample interval timer is reset. If the incoming
program material has enough silent periods, forced sampling will never
occur. This control is disabled in external trigger mode.
PAGE OVER MUSIC Determines how much music signals are attenuated (ducked) during
paging,from0 to15dB.
RATIO:∆∆
∆∆
∆SENSE:∆∆
∆∆
∆OUTPUT Sets the ambient gain ratio: from 2:1 to 1:2. This determines whether the
572 makes a smaller change than the ambient (2:1) or a larger change
thantheambient(1:2).
GAIN LEDdisplay LED bargraph that indicates the amount of gain being added to the
sound system by the 572. In cal mode, the display serves as an error-
condition indicator and as a prompting device.
LEVEL SET MIN control Active only during calibration; sets the minimum operating level of the
sound system: from 0 to -20 dB.
LEVELSET MAXcontrol Active only during calibration; sets the maximum operating level of the
sound system: from 0 to +20 dB.
CALIBRATE switch Momentary switch alternates the 572’s mode from operate to calibrate.
Operate is the initial power-up state, and is indicated during use by the
LED display showing gain change and either the sense or music/page
LED being activated. Depressing the CALIBRATE switch once alternates
states to calibration mode as indicated by flashing SET MIN indicator
on the LED bargraph display.
OPTIONS DIP switch These four switches allow several of the 572’s operating parameters to
be adjusted.
OPTIONS
NORM
BYPASS LOW
HIGH
SAMPLE
INTERVAL (MIN)
014
PAGE OVER
MUSIC (dB)
2:1 1:2
STTPOUE:ENS
RATIO (dB) U
GAIN (dB)
BYPASS
4030915202625
PAGE/MUSIC
INPUT ERROR
10
15
200
MAX
MODE
-10
-5
0
-15
-20
MIN
5
LEVEL SET (dB)
CALIBRATE
SPL COMPUTER
572
ABCD
1234
PAGE
MIC
GAIN
BYPASS SENSE
GAIN
SENSE MUSIC/
PAGE
5
10 15
20
126

572
8
Rear Panel Overview
Feature Description
SERIAL NUMBER [Please send in the completed warranty card.]
ACPOWERINPUT Power cord. Connect only to appropriate AC power source. Refer to
rear-panelmarking for correct ACsourcevalue.
FUSE AC mains fuse. Replace only with same type of fuse, as noted on the
rear of the chassis. Domestic: 1/4A, 250V ac, fast blowing (Bussman
typeAGC-1/4)Export:1/8A,250Vac,fastblowing(BussmantypeGDA-
125mA).
PAGE MIC INPUT Balanced, mic level input for paging microphone. Phantom powering is
not present. If using a phantom powered microphone, ensure that the
phantom voltage does not exceed 15V. Higher voltages may be used if
the powering device contains blocking capacitors or isolation trans
formers to prevent the phantom supply voltage from appearing at the
micinputof the572.
AC INPUT
18W MAXIMUM
POWER
MIC
PAGE
MUSIC
PAGE
LINE INPUTS
OUTPUT
LINE
SPARE
TRIG
SENSE
EXT
CNTRL
RELAY
EXT
AMP
FROM
SPEAKER
TO
123456789011BT123456789012BT
Vc
THIS UNIT CONTAINS NO USER SERVICABLE PARTS.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
UNITED STATES OF AMERICA
LYNNWOOD WASHINGTON,
MANUFACTURED IN
FUSE
PRESS

572
9
Terminal Strip Connections
Feature Term.# Description
TOSPEAKER TB2(10,9) Connect speakers used for sensing and sound system
usage here. Speakers may be speaker impedance or
constant voltage.
FROMAMP TB2(8,7) Connectamplifierhere.Amplifieroutputmaybe
speaker impedance or constant voltage.
GROUNDS TB2(6,4,2) Connect to circuit ground inside the 572.
EXTRELAYCNTRL TB2(5) NPN open collector output for driving external relay.
Youmust supply power fortherelay coil. Remember
to connect a diode across the relay coil to absorb the
backEMFgenerated bytherelaycoil. Themaximum
voltage at this point is 40 V dc at 625 mA.
EXT SENSE TRIG TB2(3) Active low input. When option switch D is up,
grounding this terminal forces a sense operation. The
unit remains in sense mode for as long as this terminal
is grounded. The terminal must remain grounded for at
least one second in order to perform sensing.
SPARE TB2(1) Not used, not connected.
GROUNDS TB1(10,6,3) Connect to circuit ground inside the 572.
LINE OUTPUT TB1(9,8) Balanced (differential) outputof the 572.
For unbalanced usage, use TB1(9) and TB1(10).
TB1(8)shouldfloat.
VCTB1(7) Monitor point for the control voltage for the VCA.
The gain relationship is -159mv/dB. Use this voltage
to verify that the VCA is actually being told to change
the gain or to connect a stereo-slave unit.
PAGE INPUT TB1(5,4) Balanced line-level input for paging signals. Signals at
these terminals cause signals applied to the music
inputs to attenuate (duck). For unbalanced signals,
use TB1(5) for signal and connect TB1(6,4) to ground.
MUSICINPUT TB1(2,1) Balanced line-level formusicsignals.Normallyused
for background music. Signals applied to these
terminals are attenuated (ducked) whenever signals
are present at either of the page inputs.

572
10
572 Basics Chapter 5
An SPL computer periodically samples the ambient sound in a room. Having this information, the
SPL computer uses a combination of historical data and information stored during the unit's initial
calibration to determine the optimum gain setting for the sound system.
How Does It Work?
The 572 uses the combination of analog circuitry and digital circuitry under the control of a
microprocessor. The microprocessor excels at following a set of instructions and making decisions.
Since really high-performance digital audio circuitry is still quite expensive, the 572 uses a record-
ingstudio-qualityvoltage-controlled-amplifier(VCA) tocontrolaudiolevels.
In operation, the 572 monitors its input signals for silence. Anytime that silence occurs (an option
switch allows changing the silence threshold), the 572 switches to sense mode. In sense mode, the
572 reduces the amplifier input by at least 30 dB, the loudspeakers are disconnected from the power
amplifier and connected to a high-gain differential amplifier (which cancels the hum and other junk
picked up by the unshielded speaker wires). The 572’s microprocessor monitors the output of the
sense preamp and compares that signal to the calibration conditions stored in the 572’s parameter
storage RAM, and at the last sample period. Based on this information and the front-panel set-
tings, the 572 decides how loud the sound system must operate to restore audibility.
The 572 also has an internal timer, controlled by the front-panelSAMPLE INTERVAL control that
forces a sample if there haven’t been any silent periods in the input signal. Anytime that the input
signal causes a sample period, the timer resets. If the input material has sufficient silent periods,
the timer-generated sample periods never occur.
In CAL mode, the 572 acquires a history of the environment’s sonic behavior. The 572 takes three
measurements: the environment's minimum level, the sound system's minimum level, and the sound
system’s maximum level. By running the system for about 8 seconds at the desired minimum and
maximum sound pressure levels, the microprocessor remembers these three key performance
parameters,which areautomatically storedinnonvolatile memory.
Duringcalibration, theinstaller sets minimumand maximumlevels-the 572“reads”the controlsas
they are changed, and stays in the appropriate calibration mode for about 8 seconds after the last
change is made. This allows the installer time to reset operating levels as necessary.
When the system switches itself back to operate mode, the acoustical performance history
acquired during calibration becomes the baseline for gain change decisions. In operate mode, the
system goes about measuring environmental noise levels and internal signal levels. Because the
computer has already committed to memory the parameters stored during calibration, it is able to
predict the gain setting required.
What About the Sensing Microphone?
Microphone? What microphone? The 572 doesn’t use sensing microphones. It does use the sound
system’s loudspeakers as microphones during sensing . There aren’t many constraints on your
choice of loudspeakers. Horn-type speakers are more directional as well as being highly efficient
(both as speakers and as microphones). We have found that planar-type speakers do not work well
as microphones. Internally, the sense signal drives a bandpass filter (A-weighting approximation)
before the 572 measures its level (strength).

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Where Should I Put the Sensing Microphone?
The sensing microphone needs to “hear” the ambient sound within the controlled space. In large
spaces it may be better to only use a few of the sound system speakers for sensing. In the remain-
der of this manual, we’ll use the term “sensing speaker” to mean a speaker that is connected to the
572’s TO SPEAKER terminals that is used during sensing periods as a microphone.
Where Shouldn’t I Put the Sensing Speaker(s)?
Avoid the following situations:
• Placing the sensing speaker(s) where it is within the noise field of a machine or other noise
source, unless you want the source’s noise contribution to more or less control the level
of the sound system. For example, how about a speaker in a newspaper plant near one of
the printing press(es).
• Placing the sensing speakers where they always hear a nearby noise source. For instance,
how about a shopping mall near the kiddie area. You can work around this by connecting
these speakers to the TO AMP terminals so that they aren’t used for sensing.
What Does the Ratio Control Do?
The RATIO control acts much the same as the ratio control on a compressor or expander: it affects
the amount of change at the output for a given change at the input. In the 572, the RATIO control
determines how much the output changes for a given change at the sense input. In the 12:00
position, the ratio is 1:1; a 1 dB sense change results in a 1 dB output change. Turning the RATIO
control clockwise results in expansion: in the 1:2 position (full CW), a 2 dB change at the sense
input results in a 4 dB output change. Turning the RATIO control counterclockwise results in
compression: in the 2:1 position, a 2 dB sense input change results in only a 1 dB output change.
Use the RATIO control when you either want the 572 to more than keep up with the crowd (expan-
sion), or when you want it to lag behind when the crowd is loud (compression). Another reason to
use “compression” might be when the available amplifier power is limited. Last, you must decide
whether or not you want the sound system to be capable of “out-shouting” the crowd.
Remember
• Calibration must occur when the noise level in the controlled space is at it’s normal
minimum(which may ormay notbe dead quiet).
• Ithelps ifyou havean estimate(SPL) ofthe maximumlevel required.
• The sound system must be capable of attaining the maximum level required.
• You can learn a great deal by listening to the sensing speakers. You’ll need an external
microphone preamp to do this.
• You may need to create a second non-controlled zone to prevent the sound system level
from changing in spaces where the ambient conditions are stable (rest rooms, elevators,
breakrooms,etc.)

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Technical Tutorial
Matching Levels vs Matching Impedances
In any audio equipment application, the question of “matching” inevitably comes up. Without
digging a hole any deeper than absolutely necessary, we offer the following discussion to (hope-
fully) clarify your understanding of the subject.
Over the years, we have all had impedance matching pounded into our heads. This is important
only for ancient audio systems, power amplifiers, and RF. Technically speaking, the reason is
power transfer, which reaches a maximum when source and load are matched. Modern audio
systems are voltage transmission systems and source and load matching is not only unnecessary,
but undesirable as well.
Ancient audio systems operate at 600 ohms (or some other impedance value), and must be
matched, both at their inputs and at their outputs. Generally speaking, if you are dealing with
equipment that uses vacuum tubes, or was designed prior to 1970, you should be concerned about
matching. These units were designed when audio systems were based on maximum power transfer,
hence the need for input/output matching.
Power amplifiers are fussy because an abnormally low load impedance generally means a visit to
the amp hospital. Thus, it’s important to know what the total impedance of the pile of speakers
connected to the amplifier really is.
RF systems are matched because we really are concerned with maximum power transfer and with
matching the impedance of the transmission line (keeps nasty things from happening). Video
signals (composite, baseband, or otherwise) should be treated like RF.
Some folks seem to believe that balanced/unbalanced lines and impedances are related; or even
worse that they are associated with a particular type of connector. Not so. Unbalanced signals are
not necessarily high-impedance and balanced signals/lines are not necessarily low-impedance.
Similarly,although 1/4-inchjacks aretypically usedfor thingslike guitars(which arehigh-imped-
ance and unbalanced), this does not predispose them to only this usage. After all, 1/4-inch jacks
are sometimes used for loudspeakers, which are anything but high-impedance. Therefore, the
presence of 3-pin XLR connectors should not be construed to mean that the input or output is low-
impedance (or high-impedance). The same applies to 1/4-inch jacks.
So, what is really important? Signal level, and (to a much lesser degree), the impedance relation
between an output (signal source) and the input that it connects to (signal receiver).
Signal level is very important. Mismatch causes either loss of headroom or loss of signal-to-noise ratio.
Thus, microphone inputs should only see signals originating from a microphone, a direct (DI) box, or an
output designated microphone-level output. Electrically, this is in the range of approximately -70 to -20
dBm.Lineinputs should only seesignals in the -10 to+24 dBm/dBu range. Guitars, high-impedance
microphones, and many electronic keyboards do not qualify as line-level sources.
The impedance relation between outputs and inputs needs to be considered, but only in the following way:
Alwaysmakesurethatadevice’sinputimpedanceishigherthantheoutputsourceimpedanceof
thedevicethatdrivesit.
Some manufacturers state a relatively high-impedance figure as the output impedance of their
equipment. What they really mean is that this is the minimum load impedance that they would like
their gear to see. In most cases, seeing an output impedance figure of 10,000 (10K) ohms or higher
from modern equipment that requires power (batteries or AC) is an instance of this type of rating. If
so, then the input impedance of the succeeding input must be equal to or greater than the output
impedance of the driving device.
Symetrix equipment inputs are designed to bridge (be greater than 10 times the actual source
impedance) the output of whatever device drives the input. Symetrix equipment outputs are
designed to drive 600-ohm or higher loads (600-ohm loads are an archaic practice that won’t go
away). You don’t need to terminate the output with a 600-ohm resistor if you aren’t driving a 600-
ohm load. If you don’t understand the concept of termination, you probably don’t need to anyway.
Chapter 6

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The two facts that you need to derive from this discussion are:
1. Match signal levels for best headroom and signal-to-noise ratio.
2. For audio, impedance matching is only needed for antique equipment and power amplifier
outputs. In all other cases, ensure that your inputs bridge (are in the range of 2 to 200 times the
output source impedance) your outputs.
Signal Levels
The 572 is designed around studio/professional line levels: +4 dBu or 1.23 volts. The unit is quiet
enough to operate at lower signal levels such as those found in semipro or musical-instrument (MI)
equipment(-10dBVor316millivolts).
I/O Impedances
The 572 is designed to interface into almost any sound reinforcement application or background/
foreground music application. This includes:
1. 600-ohm systems where input and output impedances are matched.
2. Unbalanced semiprofessional equipment applications.
3. Modern bridging systems where inputs are bridged and outputs are low source impedances
(voltage transmission systems).
The 572’s line input impedance is greater than 40k Ohms balanced, and greater than 40k Ohms
unbalanced. The inputs may be driven from any source (balanced or unbalanced) capable of
delivering at least -10 dBV into the aforementioned impedances.
XLR Polarity Convention
The 572 uses the international standard polarity convention of pin 2 hot. The following chart shows the
connections for each type of connector:
Input and Output Connections
Appendix B illustrates how to connect the 572 to various balanced and unbalanced sources.
To operate the 572’s balanced line inputs from unbalanced sources, run a 2-conductor shielded cable
(that’s two conductors plus the shield) from the source to the 572. At the source, connect the low/minus
side to the shield, these connect to the source’s ground; connect the high/plus side to the source’s
signal connection. At the 572, the high/plus wire connects to the screw terminal marked with a “+”, the
low/minus wire connects to the screw terminal marked with a “—”, and the shield (always) connects to
screw terminal marked GND. This is preferred as it makes best use of the 572’s balanced input (even
though the source is unbalanced). The other alternative shown in Appendix B converts the 572’s
balanced input into an unbalanced input at the 572’s input terminals. This works, but is more suscep-
tible to hum and buzz than the preferred method. There is no level difference either way.
We do not recommend unbalancing the 572’s microphone inputs. Doing so makes these inputs
considerably more susceptible to hum and induced noise.
XLR Tip-Ring-Sleeve Signal
1 Sleeve Ground
2 Tip High
3 Ring Low

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Condenser Microphones and the 572
The 572’s paging microphone input is not equipped with phantom powering for condenser micro-
phones. If you wish to use a phantom powered microphone you must provide a power source exter-
nally.
Note The microphone input is direct coupled: there are no dc blocking capacitors. If you use a
phantom powered microphone, the phantom supply voltage must be 15 volts or less. ( 15 volts
isthecommon-modelimitationofthemicrophonepreamp.)Ifyourparticularmicrophone
operates at a higher supply voltage than 15 volts the phantom power supply must dc-block its
output using capacitors or a transformer.

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This section is intended for more advanced users. If you are a first-time user, we recommend that
you start out by using the procedure found in Chapter 3, “Setup.”
Installation
The 572 may be installed freestanding or rack- mounted. Multiple unit installations require no
additional breathing space between units.
InstallationRequirements
Mechanical One rack space (1.75 inches) required, 12.5 inches depth
(includingconnector allowance).
Electrical 105-125VAC,18Wattsmaximum.
Connectors Female XLR connectors and screw terminals for inputs. Pin 2 of the XLR
connectors is “Hot.” Screw terminals for outputs and other connections.
Block Diagram
On the following page you will find the block diagram for the 572. Please take a moment and take
note of the following:
• The balanced input amplifiers (mic and line) are direct coupled. This is only noteworthy if there
is significant common-mode dc voltages present on the signal lines (greater than 15V).
Phantom powering for condenser microphones falls into this category.
• The EXT RELAY CNTRL terminalis the opencollector of a2N4401 NPN transistor .You must
supply power for any external relay used. The transistor’s limits are: VCEO = 40V
and Icmax = 625 mA.
• In when the BYPASS switch is pressed, the line-level MUSIC and PAGE inputs are resistively
mixed and sent to the outputs. There is no automatic hard-wire bypass in the event of a power
failure.
• Paging signals (mic and line) are mixed and drive the ducker (PAGE OVER MUSIC)circuitry.
• The EXT SENSE TRIG input is not edge driven. The 572 remains in sense mode as long as this
input is held low.
• Option switch B switches the LED bargraph to read the output of the sense preamplifier and
forces the 572 into sense mode. This allows you to make sure that you have enough signal
level for proper ambient sensing. The correct reading is more than one LED lit and less than all
LEDs lit under all ambient conditions. The sense gain switch located on the front panel
changes the gain of the sense preamp. Use either setting as long as the LED bargraph reads as
describedearlier.
The relay contacts used to switch the speakers to and from sense have a 5 ampere rating. If your
load requires more current than this, use the EXT RELAY CNTRL terminal (TB2-5) to control an
externalhigh-currentrelay.
Chapter 7 Using the 572

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OperatingFormat
The 572 has three operating modes: OPERATE, CALIBRATE, and BYPASS. You access these modes by
sequentially operating the MODE switch or by pressing the BYPASS switch. Each push of the mode
switch toggles the operating mode between CALIBRATE and OPERATE.
Bypass, Calibrate and Error Indicators
The front-panel LED bargraph also serves as a status
indicator. Two of the LEDs serve as prompts during
calibration, one other LED serves as an error indicator
duringcalibration.
If the error indicator flashes during calibration, the calibra-
tion procedure automatically aborts and the 572 returns to
operate mode using the calibration values previously
stored in nonvolatile memory. The 572 cannot be
recalibrated until the problem causing the error is corrected.
Options, Options, Options
The 572 has many operational options, mostly controlled by a 4-wide DIP switch located on the
front panel. The microprocessor scans the switches continuously; any changes in their settings
are acted upon almost instantaneously.
The four option switches set the music silence threshold level, sense view (displays sense level on
front panel bargraph), ambient sample averaging, and external sense control.
REV-B
LINE
OUTPUT
MICROPROCESSOR
D/A
CONVERTER
PUSHBUTTON
MODE
OPTIONS
+5V
1 2 3 4
PAGE
INPUTS
MUSIC
INPUT
2
3
LINE
1
TB1
PAGE
DETECTOR
4
5
6
LINE
PAGE MIC
TB1
P R E S S
PAGE MIC
GAIN
TB2
EXT SENSE
TRIGGER
JP2-A.G.C.
THRESHOLD
3 2
B A
+5V
+5V
OUT
7
Vc
2 9 5 1 5 20 2 5 3 0 4 0
RATIO
MULTIPLEX AND A/D CONVERTER
MUSIC
VCA
MUSIC
BYPASS
JP1
VCA
TB1
A B
+5V
PAGE OVER
"GAIN" DISPLAY
SAMPLE
INTERVAL
MIN MAX
GAIN
SENSE
HARDWARE BYPASS
9
8
0 1
TB1
EXTERNAL
RELAY
CONTROLL
5
4
TB2
FROM
SPEAKER
7
0
8
9
1
AMP
TO
TB2
VCA
Figure 7-2 LED Bargraph
Figure 7-1. 572 Block Diagram.
T
GAIN (dB)
BYPASS
4030915202625
PAGE/MUSIC
INPUT ERROR

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Calibration
Calibration must be performed when the ambient noise in the loudspeaker coverage area is at its
normalminimum level forthe area.(NOT dead quiet,unless thatis normal.)
1. Complete all input and output connections. There must be program audio present at a
LINE INPUT connection before calibration can be completed. If the system is used for
paging, activate the paging system by having an assistant count or recite the alphabet
during the entire calibration procedure. The audio input level must be greater than -35 dBu
or the 572 will not recognize the presence of audio and the MUSIC/PAGE ERROR light will
flash.
2. Warn any people present that sound system may get momentarily loud.
3. Set the front panel controls as described in Calibration Settings Table (previous page).
4. Verify that program audio is audible in the system speakers.
5. Set the system power amplifier’s volume control to a comfortably loud level. Do not
readjust this control after calibration of the 572 or your calibration will be invalid.
6. Set the BYPASS switch to the OUT position.
7. Use a pencil to push the CALIBRATE button in and then release it.
8. The red MIN lamp lights. Adjust the MIN CALIBRATE knob to a comfortable listening level.
The system audio level will stay at this level for 10 seconds. This level is the minimum
level that the 572 allows in the space, regardless of how quiet the ambient noise level may
be or get.
9. When the red MAX lamp lights adjust the MAX CALIBRATE knob to set the system level to
as loud as you ever want the volume to go during noisy times. Check that the power
amplifier(s) aren’t clipping. The system audio level will return to normal in 10 seconds. It
may be helpful to monitor the acoustical level in the space with a sound level meter.
10. Calibration is complete. The 572 will adjust the system level as the ambient noise in the
area increases.
Quick System Test
• While talking loudly or making noise near a system speaker turn the SAMPLE INTERVAL
control to “1” and then quickly return it to “5”. This forces the system to sense. The
system level should increase in response to the increase in ambient noise.
• While remaining quiet, turn the SAMPLE INTERVAL control to “1” and then quickly return it
to “5”. This forces another sense. The system level should return to the minimum level.
Options, Options and More Options
The option switches allow tailoring the 572 to different installation scenarios. There are four option
switches.
Option A sets the music silence threshold. This threshold is the signal level at the MUSIC LINE
INPUT that the 572 considers silent. Signals below this threshold are considered silent, and are fair
game for sense intervals. In installations where the ambient noise level is fairly low, and where the
background music has a great deal of dynamic range (like classical music from a CD player), you
may need to keep the signal level through the 572 quite high, as well as using the lower silence
threshold, and reducing the gain at the power amplifier input to put the music back to a comfortable
level. This prevents the 572 from punching holes in the program material during quiet passages.
Option B forces the 572 to sense mode and displays the output of the sense preamplifier on the
front-panel bargraph. Use option B to view the signal level returned from the loudspeakers in sense
mode and to verify that the signal level falls within the 572’s limits for proper operation. The ideal

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indication should fall between the 5 dB and 26 dB LEDs on the calibration display. If necessary,
use the SENSE GAIN switch on the front panel. Don't leave SENSE VIEW engaged as it prevents
normaloperation!
Option C enables sample averaging. If option switch C is down, the 572 computes the gain change
solely on the basis of the current sample. If option switch C is up, the 572 computes the gain
change based on the average of the current sample and the running average level (the 572 then
squirrels away the new average for the next sample period).
Option D enables the EXTERNAL SENSE feature accessed from TB2-3 on the rear panel. Use this
feature as described in Appendix B of the manual, or to force a sense period based on an external
contact closure (sense triggering occurs when TB2-3 is connected to TB2-4/ground). The 572
remains in sense mode for the duration of the contact closure. This option also disables the
SAMPLE INTERVAL timer and the 572 will only enter sense mode when TB2-3 is grounded.
OptionSwitchA SILENCETHRESHOLD UP -20dBu
DOWN -35dBu
OptionSwitchB SENSEVIEW UP Enabled
DOWN Disabled
OptionSwitchC SAMPLEAVERAGING UP Running Average
DOWN No Average
OptionSwitchD EXTERNALSENSE UP Enabled
DOWN Disabled
What Could Go Wrong?
Here are the two most common situations and some things to look for.
TheredMUSIC/PAGElampflashesduringcalibration:
1. There is no audio at the LINE INPUT from the program source. In a Paging Only system there
must be a page in progress during the entire calibration procedure.
2. The audio input level to the 572 is too low. With the OPTIONS dip switch “A” in the up
position the input level must be greater than -20 dBu. If the switch is in the down position the
input level must be greater than -35 dB.
3. There are no speakers connected to terminals 9 and 10, TOSPEAKER. The 572 uses the system
speakers as microphones when sensing.
The572doesnotaccuratelyadjustthesystemlevelasambientnoisechanges:
1. Repeat thecalibration procedure.Calibration mustbe madeduring timesof minimum
background noise or the minimum system level will be inaccurate.
2. If the maximum level was set too high during calibration the system will get too loud as the
background noise level increases.
3. If the maximum level was set too low the system will not be loud enough when the ambient
noise level reaches its peak.
4. Ensure that all speakers are operating in-phase.