Symetrix 371 spl User manual

371 SPL Computer

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Safety

371 SPL Computer

Safety

GThe 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 Quick Start Guide).

GCAUTION: To prevent electric shock,

do not use the polarized plug supplied

with the unit with any extension cord,

receptacle, or other outlet unless the

prongs can be fully inserted.

GPower Source: This Symetrix hardware

uses a switching power supply that

automatically adjusts to the applied

voltage. Ensure that your AC mains

voltage is somewhere between 100-240

VAC, 50-60 Hz. Use only the power

cord and connector speciﬁed for the

product and your operating locale. A

protective ground connection, by way of

the grounding conductor in the power

cord, is essential for safe operation. The

appliance inlet and coupler shall remain

readily operable once the apparatus has

been installed.

GUser Serviceable Parts: There are no

user serviceable parts inside this Symetrix

product. In case of failure, customers

inside the U.S. should refer all servicing to

the Symetrix factory. Customers outside

the U.S. should refer all servicing to an

authorized Symetrix distributor. Distributor

contact information is available online at:

http://www.SymetrixAudio.com.

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

No 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

Important Safety

Instructions

!Read these instructions.

@Keep these instructions.

#Heed all warnings.

$Follow all instructions.

%Do not use this apparatus near water.

This apparatus shall not be exposed to

dripping or splashing and no objects

ﬁlled with liquids, such as vases, shall be

placed on the apparatus.

^Clean only with dry cloth.

&Do not block any ventilation openings.

Install only in accordance with the

manufacturer’s instructions.

*Do not install near any heat sources such

as radiators, heat registers, stoves, or

other apparatus (including ampliﬁers) that

produce heat.

(This apparatus shall be connected to

a mains socket outlet with a protective

earthing connection. Do not defeat

the safety purpose of the polarized or

grounding-type plug. A polarized plug has

two blades with one wider than the other.

A grounding type plug has two blades

and a third grounding prong. The wide

blade or the third prong are provided for

your safety. If the provided plug does not

ﬁt into your outlet, consult an electrician

for replacement of the obsolete outlet.

BL Protect the power cord from being

walked on or pinched particularly at

plugs, convenience receptacles, and the

point where they exit from the apparatus.

BM Only use attachments/accessories

speciﬁed by the manufacturer.

BN Use only with the cart, stand,

tripod, bracket, or table

speciﬁed by the manufacturer,

or sold with the apparatus.

When a cart is used, use

caution when moving the cart/apparatus

combination to avoid injury from tip-over.

BO Unplug this apparatus during lightning

storms or when unused for long periods

of time.

BP Refer all servicing to qualiﬁed service

personnel. Servicing is required when

the apparatus has been damaged in any

way, such as power-supply cord or plug

cord 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.

What Ships in the Box

• A371hardwareunit.

• OnePS-3(115VAC),orPS-3E(230

VAC) power supply.

• ThisUser’sGuide.

Getting Help

Voice Processor 2x, the Windows

application that controls the hardware,

includes a help module which acts as a

complete User’s Guide for both hardware

and software.

If you have questions beyond the scope

of this Quick Start Guide or the help

module, contact our Customer Support

Group in the following ways:

Tel: +1 (425) 778-7728

8:00 am to 4:30 pm

Monday through Friday,

Pacific Time

Web: http://www.SymetrixAudio.com

This device complies with part 15 of

the FCC Rules. Operation is subject

to the following two conditions: (1)

This device may not cause harmful

interference, and (2) this device must

accept any interference received,

including interference that may cause

undesired operation.

This Class B Digital apparatus meets

all requirements of the Canadian

Interference-Causing Equipment

Regulations

Cet appariel numerique de la classe

B respecte toutes les Exigences du

Reglement sur le materiel brouilleur

du Canada.

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Overview

Introduction

This simple, yet sophisticated SPL Computer is

designed to ensure that foreground music and/or paging

announcements are always clearly audible and distinct,

but never too loud. Proprietary AmbiSense™ technology

monitors ambient noise levels continuously, not just during

gaps in the audio program, and responds quickly to sudden

changes. Setup is simple: enter the parameters of the

“normal” acoustic environment, then tell the 371 how much

to change the

gain, and how quickly to raise or lower it, whenever

measured noise levels deviate from the parameters you

have set. The front panel LCD guides you with step-through

menus. Install a simple, precise and cost-effective solution:

the 371 SPL Computer, backed by over 15 years of SPL

processing innovation from Symetrix, the engineering-driven

company of signal processing specialists.

External Microphone connec-

tion for Continuously Monitoring

Ambient Noise Levels

Using an external microphone to measure changes in the ambient noise level, AmbiSense™ technology responds to environmen-

tal noise changes in realtime — not just during gaps in audio program.

Headphone Monitoring Monitor the sense signal using a separate front panel headphone output.

3 Operating Modes Active: Indicates continuous measurement of the ambient noise level.

History: Displays the lowest and highest SPL readings from when the unit was last reset

Bypass: Bypasses the unit. Audio passes through at unity gain.

Signal Path Accepts mono or stereo signals via Euroblock connectors.

Easy Calibration Uses step-through menus on the front panel LCD. Calibration performed under typical installation conditions. No waiting for the

quietest or noisiest ambient conditions.

Ratio Adjustment Choose an adjustment ratio of SPL change vs. program level change.

Sense Signal Measuring Display numeric reading and relative bargraph of the signal appearing at the sense terminals.

Gain Controls Set minimum and maximum limits for SPL gain range. Gain range is –30 dB to +20 dB.

Averaging Time Choose integration time of the running average SPL.

Phantom Power Sense input provides 15 VDC phantom power to microphone. Enable or disable in front panel LCD menu.

Ducker Control Ducker input provides momentary reduction of program level (from 0 dB to –40 dB) and inhibits sense operation for the duration

of the externally supplied line level ducking control signal.

Remote Control Option Connect rotary potentiometer or Symetrix RC-3 for remote control of output level.

Feature Summary

371 SPL Computer

Front/Rear Panel

NOTE: Detachable Euroblock connectors are designed for use with bare wire. Do not tin

stranded wires before inserting them into the connectors.

Front Panel

Item Description

LCD Display Two lines show levels and settings of selected menu option.

Next From normal operation, the first press enters the setup mode; subsequent presses step through the setup process and save settings.

Exit Exits the setup mode and saves changes to settings. The unit reverts to normal operation.

Adjust Turn to change the selected parameter.

Cal Press to have the 371 read the current ambient level and equate this reading to 0 dB (unity) gain. Displays the relative ambient reading

which it considers as normal. CAL is only active in normal operating mode and when setup is unlocked.

Headphone 1/4 inch TRS jack suitable for headphone impedances of 60 Ohms or higher, stereo or mono. Enables listening to the output of the

sensing system. Helpful for troubleshooting or for figuring out what the 371 sense mic is actually ‘hearing’.

Monitor Adjusts the volume level at the headphone jack.

Rear Panel

Item Description

7-pin DIN Connector Connect the 7-pin DIN plug end of a Symetrix PS-3 (115 VAC) or PS-3E (230 VAC) here. Connect the AC power connector end of the

PS-3 or PS-3E to an AC power source that is of the correct voltage and frequency as marked on the PS-3 or PS-3E.

Remote Gain Supplies 10 VDC, a ground, and a signal input for a remote gain trim control. Use standard 10k Ohm linear potentiometer or Symetrix

model RC-3.

Ducker Control Balanced input for the 371. 20k Ohm balanced bridging. If connecting unbalanced sources, refer to the Input and Output Connector

Wiring section. Triggers the internal ducker circuit to duck program audio and / or “freeze” the SPL computing functions.

Line Output These connectors deliver a differential balanced output at 200 Ohm source impedance. If connecting unbalanced loads, refer to the

Input and Output Connector Wiring section.

Line Input Balanced input for the 371. 20k Ohm balanced bridging. If connecting unbalanced sources, refer to the Input and Output Connector

Wiring section.

Sense Input Accepts most standard dynamic and condenser microphones. Built-in mic preamp can supply 15 VDC phantom power and gain

ranging from 0 dB to 70 dB in 10 dB steps.

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Basic Setup

Required Optional Task to do

6Connect page/program input source

6Connect 371 to output device

6Connect sense microphone

6Connect input source for ducking

6Connect remote volume control pot

6Connect switch for external

ducking control

6Connect to AC power supply

6Connect headphones to hear what the 371 is

sensing

Hardware Set-up Checklist

371 SPL

COMPUTER

www.SymetrixAudio.com

ENGINEERED AND ASSEMBLED OF U.S. AND IMPORTED MATERIALS

BY SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA

THIS UNIT CONTAINS NO USER SERVICEABLE PARTS

Engineered by Symetrix

in the U.S.A.

CONÇU ET ASSEMBLÉ DES MATÉRIAUX DES ÉTATS UNIS ET

IMPORTÉS PAR SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA.

PAS DES ELEMENTS SERVIABLE PAR UTILISATEUR

SENSE

INPUT

LINE INPUTLINE OUTPUT

DUCKER

CONTROL

REMOTE

GAIN

+10V

RIGHT LEFT RIGHT LEFT

CONNECT TO

SYMETRIX

PS-3 OR PS-3E

POWER SUPPLY

ONLY

POWER

INPUT

2Connect Output

to Amplifiers,

EQs, Speakers, etc.

3Connect PS-3 Power

Supply to AC Power.

1Connect your input devices.

Speakers

CD Player Sensing Mic 2

(optional)

Sensing Mic

Amplifier

PS3 Power

Supply

371 SPL Computer

Sensing Microphone Considerations

Type of Microphone

For most applications, an inexpensive low-impedance,

omnidirectional microphone, such as a lavalier microphone

works adequately.

Some installers have used boundary microphones with good

success (they’re unobtrusive).

Other installers have mounted microphone cartridges

(available from Mouser Electronics in the U.S.) inside

electrical boxes equipped with a single-holed cover.

In smaller rooms or acoustically live spaces, a directional

microphone is a good choice, because you can use its

position to favor the ambient sound and minimize pickup

from the sound system loudspeakers.

If the sense mic is positioned a relatively long distance from

the ambient noise source(s), a directional microphone may

improve system performance.

NOTE: No matter what kind of microphone you

choose, during calibration the 371 will adapt itself to the

characteristics of that mic.

Disclaimer: In recognition of the relative risks and

beneﬁts to both the Integrator and SYMETRIX, INC,

any recommendation or suggestion relating to the use

of the Products made by SYMETRIX, INC or any other

manufacturer either in technical literature or in response

to a speciﬁc inquiry or otherwise, is given in good faith.

HOWEVER, it is for the Integrator to satisfy himself that

the products are ﬁt for the purpose of being utilized by a

Consumer as the end-user of the Products. To the fullest

extent permitted by law, SYMETRIX, INC is not liable for any

and all claims, losses, costs, or unforeseen damages of any

nature whatsoever. It is intended that this limitation apply

to any and all liability or cause of action however alleged or

arising, unless otherwise prohibited by law.

Location of Microphone

The sensing microphone needs to “hear” the ambient sound

within the controlled space. It is vital that you place the

microphone where it primarily picks up a majority of noise

rather than the paging or music that is going through the

system.

Do not locate the sensing microphone near a localized noise

source that is not typical of the ambient noise level of the

controlled zone, for example, the noise from a large machine

of some sort, or maybe a kids play area, or a video game. If

you do this the 371 will think that the zone is noisier than it

really is.

The best sense mic placement ensures that the majority of

the signal picked up by the sensing microphone is ambient

noise. AmbiSense allows music or page pickup without ill

effects on its operation—up to about a 50:50 mix of music/

page to ambient. In an extreme case where the sense

microphone picks up 100% music/ page (0% ambient

noise), AmbiSense will not be able to extract enough

information to use for gain control.

Capability of Sound System to Match the

Maximum Required Level

Calibrate at a quiet-to-average time in the controlled space.

It helps if you have an estimate (sound pressure level) of the

maximum desired level. Check the sound system to see that

it is capable of delivering that level.

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Connecting a Volume Controller

The 371 allows you to have remote gain

control. You can connect a potentiometer or

the Symetrix RC-3 Remote Control to the

REMOTE GAIN Euroblock connectors.

Connect a potentiometer or another device

which generates voltage between the 10 VDC

output and ground of the 371. The value of the

potentiometer isn’t critical; anything between

10k and 100k (linear taper) will do. For best

accuracy, use the supplied 10 VDC reference

at Pin 1 of the connector to drive the high side

of the potentiometer.

Enable Remote Control From the

LCD menu

For the remote volume control to work, you

must enable remote control.

To enable remote control:

!From the LCD menu display, select the

menu option Output Trim.

@Turn ADJUST fully counterclockwise (below

the setting for –10) to choose Remote. The

actual gain according to the remote pot

setting now displays.

#Press EXIT or NEXT to save setting.

Keep gain in –10 dB to +10 dB range for

accurate operation. However, a remote pot can

“dim” the audio down to –50 dB temporarily.

www.SymetrixAudio.com

ENGINEERED AND ASSEMBLED OF U.S. AND IMPORTED MATERIALS

BY SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA

THIS UNIT CONTAINS NO USER SERVICEABLE PARTS

CONÇU ET ASSEMBLÉ DES MATÉRIAUX DES ÉTATS UNIS ET

IMPORTÉS PAR SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA.

PAS DES ELEMENTS SERVIABLE PAR UTILISATEUR

DUCKER

CONTROL

REMOTE

GAIN

+10V

CONNECT TO

SYMETRIX

PS-3 OR PS-3E

POWER SUPPLY

ONLY

POWER

INPUT

Potentiometer

CCW CW

www.SymetrixAudio.com

ENGINEERED AND ASSEMBLED OF U.S. AND IMPORTED MATERIALS

BY SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA

THIS UNIT CONTAINS NO USER SERVICEABLE PARTS

CONÇU ET ASSEMBLÉ DES MATÉRIAUX DES ÉTATS UNIS ET

IMPORTÉS PAR SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA.

PAS DES ELEMENTS SERVIABLE PAR UTILISATEUR

DUCKER

CONTROL

REMOTE

GAIN

+10V

CONNECT TO

SYMETRIX

PS-3 OR PS-3E

POWER SUPPLY

ONLY

POWER

INPUT

Symetrix RC-3

CCW CW

371 SPL Computer

External Ducking Control

www.SymetrixAudio.com

ENGINEERED AND ASSEMBLED OF U.S. AND IMPORTED MATERIALS

BY SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA

THIS UNIT CONTAINS NO USER SERVICEABLE PARTS

CONÇU ET ASSEMBLÉ DES MATÉRIAUX DES ÉTATS UNIS ET

IMPORTÉS PAR SYMETRIX, INC. MOUNTLAKE TERRACE, WA USA.

PAS DES ELEMENTS SERVIABLE PAR UTILISATEUR

DUCKER

CONTROL

REMOTE

GAIN

+10V

CONNECT TO

SYMETRIX

PS-3 OR PS-3E

POWER SUPPLY

ONLY

POWER

INPUT

Paging System

External switch or relay contact

The DUCKER CONTROL input is normally

connected to a line level audio signal from

any source you would like to use to trigger a

momentary decrease in volume (ducking).

NOTE: The signal applied to the DUCKER

CONTROL input does not get mixed with the

program audio. In other words, the ducking

input signal functions only as a control signal.

Alternatively, you can choose to attach to the

DUCKER CONTROL a momentary switch or

relay contact to manually control ducking.

Such a switch might be a push-to-talk switch

contact within a microphone or a manual

switch on a control panel. One isolated SPST

(single pole single throw) normally open

contact is required.

To enable ducking, you must also set

parameters in the LCD menu.

Set Ducking Parameters in LCD

Setup Menu

!If you are using audio to control ducking

set the Ducker Threshold between -30

dBu and +20 dBu. The correct setting is

dependent up the average level of your

incoming signal. Experiment until it sounds

right to you.

@If you are using a switch to control ducking

then set the Ducker Threshold somewhere

between 0 and +10 dBu.

#Set the Ducker Depth for the desired

amount of signal attenuation when

ducking is active.

Ducking takes place whenever the audio

ducking signal exceeds the threshold or

whenever the switch contacts are closed,

depending upon which ducking method you

have chosen.

Sensing is inhibited while ducking is in

process, therefore gain remains ﬁxed during

the ducking event.

NOTE: If Ducker Depth is set to zero

applying a ducking signal will freeze the gain.

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Input/Output Wiring

Balanced

Terminal Strip

Terminal Strip [balanced]

Euroblock

Connector

Channel Input/Output

Euroblock

Connector

Channel Input

Euroblock

Connector

Channel Output

Euroblock

Connector

Channel Input/Output

Euroblock

Connector

Channel Input

Pin 2 = (+) Plus

Pin 3 = (–) Minus

Pin 1 = Ground

XLR Female Plug [balanced]

Pin 2

Pin 3

Pin 1

Pin 2

Pin 3

Pin 1

Pin 2 = (+) Plus

Pin 3 = (–) Minus

Pin 1 = Ground

XLR Male Plug [balanced]

Tip = (+) Plus

Ring = (–) Minus

Sleeve = Ground

TRS 1/4" Plug [balanced]

Tip = (+) Plus

Sleeve = Ground

TS 1/4" Plug [unbalanced]

Euroblock

Connector

Channel Output

Tip = (+) Plus

Sleeve = Ground

TS 1/4" Plug [unbalanced]

NOTE: Detachable Euroblock

connectors are designed for use

with bare wire. Do not tin stranded

wires before inserting them into

the connectors.

IMPORTANT NOTICE 1

The wiring diagrams on this page are included for

information purposes only.

Symetrix can not anticipate exactly what connection

is needed at the non-371 end of the cable. It is

the user’s responsibilty to determine what

connection is needed.

In addition, Symetrix accepts no responsibilty for

injury or damage caused by user created wiring.

Input Connections

These connectors are designed for use with bare wire.

Do not tin stranded wires before inserting them into

the connectors.

For Unbalanced Connections

Connect the (–) input terminal to the source ground at

the source.

Feeding unbalanced inputs directly from balanced

outputs is not recommended due to the possibility

of ground loops. You may want to use an isolation

transformer to break the ground connection and

eliminate the ground loop.

Output Connections

These connectors deliver a differential balanced output

signal (mimics a grounded center tap transformer winding).

For Unbalanced Loads

With unbalanced loads, it is preferable to carry the

low side of the input all the way back to the ground

connection of the source.

Use the (+) output terminal and the ground terminal.

Ignore (ﬂoat) the (–) output terminal.

371 SPL Computer

System Setup

Required Recommended Optional Task to do

6Choose Operating Mode

6View calibration Status

6Collect History of highest and lowest SPLs

6View Sense levels

6Enable Phantom Power

6Set Sense Input Gain

6Specify Output Trim

6Set MIN Limit

6Specify Averaging Time

6Specify Gain: Sense Ratio

6Set Ducker Depth

6Set Ducker Threshold

6Lock or Unlock Setup

System Set-up Checklist

General Operation of the 371’s

LCD Menu Screen

Use the two push buttons, NEXT and EXIT, along

with the parameter adjustment knob, ADJUST, to gain

access to menu setup options in the LCD display.

!Press NEXT to enter the setup mode.

@Turn ADJUST to select a speciﬁc value or choice.

#Press NEXT again to gain access to another menu

option. Subsequent presses of NEXT change menu

options and save settings.

$Press NEXT or EXIT to end the setup process, save

any changes made, and return the unit to normal

operation.

—or—

Allow 20 minutes of inactivity, after which the unit

automatically returns to normal operation.

After setup is complete, calibrate the unit

(See the Calibration section).

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

System Setup

Press NEXT to advance through the different

Menu selections

Startup Screen

Startup Screen displays current gain applied by the unit.

When the 371 senses a signal at the DUCKER INPUT, Duck

displays.

Operating mode

Turning the ADJUST knob lets you select one of these three

operational modes

Active

Select this mode if you want the 371 to vary the gain of this

program channel to match the ambient noise level.

How Sampling Works—The 371 takes SPL measurements

every 10 ms through the sensing microphone.

History

Select this mode if you only want the 371 to collect data

about the highest and lowest ambient SPL in the installation

zone(s).

The 371 does not perform any gain control in this mode. You

can determine the start of the history period or collection

of data. See in this section History to reset or start the

collection of the relative SPL history.

Ducking can be made active in this mode if desired.

Bypass

Select this mode when you want to leave the 371 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 371 until you

have the time to correct the problem. Or when the action

of the 371 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 this mode.

Bypass mode is not a hard-wire bypass.

Status

Displays the current calibration status of the 371.

Cal:

Ambient signal level measured at the last sense period.

Min:

Minimum gain that the 371 is permitted to have.

Max:

Maximum gain that the 371 is permitted to have.

History: Reset to Zero

Displays numeric readings of the highest and lowest SPLs

from whenever the 371 unit was calibrated or from when the

setting was last reset.

Resetting the 371 to Zero starts a new history period, where

the 371 begins to collect the highest and lowest relative SPL

readings.

Sense

Displays bargraph of current ambient noise level.

Phantom Power

ON +15 V, OFF

To turn on or off 15 V phantom power for the sense

microphone. Enable only if your microphone requires it.

Sense Input Gain

0, 10, 20, 30, 40, 50, 60, 70 dB

Select the amount of gain that is required for the sense

microphone.

For proper calibration, the internal preamp must produce

a signal in the range of –45 dB to 20 dB. Refer to Sense

(above) for relative SPL readings.

Output Trim

–10 dB to +10 dB in 1 dB increments

To add to or subtract from the overall output gain from the

front panel or via remote (control the output trim

with a potentiometer or with the RC-3 Remote Control).

Keep gain in –10 dB to +10 dB range for accurate

operation. However, a remote pot can “dim” the audio

down to –50 dB temporarily.

371 SPL Computer

System Setup

Set MIN Limit

–30 dB up to the actual setting of the maximum limint in 1

dB increments

To adjust the lowest gain setting that the 371 uses. This

ensures a known minimum level from the sound system,

even if the ambient drops to dead silence.

Averaging Time

1, 3, 10, 30 seconds – 1.5, 5, 15 minutes

To adjust the reaction time at which the 371 adjusts to the

ambient level. Longer running averages make the system

respond more to the trend of the ambient level rather than

the most recent events.

Gain:Sense Ratio

0.5:1, 1:1, 1.5:1, 2:1 NOTE - The displayed ratio values are

guide lines only and not absolute values. The AmbiSense

algorithm may modify these ratios based upon the data it

gathers during the calibration process.

Refers to the change in gain of the 371 versus the change in

the ambient.

0.5:1 changes gain 0.5 dB for every 1 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.

NOTES:

• Ata2:1ratiowithhighambientlevels,the371caneasily

“out shout” the crowd.

• Atlowerambientlevels,the371mightletthesound

system get lost in the ambient. To avoid this, choose a

higher (closer to 0 dB) minimum gain and/or a higher

ratio.

Ducker Depth

0 dB to –40 dB

To set the ducking range. Upon ducking, the program

outputs drop according to the value selected. External

DUCKER CONTROL signal does not mix with internal

program signal. The external control signal merely initiates

ducking action.

Ducker Threshold

+20 dB to –30 dB

To set the minimum signal level needed for the 371 to

acknowledge ducking input. The 371 program outputs drop

to the Ducker Depth if the DUCKER CONTROL input rises

above the Ducker Threshold.

Setup Unlocked

Unlocked, Locked

Choose to protect front panel LCD menu settings from being

altered. To lock, press and hold CAL while turning ADJUST.

Once it’s locked, pressing NEXT shows the current settings.

Any attempt to alter settings results in the display of the

message “Setup is Locked”. To unlock, press NEXT until the

display reads Setup is Locked. Press and hold CAL while

turning ADJUST. The front panel is now unlocked.

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Calibration

What Does Calibration Do?

The calibration process correlates the current ambient noise

level to 0 dB (unity) gain. As the ambient SPL becomes less,

the 371 lowers its gain. Conversely, when the SPL increases,

the gain of the 371 increases.

Proper calibration is vital to the proper operation of the 371.

The AmbiSense algorithm will not function correctly if the

calibration procedures are not executed.

What To Do Before Calibration

Before calibration, setup the SENSE INPUT. System setup

menu items that control the Sense Input are Phantom Power

and Sense Input Gain.

THIS IS IMPORTANT!

• Calibratewhentheambientnoiseintheareabeing

controlled is at a level typical of normal conditions.

• Usethehighestpagingormusicinputlevelsthatyouare

likely to encounter during normal operation.

Adjust Sense Input Gain until Sense displays a bargraph

showing a mid-level sense signal. Make sure you leave

enough headroom so that increased ambient levels do not

overdrive the sense input. For example, if you expect that

ambient noise levels will rise 20 dB above the currently

observed levels, adjust the Sense Input Gain to leave more

than 20 dB of headroom under current conditions.

Only perform calibration when the setup for the 371

is unlocked (See System Setup>Description of Menu

Options>Setup Unlocked). Pressing CAL when the setup is

locked will do nothing.

How to Calibrate

!On the front panel, press CAL. The 371 sets software

controlled gain to 0 dBu (unity). The LCD menu displays

Unity Gain … Cal to proceed.

@Adjust the other components in the sound system (music

level, power amp gain, etc.) for the desired program level

during average conditions.

#If you wish to continue with calibration then press CAL

again. If you do not wish to continue with calibration then

press EXIT and the calibration process will abort.

The 371 reads the ambient level on the SENSE INPUT.

This level will be the unity reference (0 dB) for the 371.

$When the LCD menu displays Adjust to Maximum, turn

ADJUST to set the maximum gain for the program output.

The gain range is 0 dB to +20 dB in 1 dB steps.

%Next, the LCD menu displays whether calibration

succeeded or not.

^When calibration is ﬁnished, the 371 displays the relative

ambient SPL reading which it considers as normal.

What to Do If Calibration is Unsuccessful

Calibration can fail if the Sense Input Gain is set too low

(–45 dB) or too high (+20 dB). In the LCD setup menus,

adjust Sense Input Gain for a proper gain setting.

Check Sense for the current sense input level. The setting

should be between –45 dB and +20 dB.

You can also check the SENSE INPUT by listening with

headphones connected to AMBIENT SENSE MONITOR on

the front panel to hear what the 371 is reading.

What You Should Not Do After Calibration

Do not adjust the level of any volume controls in the sound

system signal path after the 371. Doing so will cause the

AmbiSense technology to yield erroneous results. Controls

that must remain ﬁxed include ampliﬁer input level controls,

wall-mounted L-Pad style speaker attenuators, etc.

Also, do not insert compressors or limiters into the signal

path after the 371. If you need to adjust ampliﬁer input

levels, re calibrate the 371 afterward to reset the data

collected by the AmbiSense algorithm. If you need to trim

the overall system level up or down after calibration, you can

do this by adjusting the Output Trim.

371 SPL Computer

Block Diagram

VCA

RMS

DETECT

SPL

CPU

AVERAGE

LEVEL

DETECT

BAL

INPUT

LINE

INPUT

LEFT

BAL

INPUT

DUCKER

CONTROL

AVERAGE

LEVEL

DETECT

DC AMP

REMOTE

GAIN

SENSE

GAIN BANDPASS

FILTER SENSE

HEADPHONE

SENSE

MONITOR

VOLUME

PHANTOM

POWER RMS

DETECT

MIC/LINE

INPUT

SENSE

INPUT

LINE

OUTPUT

LEFT

VCA

ADJUST

CALIBRATE

MENU EXIT

MENU NEXT

BAL

INPUT

LINE

INPUT

RIGHT

LINE

OUTPUT

RIGHT

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Troubleshooting

No output signal

Check to see that the LCD display is illuminated and the unit

is plugged in.

Check cables and connections to see if:

• Outputsaredrivinginputsandinputsarefedfrom

outputs.

• Signaliscomingfromthesource(s)andthatitisgetting

to the 371.

• Thesignalchainafterthe371isfunctioning.

Unit will not calibrate

Check that input levels are normal.

Use headphones to hear what the 371 reads. Check Sense

Input Gain to to see if the setting is between –45 dB and

+20 dB. Calibration will fail if it is below or above these

levels.

Check sensing microphone connections. Enable Phantom

Power if you are using a microphone that requires it.

Music always plays too loud

Check levels in Set MIN Limit.

Check if the level is set too high in the Gain: Sense Ratio.

Check in calibration if the maximum limit in Adjust to

Maximum is set too high.

Unit seems to have no effect

Check the ratio setting for Gain: Sense Ratio. At 0.5:1, the

gain changes are very subtle. Choose a larger value for more

change.

Check the bargraph in Sense to see if the sense level is

always the same, because then the gain will always be the

same.

Check to see if it’s in HISTORY or BYPASS mode.

Unit does not control levels as expected

Using headphones connected to the front panel headphone

jack, listen to the sense signal to verify that the SENSE

INPUT is receiving a signal that accurately represents

ambient noise conditions. Listen for hums, buzzes, or

interference that might be masking true ambient noise. Move

sense mic if necessary. Adjust Sense Input Gain to proper

level.

Also, it may be possible that someone accidentally changed

downstream level controls after the unit was last calibrated.

This change causes AmbiSense to produce erroneous

results. Correct this by recalibrating the unit.

NOTES:

• Theaccuracyofthe371isonlyasgoodasthequalityof

your microphones.

• Theactualgain-senseratiomaydifferfromthesetting

chosen during set up and diplayed on the LCD. The

displayed ratios are guidelines only. The AmbiSense

algorithm may modify the actual ratios based upon

the data it gathers during the calibration process as

necessary.

Unit is at minimum gain all the time

Check if microphone is connected or turned on.

Check signal at sense input.

Ducker doesn’t work

Ducker Threshold set too high.

Ducker Depth set to 0.

Check connections to see if input signal is connected and

turned on.

Noise (hiss)

Check input signal levels and level control settings.

Check gain settings on downstream equipment for presence

of noise in input signal.

371 SPL Computer

Troubleshooting

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.

Distortion

Check input signals for distortion.

Check if line input signal is 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 Adjust to Maximum in calibration,

you may be overloading the input to your ampliﬁer; select

a lower value. Ensure that something downstream isn’t

clipping.

No audio using remote volume controls

Check Output Trim to see if Remote is enabled.

371 is inoperative

Certain uncontrollable events (lightning, ﬂood, nuclear blast,

other catastrophic disturbances) can corrupt the 371’s

memory rendering it inoperable.

To return the 371’s memory to its factory default state:

!Disconnect AC power.

@Press and hold in the NEXT and EXIT buttons.

#Re-connect AC power.

$Release the NEXT and EXIT buttons.

%Press and release EXIT three times. Now the LCD screen

will display “EEPROM defaults restored” followed by the

software version number. After doing this, all previous

setup and calibration data will have been lost and must

be re-entered as if it were a brand new installation.

^Give to you favorite charity generously.

Music/page is too loud

Try re-calibrating making sure that music/page is playing

continuously during the calibration process at it’s normal or

normal to high level.

User’s Guide

6408 216th Street SW |Mountlake Terrace, WA 98043 USA

T+1.425.778.7728 F+1.425.778.7727 |www.SymetrixAudio.com

Specs•DeclarationofConformity

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 continuously, not just during gaps in the audio program.

The ALC shall utilize microphones to sense the ambient noise level. The

unit shall incorporate front-panel headphone output enabling the user to

monitor the ambient sense signal system.

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, noise sensing

protocol, gain:sense ratio, ducker control, output trim, and averaging

time. In addition, the ALC shall provide an active signal mode, bypass

mode, 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.

In addition to the audio input/output connections, there shall be

connections provided for a sense input and remote trim control.

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 371 SPL Computer.

Speciﬁcations

Input/Output

Maximum Input Level +20 dBu balanced

Program Input Impedance > 20k Ohms balanced,

> 10k Ohms unbalanced

Input Common Mode Rejection Ratio > 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+Noise < 0.025% (+4 dBu in, +4 dBu out)

Output Gain Range +20, -30 dB

Sense Channel Frequency Response -3 dB at 300 Hz and 6000 Hz,

3-pole Butterworth

Sense Channel Gain selectable, 0 dB to +70 dB

Headphone Monitor Gain 28 dB maximum

Program Channel Output Noise -95 dBu @ unity gain, typical

Output Trim Range +/- 10 dB

Connections

All Inputs, Outputs and Control Ports Euroblock

Power In 7-pin DIN

Physical

Size (hwd) ½ rack unit

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

Shipping Weight 4.5 lbs / 2.03 kg

Environmental

Maximum Ambient Operating Temperature 40˚ C (104˚ F)

Declaration of Conformity

We, Symetrix Incorporated, 6408 216th St. SW, Mountlake Terrace,

Washington, USA, declare under our sole responsibility that the

product:

371 SPL Computer

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

standards:

EN 60950

Safety requirements for mains operated electronic and related

apparatus for household and similar general use.

EN 55103-1

Product family standard for audio, video, audio-visual and

entertainment lighting control apparatus for professional use.

Part 1: Emission

EN 55103-2

Generic immunity standard.

Part 1: Residential, commercial, and light industry.

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, U.K.

Date of issue: January 1, 2001

Place of issue: Lynnwood, Washington, USA

Authorized signature:

Dane Butcher, President, Symetrix Incorporated.

Speciﬁcations... continued

Electrical

Power Requirements 115 VAC nominal, 95 to 130 VAC, 50 to 60 Hz

230 VAC nominal, 207 to 253 VAC, 50 Hz

10 watts maximum, PS-3 or PS-3E only

371 SPL Computer

Warranty and Service

The Symetrix Limited 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.

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 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.

Servicing Your Symetrix Product

If you have determined that your Symetrix product 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:

Return Authorization

At the Symetrix factory, Symetrix will perform in-warranty or out-of-

warranty service on any product it has manufactured for a period of

three (3) years from date of discontinued manufacture.

Before sending anything to Symetrix, please contact our Customer

Service Department for a Return Authorization (RA) number. The

telephone number is +1 (425) 778-7728. Additionally, support is

available via the web site: http://support.SymetrixAudio.com.

In-warranty Repairs

To get your Symetrix product repaired under the terms of the warranty:

1. Call us for an RA number (have the serial number, shipping and contact

information and description of the problem ready).

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 pay the return freight.

If you don’t have the factory packaging materials, we recommend using

an oversize box. Wrap the unit in a plastic bag, surround it with bubble-

wrap, and place it in the box surrounded by Styrofoam peanuts. Be sure

there is enough clearance in the box to protect the rack ears. We won’t

return the unit in anything but Symetrix packaging for which we will have

to charge you. If the problem is due to operator misuse or error, you will

have to pay for both parts and labor. In any event, if there are charges

for the repair, 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.

Item No. 53-0005

371 SPL Computer User’s Guide

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 brochure 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. The following are