Symetrix 571 SPl User manual

571
571 SPL Computer
Users Guide

i
Table of Contents
Rev C.00, 24 March, 1999
Symetrix part number 53571-0C00
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.
571
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 5 571 Basics 9
Chapter 6 Technical Tutorial 11
Chapter 7 Using the 571 14
Chapter 8 Applications 16
Chapter 9 Troubleshooting 18
Chapter 10 Specifications 19
Chapter 11 Warranty & Service 20
Appendix A Calibration: Special Cases 22
Appendix B Stereo Slave Operation 23
Appendix C Connections 24
Appendix D Declaration of Conformity 25

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1
IntroductionChapter 1
The Symetrix 571 is an ambient noise sensing automatic level controller or SPL computer.
The 571 uses one or two sensing microphones, located in the coverage zone of the sound system,
to continuously sample the loudness of ambient sounds.
The 571s microprocessor, running proprietary embedded software, computes how loud the sound
system should be, based on the current ambient conditions measured by the sensing
microphone(s). The gain computation uses a combination of the current ambient environment and
experience gained during the units on-site calibration procedure. The 571 adds or subtracts
enough gain to operate the sound system at the computed level.
Semiautomatic calibration makes the 571 very easy to set up. The calibration procedure requires no
test equipment and typically takes less than one minute. Internal nonvolatile memory stores the
calibration parameters until they are changed, and the memory will survive indefinitely in the
absence of AC power. Once calibrated, the 571 predicts how the environment should respond
under all possible operating conditions. The SPL computers proprietary software allows the 571 to
differentiate between environmental noise and music/paging signals.
Calibrate the SPL computer and its associated sound system when the room is at its quietest.
Pressing the mode switch tells the microprocessor to begin the calibration routine. When the SET
MIN indicator flashes, use the LEVEL SET MIN control to set the sound systems minimum output
level. When the SET MAX indicator flashes, use the LEVEL SET MAX control to set the sound
systems maximum operating level. The SPL computer puts those settings into memory along with
their respective SPLs, then returns the unit to normal operating mode.
The 571 also includes a mic-level paging input, a balanced line-level paging input, a balanced input
for background or foreground music, and page-over music capability (music ducking).
A multi-segment LED bargraph indicates the internal gain of the 571 during operation and serves as
a prompting device during calibration.
The inputs of the 571 are a combination of XLR connectors and screw terminals. The output
connections are also screw terminals. All audio inputs and outputs are balanced. Mic-level inputs
(sensing and paging) accept 150 Ohm balanced sources. Line-level inputs are 10k Ohm balanced
bridging, +4 dBu signal level.
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
SPL COMPUTER
571
AC INPUT
15 WATTS
MAX.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
LYNNWOOD, WA, USA
MANUFACTURED IN
PAGE MIC
FORMAT
MUSIC
PAGE
SENSE MIC 2
MUSIC IN
GND
IN
Vc
GND
HOUSE PAGE
1
2
3
4
5
76
8
9
SENSE MIC 1
GND
GND 50K LIN
REMOTE GAIN TRIM
10
TB1
1
2
3
654
CIR
GND
7
TB2
GND
CHAS OUTPUT
CALIBRATE
SENSE INPUT
ERRORINPUT ERROR
SPL COMPUTER
571
POWER
10
15
MAX
200
MODE
-10
-5
0
-15
-20
30 4020159 26
GAIN (dB)
MIN
LEVEL SET (dB)
5
+5
52
+10
TUP
-5
TUO:ESNERATIO (dB)
1:1
-10
1:2
2:1
0
GAIN TRIM (dBr)
OUTPUT
BYPASS
S
7
MUSIC (dB)
PAGE OVER
14
0
TIME
32
1.5
AVERAGING
4
5
MIN
1.2
60
30
SEC
SENSE SENSE
12
PAGE
MIC
PAGE/MUSIC

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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.

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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 571.
Caution Identifies information that, if not
heeded, may cause damage to the
571 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 571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
important operating 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
essential for safe operation. Do not defeat the
safetypurpose ofthe groundingplug. 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.
Danger from Loss of Ground If the protective
ground connection is lost, all accessible conduc-
tive parts, including knobs and controls that may
appear to be insulated, can render an electric
shock.
Proper Power Cord Use only the power cord and
connector specified for the product and your
operating locale. Use only a cord that is in good
condition.Protect thepower cordfrom being
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 IEC AC inlet connector. The fuseholder
accepts5 x20mm diameter fuses. For 117VAC
operation, the correct value is 0.25A, 250VAC,
standard. For 230VAC operation, the correct
valueis 0.125A, 250VAC,standard.
OperatingLocation Do notoperatethis equip-
mentunder anyofthe followingconditions:
explosive atmospheres, in wet locations, in
inclement weather, improper or unknown AC
mains voltage, or if improperly fused. 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.
Stay Out of the Box To avoid personal 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-serviceable parts There are no user
serviceable parts inside the 571. In case of failure,
refer all servicing to the factory. Servicing is
required when the 571 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.

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4
Setup Chapter 3
Place the 571 in the signal chain as the final level controlling device. It is imperative that any gain
or level controls used in the signal chain after the 571 remain unchanged once the unit has been
calibrated. This includes wall mounted autoformer and L-pad speaker-level controls used for zone
balancing.
Equalizers following the 571 are acceptable IF their controls (both EQ and level) will not be
changed after calibration.
Level controls in the signal chain before the SPL Computer are acceptable, because the unit
reads input level changes. Note that the 571 is equipped with a remote-controllable output gain
trim control that provides overall level control. This is discussed in greater detail in Chapter 5.
The rear panel format (page/music) switch must reflect how the unit will be used. The 571 must be
calibrated in the same conditions in which it will be used. Erratic operation results from calibrating
the unit with this switch in the wrong position.
Music and Paging - When the system will be used for both foreground/background music and
paging, set the FORMAT switch to MUSIC mode.
Paging only - When the system will be used for paging only, set the FORMAT switch to PAGE mode.
In this mode, the music input is disabled.
Calibrate the 571 when ambient noise is at its lowest level. Lowest level means the ambient
noise level that is the minimum for that particular environment, no matter what the actual level may
be.
The ambient noise level measured by the 571 during the calibration procedure is used by the
microprocessor as a baseline for calculating gain changes. Thus, the ambient level in the controlled
space should be at a normal minimum level. If the ambient noise level is too high during calibration,
the overall control range may be inadequate. For additional information, refer to Appendix B.
During calibration, run normal program signals through the system. 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. For additional information, refer to Appendix B.
Connections
A drawing of a typical music with paging system is shown in Figure 3-1 on the next page. Make all
of the following connections:
1. One or more sensing microphones to the SENSE MIC 1 and SENSE MIC 2 XLR connectors. For
most installations, only one mic is needed.
2. Paging microphone (or mic-level mixer output) to the PAGE MIC XLR connector.
3. Line-level paging source (or other source) to the HOUSE PAGE INterminals on TB1.
4. Line-level music source to the MUSIC INterminals on TB1.
5. SPL Computer output from TB1 to your sound systems amplifier(s).
6. Ensure that TB2-3 and TB2-4 are bridged (connected), or that a remote gain pot is connected.
7. Ensure that TB2-1 and TB2-2 are bridged (connected), or that a remote gain pot is connected.
Caution Failure to connect the 571 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 Lethal voltages are present inside the chassis. There are no user serviceable parts
inside the chassis. Refer all service to qualified service personnel or to the factory.
Connect the AC input to an AC power source of the proper voltage and frequency, as marked on
the rear of the unit.

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5
Figure 3-1. 571 generic hookup diagram.
FUSE
1/4 AMP (220/240VAC)
1/2 AMP (117VAC)
MANUFACTURED BY SYMETRIX INC, SEATTLE, WA, USA
THIS PRODUCT CONTAINS NO USER SERVICABLE PARTS
S/N
CIR
GND
ON
OFF
POWER
FUSE:
50K LIN
REMOTE GAIN TRIM
GND
CHAS
GND
SENSE MIC 2
MUSIC IN
GND
OUTPUT Vc
GND GND
HOUSE PAGE
IN FORMAT
PAGE
MUSIC
SENSE MIC 1 PAGE MIC
PRESS PRESS PRESS
710TB2 TB169584736251 432 1
TO HOUSE
SPEAKER SYSTEM
TO SENSING
MICROPHONES
HOUSE
AMPLIFIER
TELEPHONE
SYSTEM BACKGROUND
MUSIC
PAGE
MICROPHONE
Settings
Set the controls and switches on the front and rear panel as shown in Table 3-2.
Table 3-2. Front and rear panel control and switch settings.
Front Panel Control Setting Rear Panel Connection or Setting
PAGE MIC trimpot 12:00 oclock OUTPUT Connect to power amplifiers.
SENSE 1 AND 12:00 oclock SENSE INPUTS Connect balanced, low-impedance
SENSE 2 trimpots sensing microphones.
AVERAGING TIME 8:00 oclock PAGE MIC Connect balanced, low-impedance
page microphone.
PAGE OVER MUSIC 8:00 oclock MUSIC INConnect line-level music source.
RATIO 12:00 oclock HOUSE PAGE INConnect line-level paging source.
OUTPUT GAIN TRIM 12:00 oclock FORMAT Switch OUT
LEVEL SET MIN 9:00 oclock
LEVEL SET MAX 8:00 oclock

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6
CalibrationChecklist
Initiate the calibration procedure by pressing the MODE switch once (from OPERATE mode). The
rear-panel FORMAT switch sets the overall control format.
Note The format switch must be in the proper position for calibration.
Complete the following checklist before beginning the calibration procedure.
1. Complete all input and output connections.
2. Verify that the unit passes signal in the BYPASS mode. Enter BYPASS mode by pressing the
MODE switch twice, from OPERATE mode. Press the MODE switch once more to return to OPERATE
mode.
3. Set the FORMAT switch to the proper position.
 In PAGE mode, the calibration procedure cannot be completed without normal level
paging signals at either the PAGE MIC input or the HOUSE PAGE input.
 In MUSIC mode, the calibration procedure cannot be completed without normal level
signals at the MUSIC INor PAGE INline inputs, or at the PAGE MIC input.
4. Connect at least one sensing mic. Be sure to turn it on if it has a switch.
5. Set the front panel controls as shown in Table 3-2.
6. Set the rear panel controls as shown in Table 3-2.
Caution The OUTPUT GAIN TRIM control is ignored during calibration. When calibration is
completed and the unit returns itself to OPERATE mode, the output level reflects the
setting of this control.
When the unit is put into BYPASS mode, the unit ignores the setting of the OUTPUT
GAIN TRIM control. If, for example, it is set for reduced gain, the overall gain returns
to unity when the unit goes into BYPASS mode.
The 571 delivers unity gain when the output is operated unbalanced, and the gain
is +6 dB when the balanced output is used.
Calibration Procedure
1. Press the MODE switch once to enter CALIBRATION mode.
2. Using the 571s LEVEL SET MIN control, adjust the control for the minimum desired operating
level when the LED bargraph indicator marked SET MIN flashes.
3. Using the 571s LEVEL SET MAX control, adjust the control for the maximum desired operating
level when the LED bargraph indicator marked SET MAX flashes.
The 571 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 nonvolatile memory along with the minimum and maximum level settings. The unit will
operate under 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, and the 571 is
recalibrated, does the unit put new operating values into memory.

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7
Front & Rear Panel OverviewChapter 4
PAGE MIC Trimpot - Screwdriver adjust level control provides up to 26dB attenuation of signals
from the page mic preamp. This control does not affect the House Page input. This control is
always active, regardless of the 571s operating mode.
SENSE MIC 1 Trimpot - Screwdriver adjust level control provides up to 40dB attenuation of
signals from the sense mic1 preamp. This control is always active, regardless of the 571s operat-
ing mode. Do not adjust this control after calibration.
SENSE MIC 2 trimpot - Screwdriver adjust level control provides up to 40dB attenuation of signals
from the sense mic2 preamp. This control is always active, regardless of the 571s operating mode.
Do not adjust this control after calibration.
AVERAGING TIME Control - Sets the time period, in seconds or minutes, used by the 571 for
averaging sound pressure level changes: from 1.2 seconds to 5 minutes. Also affects the time
required to change the SPL to its newly computed value.
PAGE OVER MUSIC control - Determines attenuation applied to music signals during paging
announcements: from 0dB to -14dB.
RATIO ∆SENSE: ∆OUTPUT Control - Sets the ambient/gain ratio: from 2:1 to 1:2. This deter-
mines whether the 571 makes a smaller gain change than the ambient level(2:1) or a larger gain
change than the ambient level(1:2).
OUTPUT GAIN TRIM control - Provides manual adjustment of overall output gain over a 20 dB
range, at any time. This control may be remotely located, which disables the front panel output
gain control.
GAIN (dB) display - LED bargraph that indicates amount of gain being added to the sound system
by the 571. In calibrate 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 -20dB.
LEVEL SET MAX control - Active only during calibration; sets the maximum operating level of the
sound system: from 0 to +20dB.
MODE switch - Switches the 571s operating mode sequentially between Operate mode, Cal mode
and Bypass mode, in that order.
Cal mode is indicated by the flashing Set Min or Set Max indicators in the bargraph display.
Bypass mode is indicated by the flashing bypass LED in the bargraph display.
Operate mode is indicated by the absence of flashing indicators; in this mode, the bargraph display
shows gain change.
POWER LED - Indicates presence of AC power.
CALIBRATE
SENSE INPUT
ERRORINPUT ERROR
SPL COMPUTER
571
POWER
10
15
MAX
200
MODE
-10
-5
0
-15
-20
30 4020159 26
GAIN (dB)
MIN
LEVEL SET (dB)
5
+5
52
+10
TUP
-5
TUO:ESNERATIO (dB)
1:1
-10
1:2
2:1
0
GAIN TRIM (dBr)
OUTPUT
BYPASS
S
7
MUSIC (dB)
PAGE OVER
14
0
TIME
32
1.5
AVERAGING
4
5
MIN
1.2
60
30
SEC
SENSE SENSE
12
PAGE
MIC
PAGE/MUSIC

571
8
Serial Number - Write this number down somewhere safe, and please send us the completed warranty card.
AC POWER INPUT - Power cord. Connect only to appropriate AC power source. Refer to rear-
panel marking for correct AC source value.
TB2-7 - Circuit ground. Connects to the internal power supply ground.
TB2-6 - Chassis ground. Connects to the chassis of the 571. TB2-6 and TB2-7 are connected via a
10 Ohm resistor in parallel with a 0.01 mfd capacitor.
TB2-5 to TB2-1 - Remote gain trim connections.
Normal usage: Strap TB2-1 to TB2-2 and TB2-3 to TB2-4.
Remote usage: Remove strap between TB2-1 and TB2-2. Remove strap between TB2-3 and TB2-4.
Connect a 50k Ohm, linear-taper potentiometer to TB2-2 (high side), TB2-4 (wiper), and TB2-5 (low
side/ground). Be sure to connect the case of the potentiometer to TB2-5 as well. Up to 250 feet of
2-conductor shielded cable may be used to connect the remote gain control. The front-panel
control is disabled by these connections.
TB1-10 to TB1-8 - Balanced output connections.
TB1-7 - Control voltage. This connection is the gain control voltage applied to the VCA. The
scaling is: 155 mv/dB.
TB1-6 to TB1-4 - HOUSE PAGE Input. This is a balanced line-level input to the page side of the 571.
TB1-3 to TB1-1 - Music Input. This is a balanced line-level input to the music side of the 571. If
the Page Over Music control is turned up, signals applied to either the House Page input or to the
Page Mic input attenuate signals applied to the Music input.
FORMAT PAGE/MUSICswitch - Determines the format of the 571. In page mode, the music input
is disabled.
For systems that are used for paging only, set this switch to the in position.
For systems that are used for both music and paging, set this switch to the out position.
SENSE MIC 2 - Low-impedance, balanced input for the #2 sensing microphone. Supplies 15V phantom
power. If your microphone(s) is phantom powered, refer to page 14 for additional information.
SENSE MIC 1 - Low-impedance, balanced input for the #1 sensing microphone. Supplies 15V phantom
power. If your microphone(s) is phantom powered, refer to page 14 for additional information.
PAGE MIC - Low-impedance, balanced input for the paging microphone. Supplies 15V phantom
power. If your microphone(s) is phantom powered, refer to page 14 for additional information.
Grounding
The 571 can be configured to conform to several different grounding conventions (float circuit,
ground circuit) via connections on the rear-panel barrier strip. The factory supplied configuration
has the chassis connected to the circuit ground via a 10-ohm resistor paralleled with a 0.01-mfd
capacitor. The U-ground (third wire/safety ground) connection in the power cord is directly
connected to the chassis.
In most installations, the factory grounding configuration works best. In some instances (high RF
levels, or consultants specification), it may be necessary to directly connect the circuit ground to
the chassis. This can be accomplished via the connections found on the terminal strip located on
the rear panel.
SPL COMPUTER
571
AC INPUT
15 WATTS
MAX.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
LYNNWOOD, WA, USA
MANUFACTURED IN
PAGE MIC
FORMAT
MUSIC
PAGE
SENSE MIC 2
MUSIC IN
GND
IN
Vc
GND
HOUSE PAGE
123457689
SENSE MIC 1
GNDGND 50K LIN
REMOTE GAIN TRIM
10TB1123654
CIR
GND
7TB2
GND
CHAS OUTPUT

571
9
571 BasicsChapter 5
An SPL computer monitors the ambient sound in a room, taking into account that portion of the
ambient sound that is caused by the sound system. 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 571 uses a combination of analog and digital circuitry under the control of a microprocessor.
The microprocessor excels at following a set of instructions and making decisions. This uses a
studio-quality voltage-controlled-amplifier (VCA) that controls audio levels.
In operation, the microprocessor controls the VCAs gain based upon information gathered from
the two sensing mic inputs, the paging mic input, the music input, and all of the front-panel
controls. This real-time data is then compared to the data stored in memory during the calibration
procedure.
In calibrate mode, the 571 acquires a history of the environments sonic behavior. Two acoustical
snap shots are taken, first with the system and the environment at its minimum operating level,
and then at its maximum level. In calibrate mode, the 571 prompts the installer to set the systems
minimum operating level, then its maximum operating level. By running the system for about 8
seconds at the desired minimum and maximum levels, the microprocessor gives itself time to run
though a routine that develops a digitized acoustical performance history of the environment,
which is automatically stored in nonvolatile memory. With this information safely stored away, the
571s sensing circuitry can differentiate between those signals originating in the sound system,
and those caused by noise in the environment.
The installer sets minimum and maximum levels during calibrationthe 571 reads the controls as
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 ac-
quired 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 a sonic performance history of the room, it is able to
predict what should happen, rather than to simply react to what has already happened.
What About The Sensing Microphone?
The choice of sensing microphone is important, but it is not nearly as critical as the placement of
the microphone. Internally, the sense signal passes through a bandpass filter before its level
(strength) is measured. For most applications, an inexpensive low-impedance, omnidirectional
microphone, such as a lavalier microphone works adequately. Some installers have used boundary
microphones with good success (theyre unobtrusive). Still other installers have mounted micro-
phone cartridges (available from Mouser Electronics) inside electrical boxes equipped with a single-
holed cover. For installations in smaller spaces or noisy spaces, a directional microphone is a good
idea because you can use its position to optimize the performance of the system.
Where Should I Put the Sensing Microphone? The sensing microphone needs to hear the
ambient sound within the controlled space. It is not necessary to put the microphone where it only
hears the ambient sound; the 571s software can discern the difference between ambient sound
caused by the sound system and that which is purely environmental.
Place the microphone(s) where it primarily hears the sounds that should determine the operating
level of the sound system. In smaller rooms, use a directional microphone aimed to favor the
ambient sound and to reject or minimize the sound system loudspeakers.

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Where Shouldnt I Put the Sensing Microphone? Avoid the following situations:
Placing the sensing microphone where it primarily hears the sound system.
Placing the sensing microphone where it is within the noise field of a machine, unless you
want the machines noise contribution to more or less control the level of the sound system
(for example, a newspaper plant in the vicinity of the printing press).
Placing the sensing microphone(s) where the desired ambient sound source is masked by a
nearby noise source (for instance, placing the sensing microphone(s) near the constant noise
of the kiddie play area in a shopping mall).
Tips To Remember
Calibration must occur at a quiet time in the controlled space.
It helps if you have an estimate (SPL) of the maximum level required.
The sound system must be capable of delivering the maximum level required.
You can learn a great deal by listening to the sensing microphones. Youll need an
external microphone preamp to do this.
You may need to create a second noncontrolled zone to prevent the sound system level from
changing in spaces where the ambient conditions are stable, such as office areas or
restrooms.

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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-inch jacks are typically used for things like guitars (which are high-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. Line inputs should only see signals 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:
Always make sure that a devices input impedance is higher than the output source impedance of
the device that drives it.
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 571 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 (-10 dBV or 316 millivolts).
I/O Impedances
The 571 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 571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 571 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 C illustrates how to connect the 571 to various balanced and unbalanced sources.
To operate the 571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 571. 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 571, 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 571s balanced
input (even though the source is unbalanced). The other alternative shown in Appendix C converts the
571s balanced input into an unbalanced input at the 571s input terminals. This works, but is more
susceptible to hum and buzz than the preferred method. There is no level difference either way.
We do not recommend unbalancing the 571s microphone inputs (the sense inputs as well as the page
mic input). Doing so makes these inputs considerably more susceptible to hum and induced noise. In
the case of the sense microphones, it could cause problems that do not make themselves directly heard.
Caution 15V phantom power is applied to pins 2 and 3 on all of the 571s microphone
inputs. Never use a mic or mic cord/adapter that shorts pins 2 or 3 of the XLR
XLR Tip-Ring-Sleeve Signal
1 Sleeve Ground
2 Tip High
3 Ring Low

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Phantom Power
All of the microphone inputs on the 571 provide 15V phantom power for condenser microphones.
Note There is no external switch to turn the phantom power off. This is not likely to be a
problem since 99.99% of the dynamic microphones you are likely to use with the 571 will
not be harmed in any way. However, if you really do need to disconnect the phantom
power from any or all of the mic inputs, please call us or a qualified service center.
Remote Gain Trim Control
The output gain trim control of the 571 may be remotely located. The connection points for the
remote gain trim control are terminals TB1-1 through TB1-5. These terminals are located at the rear
of the 571, on the screw terminal strip labeled TB1.
For local operation, (front panel control only), terminal pairs 1 & 2 and 3 & 4 must be connected
with the factory installed U shaped straps. These connections are required for operation of the
front panel control.
For remote operation of the gain trim function, the straps must be removed. Connect a 50 kilo ohm
linear taper potentiometer (pot), wired as shown on the back panel and in Figure 6-1. Up to 250 feet
of 2-conductor shielded cable may be used, Be sure to connect the case of the control to the shield
of the cable. The front-panel OUTPUT GAIN TRIM control is disabled once the remote gain trim control
is connected.
Grounding Options
The 571 can be configured to conform to several different grounding conventions via connections
on the rear-panel barrier strip. The factory supplied configuration has the chassis connected to the
circuit ground via a 10-ohm resistor paralleled with a 0.01-mf capacitor. The U-ground (third wire/
safety ground) connection in the power cord is directly connected to the chassis.
In most installations, the factory grounding configuration works best. In some instances (high RF
levels, or consultants specification), it may be necessary to directly connect the circuit ground to
the chassis. This can be accomplished via the connections found on the terminal strip located on
the rear panel.
Figure 6-1. Remote gain trim control wiring.
REMOTE GAIN TRIM
CHAS
REV-A
GNDGND
CIR
GND
50K LIN
SHIELD POT BODY
BY CONNECTING TO GROUND

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Using the 571 Chapter 7
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 571 may be installed freestanding or rack- mounted. Multiple unit installations require no
additional breathing space between units.
Installation Requirements
Mechanical One rack space (1.75 inches) required, 12.5 inches depth
(including connector allowance).
Electrical 105-125VAC, 18Watts maximum.
Connectors Female XLR connectors for mic inputs. Pin 2 of the XLR connectors is Hot.
All other connections are via barrier strips.
OperatingFormat
The 571 has two different operating formats allowing for differences in sound system programming:
Page The program material sent to the 571 is paging, or pre-mixed music and paging.
Music The program material sent to the 571 is paging and background music, on separate lines.
The 571 mixes the two signals, and ducks (reduces the volume) the music source during
paging when the page over music control is set for ducking.
Page Format - In page format, the 571s music input is disabled. Use this setting for page-only or
pre-mixed music-page systems.
Music Format - In music format, the 571 monitors the signals at both the music and page inputs.
Paging signals duck the music signal by the amount determined by setting of the PAGE OVER MUSIC
control. Use this format when the 571 is the mixer for music and paging signals.
OperatingMode
The 571 has three operating modes: OPERATE, CALIBRATE, and BYPASS. You access these modes by
sequentially operating the MODE switch. Each push of the mode switch changes the operating
mode to the next mode; the next mode after BYPASS is OPERATE.
Bypass, Calibrate and Error Indicators
The front-panel LED bargraph also serves as a status indicator. Refer to Figure 7-1. One of the
LEDs serves as the Bypass mode indicator, two others serve as error indicators.
If an error indicator flashes during calibration,
the calibration procedure automatically aborts
and the 571 returns to operate mode using the
calibration values previously stored in non-
volatile memory. The 571 cannot be
recalibrated until the problem causing the error
is corrected. The following explains the error
indicators and the possible sources of error.
CalibrationError Indications
Page/Music Input Error. Not enough
program material or insufficient signal level of
program material at the input of the 571.
Sense Input Error. Sense microphones missing or
disconnected. Sense trim controls (front panel)
need to be turned up.
Figure 7-1. The LED Bargraph
SENSE INPUT
ERRORINPUT ERROR
30 4020159 26
GAIN (dB)
52
BYPASS
PAGE/MUSIC

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Block Diagram
Figure 7-2 is the block diagram for the 571. Please take a moment and take note of the following:
 All signal inputs and outputs are balanced transformerless.
 The line inputs, HOUSE PAGE INand MUSIC IN, are unity gain.
 The mic inputs (PAGE MIC and SENSE MIC) have up to 48 dB of gain. They are equipped with
15V phantom power for condenser mics.
 All of the trimpots (page mic and sense) have stop resistors at the CCW end of their rotation
which prevents them from attenuating to infinity. The range is limited to -26 dB for the PAGE MIC
trimpot, and -40dB for the SENSE 1 and SENSE 2 trimpots.
 Signals on either page input operate the ducker. The ducker attenuates music signals whenever
there are signals present on either page input. The PAGE OVER MUSIC control determines the
amount of ducker action.
 The format switch defeats the music input and selects the source for the 571s program level
detector.
 Using the remote OUTPUT GAIN TRIM control defeats the front-panel mounted control.
 Different grounding options are possible via TB2-6 and TB2-7.
 The microprocessor runs the show.
Figure 7-2. 571 block diagram.
SS E R P
P R E SS
R P SS E
1
4
2
5
3
6
HOUSE
PAGE
IN
PAGE
MIC
PAGE
MIC
TRIM
SENSE 1
TRIM
SENSE 2
TRIM
SENSE
MIC 1
SENSE
MIC 2
MICROPROCESSOR
LEVEL
DECTECTOR
LEVEL
DECTECTOR
DUCKER
SIDECHAIN
MULTIPLEXER AND
A/D CONVERTER
OUTPUT
GAIN TRIM
MAX
LEVEL
AVERAGING
TIME
PAGE OVER
MUSIC
FORMAT
MUSIC
MUSIC
PAGE
PAGE
RATIO
D/A
CONVERTER
MEMORY
DISPLAY
MUSIC
IN
VCA CHASSIS GROUND
AUDIO
OUTPUT CIRCUIT GROUND
TB2
10ohm
.01mFd
TB2
TB1
JP1
B7Vc
A
TB1
TB1
TB1
7
1
2
3
4
5
9
10
6
8
VOLTAGE
REFERENCE

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Applications Chapter 8
Airports
The 571 is ideally suited to managing the sound pressure levels within airports. Because there is
too much variation in ambient sound level within the average airport to allow one gain setting to
suit all areas, we recommend that you use at least one 571 per paging zone. A typical airport
installation would designate each gate as a separate paging zone, so that the sound system level at
each gate would be adjusted upward as passengers gather at that gate, and then brought back
down when they depart, without affecting the sound system level at the other gates.
Train Stations and Highly Reflective Acoustic Environments
When using the 571 in an above-ground train station installation, many installers have had success
installing one sense mic over the tracks at the end of the platform that the train will reach first. In the
case of a subway train station installation, this sense mic would be placed over the tracks near the
mouth of the tunnel from which the train will emerge. Many installers also place a second sense mic
over the passenger queueing area. Use a short AVERAGING TIME control setting so that the 571 can
respond quickly as trains arrive and depart.
Reflective environments, such as subway stations, can present a unique set of acoustic challenges
to the sound system installer. One of these challenges can be getting correct ambient sound level
information to the 571s sensing mics, so that the 571 can respond appropriately. Misinformation,
such as acoustic phase coupling and cancellation, can result from a high level of reflected sound
system audio reaching the 571s sensing mics.
Acoustic treatment such as SonexTM can help in reflective acoustic environment installations. If
you notice that the 571 makes inappropriate gain changes when a page is made (inappropriate
increases or decreases in level), then you are probably having problems with misinformation in the
audio that is reaching the sense mics. In this case, you may need to perform a modification to
prevent the 571 from responding to changes in ambient level when a page is occurring. Please call
Symetrix Technical Support at (425)-787-3222 for further information on this modification.
Factories
In this application, the 571 monitors the ambient noise level within a factory and adjusts the sound
systems operating level so that it is always audible. Install the sensing mics so that they receive
an average of the noise sources within the space. This ensures that a loud, localized noise source
will not dominate the control of the sound system. You may need to create a separate controlled
zone for the loud, localized noise source by dedicating a 571, sense mic(s), speaker(s) and an
amplifier to that purpose.
Speakers serving quiet zones, such as break rooms, offices, and restrooms should probably be
on their own amplifier. This amplifier could either be fed from a separate, dedicated 571, or it could
be fed the same signal that appears at the input of the factorys 571 (so that the quiet zones are
unaffected by the sound system level changes of the 571).
Shopping Malls
In this application, the 571 ensures that announcements within the public spaces are always
audible, but never too loud. This application requires multiple sensing mics for best results. You
can connect the mics in parallel for this, however very large installations may require an external
mic mixer just for the sensing mics. Be sure to reduce the mixers output level so that it is appropri-
ate for the 571s sensing mic inputs.
In mall applications, its a good idea to avoid sense mic locations near localized noise sources (like
the kiddie area or food courts). Like the factory application, you want the sense mics to average
out all of the various noise sources within the mall. Finally, high noise areas, such as the ones
previously mentioned, should be individual zones unless they are physically nearby each other.

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Sports Facilities
Sports facilities can also benefit from the 571. Typically, the 571 is used to track the ambient conditions
on the concourses, other access areas, and the refreshment stands. Consider using multiple 571s to
isolate specific environments from each other, such as the refreshment stands from the concourse
environment.
RaceTracks
Different race tracks have different noise sources. In auto racing, the cars make far more noise than the
spectators. If youre going to use a 571 in a speedway installation, position the sensing mikes so they
are in a good spot to pick up the cars. Since this is outdoors, some sort of weatherproof microphone is
needed. A reasonable substitute is a small paging speaker, with a 70V transformer. Use a moderate
transformer tap, like 10 watts. You may even be able to do away with the transformer. Tie the sense mic
cable shield to the case of the speaker (or float it if its plastic!).
In horse (and dog) racing, the spectators make more noise than the animals. In this case, position the
sensing mics to pick up the spectators. If the sense mic location is sheltered, then the weatherproofing
needed for auto race tracks isnt necessary, although it is a good idea to find a location and mounting
arrangement that is at once people-, bird-, and rodent-proof.
Off-Track Betting Parlors and Casinos
In these facilities, the crowd reaction is likely to be sudden and intense. For the betting parlor, its a
good idea to include the remote-track audio in the 571s input signal so that the unit doesnt consider it
part of the crowd reaction.
In the betting parlor, use directional sensing mics placed to favor the audience. You may need to use the RATIO
control to help overcome the leakage from the sound system into the sensing mics.
In casinos, be sure to place the sensing mikes up high where they hear an average of the crowd
and the slot machines. Use longer averaging times.
Restaurants, Bars & Theme Stores
All of these establishments have one thing in common: they all use background or foreground music as
an integral part of their ambience. The volume level of the music is important: audible, but not too loud.
The 571 allows management to determine the appropriate music volume level at a given ambient noise
level. The 571 also helps guarantee the audibility of the music, regardless of actual conditions during
operation. Again, picking the right sense mic location is the key. In a restaurant, keep it away from the
kitchen and away from the entry areas. Definitely avoid espresso machines and vending machines..
In bars and lounges, several mics work better than one or two, since they help average the overall noise
level of the space. Stay away from the blenders and dishwashers behind the bar. Remember that any
extraneous sound sources (like the TV in a sports bar) will be regarded as extra ambient noise by the 571
and the sound system level will increase as a result. You can avoid this by running the TV audio output
into the music input of the 571, so that the TV audio becomes part of the 571s program material.
Auditoriums & Hotel Lobbies
Here the 571 keeps track of the ambient conditions in the outer areas such as the lobbies and foyers. If
you have speakers in the rest rooms, these speakers should probably not be under the 571s control,
since these areas are generally more subdued than the outer areas. Of course, the rest rooms could have
theirown 571.
Museums
The 571 can greatly enhance the impact of automated museum exhibits. The 571 monitors the
crowd, and sets the gain accordingly. If there are adjacent exhibits that also produce sound, be
sure to place the sense microphone to favor the local crowd, and to reject the other exhibit.

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Troubleshooting Chapter 9
There is no output signal:
Check the AC power connections to the
571.
Check input and output cables and
connections. Are inputs driven by
outputs, and outputs driving amplifiers?
Determine that there really is a signal
coming from the source and that it is
getting to the 571.
Are the loudspeakers and amplifiers
working?
Unit will not calibrate:
Are input levels normal?
Are the error LEDs coming on during
calibration?
Is the sensing mic(s) plugged in and
turned ON?
Increase SENSE 1 and/or SENSE 2 gain.
Music always plays too loud:
571 is being used for music, but was
calibrated with the FORMAT (PAGE/MUSIC)
switch in Page position. Change rear panel
FORMAT (PAGE/MUSIC) switch to MUSIC,
then recalibrate.
Did someone turn up the level of the music
feeding the 571 after it was calibrated?
Did someone turn up the output gain trim
pot?
Unit seems to have no effect:
Check the RATIO control. At 2:1, the gain
changes are very subtle. Turn the RATIO
control clockwise for more change.
Check the AVERAGING TIME control. When
this control is set other than fully counter
clockwise (1.2 sec), the unit does not
respond immediately.
Unit does not increase gain sufficiently at
high ambient levels:
You may be overloading the sense mic
preamps. Insert 15 dB pad and recalibrate.
PAGE/MUSIC I NPUT E RROR LED flashing during
calibration:
Not enough signal level on either PAGE or
MUSIC inputs.
SENSE I NPUT E RROR LED flashing during
calibration:
Not enough signal coming from sense
mics. Try turning up the SENSE GAIN
trimpots.
Check sense mics and cables.
Hum or buzz in output:
Check input connector wiring (refer to
Appendix D).
Ground loop. Check related system
equipment grounding. Are all system
components on the same AC ground?
Distortion:
Check input signal. Is it already dis-
torted?
Line input signal may be too hot.
Page mic signal may be too hot.
Does the sound system have sufficient
power for the SPL that you are trying to
attain?
If you are using a high Max setting, you
may be overloading the input to your
amplifier. Reduce MAX setting. Is
something else clipping?
Are the amplifiers and speakers okay?
Check in BYPASS.
Noise (hiss) :
Check input signal levels, and level
control settings.
Check gain settings on downstream
equipment.
Is the input signal already noisy?
Noaudio:
Is the unit plugged in?
Is the unit in BYPASS mode?