572 SPL Computer
572 User’s Guide
572 SPL Computer
Table of Contents
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
26
Chapter 11 Warranty & Service
27
Appendix A External Sensing & Multi-Unit Installations
29
Appendix B Connections
31
572
Chapter 10 Specifications
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.
i
14926 35th Ave. West
Lynnwood, WA 98037 USA
Tel (425) 787-3222
Fax (425) 787-3211
Email [email protected]
Chapter 1
Introduction
The Symetrix 572 SPL Computer is an automatic level controller that maximizes intelligibility by
changing gain in proportion to environmental noise level changes; in essence, controlling the
volume of the background/paging system by measuring the volume of the ambient noise and then
adjusting the system gain accordingly. Unique to the 572 is its ability to utilize the sound system’s
loudspeakers as noise measurement transducers, in place of the usual microphones. The 572
switches the speaker line from the amplifier’s output to its own sensing input. In less than one
second it reads the ambient noise level and switches the speaker line back to the amplifier. Special
impedance matching, frequency shaping, and level shifting circuits allow the 572 to acquire precise
relative noise measurements from virtually any speaker line, with any number of speakers of any
impedance, transformer coupled or direct coupled, 25V or 70V.
The operating characteristics of the SPL computer are controlled by a powerful microprocessor,
running under Symetrix proprietary software. This reduces the 572’s calibration time and allows the
installer to optimize performance for any situation. No test gear is needed because the 572 obtains
and stores the information it needs during calibration.
The 572 has separate inputs for paging and music as well as a direct paging microphone input.
Both the speakers and the amplifiers connect directly to the 572. A front panel page over music
function enables up to 14 dB of music attenuation during announcements. There are multiple
option switches for telling the 572 how to treat the page/music signal as well as how to react to
changes in the acoustic environment. The LED meter on the front not only indicates gain change
but also aids in setup and calibration and identifies errors.
You show the 572 the parameters of the acoustic environment during calibration and then set the
way you want the unit to respond to changes. The 572 then takes the information it has stored in
memory and makes smooth, appropriate changes to keep the levels exactly where you want them.
In order for the speakers to act as loudspeakers and sensors, there must be times when no audio is
passing through the speakers to allow the sample of the ambient noise to be taken. Thus the 572
takes advantage of silent periods in the paging or music to take a sample, or it forces a sample
based on the front panel setting at timed intervals. The 572 will unobtrusively fade out the music,
take a sample, and then fade the music back in, all in a matter of seconds. The 572 will not, however, 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.
Phone:
(425) 787-3222
Fax:
(425) 787-3211
Email:
[email protected]
Website:
www.symetrixaudio.com
BYPASS
572
PAGE
MIC
GAIN
SAMPLE
INTERVAL (MIN)
SENSE
GAIN
10
HIGH
LOW
BYPASS
NORM
SPL COMPUTER
5
SENSE
PAGE OVER
MUSIC (dB)
CALIBRATE
RATIO (dB)
S ENS E: OUT P UT
GAIN (dB)
15
PAGE/MUSIC
INPUT ERROR
20
MUSIC/
PAGE
2
1
26
0
14
2:1
5
9
LEVEL SET (dB)
-10
-15
BYPASS
15 20 26 30 40
-5
-20
1:2
0
572
Feel free to contact us if you have questions, comments, or suggestions:
OPTIONS
10
MODE
15
5
0
A BCD
20
1
2
3
4
MAX
MIN
Front panel
FROM
TO
SPEAKER AMP
AC INPUT
18W MAXIMUM
FUSE
POWER
EXT
SENSE
TRIG
EXT
RELAY
CNTRL
SPARE
LINE
OUTPUT
PRESS
LINE INPUTS
PAGE
MUSIC
Vc
PAGE
MIC
MANUFACTURED IN
LYNNWOOD WASHINGTON,
UNITED STATES OF AMERICA
THIS UNIT CONTAINS NO USER SERVICABLE PARTS.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
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T B1 1 0
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Rear panel
1
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.
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Feature
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.
2
571
Equipment Markings
CAUTION
RISK OF ELECTRIC SHOCK
DO NOT OPEN
TO REDUCE THE RISK OF FIRE OR
SHOCK DO NOT EXPOSE
WARNING: ELECTRIC
THIS EQUIPMENT TO RAIN OR MOISTURE
DE CHOC ELECTRIQUE
AVIS: RISQUE
NE PAS OUVRIR
SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.
No user serviceable parts inside. Refer servicing to qualified service personnel.
Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.
S’adresser a un reparateur compétent.
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.
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
Caution
Warning
CAPITALS
Boldface
Identifies information that needs
extra emphasis. A Note generally
supplies extra information to help
you to better use the 572.
Identifies information that, if not
heeded, may cause damage to the
572 or other equipment in your
system.
Identifies information that, if
ignored, may be hazardous to your
health or that of others.
Controls, switches or other markings
on the 572’s chassis.
Strong emphasis.
Important Safety Instructions
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
Operator Safety Summary
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
safety purpose of the grounding plug. 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 conductive 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 the power cord from 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 attached AC connector. The fuseholder
accepts 5 x 20mm diameter fuses. For 117VAC
operation, the correct value is 0.5A, 250VAC,
standard. For 230VAC operation, the correct
value is 0.25A, 250VAC, standard.
Operating Location Do not operate this equipment under any of the following conditions:
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 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.
3
572
Chapter 2
Setup
Chapter 3
What You’ll Need
To install a 572, you’ll need the following items:
1.
The 572.
2.
Access to the power amplifier input (line level), mixer output (line level), power amplifier
output (speaker level), speaker line connections.
3.
Background music feed (usually the mixer 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.
Place the 572 in the signal chain as the final level controlling device.
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.
Calibrate the 572 when the coverage zone’s ambient noise level is it’s nominal minimum.
“Nominal minimum” means whatever ambient noise level is the minimum for that particular environment, 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.
572
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.
Pre-installation Considerations
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.
Horn speakers may require modification of the 572, especially if the ambient noise level is 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
electrically located after the 572.
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
wire at the expense of flexibility.
4
8.
If there are multiple loudspeaker zones, there probably ought to be a separate 572 for each
zone.
If the power amplifier is larger than 300 watts (70-volt systems), 200 watts (8-ohm systems),
or 100 watts (4-ohm systems), then the internal 5-amp relay can’t handle the load current.
You must use an external relay.
It is good to know the minimum and maximum ambient levels (dB SPL) that the 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).
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
the 572 with a mix of everything). The 572 monitors its paging inputs and immediately
terminates a sense period when a paging signal is present. This is not true for the music
input.
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.
9.
10.
11.
12.
Connections
A drawing of a typical music with paging system is shown in below. Make all of the following
connections:
1.
Paging microphone (or mic-level mixer output) to the PAGE MIC XLR connector. 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.
TO
SPEAKER
AC INPUT
18W MAXIMUM
FUSE
POWER
FROM
AMP
EXT
SENSE
TRIG
EXT
RELAY
CNTRL
SPARE
LINE
OUTPUT
PRESS
LINE INPUTS
PAGE
MUSIC
Vc
PAGE
MIC
MANUFACTURED IN
LYNNWOOD WASHINGTON,
UNITED STATES OF AMERICA
THIS UNIT CONTAINS NO USER SERVICABLE PARTS.
SPEAKER USED FOR
P.A AND SENSE
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T B1 1 0
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TO/FROM HOUSE
SPEAKER SYSTEM
SPEAKER USED
FOR P.A.
DOES NOT SENSE
PAGE
MICROPHONE
TELEPHONE
SYSTEM
HOUSE
AMPLIFIER
Figure 3-1.
BACKGROUND
MUSIC
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
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.
5
572
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
Calibration Settings Table
Set the controls and switches on the front and rear panel as shown below.
Front Panel Control
Setting
Rear Panel
Setting
BYPASS switch
out (NORM)
OUTPUT
Connect to power amplifiers.
PAGE MIC gain
12:00 o’clock
PAGE MIC
Connect balanced, low-impedance
page microphone here.
SENSE GAIN switch
out (HIGH)
MUSIC IN
Connect line-level music source here.
SAMPLE INTERVAL
8:00 o’clock
PAGE IN
Connect line-level paging source here.
PAGE OVER MUSIC
8:00 o’clock
RATIO
12:00 o’clock
LEVEL SET MIN
9:00 o’clock
LEVEL SET MAX
8:00 o’clock
OPTION switches
All down
Calibration Checklist
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
Apply program or paging signals to the 572’s input(s).
Press the MODE switch once to enter CALibration mode.
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 S ET 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
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 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.
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1.
2.
3.
6
Chapter 4
BYPASS
572
PAGE
MIC
GAIN
Front & Rear Panel Overview
SAMPLE
INTERVAL (MIN)
SENSE
GAIN
BYPASS
NORM
10
HIGH
LOW
SPL COMPUTER
5
SENSE
PAGE OVER
MUSIC (dB)
CALIBRATE
RATIO (dB)
S ENS E: OUT P UT
GAIN (dB)
15
PAGE/MUSIC
INPUT ERROR
20
MUSIC/
PAGE
2
1
26
0
14
2:1
1:2
5
9
LEVEL SET (dB)
-10
BYPASS
15 20 26 30 40
-15
-5
-20
0
MIN
OPTIONS
10
15
5
0
MODE
20
A BCD
1
2
3
4
MAX
Front Panel Overview
Description
BYPASS switch
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.
SENSE LED
Indicates that the 572 is sensing the ambient conditions in the
controlled area.
MUSIC/PAGE LED
Indicates that the 572 is in its music/page mode.
SAMPLE INTERVAL
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, from 0 to 15 dB.
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
than the ambient (1:2).
GAIN LED display
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 errorcondition 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.
LEVEL SET MAX control
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.
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Feature
7
FROM
TO
SPEAKER AMP
AC INPUT
18W MAXIMUM
FUSE
POWER
EXT
SENSE
TRIG
EXT
RELAY
CNTRL
SPARE
LINE
OUTPUT
PRESS
LINE INPUTS
PAGE
MUSIC
Vc
PAGE
MIC
MANUFACTURED IN
LYNNWOOD WASHINGTON,
UNITED STATES OF AMERICA
THIS UNIT CONTAINS NO USER SERVICABLE PARTS.
FABRIQUÉ AUX E.-U. PAR SYMETRIX INC., LYNNWOOD, WASHINGTON.
RÉFÉREZ TOUTE RÉPARATION À UN TECHNICIEN QUALIFIÉ.
T B2 1 0
9
8
7
6
5
4
3
2
1
T B1 1 0
9
8
7
6
5
4
3
2
1
Rear Panel Overview
Feature
SERIAL NUMBER
AC POWER INPUT
FUSE
572
PAGE MIC INPUT
8
Description
[Please send in the completed warranty card.]
Power cord. Connect only to appropriate AC power source. Refer to
rear-panel marking for correct AC source value.
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
type AGC-1/4) Export: 1/8A, 250V ac, fast blowing (Bussman type GDA125mA).
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
mic input of the 572.
Terminal Strip Connections
Feature
Term. #
Description
TO SPEAKER
TB2(10,9)
Connect speakers used for sensing and sound system
usage here. Speakers may be speaker impedance or
constant voltage.
FROM AMP
TB2(8,7)
Connect amplifier here. Amplifier output may be
speaker impedance or constant voltage.
GROUNDS
TB2(6,4,2)
Connect to circuit ground inside the 572.
EXT RELAY CNTRL
TB2(5)
NPN open collector output for driving external relay.
You must supply power for the relay coil. Remember
to connect a diode across the relay coil to absorb the
back EMF generated by the relay coil. The maximum
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) output of the 572.
VC
TB1(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.
MUSIC INPUT
TB1(2,1)
Balanced line-level for music signals. Normally used
for background music. Signals applied to these
terminals are attenuated (ducked) whenever signals
are present at either of the page inputs.
9
572
For unbalanced usage, use TB1(9) and TB1(10).
TB1(8) should float.
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 recording studio-quality voltage-controlled-amplifier (VCA) to control audio levels.
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 settings, the 572 decides how loud the sound system must operate to restore audibility.
The 572 also has an internal timer, controlled by the front-panel SAMPLE 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 are automatically stored in nonvolatile memory.
During calibration, the installer sets minimum and maximum levels-the 572 “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.
572
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).
10
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 remainder 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.
572
Use the RATIO control when you either want the 572 to more than keep up with the crowd (expansion), 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 or may not be dead quiet).
•
It helps if you have an estimate (SPL) of the maximum level 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,
break rooms, etc.)
11
Technical Tutorial
Chapter 6
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 (hopefully) 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-impedance 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 lowimpedance (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).
572
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 600ohm load. If you don’t understand the concept of termination, you probably don’t need to anyway.
12
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 (-10 dBV or 316 millivolts).
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:
Tip-Ring-Sleeve
Signal
1
Sleeve
Ground
2
Tip
High
3
Ring
Low
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 susceptible 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.
13
572
XLR
Condenser Microphones and the 572
The 572’s paging microphone input is not equipped with phantom powering for condenser microphones. If you wish to use a phantom powered microphone you must provide a power source externally.
572
Note
14
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
is the common-mode limitation of the microphone preamp.) If your particular microphone
operates at a higher supply voltage than 15 volts the phantom power supply must dc-block its
output using capacitors or a transformer.
Chapter 7
Using the 572
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.
Installation Requirements
Mechanical
One rack space (1.75 inches) required, 12.5 inches depth
(including connector allowance).
Electrical
105-125 VAC, 18 Watts maximum.
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
•
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 terminal is the open collector of a 2N4401 NPN transistor . You must
supply power for any external relay used. The transistor’s limits are: V CEO = 40V
and Icmax = 625 mA.
•
In when the BYPASS switch is pressed, the line-level M USIC 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
described earlier.
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
external high-current relay.
15
572
On the following page you will find the block diagram for the 572. Please take a moment and take
note of the following:
TB1
PAGE MIC
GAIN
10
9
LINE
OUTPUT
8
PRESS
TB2
VCA
PAGE MIC
10
9
TB1
8
PAGE 4
LINE 5
INPUTS 6
7
TO
SPEAKER
FROM
AMP
HARDWARE BYPASS
PAGE OVER
MUSIC
+5V
PAGE
DETECTOR
RATIO
SAMPLE
INTERVAL
MIN
MAX
SENSE
GAIN
A
B
JP1
MULTIPLEX AND A/D CONVERTER
TB1
MUSIC 1
LINE 2
INPUT 3
MUSIC
VCA
BYPASS
VCA
TB1
"GAIN" DISPLAY
TB2
Vc
7 OUT
D/A
CONVERTER
2
5
9
15
20
25
30
4 EXTERNAL
RELAY
5
CONTROLL
40
MICROPROCESSOR
+5V
REV-B
+5V
+5V
A
1 2
MODE
PUSHBUTTON
B
3 4
OPTIONS
TB2
JP2-A.G.C.
THRESHOLD
3 2
EXT SENSE
TRIGGER
Figure 7-1. 572 Block Diagram.
Operating Format
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.
572
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
during calibration.
If the error indicator flashes during calibration, the calibration 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.
T
GAIN (dB)
PAGE/MUSIC
INPUT ERROR
2
5
9
BYPASS
15 20 26 30 40
Figure 7-2 LED Bargraph
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.
16
Calibration
Calibration must be performed when the ambient noise in the loudspeaker coverage area is at its
normal minimum level for the area. (NOT dead quiet, unless that is 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.
•
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
17
572
Quick System Test
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
normal operation!
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.
Option Switch A
Option Switch B
Option Switch C
Option Switch D
SILENCE THRESHOLD
SENSE VIEW
SAMPLE AVERAGING
EXTERNAL SENSE
UP
-20 dBu
DOWN
-35 dBu
UP
Enabled
DOWN
Disabled
UP
Running Average
DOWN
No Average
UP
Enabled
DOWN
Disabled
What Could Go Wrong?
Here are the two most common situations and some things to look for.
The red MUSIC/PAGE lamp flashes during calibration:
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.
572
1.
3.
There are no speakers connected to terminals 9 and 10, TO SPEAKER. The 572 uses the system
speakers as microphones when sensing.
The 572 does not accurately adjust the system level as ambient noise changes:
1.
Repeat the calibration procedure. Calibration must be made during times of 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.
18
SPEAKERS
MONITORING
HEADPHONES
CONNECTED TO
PINS 2 & 3.
(PIN 1 MAY NEED
TO BE CONNECTED
TO SYSTEM GROUND)
TO OTHER
SPEAKERS
MICROPHONE 2
MICROPHONE 1
GAIN (dB)
DUAL MICROPHONE
PREAMPLIFIER
PHANTOM POWER
GAIN (dB)
15dB PAD
40
302
POLARITY
IN
OUT
CLIP
15dB PAD
40
180°
0°
IN
OUT
POLARITY
180°
0°
ON
OFF
CLIP
20
60
20
60
PWR
SYMETRIX 302 OR EQUIVALENT
LOW-Z MICROPHONE PREAMP
Figure 7-3 Using a microphone preamp to hear the sense speakers.
5.
If hum is being induced in the speaker wiring the 572 will treat this noise as “sense” audio
when sensing. Make sure that the speaker wiring is not routed next to AC wiring or unrelated
70V speaker wiring. Disconnect the speakers from the system and using a microphone
preamplifier connected to the speaker(s), listen in headphones to what the 572 “hears” when it
is sensing. Listen for any noises that could falsely trigger a gain change. Listen for any hum or
buzz.
6.
The accuracy of the 572 is only as good as the sample audio that your speakers provide when
the unit is sensing. If any of the system speakers are located near noisy equipment such as
vending machines, ice machines, air conditioning blowers, or separate paging speakers the
level of the 572 system will increase disproportionately with the noise level of the noisy
equipment. Disconnect the speakers from the system, connect them to the input of a balanced,
low-impedance microphone preamp (like the Symetrix 302 shown in Figure 7-3) and listen in
headphones to what the 572 “hears” when it is sampling!
7.
Check Chapter 9 in this manual.
If all else fails, call Symetrix.
In noisy locations, it's important to locate the speakers where they do the most good, both for the
listener as well as the 572. Remember that if the speaker is next to a noisy machine, the machine's
noise output will probably cause the 572 to raise the level when the machine is operating. If this
isn't desirable, then exclude that particular speaker from the speakers used for sensing by connect
the offending speaker(s) directly to the amplifier output, bypassing the 572. In other cases,
directional (horn) speakers may help by directing the sound to the listener. Horns are also more
efficient, making your amplifier power go further. You can also put a sensing speaker somewhere
where the noise level is more representative of the average noise level in the space even though
there may not be anyone who can hear it. On the other hand, this may be a more appropriate
application for the 571 (which uses a sensing microphone).
Low Frequency Sensitivity
The sensing circuit of the 572 includes a 3-pole high pass filter. The 572 will not respond to
background noise below 300 Hz. This design makes the system insensitive to building rumble and
air handling noise. The sense circuit responds to signals between 500 Hz and 15 kHz.
Using the 572 With Horn Speakers
Several users have had difficulty getting the 572 to calibrate and operate properly when connected
to strings of high gain horn speakers in high noise environments. The horns returned too much
signal to the 572 when it was sampling, which overloaded the A/D converter. In one case we were
able to get the system to operate by increasing R13 and R14 to 91K0. If you set OPTION switch B
19
572
Using the 572 in High-noise Environments
UP and the sense level indication exceeds the 26 dB LED in both positions of the SENSE GAIN
switch, you need to increase R13 and R14.
In other cases using a single speaker as the sensing transducer was the only answer. In these
cases the output of the power amplifier connects directly to the speaker string and the single
sampling speaker is wired to TB2-9 and TB2-10 (TO SPEAKER terminals) of the 572. Terminals TB27 and 8 (FROM POWER AMP) are not connected. When the 572 samples it only looks at the single
speaker for a reference level of ambient noise. In these cases the Symetrix 571 should have been
specified for the job.
Using the 572 With Planar or Low Output Speakers
Some speakers make lousy microphones. In a situation like this, we recommend using a separate
speaker(s) for sensing. To do this, connect all of the speakers used to produce sound to the
amplifier output. Connect all of the speakers used for sensing to the 572’s TO SPEAKER terminals. If
you wish these speakers to produce sound, then connect the 572’s FROM AMP terminals to the
amplifier output, otherwise leave the FROM AMP terminals unconnected. During sensing, the 572
sets the VCA to about 30 dB attenuation, so the speakers connected directly to the amplifier
outputs are effectively silenced.
70V Systems
The 572 has been designed with both 70V (or other constant-voltage system) and speakerimpedance systems. Aside from the amount of current flowing through the 572’s sense relay, the
only other difference arises from the signal level returned by the speakers when the 572 switches to
sense mode. In 70V systems, the signal level is higher, because of the step-up action of the line
transformers. With highly-efficient speakers, this may present a problem because the sense input
of the 572 may be overloaded. Use OPTION switch B to check the level coming back. Refer also to
the discussion of option switches on pages 17 -18. The sense relay’s 5A contact current limit
forces a 300-watt wattage limit for 70V systems.
572
In 70V systems, it is common practice to provide autotransformers or L-pads after the line transformer to allow local volume control. NOT! Allowing any sort of level control after the 572 invalidates the settings made during calibration. If you must provide a local level control, then ensure
that the controlled zone is a minor part of the entire system, that the users understand that the
volume level of the system may not always be ideal, and (finally) that the locally controlled zone is
not used for sensing.
Finally, it is imperative that every speaker and transformer in the system operates in-phase.
Impedance
16-ohms
8-ohms
4-ohms
Limit
400 watts
200 watts
100 watts
4, 8, and 16-ohm systems
In 4, 8, and 16-ohm systems (speaker-impedance systems), the levels returned to the 572 are low;
you'll probably need to use the high-gain position of the SENSE GAIN switch. The 5A contact
current limit forces the following limitations:
Refer also to the paragraph regarding zone volume controls in the preceding section.
Using the External Relay Provisions
When controlling amplifiers larger than 200 watts (8-ohms) you really should be using the Symetrix
571. If you insist on using the 572, you must use an external DPDT relay. The 572’s internal relay
cannot handle more than 5-amps of load current. This corresponds to 300 watts at 70V, 200 watts at
8-ohms, and 100 watts at 4-ohms. The 24-volt version of the Potter & Brumfield PRD11DGO works
well. Its DPDT contacts are rated at 30 amps. Figure 7-4 shows how to connect everything.
20
EXTERNAL
D.C. COIL RELAY
LOW(-)
LOW(-)
P
AM
HIGH(+)
HIGH(+)
1N4002 OR
EQUIVALENT
DIODE
(+)
572
REAR
TERMINALS
(-)
D.C.
POWER
SUPPLY
GND
EXT.
RELAY
CONTROL
-
+
-
+
FROM
TO
POWER SPEAKER
AMP
EXTERNAL
HIGH CURRENT A.C. RELAY
LOW(-)
LOW(-)
P
AM
The 572 provides a contact
closure through a transistor
switch to operate the external
relay. This closure can be
found on the rear panel barrier
strip TB2-5 which is labeled
EXT RELAY CNTRL. Terminal
TB2-6 is ground. Wire the
negative output of your
external power supply to TB2-6
(Ground). Connect the
positive output of the power
supply to one side of the
external relay coil. Connect the
other side of the relay coil to
TB2-5. The user supplied
power supply and external
relay coil circuit is closed
whenever the 572 goes into the
SENSE mode. Be sure to put a
back-biased diode (1N4002 or
better) across the relay coil.
HIGH(+)
HIGH(+)
EXTERNAL
D.C. COIL RELAY
120VAC
POWER
1N4002 OR
EQUIVALENT
DIODE
(+)
572
REAR
TERMINALS
(-)
D.C.
POWER
SUPPLY
Rev-A
GND
EXT.
RELAY
CONTROL
-
+
-
+
FROM
TO
POWER SPEAKER
AMP
Figure 7-4 Using the External Relay connections.
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 (expansion), 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.
Monitoring the VCA Gain Via the Vc Terminal
You can monitor what the VCA is doing via the VC terminal on TB1-7. The gain relationship is -159
mv/dB. Don’t worry about what the actual value of the gain or loss (it’s unity gain @ 0 V), it’s the
change in gain and the actual starting/stopping values that count. For instance, after calibration,
the VCA control voltage is sitting at 1 volt (-6.289 dB loss through the VCA). After the first sense
interval, the control voltage now sits at -1 volt (about 6.289 dB gain). The VCA gain has changed
by 12.58 dB (overall gain increase). The front panel gain display will read 9.
21
572
What does the Ration Control Do?
Calibration Issues
If you want the 572 to operate correctly then proper calibration is an absolute necessity. The
calibration procedure establishes the high and low limits (level-wise) for the sound system. It also
establishes the baseline noise level for the space. Therefore, it is imperative that the calibration be
performed at a time when the space is at or near its nominal minimum and that you have the ability
to operate the sound system at its maximum desired level for short periods of time.
It is not possible to calibrate the 572 properly at other than the lowest normal ambient for the
space. Do not calibrate when the space is dead quiet, unless that is the lowest normal ambient
level.
Effects of Calibration Level on Performance
The calibration procedure sets two gain values (MINL and MAXL), and establishes a baseline SPL
threshold level (BTL). The baseline SPL threshold is the lowest SPL that the 572 will respond to.
Below the BTL, there will be no gain changes. Thus, the level set by the MIN pot during calibration
becomes the minimum output level (MINL) of the 572. If the room ambient falls below the BTL, the
output of the 572 remains at MINL.
The MAXL corresponds to the maximum output level of the 572, regardless of the setting of the
RATIO control, or the ambient noise level. The rule here is the change in ambient level times the
slope may not exceed MAXL. If the computed gain change passes the test, then that value drives
the VCA, if not, then the change is limited to MAXL.
If the BTL level is too low, relative to the actual minimum ambient level (AMAL), then the 572
could run out of control range. This is what would occur if you tried to use silence to set the BTL.
If the AMAL level is marginally too low, then simply ensure that there is a low enough MIN setting
to allow the sound system to track this minimum level. On the other hand, you could establish a
minimum level (to ensure that the sound system is always heard) by making this the difference
between the BTL and MINL.
If the BTL level is higher than the AMAL, then the sound system is likely to be too loud when the
space is at its quietest. Reducing the amplifier gain will work, but you must ensure that there is
enough gain-change range (difference between MIN and MAX controls) to keep up with a noisy
environment.
572
Summary of Level Considerations
1.
It is best to try to hit the Baseline SPL Threshold Level on the head, or certainly within 6 dB.
2.
Be sure that you have more Maximum Level than you need, which will help compensate if the
3.
Baseline SPL Threshold Level is higher than the Actual Minimum Ambient Level.
22
Chapter 8
Applications
Here are a few applications that the 572 lends itself to. It’s important in every one of these applications (actually, any 572 application) that the unit has been properly calibrated and that the program
material has sufficient silence periods for ambient sensing.
Factories
In this application, the 572 monitors the ambient noise level within a factory and adjusts the sound
system’s operating level to ensure that it is always audible. Ensure that all speakers that are used
for sensing are installed so that they receive an average of the noise sources within the space to
ensure that a loud, localized noise source does not dominate the control of the sound system. For
speakers that are near a noise source, you may need to wire these speakers directly to the power
amplifier, bypassing the 572. If the sound system needs to be heard consistently in spite of the
localized noise source, you may need to create a controlled zone at the source by dedicating a 572,
speaker(s) and an amplifier to that purpose.
Speakers serving “quiet zones,” such as break rooms, offices, and rest rooms, should probably be
on their own amplifier, fed from the input of the 572 (so that they are unaffected by the 572).
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 ambiance. The volume level of the music is important; audible, but not too
audible. How audible is not the judgement of the kid that works the counter. It’s a management decision.
The 572 helps guarantee the audibility of the music regardless of actual conditions during operation.
Again, picking the right speaker locations is the key. In a restaurant, avoid using speakers near the
kitchen, entry areas, and espresso machines for sensing.
In bars and lounges, keep any speakers mounted near the blenders and dishwashers behind the bar
out of the sensing circuit. Remember that any extraneous sound sources (like the TV in a sports
bar) will be regarded as extra ambient noise by the 572 and the sound system level will increase as a
result. You can try to avoid this by running the TV sound through the 572 so that the TV sound
becomes part of the 572’s throughput. The 572 will force a sample if it doesn’t see silent periods
that are long enough to use for sensing in the TV programming. This could be a problem during
“Monday Night Football.”
In this application, the 572 ensures that announcements within the public spaces are always
audible, but never too loud. In mall applications, it’s a good idea to wire speakers mounted near
localized noise sources (like the kiddie area) directly to the power amp so that they are not used for
sensing. Like the factory application, you want the sense speakers to average out all of the various
noise sources within the mall.
For high-noise areas, it’s a good idea to create separate coverage zones each with their own 572.
Auditoriums and Hotel Lobbies
Here the 572 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
572’s control since these areas are generally more subdued than the outer areas and you wouldn’t
want flushing a toilet to raise the SPL in the lobby (or maybe you do...).
Sports Facilities
Sports facilities, like auditoriums, can benefit from the 572. Again, the 572 tracks the ambient
conditions on the concourses, other access areas, and the refreshment stands. Consider using
multiple 572s to isolate specific noise sources and their environments from each other, such as the
refreshment stands from the concourse environment. Since the 572 uses the existing speakers, this
could be an aftermarket add-on.
23
572
Shopping Malls
Off-Track Betting Parlors and Casinos
In these facilities, the crowd reaction is likely to be sudden and intense. If the program material
doesn’t have long enough silent spots for sensing, the 571 is a better idea since it works in real
time.
In casinos, be sure to place the to average the crowd and the machines, especially the dollar
machine with the 20-jillion dollar jackpot.
Museums
Now why would you want to put a 572 into a museum? When the museum has an overall paging
system. That when.
What about when the museum has automated exhibits? That’s not when. Use a 571 instead
because the 571 works in real time. The time delays between sensing periods and operating periods
would most likely result in sound systems that are too loud for the current ambient condition.
Airports, Train Stations, etc.
The 572 is ideally suited to managing the SPLs within airports and other transportation hubs.
Within airports, use at least one 572 per paging zone.
In subway stations, pick a speaker location that favors the crowd but still ‘hears’ the trains. Doing
so ensures that the level increases when a train is present.
Make sure that there are sufficient silent periods for sensing. You can use the mic-level page input
for the local paging mic and the line-level paging input for facility-wide paging. Use the music input
for background music, if any.
Race Tracks
Different race tracks have different noise sources. In auto racing, the cars usually make more noise
than the spectators. If you’re going to apply a 572 to a speedway, position the speakers so they
are in a good spot to pick up the cars as well as the crowd.
572
If this isn’t practical, consider using a small paging speaker(s), with a 70V transformer 1 that is only
used as a microphone. Use a moderate transformer tap, like 10 watts. You may even be able to do
away with the transformer. Use shielded twisted-pair cable and don’t forget to tie the shield to the
case of the speaker (or float it if it’s plastic or to avoid a ground loop.). Position the speaker so it
has a nearby view of the stands and connect it to the 572’s T O SPEAKER terminals. Do not connect
the amplifier to the FROM AMP terminals. Instead, connect the amplifier directly to the other loudspeakers.
In horse (and dog) racing, the spectators make more noise than the animals. In this case, the
spectator area speakers serve as expected, both for paging as well as for sensing.
Use a short AVERAGING TIME. Ensure that the program material has enough dead spots to ensure
frequent sensing. Definitely use a live mic when calibrating. Beware of acoustic feedback, especially when calibrating the M AX level.
1
The ElectroVoice PA15BT-7 or PA30-AT are both suitable units.
24
Troubleshooting
Symptom:
Probable cause
There is no output signal:
Check cables and connections. Are inputs driven by outputs, and outputs driving inputs?
Determine that there really is a signal coming from the source and that it is getting to the 572.
Is the signal chain after the 572 functioning?
Check for AC power presence. Power LED on?
Is the fuse OK?
Unit will not calibrate:
Are input levels normal?
Use Option Switch B to check sense gain. Change setting of SENSE GAIN switch.
Music/Page LED flashes during calibration:
No audio at either line input or the page mic input.
Input signal level too low. Change Option Switch A to the UP position.
Speakers not connected at TO SPEAKERS terminals.
Music always plays too loud:
MIN and/or MAX levels set incorrectly during calibration.
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.
Bad calibration. Repeat calibration procedure during quiet time.
MAX level set too low.
Unit never senses, even during silence:
Option Switch D up. Change switch setting.
Unit loses the beginnings of paging messages:
Paging signals should always drive the PAGE LINE INPUT or the PAGE MIC INPUT.
Unit does not accurately adjust system as ambient noise changes:
Bad calibration. Repeat procedure during quiet time.
Hum induced in speaker wiring. Ensure that speaker wiring is not routed adjacent to AC wiring.
Disconnect speakers from 572 and connect to low-Z balanced mic preamp and listen on
headphones.
Speaker mounted near continuous noise source. Take the speaker out of the sensing system
by connecting it directly to the amplifier output.
Note
The accuracy of the 572 is only as good as the sample audio that the speakers provide
during sensing.
Unit interrupts paging:
Use either of the PAGE inputs. They have a higher priority than the music input.
Unit senses during paging:
Caused by long silent pauses during paging.
Hum or buzz in output:
Check input connector wiring (refer to Appendix B).
Ground loop. Check related system equipment grounding. Are all system components on the
same AC ground?
Distortion:
Check input signal. Is it already distorted?
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?
Noise (hiss) :
Check input signal levels, and level control settings. Check gain settings on downstream
equipment. Is the input signal already noisy?
No audio:
25
572
Chapter 9
Specifications
Chapter 10
572 Specifications
Input/Output
Inputs
Paging Mic
(For microphone level
paging signals)
All Balanced, Transformerless
Impedance >1800 Ohms
Nominal Level -80 dBu to -40 dBu
Maximum Level -30 dBu
CMRR >60 dB
Paging
Impedance >40 kilohms
(For line level paging signals)
Nominal Level 0 dBu,
Maximum Level +18 dBu
CMRR >40 dB
Music
Impedance >40 kilohms
(For line level music signals)
Nominal Level -10 dBu,
Maximum Level +18 dBu
CMRR>40 dB
+21.5 dBu
Output
Balanced, Transformerless
Impedance
200 Ohms Balanced, 100 Ohms Unbalanced
Minimum load: 600 Ohms Balanced
Nominal Level 0 dBm
Maximum level +24 dBm (into 600 Ohms)
Performance Data
Control Range
Noise to Gain Ratio
Sample Interval
Frequency Response
THD+Noise
Signal to Noise Ratio
Gain (VCA at unity)
Voltage Control Scale
Software
Physical
Size
Weight
Variable, up to 40 dB (-20 dB to +20 dB)
Variable, 2:1 to 1:2
Forced: Variable, 1 min. to 26 min
Auto: Silence periods (< -30 dBm) > 800 ms
Page-Over Music: Variable, 0 to 15 dB
20 Hz to 20 kHz + 1 dB, -0 dB
<0.05% THD, unity gain, 1 kHz
music into balanced output
>70 dB, ref: 0 dBu, unity gain
(30 kHz noise bandwidth)
Balanced Input to Unbalanced Output = 0 dB
Unbalanced Input to Balanced Output = 6 dB
156 mV/ dB
Copyright Symetrix, Inc. 1989
1.74 x 19 x 6.25 inches, 4.42 x 48.3 x 15.875 centimeters
8lbs (3.6 kgs)
Electrical
Power Requirements
117 V AC, 60 Hz, 0.1amp (approx. 12 watts)
Note:
The maximum operating ambient temperature is
25 degrees C.
In the interest of continuous product improvement, Symetrix Inc.
reserves the right to alter, change, or modify these specifications
without prior notice.
572 Architects and Engineers Specifications
572
The ambient sensing automatic level controlling device shall regulate the operating level of a
sound system in proportion to changing noise levels in the sound system’s operating area. The
device shall be capable of adjusting gain control over 40 dB overall (max) range, and shall be
governed by a microprocessor which shall be controlled by embedded software. The device shall
vary its gain based upon measurements of the sound pressure level of ambient noise in the
environment. These sound level measurements shall be made by the level controlling device
through the loudspeakers otherwise used for the system’s output. To facilitate the use of the
system’s loudspeakers as noise measuring “microphones” the device shall provide relay switching
of the speaker line circuit so as to disconnect the speakers from the amplifier output and connect
the speakers to its own sensing input. The device shall provide inputs for paging signals at
microphone level (nominal -40 dBv) or line level (nominal 0 dBv), and for music signals at line level
(nominal 0 dBv). The device shall have a Ratio control to vary the ambient noise-to-gain ratio
continuously from 2:1 to 1:2, and a front panel switchable hard-wired bypass. Calibration of the
automatic level controlling device shall be semiautomatic, and shall require switching the device to
CAL Mode, and adjusting the minimum desired operating level and the maximum desired operating
level. Calibration settings shall be continuously maintained in nonvolatile memory without the
need for battery pack up power.
In addition to the various functions and general specifications mentioned above, the ambient
sensing automatic level controlling device shall meet or exceed the following overall performance
criteria: frequency response ±1 dB 20 Hz to 20 kHz, total harmonic distortion less than .05% at any
attenuation from -40 dB to 0 dB (2 kHz), maximum paging microphone input level -30 dBv, maximum
line input level +18 dBu, maximum output level +24 dBm into 600-Ohms (balanced). Minimum
impedance at the microphone inputs shall be 1800 Ohms, minimum impedance at the line inputs
shall be 10 kilohms. The device shall be housed in an all steel chassis designed to be mounted in a
1U (1.74") space in a standard 19" rack.
The ambient sensing automatic level controlling device shall be the Symetrix model 572 SPL
Computer.
26
Chapter 11
Warranty & Service
572 Limited Warranty
Symetrix, Inc. expressly warrants that the product will be free from defects in material and workmanship for one (1) year. Symetrix's obligations under this warranty will be limited to repairing or
replacing, at Symetrix's option, the part or parts of the product which prove defective in
material or workmanship within one (1) year from date of purchase, provided that the Buyer
gives Symetrix prompt notice of any defect or failure and satisfactory proof thereof. Products
may be returned by Buyer only after a Return Authorization number (RA) has been obtained
from Symetrix. Buyer will prepay all freight charges to return the product to the Symetrix
factory. Symetrix reserves the right to inspect any products which may be the subject of any
warranty claim before repair or replacement is carried out. Symetrix may, at its option, require
proof of the original date of purchase (dated copy of original retail dealer's invoice). Final
determination of warranty coverage lies solely with Symetrix. Products repaired under warranty
will be returned freight prepaid by Symetrix via United Parcel Service (surface), to any location
within the Continental United States. At Buyer's request the shipment may be returned via
airfreight at Buyer's expense. Outside the Continental United States, products will be returned
freight collect.
The foregoing warranties are in lieu of all other warranties, whether oral, written, express,
implied or statutory. Symetrix, Inc. expressly disclaims any IMPLIED warranties, including
fitness for a particular purpose or merchantability. Symetrix's warranty obligation and
buyer's remedies hereunder are SOLELY and exclusively as stated herein.
This Symetrix product is designed and manufactured for use in professional and studio audio
systems and is not intended for other usage. With respect to products purchased by consumers for personal, family, or household use, Symetrix expressly disclaims all implied warranties, including but not limited to warranties of merchantability and fitness for a particular
purpose.
This limited warranty, with all terms, conditions and disclaimers set forth herein, shall extend
to the original purchaser and anyone who purchases the product within the specified warranty
period.
Symetrix does not authorize any third party, including any dealer or sales representative, to
assume any liability or make any additional warranties or representation regarding this product
information on behalf of Symetrix.
This limited warranty gives the buyer certain rights. You may have additional rights provided
by applicable law.
Limitation of Liability
The total liability of Symetrix on any claim, whether in contract, tort (including negligence) or
otherwise arising out of, connected with, or resulting from the manufacture, sale, delivery,
resale, repair, replacement or use of any product will not exceed the price allocable to the
product or any part thereof which gives rise to the claim. In no event will Symetrix be liable for
any incidental or consequential damages including but not limited to damage for loss of
revenue, cost of capital, claims of customers for service interruptions or failure to supply, and
costs and expenses incurred in connection with labor, overhead, transportation, installation or
removal of products or substitute facilities or supply houses.
27
572
Warranty Registration must be completed and mailed to Symetrix within thirty (30) days of the
date of purchase.
Servicing the 572
If you have determined that your 572 requires repair services and you live outside of the
United States please contact your local Symetrix dealer or distributor for instructions on how
to obtain service. If you reside in the U.S. then proceed as follows:
At the Symetrix factory, Symetrix will perform in-warranty or out-of-warranty service on any
product it has manufactured for a period of five years from date of manufacture.
Before sending anything to Symetrix, contact our Customer Service Department for a return
authorization (RA) number. The telephone number is (425) 787-3222, Monday through Friday,
8AM (800 hours) though 4:30 PM (1630 hours), Pacific Time.
In-warranty Repairs
To get your 572 repaired under the terms of the warranty:
1.
Call us for an RA number.
2.
Pack the unit in its original packaging materials.
3.
Include your name, address, daytime telephone number, and a brief
statement of the problem.
4.
Write the RA number on the outside of the box.
5.
Ship the unit to Symetrix, freight prepaid.
We do not accept freight collect shipments.
Just do these five things, and repairs made in-warranty will cost you only one-way freight
charges. We'll prepay the return (surface) freight.
572
If you choose to send us your product in some sort of flimsy packaging, we'll have to charge
you for proper shipping materials. If you don't have the factory packaging materials, then do
yourself a favor by using an oversize carton, wrap the unit in a plastic bag, and surround it
with bubble-wrap. Pack the box full of Styrofoam peanuts. Be sure there is enough clearance in
the carton to protect the rack ears (you wouldn't believe how many units are returned with bent
ears). We won't return the unit in anything but Symetrix packaging for which we will have to
charge you. Of course, if the problem turns out to be operator inflicted, you'll have to pay for
both parts and labor. In any event, if there are charges for the repair costs, you will pay for the
return freight. All charges will be COD unless you have made other arrangements (prepaid,
Visa or Mastercard).
Out-of-warranty Repairs
If the warranty period has passed, you'll be billed for all necessary parts, labor, packaging
materials, and freight charges. Please remember, you must call for an RA number before
sending the unit to Symetrix.
28
Appendix A
External Sensing & Multi-Unit Installations
OPTION switch D enables the external sense input and prevents both periodic sensing and silencebased sensing. When OPTION switch D is UP, sensing only occurs when TB2-3 is held low
(grounded). The unit remains in sense mode for as long as TB2-3 is grounded and you must
ground the external sense line for a minimum of one second.
You use this feature when it is inappropriate to interrupt the program material based on either time
or silence. Of course, you must have some other means of telling the 572 when to sense (electronic
wizardry, slave labor, etc.).
OPTION switch D has one additional use: forcing multiple 572s to sample simultaneously. There are
two reasons for doing this:
1.
Adjacent sound systems to the controlled area are noise sources as far as the 572 is
concerned. Their acoustical output influences the ambient sampling of other units.
Simultaneous sampling removes adjacent systems from consideration as noise sources.
2.
During sampling, the sampling speakers are connected to an extremely high-gain amplifier.
Adjacent speaker wiring, in the same conduit or raceway, may cause crosstalk into the speaker
wiring connected to the sampling speakers, which will cause erroneous results in the
controlled zone.
Figure Appendix A-1 shows what is necessary for externally controlled sampling. Figure Appendix
A-2 shows how to interconnect multiple 572s for simultaneous sampling.
A BC
1
2
D
FROM
TO
SPEAKER AMP
UP
EXT
RELAY
CNTRL
EXT
SENSE
TRIG
SPARE
LINE
OUTPUT
P RE
LINE INPUTS
PAGE
MUSIC
Vc
3
OPTIONS
TB2 10
9
8
7
6
5
4
3
2
1
TB1 10
9
8
7
6
5
4
3
2
1
MASTER UNIT
SH
T O SA M
PL
MOMENTARY SPST
PUSHBUTTON SWITCH
572
P
U
E
SAMPLE
Figure Appendix A-1. Using option switch D and a remote momentary
pushbutton for externally controlled sampling.
29
A BC
1
2
D
DOWN
FROM
TO
SPEAKER AMP
EXT
RELAY
CNTRL
EXT
SENSE
TRIG
SPARE
LINE
OUTPUT
P RE
LINE INPUTS
PAGE
MUSIC
Vc
3
OPTIONS
TB2 10
9
8
7
6
5
4
3
2
1
TB1 10
9
8
7
6
5
4
3
2
1
MASTER
A BC
1
2
D
UP
FROM
TO
SPEAKER AMP
EXT
RELAY
CNTRL
EXT
SENSE
TRIG
SPARE
LINE
OUTPUT
PRE
LINE INPUTS
PAGE
MUSIC
Vc
3
OPTIONS
TB2 10
9
8
7
6
5
4
3
2
1
TB1 10
9
8
7
6
5
4
3
2
1
SLAVE UNIT #1
A BC
1
2
D
UP
FROM
TO
SPEAKER AMP
EXT
RELAY
CNTRL
EXT
SENSE
TRIG
SPARE
LINE
OUTPUT
P RE
LINE INPUTS
PAGE
MUSIC
Vc
3
OPTIONS
TB2 10
9
8
SLAVE UNIT #2
7
6
5
4
3
2
1
TB1 10
9
8
7
6
5
4
3
TO ADDITIONAL
SLAVE 572’S
572
Figure Appendix A-2. Multiple 572 master-slave connections for simultaneous sampling.
30
2
1
Appendix B
Connections
Input and output connector wiring. These diagrams represent the majority of connectors used in modern
audio equipment. Locate the source connector in the left column and match it up with the destination
connector in the right column. Wire your cable according to the diagrams.
TO BALANCED IN
2 31
13 2
FROM BALANCED OUT
FEMALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
TO UNBALANCED IN FROM
TRANSFORMER COUPLED OR
FLOATING BALANCED OUTPUT
FROM BALANCED OUT
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
MALE XLR
PIN 1 = GROUND
PIN 2 = HIGH
PIN 3 = LOW
TIP
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
RING
SLEEVE
TO BALANCED IN
FROM UNBALANCED OUT
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
TIP
RING
MALE TRS PLUG
TIP = HIGH
RING = LOW
SLEEVE = GROUND
SLEEVE
FROM BALANCED OUT
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
TO BALANCED IN
FROM UNBALANCED OUT
TERMINAL STRIP
(+) = HIGH
(-) = LOW
= GROUND
FROM NON-TRANSFORMER (ELECTRONIC)
BALANCED OUTPUT
(TYPICAL OF SYMETRIX PRODUCTS)
2 31
FEMALE XLR
PIN 1 = GROUND + LOW
PIN 2 = HIGH
PIN 3 = NOT USED
TO UNBALANCED IN
MALE TS PLUG
TIP = HIGH
SLEEVE = GROUND +
LOW
REV-B
31
572
TERMINAL STRIP
(+) = HIGH
(-) = NOT USED
= GROUND
572
32
Symetrix, Inc.
14926 35th Ave. West
Lynnwood, WA, 98037-2303
USA
Tel: (425) 787-3222
Fax: (425) 787-3211
Website: http://www.symetrixaudio.com
Email: [email protected]
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