Symetrix 372 SPL Computer User manual

372 SPL Computer
USERNGUIDE

372 SPL Computer User’s Guide
© January 2001Symetrix, Inc.
All rights reserved.
Printed in the United States of America
Symetrix Part Number 53372-0C00
The information in this guide is subject to
change without notice. Symetrix, Inc. shall
not be liable for technical or editorial
errors or omissions contained herein; nor
is it liable for incidental or consequential
damages resulting from the furnishing,
performance, or use of this material.
Mention of third-party products is for in-
formational purposes only and constitutes
neither an endorsement nor a recommen-
dation. Symetrix assumes no responsibil-
ity with regard to the performance or use
of these products.
Under copyright laws, no part of this user
guide may be reproduced or transmitted
in any form or by any means, electronic or
mechanical, without permission in writing
from Symetrix, Inc. If, however, your only
means of access is electronic, permission
to print one copy is hereby granted.
Permission to copy the Architects and
Engineers Specificiations for written
proposals specifying equipment for sound
reinforcement systems is, also, granted.
Symetrix, Inc.
6408 216th St. SW
Mountlake Terrace WA 98043
USA
Tel:[phone]
Fax:[phone]
Web: www.symetrixaudio.com
Email: [email protected]

1
Contents
Before You Begin 2
What Ships in the Box 2
Getting Help 2
Optional Rackmount Accessories 2
Notational Conventions in this User Guide 2
Operational Safety Summary 3
Equipment Markings 3
Features of the 372 4
Checklist of Tasks for Hardware Connections,
System Setup, and Calibration 5
Making Hardware Connections 6
Overview of Rear Panel Connectors and Connections 6
Sensing Speaker Considerations 8
372 Basic Connection 9
Connecting an External Relay to Drive Amplifiers
Larger than 200W 10
Connecting Up to 20 Slaves 11
Connecting an External Relay to Attach Slaves 12
Connecting a Push Button Switch to Force or
Prevent Sensing 13
System Setup 14
Overview of Front Panel 14
How System Setup Works 15
Description of Menu Features 16
Operating Mode 16
Status 18
History 18
Listen 18
Set MIN Limit 19
Set MAX Limit 19
Averaging Time 19
Gain: Sense Ratio 19
Symetrix 372 SPL Computer User’s Guide
Gap Threshold 20
Force Sense Time 20
AGC 20
Trigger Input 21
Setup Unlocked 21
Calibrating the 372 22
Conditions Under Which the 372
Will Not Sense 23
Signal Flow Diagram 24
Input and Output Connector Wiring 25
Troubleshooting 26
Hardware Specifications 28
Architects and Engineers Specifications 29
Warranty 30
Service 31
Declaration of Conformity 32

2
What Ships in the Box Getting Help
If you have questions beyond the scope of this guide, contact our Customer
Service Department in the following ways:
TUS customers
[phone]
International customers
[phone]
8:00 am to 4:30 pm Monday through Friday, Pacific Time
F
[phone]
[email protected]
www.symetrixaudio.com
Optional Rackmount Accessories
MODEL ITEM DESCRIPTION
RM-3 19" Rackmount Tray 1U shelf
FP-3 Filler Panel Covers unused half of rack tray when
one 372 unit is mounted
PY-3 Y Power Cable Connects a 372 with any other 300
Series product
Contact your dealer or Symetrix for purchasing information.
Notational Conventions in this User Guide
Note Identifies information that needs extra emphasis. Generally
supplies extra information to help you to better use the 372.
CAUTION Identifies information that, if ignored, may cause damage to
the 372 or other equipment in your system.
WARNING Identifies information that, if ignored, may be hazardous to
your health or that of others.
SMALL CAPS Controls, switches or other markings on the chassis of the 372.
Bold Face Indicates menu option in the 372 LCD display.
Before You Begin
| What Ships in the Box | Getting Help | Optional Rackmount Accessories | Notational
Conventions in this User Guide | Operator Safety Summary | Equipment Markings
The 372 unit
One PS-3 or PS-3E (export
version) power supply
This user’s guide
Symetrix 372 SPL Computer User’s Guide

3
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
Before You Begin
| What Ships in the Box | Getting Help | Optional Rackmount Accessories | Notational
Conventions in this User Guide | Operator Safety Summary | Equipment Markings
Operator Safety Summary
Follow all warnings and instructions. Install
in accordance with the manufacturer’s
instructions.
Power Source This product is intended
to operate from a Symetrix PS-3 or PS-3E
power supply.
Grounding The chassis of this product is
grounded through the grounding conduc-
tor of the PS-3 or PS-3E 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 the plug,
convenience receptacle, and the point
where the cord exits from the apparatus.
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 372. In
case of failure, refer all servicing to the
factory. Servicing is required when the
372 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.
Equipment Markings
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 user’s
guide).
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.
Symetrix 372 SPL Computer User’s Guide

4
Features of the 372
Uses Speakers for Noise Sensing In less than 1 second, the Symetrix 372 temporarily opens up the amplifier
connection and routes the loudspeakers to a preamplifier for the purpose of
measuring changes in the ambient noise level. Samples during absence of page
and/or music audio, or at preset intervals.
Headphone Monitoring Monitor the sense signal using a separate front panel headphone output.
5 Operating Modes MUSIC Music only or music + page. Use Gap and/or Force Sense Time.
PAGE Only paging and annoucement audio. Use Force Sense Time at
preset intervals.
SLAVE Forces all 372 units in a multi-zone system to execute a sense
sample at the same time.
HISTORY Records and displays the lowest and highest SPL readings from when
the unit was last reset.
BYPASS Bypasses the gain control of the SPL controller and the AGC.
Signal Path Controls mono or stereo signals through Euroblock connectors.
Programmable Sensing Operation Select the auto-sense mode and/or the time interval between sense samples.
Simple Calibration Use step-through menus on the front panel LCD. Perform calibration under
typical installation conditions. No waiting for the quietest or noisiest ambient
environment.
AGC Control Enables or disables auto leveling of input signals.
Ambient Adjustment Choose an adjustment ratio of SPL change vs. program level change.
Sense Signal Monitoring Display numeric reading and relative bargraph of the signal appearing at the
sense terminals.
Listen to sense signal with headphones connected to front panel mono output.
Gain Controls Set minimum and maximum limits for SPL gain range. Gain range is +20 to –30 db.
Averaging Time Choose integration time of the running average SPL.
Symetrix 372 SPL Computer User’s Guide

5
REQUIRED RECOMMENDED OPTIONAL TASK TO DO
HARDWARE Connecting input sources
Connecting output sources (use Symetrix 303 for
unbalanced outputs)
Connecting speaker for sensing and music/paging
Connecting speaker for either music or paging; does not
sense
Connecting an external relay if maximum amplifier
voltage and wattage exceeded
Connecting slave 372s
Connecting a switch or contact closure to manually force
or prevent sensing
SYSTEM SETUP Choose Operating Mode*
View calibration Status
Collect History of highest and lowest SPLs
Set gain level in Listen
Set MIN limit (gain)
Set MAX limit (gain)
Specify number of samples in Averaging Time
Specify Gain: Sense Ratio
Set Gap Threshold
Specify time for Force Sense Time
Enable AGC
Specify type of Trigger Input
Lock or Unlock Setup
CALIBRATION Equating ambient noise level to 0 db (Unity) gain
*Bold face indicates menu name in LCD display
Checklist of Tasks for Hardware Connections,
System Setup, and Calibration
CONNECTIONS
Symetrix 372 SPL Computer User’s Guide

6
Overview of Rear Panel Connectors and Connections
CONNECTION CONNECTOR TYPE WHAT IT DOES
Power Input 7-pin DIN connector Accepts power only from Symetrix
PS-3 or PS-3E power supply.
FROM AMP 2 terminal barrier strip Accepts signal from power amplifier.
This output may be grounded or
bridged. 8A maximum current rating.
If your speaker load exceeds the
following ratings, you will need to use
an external relay (See Connecting an
External Relay to Attach Slaves).
MAX AMPLIFIER OUTPUT RATINGS
16 ohms 400W
70V 300W
8 ohms 200W
4 ohms 100W
TOSPEAKER 2 terminal barrier strip Delivers signal to loudspeaker system.
Do not ground either of these terminals.
SENSE EXT RELAY Euroblock terminals Open-collector drive signal for exter-
nal sense relay. Can power amplifiers
larger than 200W at 8 ohms (See
Connecting an External Relay to
Attach Slaves). Controls as many as
20 slave 372 units directly from the
EXT RELAY output of the master 372.
This output can also drive the TRIGGER
input.
GROUND Euroblock terminals Ground return for external relay and
trigger.
TRIGGER Euroblock terminals Active low input forces sense event.
Can force or prevent a sense event
manually (See Connecting a Push
Button Switch to Force or Prevent
Sensing). Is internally pulled to the 5V
supply by way of a 20k ohm resistor.
From this connection attach slave 372
units to the master 372.
Making Hardware Connections
| Overview of Rear Panel Connectors and Connections | Sensing Speaker Considerations
| 372 Basic Connection | Connecting an External Relay to Drive Amplifiers Larger than 200W
| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves
| Connecting a Push Button Switch to Force or Prevent Sensing
LEFT
372
LINE OUTPUT
RIGHTLEFTRIGHT
LINE INPUTFROM AMP
INPUT
POWER
CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY
EXT. RELAY
SENSE
TRIGGER
TO SPEAKER
Symetrix 372 SPL Computer User’s Guide

7
CONNECTION CONNECTOR TYPE WHAT IT DOES
LINE OUTPUT Euroblock terminals These connectors deliver a differential
balanced output at 200 ohm source
impedance. For unbalanced use, use
the positive line output terminals and
the ground terminals. Ignore (float)
the minus output terminals.
The output stage is a pair of opamps,
with the plus and minus output
terminals at 180°antiphase with each
other. It emulates a grounded center-
tap transformer. The series build-out
resistors are 100 ohms in each leg.
For wiring diagram, see the section
Input and Output Connector Wiring.
LINE INPUT Euroblock terminals Balanced input for the 372. 20k ohm
balanced bridging. For unbalanced
sources, connect the minus input
terminal to the source ground at the
source.
Note
Feeding unbalanced inputs directly from
balanced outputs is not recommended
due to the possibility of ground loops.
You may want to use the Symetrix 303
isolation transformer to break the
ground connection and eliminate the
ground loop.
With unbalanced sources, it is preferable
to carry the low side of the input all the
way back to the ground connection of
the source.
For wiring diagram, see the section
Input and Output Connector Wiring.
Making Hardware Connections
| Overview of Rear Panel Connectors and Connections | Sensing Speaker Considerations
| 372 Basic Connection | Connecting an External Relay to Drive Amplifiers Larger than 200W
| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves
| Connecting a Push Button Switch to Force or Prevent Sensing
Symetrix 372 SPL Computer User’s Guide

8
Sensing Speaker Considerations
Making Hardware Connections
Speaker Location
If a sensing speaker is located near a
localized noise source that is not
typical for the ambient noise level of
the controlled zone, the 372 deter-
mines that the zone is noiser than it
really is. For example, the noise from
a large machine of some sort, or
maybe a kids play area, or a video
game. The solution is to have the
speakers that are near the noise
source driven directly from the
amplifier so that they are not used
for sensing.
| Overview of Rear Panel Connectors and Connections | Sensing Speaker Considerations
| 372 Basic Connection | Connecting an External Relay to Drive Amplifiers Larger than 200W
| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves
| Connecting a Push Button Switch to Force or Prevent Sensing
70V Systems
In a 70V system, the signal level
returned by the speakers when the
372 is sensing is higher, because of
the step-up action of the line trans-
formers. With highly-efficient speak-
ers, this may present the problem of
overloading the sense input of the
372. Use the Listen mode to check
the level of the signal while the 372
senses. You may need to lower the
gain position of the AMBIENT SENSE
GAIN switch. More information about
the gain setting is found in Listen
under the section System Setup.
A common practice in 70V systems is
to provide autotransformers or L-pads
after the line transformer to allow
local volume control. These controls
should not be used with the 372.
Allowing any sort of signal level
control after the 372 invalidates your
calibration settings. If you must
provide a local control, then ensure
that the controlled zone is a minor
part of the entire system. In this
controlled zone, volume level will not
be ideal and sensing should not be
used.
Also, it is imperative that every
speaker and transformer in the
system operate in-phase.
4, 8, and 16 Ohm Systems
In these speaker impedance systems,
the signal levels returned to the 372
are low. Use the Listen mode to
check the level of the signal while the
372 senses. You may need to select
the high gain position of the AMBIENT
SENSE GAIN switch.
Symetrix 372 SPL Computer User’s Guide