Symetrix 372 SPL Computer, 372 User Manual

372 SPL Computer

USERN GUIDE

372 SPL Computer User’s Guide

© January 2001 Symetrix, 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 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 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: [e-mail]

Symetrix 372 SPL Computer User’s Guide

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

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

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

Service 31

Declaration of Conformity 32

1

Symetrix 372 SPL Computer User’s Guide

Before You Begin

| What Ships in the Box | Getting Help | Optional Rackmount Accessories | Notational

What Ships in the Box

 The 372 unit

 One PS-3 or PS-3E (export

version) power supply

 This user’s guide

Conventions in this User Guide | Operator Safety Summary | Equipment Markings

Getting Help

If you have questions beyond the scope of this guide, contact our Customer
Service Department in the following ways:

TUS customers

International customers
8:00 am to 4:30 pm Monday through Friday, Pacific Time

F

[phone]

[e-mail]

www.symetrixaudio.com

[phone]

[phone]

Optional Rackmount Accessories

MODEL ITEM DESCRIPTION

RM-3 19" Rackmount Tray 1U shelf

FP-3 Filler Panel Covers unused half of rack tray when

PY-3 Y Power Cable Connects a 372 with any other 300

Contact your dealer or Symetrix for purchasing information.

one 372 unit is mounted

Series product

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.

2

N

.

Symetrix 372 SPL Computer User’s Guide

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 conduc­tor 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

CAUTION

RISK OF ELECTRIC SHOCK

DO NOT OPEN

TO REDUCE THE RISK OF FIRE OR

WARNING:

SEE OWNERS MANUAL. VOIR CAHIER D’INSTRUCTIONS.

o user serviceable parts inside. Refer servicing to qualified service personnel

Il ne se trouve a l’interieur aucune piece pourvant entre reparée l’usager.

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.

ELECTRIC SHOCK DO NOT EXPOSE
THIS EQUIPMENT TO RAIN OR MOISTURE

RISQUE DE CHOC ELECTRIQUE

AVIS:

NE PAS OUVRIR

S’adresser a un reparateur compétent.

3

Symetrix 372 SPL Computer User’s Guide

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.

4

Symetrix 372 SPL Computer User’s Guide

Checklist of Tasks for Hardware Connections,

System Setup, and Calibration

REQUIRED RECOMMENDED OPTIONAL TASK TO DO

HARDWARE  Connecting input sources
CONNECTIONS

 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

5

Symetrix 372 SPL Computer User’s Guide

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

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

TO SPEAKER

EXT. RELAY

SENSE

TRIGGER

LINE OUTPUT

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

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

TO SPEAKER 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
input.

TRIGGER

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.

6

Symetrix 372 SPL Computer User’s Guide

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

CONNECTION CONNECTOR TYPE WHAT IT DOES

LINE OUTPUT Euroblock terminals These connectors deliver a differential

| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves

| Connecting a Push Button Switch to Force or Prevent Sensing

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 center­tap 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.

7

Symetrix 372 SPL Computer User’s Guide

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

Sensing Speaker Considerations

| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves

| Connecting a Push Button Switch to Force or Prevent Sensing

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 deter­mines 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.

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 trans­formers. With highly-efficient speak­ers, 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.

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.

Also, it is imperative that every
speaker and transformer in the
system operate in-phase.

8

Symetrix 372 SPL Computer User’s Guide

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

372 Basic Connection

Signal I/O Connections

These connectors are designed for
use with bare wire. Do not tin strand
wires before inserting them into the
connectors.

If using unbalanced connections, see
wiring diagram in the section Input
and Output Connector Wiring.

Note
Feeding unbalanced inputs directly from
balanced outputs is not recommended
due to the possibility of ground loops.
An option is to use the Symetrix 303
isolation transformer to break the
ground connection and eliminate the
ground loop.

1 Connect your line-level source to

the rear-panel input connectors.

These connectors may be driven
from a balanced or unbalanced
source. When using an unbal­anced source, connect the output
minus terminal to ground either at
the source or at the 372.

2 Connect the outputs as required.

These connectors deliver a
differential balanced output signal.
For unbalanced use, use the
positive line output terminals and
the ground terminals. Ignore
(float) the minus output terminals.

Amplifier and Speaker
Connections

3 Connect your amplifier and

speakers to the barrier strip
connectors.

The speaker and amplifier connec­tions are earth-free (floating).

The 372 treats the speaker
connections after its sensing relay
as if they were a balanced line.
Do not ground either side of the
speaker line. It is OK if the one
side of the amplifier output is
grounded.

| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves

| Connecting a Push Button Switch to Force or Prevent Sensing

3

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

3

Amplifier

Connect all speakers that do not sense
to the amplifier output.

Use these speakers for only music or
paging.

These speakers are optional.

TO SPEAKER

Connect all speakers used for sensing
and either music or paging to this
output.

These speakers are required.

The relay contacts handle 8A
continuous current.

SENSE

EXT. RELAY

TRIGGER

LINE OUTPUT

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

2

1

Input Source

9

Symetrix 372 SPL Computer User’s Guide

Making Hardware Connections

| Overview of Rear Panel Connectors and Connections | Sensing Speaker Considerations

Larger than 200W | Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves

Connecting an External Relay to Drive Amplifiers Larger than 200W

| 372 Basic Connection | Connecting an External Relay to Drive Amplifiers

| Connecting a Push Button Switch to Force or Prevent Sensing

When controlling amplifiers larger
than 200W, you must use an external
DPDT relay. The internal relay of the
372 cannot handle more than 8A of
load current.

RECOMMENDED MAXIMUM
AMPLIFIER WATTAGES

400W 16 ohms

300W 70V

200W 8 ohms

100W 4 ohms

You must supply power for the relay
and the relay must have a back­biased 1N4002 diode connected
across its coil to absorb the back EMF
from the relay coil. The transistor has
a 60V VCE rating (MPSA 06).

The 24V version of the Potter &
Brumfield PRD11DGO works well. Its
DPDT contacts are rated at 30A.

DC
Power
Supply

External DC
Coil Relay

Low (–)

Low (–)

High (+)

(+)

(–)

1N4002 or
Equivalent
Diode

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

TO
SPEAKER

High (+)

EXT. RELAY

SENSE

TRIGGER

LINE OUTPUT

Amplifier

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

10

Symetrix 372 SPL Computer User’s Guide

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 Up to 20 Slaves | Connecting an External Relay to Attach Slaves

| Connecting a Push Button Switch to Force or Prevent Sensing

A master 372 can direct any number
of slave 372 units to take an ambient
sample. You can parallel slave 372
units directly together from the
master unit to enable you to sense at
the same time in adjacent or multiple
installation zones. If the slave 372
units are in remote locations, use an
external relay to connect the slaves
to the master unit (see Connecting an
External Relay to Attach Slaves).

As many as 20 slave 372 units may
be controlled directly from the master

372.

MAXIMUM CABLE LENGTH

Depends upon the difference in
ground potential (if any) between the
individual units.

IMPORTANT!

As of 372 hardware revision C, an
internal jumper (J8) has been added
which must be in correctly config­ured on the master 372 in order to
properly drive the slaves.

On the master 372, remove the top
and move the jumper (J8) to con­nect pins 2 and 3. (Pins 1 and 2
are connected at the factory. This is
the default position and this jumper
should only be changed on the mas­ter 372. J8 should remain in the fac­tory default position on all slaves).

Moving J8 to connect pins 2 and
3 configures the TRIGGER input
connection on the Master 372 to
become a Slave Drive OUTPUT. This
reconfiguration is necessary to pre­vent a "false sensing" problem when
multiple zones bleed into each other.
This new way of configuring the
master 372 ensures that all 372's
will sense in sync thus avoiding false
sense readings from zone bleed.

Master 372

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

Slave 372

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

TO SPEAKER

SENSE

EXT. RELAY

TRIGGER

Connect a cable from TRIGGER and
Ground terminals of the master unit.

Connect the other end of the cable to

TRIGGER input and Ground terminals

the

of each slave unit in parallel.

From the front panel of the slave 372
LCD menu display:

Press

NEXT to gain access to Operating

Mode.

Rotate

Press

ADJUST to select Slave mode.

NEXT to locate Trigger Input.

Check to see that Force Sense is selected.
(Force Sense is the default setting.)

(See Operating Mode—Slave in the
section System Setup for additional
information)

TO SPEAKER

LINE OUTPUT

SENSE

EXT. RELAY

LINE INPUTFROM AMP

RIGHTLEFTRIGHT

TRIGGER

Slave Group up to 20 units

LEFT

POWER

INPUT

POWER

INPUT

POWER

INPUT

POWER

INPUT

POWER

INPUT

LINE OUTPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

RIGHTLEFTRIGHT

372

LINE INPUTFROM AMP

TO SPEAKER

TO SPEAKER

TO SPEAKER

TO SPEAKER

TO SPEAKER

LEFT

372

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

EXT. RELAY

SENSE

TRIGGER

EXT. RELAY

SENSE

TRIGGER

EXT. RELAY

SENSE

TRIGGER

EXT. RELAY

SENSE

TRIGGER

EXT. RELAY

LINE OUTPUT

LINE OUTPUT

LINE OUTPUT

LINE OUTPUT

LEFT

RIGHTLEFTRIGHT

372

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

11

Symetrix 372 SPL Computer User’s Guide

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 an External Relay to Attach Slaves

Use an External Relay:

To connect more than 20 slave 372
units together from the master unit to
sense at the same time in adjacent or
multiple installation zones.

—or—

To connect slave 372 units in remote
locations from the master unit.

| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves

| Connecting a Push Button Switch to Force or Prevent Sensing

Master 372

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

TO SPEAKER

SENSE

EXT. RELAY

TRIGGER

LINE OUTPUT

External Relay Pack

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

If some of the slave units are a long
distance away from the master, a
direct connection might give rise to
ground loop problems. To avoid this,
use an external relay to isolate the
connection between the master and
the distant slaves.

IMPORTANT!

Please see notes on previous page
regarding internal jumper configura­tion of the master 372.

Connect a cable from TRIGGER and
Ground terminals of the master unit to

the External Relay control and Ground
terminals on the rear panel of the
external relay.

Connect cables from the external relay
outputs to the TRIGGER and Ground

terminals of each slave unit in parallel.

From the front panel of the slave 372
LCD menu display:

Press

NEXT to gain access to Operating

Mode.

Rotate

Press

Check to see that Force Sense is selected.
(Force Sense is the default setting.)

(See Description of Menu Features,
Operating Mode—Slave in the section
System Setup for additional information)

ADJUST to select Slave mode.

NEXT to locate Trigger Input.

Slave 372

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

Ext

Relay

Control

TO SPEAKER

SENSE

EXT. RELAY

TRIGGER

LINE OUTPUT

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

372

Slave Group 1 Slave Group 2

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

LEFT

RIGHTLEFTRIGHT

TO SPEAKER

TO SPEAKER

TO SPEAKER

TO SPEAKER

TO SPEAKER

TO SPEAKER

EXT. RELAY

372

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

LEFT

RIGHTLEFTRIGHT

EXT. RELAY

372

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

LEFT

RIGHTLEFTRIGHT

EXT. RELAY

372

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

LEFT

RIGHTLEFTRIGHT

EXT. RELAY

372

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

LEFT

RIGHTLEFTRIGHT

EXT. RELAY

372

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

LEFT

RIGHTLEFTRIGHT

EXT. RELAY

372

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

LEFT

RIGHTLEFTRIGHT

EXT. RELAY

372

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

CONNECT TO

POWER

SYMETRIX

INPUT

PS-3 OR PS-3E
POWER
SUPPLY ONLY

Slaved Groups

1234

Sen Sen Sen Sen

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

RIGHTLEFTRIGHT

EXT. RELAY

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

RIGHTLEFTRIGHT

EXT. RELAY

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

RIGHTLEFTRIGHT

EXT. RELAY

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

RIGHTLEFTRIGHT

EXT. RELAY

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

RIGHTLEFTRIGHT

EXT. RELAY

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

RIGHTLEFTRIGHT

EXT. RELAY

TO SPEAKER

LINE OUTPUT

LINE INPUTFROM AMP

SENSE

TRIGGER

RIGHTLEFTRIGHT

EXT. RELAY

LEFT

372

LEFT

372

LEFT

372

LEFT

372

LEFT

372

LEFT

372

LEFT

372

12

Symetrix 372 SPL Computer User’s Guide

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 a Push Button Switch to Force or Prevent Sensing

You can manually prevent sensing or
manually control sensing by using a
push button switch.

In conjunction with the
connection on the rear panel, you
must also choose Trigger Input in
the LCD menu display to enable either
a force sense or prevent sense event.

Prevent Sense is useful in the Music
mode during voice announcements, in
conjunction with an external contact
closure. In Music mode the 372 has
no other way to know if an announce­ment is happening.

An example of an external contact
closure might be a spare set of
contacts on a push-to-talk micro­phone. The 372 is prevented from
sensing the ambient room level
whenever these contacts are pressed
closed. Otherwise, a timed sense
event might “cut off” the announcer
when he/she is speaking.

| Connecting Up to 20 Slaves | Connecting an External Relay to Attach Slaves

| Connecting a Push Button Switch to Force or Prevent Sensing

TRIGGER

POWER

INPUT

CONNECT TO
SYMETRIX
PS-3 OR PS-3E
POWER
SUPPLY ONLY

Push Button Switch

To Force a Sense Event

TO SPEAKER

EXT. RELAY

SENSE

TRIGGER

LINE OUTPUT

LINE INPUTFROM AMP

LEFT

RIGHTLEFTRIGHT

Connect a momentary contact closure
between the TRIGGER and Ground
terminals.

372

To Prevent a Sense Event

From the front panel of the slave 372
LCD menu display:

Press

NEXT to gain access to Trigger

Input.

Check to see that Force Sense is selected.
(Force Sense is the default setting.)

(For additional information, see in the
section System Setup, Description of
Menu Features—Trigger Input)

Connect a normally-open set of switch
or relay contacts between the TRIGGER
and Ground terminals.

From the front panel of the slave 372
LCD menu display:

Press NEXT to gain access to Trigger
Input.

Rotate

ADJUST to select Prevent Sense.

(For additional information, see in the
section System Setup, Description of
Menu Features—Trigger Input)

13

Symetrix 372 SPL Computer User’s Guide

System Setup

| Overview of Front Panel | How System Setup Works | Description of Menu Features

372

SPL
COMPUTER

SETUP

MENU

EXITNEXT

CALADJUST

AMBIENT SENSE

HIGH

LOW

GAINMONITOR

MID

Overview of Front Panel

CONTROL CONTROL TYPE WHAT IT DOES

SETUP LCD menu display Two line display shows levels and

settings of selected menu feature.

NEXT From normal operation, the first press

enters the setup mode; subsequent
presses step through the setup process.

EXIT Exits the setup mode. The unit reverts

to normal operation.

ADJUST Rotary control used in setup mode for

parameter setting.

CAL Press to have the 372 read the

current ambient level and equate this
reading to 0 db (Unity) gain. Displays
the relative ambient reading which it
considers as normal.
active in normal operating mode and
when setup is unlocked.

CAL is only

AMBIENT SENSE Headphone jack 1/4 inch TRS jack suitable for head-

phone impedances of 60 ohms or
higher, stereo or mono. Enables
listening to the output of the sensing
system when 372 is in Listen mode.
Helpful for troubleshooting or for
figuring out what the 372 is listening
to. For more information, see
Description of Menu Features, Oper­ating Mode—Listen.

MONITOR Adjusts the volume level at the

headphone jack.

GAIN 3-position switch adjusts the sensitiv-

ity of the sensing circuitry to accom­modate different conditions. Set the
gain level while in the Listen mode.
For more information, see Description
of Menu Features, Operating Mode—
Listen.

Note
Once the 372 has been set up, do not
change the

AMBIENT SENSE GAIN position.

14

| Overview of Front Panel | How System Setup Works | Description of Menu Features

How System Setup Works

Symetrix 372 SPL Computer User’s Guide

System Setup

Use the two push buttons, NEXT and

EXIT, with the parameter adjustment

knob,

ADJUST, to gain access to menu

setup options in the LCD display.

1 Press

2 Rotate

3 Press

4 Press

5 After setup is complete, calibrate

NEXT to enter the setup

mode.

ADJUST to select a specific

value or choice.

NEXT again to gain access

to another menu option. Subse­quent presses of Next change
menu options.

EXIT to end the setup

process, save any changes made,
and return the unit to normal
operation.

—or—

Allow 30 seconds of inactivity,
after which the unit returns to
normal operation. (Does not
apply while using the Listen
feature.)

the unit (See the section Calibrat­ing the 372).

REQUIRED RECOMMENDED OPTIONAL MENU FEATURE IN LCD DISPLAY

 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 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

*Bold face indicates menu name in LCD display

15

Symetrix 372 SPL Computer User’s Guide

System Setup

| Overview of Front Panel | How System Setup Works | Description of Menu Features

Description of Menu Features

ROTATE ADJUST TO

PRESS NEXT TO SELECT MENU FEATURE CHOICE DESCRIPTION

 Operating Mode Music This mode considers everything as if it were music,

SELECT VALUE OR

even though it may contain a mix of music and
announcement audio.

Varies the gain of this program channel to match the
ambient noise level.

How Sampling Works

silent portions in the program material. If the 372 doesn’t
find gaps, then it forces a sense period (samples for about

0.75 seconds) after which, it restores the program channel
signal.

How You Can Control Sampling

period manually and select the time of the forced event.
See Trigger Input in this section to enable this feature.

Can also perform simple AGC on the input signal to
improve the consistency of the output level. See AGC in
this section to enable this feature.

—Takes SPL measurements during

—You can force a sense

Page Select this mode if you are doing paging or

announcement audio only.

Varies the gain of the program channel to match the
ambient noise level.

How Sampling Works

program channel prevents sampling from taking place.
Sampling stays “locked out” until the program channel has
remained silent for at least 20 seconds. In the rare event
that a page or announcement begins while sampling is
taking place (samples for about 0.75 seconds), the current
sense cycle/period will complete and then further sampling
is prevented.

How You Can Control Sampling

tolerate paging interuptions, you can force sensing to
occur after a page announcement. See Force Sense Time
in this section to enable this feature.

—The presence of audio in the

—If your application cannot

REQUIRED RECOMMENDED OPTIONAL

 

Can perform simple AGC on over-threshold compression
on the paging signal at 3:1 ratio on signals above 0 dBu
(defeatable). See AGC in this section to enable this
feature.

16

Symetrix 372 SPL Computer User’s Guide

System Setup

| Overview of Front Panel | How System Setup Works | Description of Menu Features

Description of Menu Features continues

ROTATE ADJUST TO

PRESS NEXT TO SELECT MENU FEATURE CHOICE DESCRIPTION

Operating Mode continues Slave Select this mode if you want to designate the 372

SELECT VALUE OR

unit as a slave. Slave units connected to a master
372 unit enable you to sense at the same time in
adjacent or multiple installation zones.

This mode senses only in response to an external sense
command received by way of the
on the rear panel of the slave.

As many as 20 slave 372 units may be controlled directly
from the
cable from
unit to the
slave unit in parallel (See Connecting Up to 20 Slaves).

More than 20 slave 372 units may be controlled using an
external relay (See Connecting an External Relay to Attach
Slaves).

If some of the slave units are a long distance away from
the master, a direct connection might give rise to ground
loop problems. To avoid this, use an external relay to
isolate the connection between the master and the distant
slaves (See Connecting an External Relay to Attach Slaves).

On the front panel of the slave units, press

Trigger Input in the LCD menu display. Check to see that
Force Sense is selected. Force Sense is the default setting.

EXT RELAY output of the master 372. Connect a

EXT RELAY and Ground terminals of the master
TRIGGER input and Ground terminals of each

TRIGGER input connector

NEXT to locate

REQUIRED RECOMMENDED OPTIONAL

 

History Select this mode if you only want the 372 to collect

data about the highest and lowest ambient SPL in
the installation zone(s).

The 372 does not perform any gain control in this mode.
You can determine the start of the history period or collec­tion of data. See History later in this section to reset or
start the collection of the relative SPL history.

To view the current SPL readings, see Listen.

Bypass Select this mode when you want to leave the 372

physically connected in the signal path, only pass
the signal unaltered, and never take SPL samples.

This feature is useful if you encounter setup problems in an
installation. You can temporarily disable the 372 until you
have the time to correct the problem. Or when the action
of the 372 is temporarily unwanted, for example, when an
unusual event is taking place.

You can view your control settings in this mode. Any
changes you make to your control settings in this mode,
will not take effect.

The gain is always held at unity (0 dB) in Bypass mode.

Bypass mode is not a hard-wire bypass.

17

Symetrix 372 SPL Computer User’s Guide

System Setup

| Overview of Front Panel | How System Setup Works | Description of Menu Features

Description of Menu Features continues

ROTATE ADJUST TO

PRESS NEXT TO SELECT MENU FEATURE CHOICE DESCRIPTION

 Status Displays the current calibration status of the 372.

SELECT VALUE OR

Cal Level

Ambient signal level measured at the last sense period.

Min Level Minimum gain that the 372 is permitted to have.

Max Level Maximum gain that the 372 is permited to have.

 History Reset to Zero Displays numeric readings of the highest and lowest

SPLs from whenever the 372 unit was calibrated or
from when the setting was last reset.

Resetting the 372 to Zero starts a new history period,
where the 372 begins to collect the highest and lowest
relative SPL readings.

 Listen Select Listen in order to set the gain level.

There is a 2 second delay prior to entering this function.
The 372 switches the system into Listen mode, silencing
the speakers and using them as microphones to read the
ambient sound level.

The relative SPL reading then displays in numeric form
and, also, as a bargraph.

Adjust the
until the indicated level is higher than at least –40 dB, but
no more than 0 dB. This setting range allows the 372 to
have enough valid information to control the system gain.

Note
Once the 372 has been set up, the
position should never be changed.

AMBIENT SENSE GAIN switch on the front panel

AMBIENT SENSE GAIN switch

REQUIRED RECOMMENDED OPTIONAL

 

In this mode, you can plug in headphones to listen to the
ambient sound the 372 reads. Adjust the volume of the
headphones by rotating

The headphone is a helpful troubleshooting tool for identi­fying noise sources that may be misdirecting the 372 or
hum and noise picked up in the speaker wiring that may be
causing sense errors.

MONITOR.

18

Symetrix 372 SPL Computer User’s Guide

System Setup

| Overview of Front Panel | How System Setup Works | Description of Menu Features

Description of Menu Features continues

ROTATE ADJUST TO

PRESS NEXT TO SELECT MENU FEATURE CHOICE DESCRIPTION

 Set MIN Limit Select value To adjust the lowest gain setting that the 372 uses.

 Set MAX Limit Select value To adjust the highest gain setting that the 372 uses.

 Averaging Time 1, 2, 4, or 8 To average together the number of samples to make

SELECT VALUE OR

This ensures a known minimum level from the sound
system, even if the ambient drops to dead silence.

This ensures that the sound system stays out of clipping
even if the ambient level exceeds your wildest expectations.

a gain change.

Select the number of samples you want the 372 to use.
Longer running averages make the system respond more
to the trend of the ambient level rather than the most
recent sample.

 Gain: Sense Ratio 0.5:1, 1:1, Refers to the change in gain of the 372 versus the

1.5:1, or 2:1

change in the ambient.

0.5:1 changes gain 0.5 dB for every dB change in the
ambient. This makes the sound system louder in response
to increases in the ambient, but never tries to out-shout
the crowd.

1:1 matches gain changes to the ambient noise level.

1.5:1 changes gain 1.5 dB for every 1 dB increase in the

ambient noise level.

2:1 changes gain 2 dB for every 1 dB increase in the
ambient noise level.

At high ambient levels, the 372 can easily out-shout the
crowd if the control settings allow it. To limit the 372’s
ability to out-shout the crowd, pick a lower maximum gain
in Set MAX Limit.

At lower ambient levels, the 372 might let the sound
system get lost in the ambient. To avoid this, choose a
higher (closer to 0 dB) minimum gain in Set MIN Limit.

REQUIRED RECOMMENDED OPTIONAL

 

19

Symetrix 372 SPL Computer User’s Guide

System Setup

| Overview of Front Panel | How System Setup Works | Description of Menu Features

Description of Menu Features continues

ROTATE ADJUST TO

PRESS NEXT TO SELECT MENU FEATURE CHOICE DESCRIPTION

 Gap Threshold Select value To set the minimum signal level needed for the 372

SELECT VALUE OR

to not detect silence in the program channel.

In Music mode, the 372 senses anytime that the music
program level falls below the Gap Threshold setting. If
there are no gaps in the program, then the 372 senses at
the interval set by the Force Sense Time, which ranges
from never to 30 minutes. See Force Sense Time.

In Page mode, the 372 senses when directed by the

Force Sense Time or by an external trigger source. Use
Gap Threshold to prevent sensing activity during paging.

If a page is in progress, the 372 will not interrupt it for
sensing.

 Force Sense Time To force a sensing period when the program mate-

rial is too dense to contain sufficient gaps for
silence sensing.

Never, 1, 3, 5,

Selections in Music mode.

10, 20 or 30
minutes

Sense After Page,

Selections in Page mode.

1, 3, 5, 10, 20
or 30 minutes

Choose Sense After Page in situations where paging is
frequent and uninterruptible. This selection triggers a
sense period about 20 seconds after the paging signal
level falls below the Gap Threshold setting.

You can also force a sense period manually by using an
external trigger source or contact closure connected to

TRIGGER on the rear panel (See Connecting a Push Button

Switch to Force or Prevent a Sense Event).

 AGC Enable or Performs simple AGC on the input signal(s).

Disable

In Music mode, this action consists of low-ratio expansion
for signal levels below 0 dBu and moderate-ratio compres­sion for signal levels above 0 dBu. This can be useful in
reducing the dynamic range of signal sources such as CD
players.

In Page mode, this action performs over-threshold
compression at 3:1 ratio for signals over 0 dBu as referred
to the input. This can be useful in keeping the sound
system out of clipping, or for reducing the surprise factor
caused by a loud talker.

REQUIRED RECOMMENDED OPTIONAL

 

20

Symetrix 372 SPL Computer User’s Guide

System Setup

| Overview of Front Panel | How System Setup Works | Description of Menu Features

Description of Menu Features continues

ROTATE ADJUST TO

PRESS NEXT TO SELECT MENU FEATURE CHOICE DESCRIPTION

 Trigger Input You can manually prevent sensing or manually

SELECT VALUE OR

control sensing by using this feature in conjunction
with the hardware connection,

TRIGGER, on the rear

panel.

Force Sense

Forces a sense period when the program material is too
dense to contain sufficient gaps for silence sensing.
Operates independently of Gap Threshold. On the rear
panel, connect a momentary contact closure between

TRIGGER and Ground terminals to initiate an ambient

the
level sense event (See Connecting a Push Button Switch
to Force or Prevent Sensing).

—or—

Enables slave 372s connected to a master 372 to sense at
the same time in adjacent or multiple zones (See Slave
mode in this section and in the section Making Hardware
Connections, see Connecting Up to 20 Slaves).

Prevent Sense Useful in Music mode during voice announcements, in

conjunction with an external contact closure. In Music
mode the 372 has no other way to know if an announce­ment is happening.

Connect to the TRIGGER input a normally-open set of
switch or relay contacts between the
terminals on the rear panel. An example of this might be a
spare set of contacts on a push-to-talk microphone.
Whenever these contacts are pressed closed, the 372 is
prevented from sensing the ambient room level. Other­wise, a timed sense event might “cut off” the announcer
when he/she is speaking (See Connecting a Push Button
Switch to Force or Prevent Sensing).

TRIGGER and Ground

 Setup Unlocked Unlock or lock Choose to protect front panel LCD menu settings

REQUIRED RECOMMENDED OPTIONAL

 

Not Used Disables the trigger pin.

from being altered.

To lock, press and hold CAL while rotating ADJUST. Once
it’s locked, pressing
attempt to alter settings results in the display of the
message “Setup is Locked.”

To unlock, press
Locked.” Press and hold
front panel is now unlocked.

NEXT shows the current settings. Any

NEXT until the display reads “Setup Is

21

CAL while rotating ADJUST. The

To calibrate the 372

Symetrix 372 SPL Computer User’s Guide

Calibrating the 372

1 Choose a time when the ambient

noise in the area being controlled
is at a typical level.

2 On the front panel, press

The 372 reads the current
ambient level and equates this
reading to 0 dB (Unity) gain.

3 When calibration is finished, the

372 displays the relative ambient
SPL reading which it considers as
“Normal.”

CAL.

Whenever the SPL of the environment
is at this level, the program channel
of the 372 will be at 0 dB (Unity)
gain. As the ambient SPL becomes
less, the 372 lowers its gain. Con­versely, when the SPL increases, the
gain of the 372 increases.

Only perform calibration when the
setup for the 372 is unlocked (See
Setup Unlocked in section System
Setup). Pressing
is locked causes the 372 to report the
most current relative calibration level.
No settings are altered.

CAL when the setup

22

Symetrix 372 SPL Computer User’s Guide

Conditions Under Which the 372

Will Not Sense

Because the 372 uses the speakers of
a sound system as sensing micro­phones, the sound system is briefly
disabled every time a reading is
taken. To keep these interruptions to
a minimum, the 372 follows several
rules to prevent sensing under
specific conditions.

The 372 Will Not Take Samples When:

1 In Music mode, whenever the program audio is above the Gap Threshold

level. (You can override the Gap Threshold level by manually controlling
sensing. See in Description of Menu Features, Trigger Input—Force

Sense in the section System Setup.)

2 In Page mode, whenever the program audio is above the Gap Threshold

level.

3 In Page mode, for about 20 seconds after any program signal above the

Gap Threshold level has disappeared.

4 In any mode, for about 4 seconds after the last sample was taken.

5 In any mode, as long as the

has been selected for Trigger Input in the LCD menu display.

6 In Bypass mode.

TRIGGER input is grounded, if Prevent Sense

23

MONITOR

ROOM SENSE

LOW

MID

HIGH

GAIN

RMS

DETECTOR

FILTERS

SWITCHABLE

ATTENUATOR

AMP

FROM

SPEAKER

TO

DETECTOR

RMS

LCD DISPLAY

DAC

8-BIT

SENSE TRIGGER

AND

EXTERNAL RELAY

VCA

LINE IN

BALANCED

LEFT

VCA

LINE IN

BALANCED

RIGHT

MENU EXIT

MENU NEXT

CALIBRATE

ADJUST

CIRCUITRY

CPU

8-BIT

LINE OUT

BALANCED

RIGHT

LEFT

LINE OUT

BALANCED

Symetrix 372 SPL Computer User’s Guide

Signal Flow Diagram

24

Symetrix 372 SPL Computer User’s Guide

Input and Output Connector Wiring

METHOD CONNECTOR CHANNEL

Balanced Terminal Strip

Balanced Female XLR

Pin 1 = Not Connected
Pin 2 = High
Pin 3 = Low
Connector Shield = Not Connected

Balanced TRS Plug

Tip = High
Ring = Low
Sleeve = Shield

Unbalanced TS Plug

Tip = High
Sleeve = Low + Shield

Input

Input

21 3

Input

TIP

RING

SLEEVE

Input

TIP

SLEEVE

Unbalanced RCA Plug

Tip = High
Sleeve = Low
Cable Shield = Not Connected

Balanced Male XLR

Pin 1 = Circuit Ground
Pin 2 = High
Pin 3 = Low

Unbalanced TS Plug

Tip = High
Sleeve = Shield
Wire Low = Not Connected

Input

Output

12 3

Output

TIP

SLEEVE

25

Symetrix 372 SPL Computer User’s Guide

Troubleshooting

SYMPTOM PROBABLE CAUSE / WHAT TO DO

No output signal Check cables and connections to see if:

• Inputs are driving outputs, and outputs are driving inputs.

• There is a signal coming from the source and that it is getting to the 372.

• The signal chain after the 372 is functioning.

Check if the LCD display is on and unit is plugged in.

Unit will not calibrate Check that input levels are normal.

In Listen mode, use headphones to hear what the 372 reads. Set position of

AMBIENT SENSE GAIN switch between –40 and 0 dB.

Check sensing speaker connections.

Music always plays too loud Check levels in Set MIN Limit and/or Set MAX Limit.

Unit seems to have no effect Check the ratio setting in the LCD menu display for Gain: Sense Ratio. At

0.5:1, the gain changes are very subtle. Choose a larger value for more

change.

Check if level is set too low in Set MAX Limit.

Unit never senses, even Check if Gap Threshold is set too low.
during silence

Unit loses the beginnings of Gap Threshold set too high. Select Sense After Page.
paging messages

Unit does not accurately adjust Hum induced in speaker wiring. Check if speaker wiring is routed adjacent to
system as ambient noise changes

Unit senses during paging Gap Threshold set too high; choose a lower value.

Check if Bypass mode or Slave mode is selected in Operation Mode. Change
mode to Music or Page.

AC wiring.

In Listen mode, use headphones to check ambient noise level.

Check if speaker is mounted near continuous noise source.

Check that all speakers are operating in-phase.

Note
The accuracy of the 372 is only as good as the quality of your speakers.

Hum or buzz in output Check input connector wiring.

Check for a ground loop problem. Inspect related system equipment grounding
to see that all system components are on the same AC ground.

26

Symetrix 372 SPL Computer User’s Guide

Troubleshooting

SYMPTOM PROBABLE CAUSE

Distortion Check input signal for distortion.

Check if line input signal may be too hot.

Check if page mic signal may be too hot.

Check if the sound system has sufficient power for the SPL that you are trying
to attain.

If using a high setting for Set MAX Limit, you may be overloading the input to
your amplifier; select a lower value.

Check if something else is clipping in the signal chain.

Noise (hiss) Check input signal levels and level control settings.

Check gain settings on downstream equipment for presence of noise in input
signal.

No audio Check if the unit is plugged in.

Check if the unit is in Listen mode.

27

Symetrix 372 SPL Computer User’s Guide

Hardware Specifications

Input/Output

Maximum Input Level +20 dBu balanced, +20 dBu unbalanced
Program Input Impedance >20k ohms balanced, >10k ohms unbalanced
Input Common Mode Rejection >40 dB line inputs
Maximum Output Level +26 dBu balanced (20k ohm load)

+22 dBm balanced (600 ohm load)

Output Impedance 200 ohms balanced, 100 ohms unbalanced

Performance Data

Program Frequency Response 20 Hz to 20 kHz, +0, –1 dB
Program Path THD+N <.025% (+4 dBu in, +4 dBu out)
Output Gain +20, –30 dB
Sense Channel Frequency Response –3 db at 300 Hz and 6000 Hz

3-pole Butterworth
Sense Channel Gain selectable unity, +20 dB, +40 dB
Additional Headphone Monitor Gain 28 dB maximum
Program Channel Output Noise –95 dBu @ unity gain, typical

Connections

Program Inputs, Outputs Euroblock
Power In 7-pin DIN
External Trigger, External Relay Euroblock
Headphone 1/4 in. TRS, will drive mono or stereo headphones
Internal Relay double pole, contacts rated 8A maximum

Physical

Size (H x W x D) 1/2 rack unit

1.75 in. x 8.5 in. x 6.5 in., 4.445 cm x 21.59 cm x 15.875 cm

Shipping Weight 4.5 lbs

Electrical

Power Requirements 10W maximum, Symetrix PS-3 or PS-3E only
PS-3 115V, 60 Hz AC nominal
PS-3E 230V, 50 Hz to 60 Hz AC nominal

Note
In the interest of continuous product
improvement, Symetrix, Inc. reserves the
right to alter, change, or modify these
specifications without prior notice.

28

Symetrix 372 SPL Computer User’s Guide

Architects and Engineers Specifications

The Ambient Level Controller (ALC)
shall control the output level of the
sound system in response to the
observed acoustical noise level within
the controlled space during system
operation. These measurements shall
be made during silent portions of the
program material. Provision shall be
made to alter the noise sensing
protocol to make the noise level
measurement under timer or external
control and to accomodate musical or
paging program signals.

The ALC shall utilize the loudspeakers
of a sound system as microphones to
sense the ambient noise level.
Provision shall be made for the user
to monitor the audio signal used by
the ambient sense system by using
headphones. The ALC shall be capable
of operating from sound systems
using direct loudspeaker drive or
constant voltage distribution.

The ALC shall provide user-adjustable
parameters to alter the way that it
responds to changes in the ambient
noise level. These parameters are:
minimum and maximum gain through
the device, silence sensing threshold,
noise sensing protocol, gain:sense
ratio, program AGC or compression,
and averaging time. In addition, the

ALC shall provide music or paging
signal modes, bypass mode, slave
mode for linking multiple units, and a
history mode that collects and
displays ambient noise history from
the controlled space.

The ALC shall provide two indepen­dent line level balanced inputs and
outputs that control two audio
signals. The maximum input level
shall be +20 dBu and the maximum
output level shall be +26 dBu (+22
dBm into 600 ohms) balanced. The
balanced input impedance shall be
20,000 ohms and the output source
impedance shall be 200 ohms bal­anced, 100 ohms unbalanced. The
gain control range shall be –30 dB to
+20 dB. The frequency response shall
be 20 Hz to 20 kHz +0/–1 dB with
THD+N less than 0.25% at +4 dBu
over the same range of frequencies.
The output noise of the device shall
be less than –95 dBu (20 kHz noise
bandwidth, unity gain). The input and
output configuration shall be active
balanced.

The speaker switching relay contacts
shall be rated at 8A.

Screw terminals shall be used for all
connections except for the speaker
connections which shall utilize a
barrier-style terminal strip. In addi­tion to the audio input/outut connec­tions, there shall be connections
provided for a sense trigger input and
an open-collector sense trigger
output.

A front panel power indicator shall be
provided. A liquid crystal display shall
be provided to communicate operat­ing parameters and setup information
with the user.

The ALC shall occupy half of the width
of one rack space and shall be housed
in a metal enclosure. It shall use an
external, safety agency approved,
power supply. The Ambient Level
Controller shall be the Symetrix
model 372 SPL Computer.

29

Warranty

Symetrix 372 SPL Computer User’s Guide

Warranty

Symetrix, Inc. expressly warrants that the product will be free
from defects in material and workmanship for eighteen (18)
months from the date the product is shipped from the factory.
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 eighteen (18) months from the date the product is
shipped from the factory, 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 via United Parcel Ser­vice by Symetrix, to any location within the Continental United
States. 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.

NOTE

: Some Symetrix products contain embedded software
and may also be accompanied by control software intended
to be run on a personal computer. Said software is specifically
excluded from this warranty.

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 allocatable 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, substitute

facilities or supply houses.

30

Symetrix 372 SPL Computer User’s Guide

Service

Where to Get Service

If outside of the USA

If you have determined that your 372
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 inside the USA

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. If you reside in the
USA, then proceed as follows:

In-Warranty Repairs

Repairs made in-warranty will cost
you only one-way freight charges.
We’ll prepay the return (surface)
freight. Of course, if the repair is due
to operator error, parts and labor will
be charged. 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).
For more information see the section
Warranty.

To Get Your 372 Unit Repaired (US customers only)

1 Call Customer Service Department for a return authorization (RA) number.

[phone], Monday through Friday

8:00 am – 4:30 pm Pacific Time.

Have your serial number ready to give to the customer service representative.

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,

We do not accept freight collect shipments.

Symetrix, Inc.

6408 216th St. SW
Mountlake Terrace WA 98043

freight prepaid.

If You Don't Have Factory Packaging Materials

If you send us your product in substandard packaging, we will charge you for
factory shipping materials. If you don’t have the factory packaging materials, do
the following:

1 Select an oversized carton.

2 Wrap the unit in a plastic bag, and surround it with bubble-wrap.

3 Pack the box full of Styrofoam peanuts. Be sure there is enough clearance

in the carton to protect the rack ears.

We will return the unit in Symetrix packaging.

Out-of-Warranty Repairs

If the warranty period has passed,
you’ll be billed for all necessary parts,
labor, packaging materials, and
freight charges.

31

Symetrix 372 SPL Computer User’s Guide

Declaration of Conformity

We, Symetrix, Inc.

6408 216th ST. SW, Mountlake Terrace, Washington USA

declare under our sole responsibility that the product:

372 SPL Computer

to which this declaration relates, is in conformity with the following standards:

EN 55103-1
Electromagnetic Compatibility—Generic Emission Standard

Part 1: Residential, Commercial, and Light Industry

EN 55103-2
Electromagnetic Compatibility—Product Family Standard for Audio, Video, and

Entertainment Lighting Control Apparatus for Professional Use
Part 2: Immunity

PS-3E power supply complies with this code:

EN 60065

Safety Requirements for Mains Operated Electronic and Related Apparatus for
Household and Similar General Use

The technical construction file is maintained at:

Symetrix, Inc.

6408 216th St. SW
Mountlake Terrace, WA 98043

USA

The authorized representative located within the European Community is:

World Marketing Associates

P.O. Box 100

St. Austell, Cornwall, PL26 6YU, UK

Date of issue: June 30, 2000

Place of issue: Mountlake Terrace, Washington USA

Authorized signature:

Dane Butcher, President

32

301 Low Distortion Compressor/Limiter

302 Dual Microphone Preamplifier

303 Interface Amplifier

304 Headphone Amplifier

305 Distribution Amplifier (1x4)

306 Preamp/Ducker

307 Dual Isolation Transformer

308 VCA Volume Control/Loudness EQ

372 SPL Computer

402 Dual Output Delay

420 Stereo Power Amplifier

421M AGC-Leveler

422 Stereo AGC-Leveler

440 Foreground Audio Controller

450 Dual Zone Priority Mixer

501 Peak-RMS Compressor/Limiter

501-01 Peak-RMS Compressor/Limiter

506E Headphone Amplifier

527E Voice Processor

528E Voice Processor

531E Graphic Equalizer

532E Graphic Equalizer

533E Graphic Equalizer

551E 5-Band Parametric EQ

552E Dual 5-Band Parametric EQ

562E Windowing Expander/Gate

565E Dual Compressor/Limiter/Expander

571 SPL Computer

571S SPL Computer Slave

572 SPL Computer

581E Distribution Amplifier (4x4)

606 Delay F/x Machine

610 Broadcast Audio Delay

628 Digital Voice Processor

9022 2x2 DSP Engine

RC-1 628 Remote Control

RC-2 440 Remote Control

RC-610 Remote Control

www.symetrixaudio.com

34