SC21.1

SYSTEM CONTROLLER APPLICATIONS:
SLS & RS Full-range systems SBS & VBS Subwoofers Fixed installations Rental systems

SPECIFICATIONS

Note: 0 dBu = 0.775V

FEATURES:

Dynamic system equalization Dynamic overdrive protection IntelliSense amplifier output monitoring Electronic crossover for subwoofer Tamper-proof settings Balanced input / outputs 1 Rack space

DESCRIPTION

The SC21.1 SYSTEM CONTROLLER is designed specifically for the Community Solutions and the RS/VBS loudspeaker systems. The SC21.1 can provide the electronic control for any of these systems including a subwoofer crossover, filtering, equalization and protection functions. It has a balanced/unbalanced XLR-type input and two balanced/unbalanced XLR-type outputs - one for full-range loudspeakers and one for subwoofers. Set-up controls are located behind a security cover on the rear panel of the SC21.1. Settings are selectable for the specific loudspeaker systems being used. These include filter selection and protection threshold adjustment and a variable 0 dB to +10dB gain control for the subwoofer output. The security cover, attached by captive screws, helps prevent tampering or accidental adjustment of the controls. In addition, the SC21.1 features an internal jumper block that can be programmed to completely disable the external controls and to hardwire the settings - a real plus for permanent installations or rental use. The SC21.1 also features full range and subwoofer sense inputs with IntelliSense( circuitry that actively monitors the output of the associated power amplifiers. The IntelliSense circuits condition the audio input to the amplifiers by providing proper equalization for optimum loudspeaker performance as well as compression/limiting to help prevent overdrive and damage to the loudspeakers. The front panel has illuminated indicators to inform the operator about the controller status, including: power on, signal presence for both input and sense signals, and protect mode operation. A sensing circuit detects the absence of signal and reduces the dynamic HF boost during those periods to minimize background noise. Manufactured in Germany, the SC21.1 uses highest quality, precision tolerance components for stable, long term operation and reliability. An external AC transformer is provided to power the SC21.1s internal, regulated DC supply that is equipped with fuseless over-voltage and over-current protection. There are two versions of the controller: model SC21.1 for 110-120 VAC and the SC21.1E for 220-240 VAC. The controller meets all applicable US and European standards for equipment of this type, including the European CE-Standard.
Inputs: 1 XLR-type female 40k ohm (electronically balanced) +16 dBu maximum level Sense Inputs: Screw terminals 300k ohm (electronically balanced, polarity insensitive) Outputs: 2 XLR-type male 20 ohm - electronically balanced 600 ohm maximum load +22 dBm maximum level (+16 dBm unbalanced) Gain: Full-Range: Typically -3dB @ 1 kHz (frequency & level dependent) Sub Low:Variable 0 dB to +10 dB Distortion (THD): Full Range: < 0.05%, Sub Low: < 0.02% Hum and Noise: < 87 dBu Dynamic Range: Full Range: > 109 dB, Sub Low: > 119 dB Input CMRR: > 58 dB @ 1 kHz, > 46 dB @ 20 kHz Configuration: 1 channel x 2-way (Full Range + Sub Low) Full Range Processing: Low cut filter - 34 Hz High pass filter - selectable 50/70/90/130 Hz Low and high frequency dynamic EQ Low and high frequency limiting Sub Low Processing: Low cut filter - 27 Hz High pass filter - selectable 38/52 Hz Low pass filter - 130 Hz Dynamic EQ Sub limiting Output level - 0 dB to +10 dB Overall Processing: Input compressor/limiter Protection threshold - selectable Low, Med, High Noise gate turns off dynamic HF EQ with no signal input Indicators: Power Input signal presence Full Range signal presence/protect Sub Low signal presence/protect Power Supply (External mains transformer): SC21: 110-120 VAC 7W, 60 Hz (US) SC21E: 220-240 VAC, 6W, 50-60 Hz (Export) Dimensions: Height:1.75 inches (44 mm) Width: 19 inches (483 mm) Depth: 3.9 inches (100 mm) Weight: 3.2 lbs (1.45 kg) (not including transformer) Shipping Weight: SC21.1 6.2 lbs (2.8 kg), SC21.1E 6.4 (2.9 kg) Supplied Accessories: External mains transformer, Operating manual SC21.1 Page 1 of 2

COMMUNITY PROFESSIONAL LOUDSPEAKERS 333 East Fifth Street Chester, PA 19013-4511 USA Phone (610) 876-3400 Fax (610) 874-0190
1996, Community Light & Sound, Inc.
SYSTEM CONTROLLER DIMENSIONS
ARCHITECTS' AND ENGINEERS' SPECIFICATION
The device shall be an electronic controller for the Community Solutions and RS/VBS Series Loudspeaker Systems manufactured by Community Professional Loudspeakers. It shall provide a two-way electronic crossover, filtering, dynamic equalization and dynamic loudspeaker protection utilizing voltage controlled filters and voltage controlled amplifiers. Control signals for the dynamic circuits shall be derived from sense inputs connected to the output of the associated amplifiers. The subwoofer crossover frequency shall be selectable between 50 Hz, 70 Hz, 90 Hz and 130 Hz. A low cut filter shall be selectable between 38 Hz and 52 Hz. The loudspeaker protection circuit shall provide three threshold levels: minimum, moderate and maximum. Input and output connectors shall be 3-pin XLR-type. The input impedance shall be 40k ohm (300k for the sense inputs) and the output impedance less than 20 ohms. The maximum input level shall be +16 dBu, electronically balanced, with a minimum CMRR of 58 dB at 2 kHz and 46 dB at 20 kHz. The maximum output level shall be +22 dBu, electronically balanced and +16 dBu unbalanced, with a maximum load of 600 ohms. Harmonic distortion, including hum and noise shall be less than 0.05%. Hum and noise shall be below -87 dBu A-weighted, with an overall dynamic range greater than 109 dB. The chassis shall be constructed of steel with a black powder-coat paint finish. Power shall be supplied by an included external transformer with a primary of 110-120 VAC 7W, (220-240VAC, 6W), 50-60 Hz. Dimensions shall be 19 in. (482 mm) W, 1.75 in. (44 mm) H, 3.94 in. (100 mm) D, 1 rack unit and shall weigh 3.2 lbs (1.45 kg) without the external transformer.

LIMITED WARRANTY

The Community SC21.1 Electronic System Controller is warranted in the USA to be free from defects in materials and workmanship for a period of two years. This warranty applies to the product; therefore, the remainder of the warranty period will be automatically transferred to any subsequent owner. This warranty applies only to failure of a Community SC21.1 caused by defects in materials and workmanship during the stated warranty period. It does not apply to a unit that has been subjected to abuse, accident, modification, improper handling/installation, or repairs made without factory authorization or by anyone other than authorized Community Field Service Stations. This warranty is void if the serial number has been defaced, altered or removed. Products covered by this warranty will be repaired or replaced at the option of Community, without charge for materials or labor, provided all the terms of this warranty have been met.

SYSTEM CONTROLLER

S C 21

O W N E R S M A N U A L

REFERENCE TO EC STATEMENT OF CONFORMITY
This document confirms that the range of products of Community Professional Loudspeakers bearing the CE label meet all the requirements in the EMC directive 89/336/EEC laid down by the Member States Councel for adjustment of legal requirements, furthermore the products comply to the rules and regulations referring to the electromagnetic compatibility of devices from 30 August 1995. The Community Professional Loudspeakers products bearing the CE label comply with the following harmonised or national standards: DIN EN 55013:08-1991 DIN EN 55020:05-1995 DIN EN 50082-1:03-1993
The authorized declaration and compatibility certification lie with the manufacturer and can be viewed upon request. The responsible manufacturer is the company: Community Light & Sound, Inc. 333 East 5th Street Chester, PA 19013 USA Tel: 610 876-3400 Fax: 610 874-0190
Chester, PA USA January 1996
TABLE OF CONTENTS - SC21 OWNERS MANUAL

CONTENTS PAGE

Introduction and Safety Information... 4 Introduction to Electronically Controlled Loudspeaker Systems.. 5 Unpacking and Inspection... 6 Quick Start-Up.... 7 Front and Rear Panel Views.... 8 Indicators, Controls and Connectors...9-10 General Description.... 11 Circuit Description.... 11-12 Audio Signal Chain Block Diagram: Fig. 2... 13 Protection Signal Chain Block Diagram: Fig 3... 14 Setup and Operation.... 15-23 Internal Jumper Setting Diagrams: Figs 4,5,6... 16 Connection Diagram: Fig 7.... 18 RS/VBS Series - Equalization and Protection Settings: Table 1.. 21 SLS/SBS Series - Equalization and Protection Settings: Table 2.. 22 Operating Considerations.... 24-26 Special Operating Considerations... 27 Technical Specifications.... 28 In Case of Difficulty.... 29 Warranty Information... 30-31 Bill of Materials..... 32-33 Index..... 34 DIAGRAMS and TABLES Fig 1:.. Fig 2:.. Fig 3:.. Fig 4:.. Fig 5:.. Fig 6:.. Fig 7:.. Table 1:. Table 2:. PAGE
Front and Rear Panel Views... 8 Audio Signal Chain Block Diagram... 13 Protection Signal Chain Block Diagram.. 14 Internal Jumper Setting - Sub Low High Pass.. 16 Internal Jumper Setting - Full Range High Pass.. 16 Internal Jumper Setting - Protection Limiter threshold.. 16 Connection Diagram.... 18 RS/VBS Series - Equalization and Protection Settings.. 21 SLS/SBS Series - Equalization and Protection Settings.. 22
MANUAL COMMUNITY SC21 SYSTEM CONTROLLER OWNERS MANUAL

SC21 SYSTEM CONTROLLER

This manual contains information for the proper setup and operation of the Community SC21 (120 VAC) and SC21E (220-240 VAC) System Controllers for Community RS/VBS and Solutions SLS/SBS loudspeaker systems. While every attempt has been made to ensure this information is correct and up to date, Community continuously incorporates worthwhile improvements to each product that may include changes and/or modifications not contained in this manual. Except for the mains input voltage, the SC21 and SC21E are identical in all other respects.
IMPORTANT SAFETY INFORMATION
The terms Caution, Warning, and Danger are used throughout this manual to alert the reader to important safety considerations. If you have any questions about any aspect of these cautions, contact your local dealer, your countrys Community distributor, or Community.

CAUTION: describes an equipment operating condition or user action that may expose the equipment
or user to potential damage or danger.
WARNING: describes an operating condition or user action that will cause damage to the equipment or

injure the user.

ANGER: DANGER: describes an operating condition or user action that will immediately damage the equipment
or be extremely dangerous or possibly life-threatening to the user.
ELECTRICAL PRECAUTIONS CAUTION:
To prevent electric shock, disconnect the unit from the AC mains before opening the unit. Refer service to qualified service personnel only.

WARNING:

In order to reduce the possibility of electric shock or damage to this equipment, do not expose this device to moisture or rain.
ELECTRONICALL ALLY LOUDSPEAKER INTRODUCTION TO ELECTRONIC ALLY CONTROLLED LOUDSPEAKER SYSTEMS
In simple terms, an electronically controlled loudspeaker system consists of: 1. The loudspeaker components and cabinet 2. An associated electronic device that modifies the source signal in some fashion 3. The power amplifier used to drive the loudspeaker system Properly done, an electronically controlled loudspeaker system, in combination with a power amplifier of appropriate rating, will provide enhanced performance over a non-electronically-controlled loudspeaker cabinet in one or more of the following ways: Improved frequency response Maximized power-handling Higher acoustic output Lowered distortion Protection of the loudspeaker system components All loudspeaker systems have frequency response limitations. Flat response from a system is typically attained by lowering the output in certain portions of the systems passband to match the lower output of the system at other frequencies within its passband. As a consequence the overall sensitivity of the system is lowered. Rather than modifying the system, the input signal may be modified to compensate for those areas within the systems passband where it would normally have lower output. In this way flat frequency response can be achieved while maintaining the sensitivity of the system. All loudspeaker systems have power handling limits beyond which they can be damaged. An electronic model may be developed with characteristics that help prevent exceeding the mechanical and thermal limits of the systems components. For example, suppose it can be determined with accuracy that an input signal of 20 volts to the voice coil of a driver will cause the voice coil former to strike the rear of the magnet assembly. If the electronic model for this speaker is designed into a controller so that the input signal to the drivers voice coil may never exceed 19.5 volts, then it should never be capable of bottoming out. Some other important operational characteristics may also be addressed by a controller. One is compensating for the natural characteristics of the human hearing, which does not hear low frequencies and high frequencies as well at lower sound pressure levels. The controller can increase the output of these frequencies at low volume (in essence, a sophisticated loudness control). The controller can then reduce the output at these frequencies as the signal level is increased. Another characteristic is providing an electronic crossover function; while yet another might be to correct for phase anomalies in the loudspeaker system. A properly-designed electronic controller will inaudibly provide the necessary equalization, compression, and limiting required for the associated loudspeaker system when the loudspeaker system is operated within its rated power constraints. Even when this boundary is exceeded, it will apply control in a manner that is audibly acceptable.

UNPACKING UNPACKING AND INSPECTION
The Community SC21 is inherently rugged and is carefully packed in a well-designed carton, but it is a good idea to carefully inspect the unit after it has been removed from the packaging. Sometimes there may be hidden damage due to some unfortunate incident in shipment. Please note that once the shipment has left Community (or the dealer), the responsibility for damage is borne by the freight company. This means that if there is damage, you must file a claim with the freight company. Each freight company has its own set of regulations that must be followed and forms that must be filled out. Therefore the freight company must be contacted as soon as a shipping damage problem is discovered. Save the carton and packing material because many times shipping claims will be considered invalid if these are thrown away. The Community dealer and the factory will try to help in any way possible. Remember, though, it is up to the person receiving the shipment to file a claim. It is always a good idea to keep the carton and packing material in case the unit must be shipped back to your dealer or country distributor. The shipping carton contains the following items: SC21 Controller Unit External Power Transformer Unit Owners Manual
1) INDICA INDIC ATORS, CONTROLS AND CONNECTORS (See Figure 1

FRONT PANEL INDICATORS 1

IN: SIGNAL PRESENCE SUB & FULL RANGE: SIGNAL PROTECT POWER

DESCRIPTION

Green LED Indicates an input signal > -27 dBu. Two-color LEDs Green = Indicates a sense signal > 8 dBu. Flashing red = Indicates the output is in protect mode. Steady red = Indicates the output is in full protection mode 1. Green LED Indicates that the SC21 is on. Note: There is no power on/off switch.

REAR PANEL CONTROLS 2 5

PROTECTION Three position switch for selecting the level of loudspeaker protection. Sets the limiting thresholds used for the protect mode. MIN =Highest threshold (minimum protection) MED =Moderate threshold (normal protection: 2.5 dB lower than MIN) MAX =Lowest threshold (maximum protection: 5 dB lower than MIN) Four position slide switch for selecting the corner frequency of the high-pass filter for the FULL RANGE output. Set this switch as indicated in Tables 1 and 2 for the loudspeaker system being used with the SC21. Corner Frequencies: 50 Hz, 70 Hz, 95 Hz, 130 Hz. Two position slide switch for selecting the corner frequency of the high-pass filter for the SUB LOW output. Set this switch as indicated in Tables 1 and 2 for the loudspeaker system being used with the SC21. Corner Frequencies: 38 Hz, 52 Hz. Potentiometer (marked 1 to 10) for adjusting the gain of the SUB LOW output. The gain is variable from 0 dB to +10 dB and is used to balance the subwoofer output to the output of the full-range loudspeaker.

CAUTION:

Internal Jumpers
A jumper block on the PC board inside the SC21 can be programmed to individually disable or enable the rear panel control switches so as to fix their settings. If a control is disabled, a fixed setting must be used instead. Disabling the rear panel controls and fixing specific settings is useful when the SC21 is used in permanent installations or in rental systems where tampering with the control setting might allow damage to the loudspeaker system. Refer to Figures 4, 5 & 6 and Internal Jumpers in the Setup And Operation section to pre-program the SC21.

GENERAL DESCRIPTION

The SC21 System Controller is a single-channel device that provides the electronic crossover, filtering, equalization and protection functions for Community RS/SLS series full-range and VBS/SBS series subwoofer loudspeaker systems. The SC21 uses IntelliSense circuitry to monitor the output of the associated power amplifiers and provide appropriate control to the audio signal to prevent overdrive and damage to the loudspeaker systems. The front panel has illuminated indicators to inform the operator about the SC21s status, including power on, signal presence for both input and sense signals, and protect mode operation. Critical set-up controls are located behind a security cover on the rear of the unit. These controls include filter selections, protection threshold, and gain level for the subwoofer output. Settings are selected based upon the model of the loudspeaker system to be used. The removable cover is attached by captive screws, to help prevent tampering or accidental adjustment of these controls. An external power supply transformer is provided with and connects to the unit via a rear panel receptacle. The internal, regulated +/- 10V DC supply is equipped with fuseless over-voltage and over-current protection. The SC21.1 is an updated version of the SC21. It has a sense circuit that gates off the dynamically controlled HF Equalization when no signal is present. This modification was implemented to reduce high frequency background noise under no signal conditions.

CIRCUIT DESCRIPTION Audio Signal Chain (See Figure 2)
An input signal is applied to the SC21s electronically balanced input stage via a 3-pin female XLR-type connector. The input signal then goes to a voltage-controlled amplifier (VCA). This VCA is used as the gain reduction stage controlled by the compressor/limiter for overall overdrive protection. This circuit also functions as a balanced to single-ended signal conversion stage. The signal is then routed to a 27 Hz 2nd-order high-pass filter (HPF) with a Q of 0.9, followed by a second 2nd-order HPF. The second HPF functions as a voltage-controlled filter (VCF) with control voltage for gain and Q provided by the SUB limiter circuit. The filter frequency may be set to 38 Hz or 52 Hz by adjustment of the SUB HIGH PASS FREQ switch on the rear panel. A gain stage follows that provides an adjustment range of 10 dB via the SUB GAIN control potentiometer. The signal is then fed to a 130 Hz, 4th-order Linkwitz-Riley, low-pass filter (LPF). At the end of the signal chain is a line-driver circuit with 6 dB gain that provides the electronically balanced output, wired to a 3-pin male XLR-type connector. The FULL RANGE signal is derived from the output of the 27 Hz 2nd-order HPF. This signal connects to a 34 Hz 2nd-order Butterworth HPF, followed by a second 2nd order HPF. The second HPF functions as a VCF, with control voltage for gain and Q provided by the LF limiter circuit. The filter frequency may be set to 70 Hz, 95 Hz or 135 Hz by adjustment of the F.R. HIGH PASS FREQ switch on the rear panel. The signal then flows to a 2 dB/octave, 1st-order shelving filter that provides a smooth attenuation of the signal up to the higher frequencies of the lower mid band. The next stage is a 1st-order band pass filter (BPF) with a rising slope of 3 dB/Octave and a falling slope of 6 dB/Octave. This filter is controlled by the HF limiter. At the end of the signal chain is a line-driver circuit with 6 dB gain that provides the electronically balanced output, wired to a 3-pin male XLR-type connector. The integrated circuits used in the audio chain are NE5532 op-amps, with additional low noise, low distortion, high dynamic range SSM-series components from PMI/Analog Devices. The balanced output line-driver ICs (SSM2142) provide the properties of a transformer-balanced output. The output signal

OPERATION SETUP AND OPERATION
The SC21 System Controller is a line-level electronic device used in conjunction with a power amplifier and loudspeaker system for dynamic signal equalization, signal compression/limiting, loudspeaker system transducer protection, and active crossover. Proper installation, setup and operation of the SC21 will help ensure exceptional sonic performance of the system, while reducing the possibility of transducer damage and distortion.
Prior to installing the unit you should determine if you want to disable any or all of the rear panel switches and program the SC21 with fixed settings. This requires removal of the integral top cover/front panel that is not possible once the unit is mounted in an equipment rack. Once the unit is open, a jumper block can be accessed for this programming. The unit is shipped programmed so that all rear panel switches are enabled and therefore no settings are fixed. To program the jumper block, remove the integral top cover/front panel. This is done by removing a screw on each side of the SC21 and sliding the top cover/front panel forward about 1/2 (10 mm). Then lift the cover at the front panel and carefully hinge it back. There is a grounding wire attached to this cover that connects to the bottom chassis at the rear. Do not remove this wire. Once the unit is open, the jumper block will be seen towards the middle rear, just forward of the rear panel switches. Program the jumper block according to Figures 4, 5, and 6 for the SUB LOW, FULL RANGE and PROTECTION functions. This is done using the computer type push-on jumpers provided. Refer to Tables 1 and 2 for the recommended settings for the loudspeaker being used with the SC21. To close the cover, reverse the removal procedure, ensuring that the captive tab on the rear underside of the cover is captured by the lip on the rear panel, and ensuring that the LED indicators properly seat in their holes in the front panel.
The SC21 will not function properly unless EITHER a hardwired setting or a switch enabled setting is programmed on the jumper block for each of the functions: SUB LOW, FULL RANGE and PROTECTION.
Location In The Audio System
The SC21 should be the last device in the signal chain before the power amplifier, with its outputs going directly to the inputs of the associated power amplifier(s). In systems that have the source processing equipment (mixer, equalizers, signal delays, etc.) located at a distance from the power amplifiers, the SC21 may be located either with this equipment, or with the power amplifiers. Since the SC21 front panel has several LED indicators, a system operator should be able to view these indicators for important information about the operation of the system. However, because of the requirement that amplifier outputs must be returned to the SC21, it may be more convenient to locate it near the power amplifiers. If system is properly gain-structured, signal level indications at the source equipment location should give the operator adequate information regarding system signal levels at the SC21.

Sense Input Connections (See Figure 7)
The sense inputs must be properly connected or the SC21 will not function correctly meaning it will automatically go into a full protection mode at higher signal levels. This mode applies the maximum compression and limiting to the audio signal and cause the front panel indicators for the SUB LOW, FULL RANGE or both to be illuminated a steady red. Connect the sense input(s) on the SC21 to output of the associated amplifier(s). The sense inputs are polarity insensitive and are compatible with all types of power amplifiers, including mono-bridged amplifiers. Because only small amounts of current flow through the sense wiring, typically < 0.1 mA, #22 or #24 AWG twisted pair wire can be used. If the SC21 is located at a distance from the amplifier(s), use twisted-pair shielded audio cable for the connections. Connect the shield only to the amplifier chassis. Do not connect the other end of the shield to the SC21. If an SC21 output feeds multiple amplifiers, connect the sense line to only one amplifier output. Unless all amplifiers are set for the same voltage gain, it should be connected to the amplifier with the highest gain. This is because amplifiers with a gain higher than that of the monitored amplifier may overdrive and damage the loudspeakers connected to their outputs before the IntelliSense protection circuits are activated. Conversely, loudspeakers connected to amplifiers with a gain lower than that of the monitored amplifier will be somewhat overprotected. This will do no harm except to reduce their maximum output capability proportionally.
Full Range Only Operation
If the SC21 is to be used only for a full-range loudspeaker, the control settings should be set as in Tables 1 and 2 for the particular loudspeaker. However, because there will be no sense input for the SUB LOW IntelliSense circuitry, the SC21 will detect a sense fault at higher signal levels and cause the front panel SUB LOW indicator to be illuminated a steady red. While this will not affect the function of the SC21, it may be disturbing for the operator. To prevent this condition simply connect the sense return line from the full range amplifier in parallel to both the FULL RANGE and SUB LOW sense inputs. The front panel SUB LOW indicator will then basically track the operation of the FULL RANGE front panel indicator.

Subwoofer Only Operation

If the SC21 is to be used only for a subwoofer, the control settings should be set as in Tables 1 and 2 for the particular subwoofer. However, because of the operation of the IntelliSense circuitry, the sense return line from the subwoofer amplifier must be connected in parallel to both the FULL RANGE and SUB LOW sense inputs. If this is not done, the FULL RANGE sense circuit will detect a sense fault at higher signal levels and automatically apply full protection to the FULL RANGE output. This will also cause a full protection condition on the SUB LOW output. Connecting the subwoofer sense lines to both sense inputs avoids this situation.

Grounding

Even though the SC21 uses a low voltage (24 VAC) external transformer, grounding is still a safety consideration. Ensure that a low impedance electrical connection is made from the SC21s chassis to the electrical systems safety ground. The chassis GROUND screw on the rear panel of the SC21 is provided for this purpose.
Failure to establish a proper ground connection to the electrical system safety ground may create a personnel safety hazard. Do not use the shield of the audio wiring as a safety ground.
Interference - Hum And Noise
The circuitry of the SC21 is quite resistant, but not entirely immune, to hum pick-up from strong magnetic fields radiated by power transformers in nearby equipment. Specifically, the power transformers in compact, high-powered amplifiers can produce significant stray magnetic fields that can induce hum in equipment mounted near to them. To avoid hum pick-up it may be necessary to locate the SC21 one or two rack spaces away from such amplifiers. The SC21 has high quality electronically balanced input and output circuitry that, when connected to other balanced equipment, can provide excellent interference rejection under most conditions. If connected to unbalanced equipment, ground loops will be formed and associated hums and buzzes may result. Likewise it is sometimes impossible avoid a situation where cables are routed next to interferenceprone signal sources such as AC power cables or other sources of high-level electro-magnetic or radiofrequency interference. Also, long runs between electronically balanced equipment may be prone to interference. This is because voltage differences between the ground reference for each unit may be too high to be effectively rejected by the limited CMRR range of electronically balanced circuits.
In the above cases, use of external, audio line-level transformers may be required. The input transformer to the SC21 should have a 1:1 turns ratio and be of the bridging type, 15k:15k. Output transformers should have a 1:1 turns ratio with an input and output impedance that matches or is somewhat less than the input impedance of the amplifier to which the SC21 is connected. If more than one amplifier is fed from an SC21 output, calculate and match the combined input impedance of the amplifiers. In no case should the SC21 feed a load below 600 ohms. Other turn ratios may be used but the voltage gains or loses must be accounted for in the systems gain structure. Always use quality transformers from manufacturers such as Jensen or Reichenbach. Lesser quality transformers may seriously degrade the audio quality of the system.

Setting the Rear Panel Controls
After installing the SC21, remove the rear security cover by undoing its captive screws and adjust the controls under the cover as follows. Sub Gain Control This potentiometer (marked 1 to 10) is used to adjust the gain of the SUB LOW output. The gain is variable from 0 dB to +10 dB and is used to balance the acoustic levels between the subwoofer and fullrange loudspeaker. The correct adjustment must be determined by listening tests because a subwoofers bass response can vary significantly depending on its placement in a room. Equalization and Protection Settings Refer to Tables 1 and 2 for proper set up of the PROTECTION, F.R. HIGH PASS FREQ, and SUB HIGH PASS FREQ controls.
TO MODERATE LOW TO MODERATE POWER
FULL RANGE SYSTEM SUBWOOFER SUB POLARITY

HIGH POWER

PROTECTION PROTECTION FULL RANGE PASS HIGH PASS

SUB HIGH PASS PASS

RS880 RS880 RS880 RS660 RS660 RS660 RS220 RS220 RS220 RSJr RSJr RSJr RSFB(Biamp) RSFB(Biamp) RSFB(Passive)4 RSFB(Passive) RSFB(Passive)
VBS415 VBS212 None VBSVBS212 None VBSVBS212/112 None VBSVBS212/112 None No Addl Sub VBS212/112 VBSVBS212/112 No Addl Sub
Reverse Reverse Normal Reverse MED Normal Normal MED Normal Normal MAX Normal Normal Reverse Normal
MIN MIN MIN MIN MIN 70 Hz MED MED 130 Hz MAX MAX 130 Hz MED MED MED MED MED
70 Hz 70 Hz 70 Hz 95 Hz 95 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 70 Hz 70 Hz 50 Hz
38 Hz 52 Hz MED 38 Hz 52 Hz MED 38 Hz 52 Hz MAX 38 Hz 52 Hz MAX 52 Hz 52 Hz 38 Hz 52 Hz
MED MED 70 Hz MED MED 95 Hz MAX MAX 130 Hz MAX MAX 130 Hz MAX MAX MAX MAX MAX
70 Hz 70 Hz 95 Hz 95 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 70 Hz 70 Hz 50 Hz
38 Hz 52 Hz 38 Hz 52 Hz 38 Hz 52 Hz 38 Hz 52 Hz 52 Hz 52 Hz 38 Hz 52 Hz
TABLE 1: Recommended Equalization And Protection Settings - RS/VBS Series
PROTECTION PRO TECTION FULL RANGE PASS HIGH PASS
SLS980 SLS980 SLS980 SLS960 SLS960 SLS960 SLS920 SLS920 SLS920 SLS915 SLS915 SLS915 SLS918(Biamp) SLS918(Biamp) SLS918(Passive)4 SLS918(Passive) SLS918(Passive)
SBS45/25 SBS22 None SBS45/SBS22 None SBS45/SBS22/12 None SBS45/SBS22/12 None No Addl Sub SBS22/12 SBS45/SBS22/12 No Addl Sub
Reverse Reverse Normal Reverse Normal Normal Normal Normal Normal Normal Reverse Normal
MIN MIN MIN MIN MIN MED MED MED MED MAX MAX MAX MED MED MED MED MED

70 Hz 70 Hz 70 Hz 95 Hz 95 Hz 70 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 70 Hz 70 Hz 50 Hz
MED MED MED MED MED MED MAX MAX MAX MAX MAX MAX MAX MAX MAX MAX MAX
70 Hz 70 Hz 70 Hz 95 Hz 95 Hz 95 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 130 Hz 70 Hz 70 Hz 50 Hz
TABLE 2: Recommended Equalization And Protection Settings - SLS/SBS Series Footnotes for Tables 1 and 2 This is the optimum subwoofer polarity when the full-range cabinet is in close proximity to the subwoofer. If the full-range cabinet and subwoofer are separated by more than a few feet, optimum polarity should be determined by listening tests. Polarity is changed by reversing the connections to pins 2 and 3 on the XLR connected to the SUB LOW output. 2 Low-to-moderate power levels are indicated by the SUB and FULL RANGE LEDs on the SC21s front panel occasionally flashing red with the protection level set as indicated. 3 High power levels are indicated by the SUB and FULL RANGE LEDs on the SC21s front panel flashing red more than 25% of the time with the protection level set as indicated. 4 The RSFB or SLS918 can only be used with the VBS415 or SBS45 in passive mode. In biamplified mode the 38 Hz high pass signal for the SUB LOW output could damage the 12 driver in the RSFB or SLS918. 5 Connect the SUB ADJUST (terminal 2) to GROUND (terminal 1) when using Community 8 ohm subwoofers. See section on Use Of SC21 With 8 Ohm Community Subwoofers for further information.
Indicator Lights (See Figure 1)
In Signal Presence When an input signal of greater than -27 dBu is applied to the input stage of the unit, the green LED on the front panel labeled IN - SIGNAL PRESENCE is illuminated green. Sub & Full Range Signal Protect The IntelliSense circuits of the SC21 include two 2-color LED indicators on the front panel: one for the FULL RANGE section and one for the SUB LOW section. They function as both signal presence and protect indicators. The LEDs are illuminated green when there is a signal level of 8 dBu or greater present on the sense inputs. The LEDs turn red and blink on and off when the sense voltage input is sufficient to activate the loudspeaker protection circuits of the SC21. Each indicator provides valuable information about system operation as follows: 1. Indicator off: Normal operation but indicates the signal level is below 8 dBu (2.5V) from the associated power amplifier. 2. Blinking or steady green: Normal operation. 3. Blinking red: As system power levels approach maximum, the LED will turn from green to red and blink on and off. This indicates that the compression/limiting circuits are activated. It is normal during high level operation for this to occur. As power is increased further it will blink more often. If an indicator is blinking red more than 50% of the time, reduce the signal level to the loudspeaker.

If either protection LED is blinking red constantly (over 50% of the time), the loudspeakers are probably being overpowered. The signal level should be reduced to avoid excessive distortion and possible transducer damage in the loudspeaker system. 4. Steady red condition: Indicates excessive power to the loudspeaker or indicates a fault in the sense wiring, perhaps due to a broken cable or an improper termination at either the amplifier or at the SC21. It may also indicate that the amplifier connected to the SC21 has not been turned on or that it is in a protection or failure mode.
Any fault in the sense circuit may cause serious damage to the speaker system. If the LEDs are steady red, the cause should be immediately investigated and the fault corrected.
Power When this front panel LED is illuminated green it indicates that the SC21 is powered on. This LED is powered from the internal minus 10 VDC supply.
OPERATING CONSIDERATIONS OPERATING CONSIDERATIONS Loudspeaker Protection
The dynamic equalization and compression/limiting circuits of the SC21 have filter slopes and time constants chosen to make the operation as unobtrusive as possible yet still provide a high degree of protection for the loudspeaker components. However, the SC21 cannot provide absolute protection against speaker damage under all operating conditions. It is important that reasonable care be taken in the setup and operation of the loudspeaker systems to protect them against damage due to system overload.

External Equalization

Great care must be taken when applying external equalization to Community loudspeaker systems. The SC21s dynamic equalization circuits reduce the amount of signal at the low and high frequency ends of their operating range at high power levels. If external equalization is used to boost these frequencies, already attenuated by the dynamic compression circuits, the result may defeat the SC21s protection function, possibly resulting in loudspeaker damage. If additional equalization is used, it should only be used moderately to adjust the response of the system or for equalizing against feedback.

22m Alu_E H380 LED grn H370 LED grn/red *opt 1% 100k Array 4Y104G 100k 1% 47k 1% 56k 1% 43k 1% 24k 1% 150k 1% 10k 1% 100R 1% 62k 1% 120k 1% 560k 1% 200k 1% 470k 1% 33k 1% 51k 1% 4k7 1% 5M6 1% 680k 1% 68k 1% 1M 1% 330k 1% 27k 1% 1M2 1% 180k 1% 1k8 1% 390R 1% 1k 1% 220R 1% TL084CN Amp LM324N Amp LM339N Comparator 1N4148 Diode 0R Wire 102-206 Screw terminal 470m Alu_E 0m47 Alu_E 0m1 CerCo H380 LED grn RXE050 Polyswitch 07K20 Varistor 1k Trimpot PT6v 2k7 1% 390R 1% 10k 1% 56R 1% 620R 1% B40C800 Rectifier TL082CP Amp 7812CT Voltage Regulator +KK/Clip CJ180 Coax-Connector External Transformer
A Audio Signal Chain... 11 Audio Signal Connections... 19 B Biamplified Community Loudspeakers.. 27 Bill Of Materials... 32 C Circuit Description... 11 Compression/Limiting... 24 Compressors/Limiters... 25 Connection Diagram... 18 E EC Statement Of Conformity... 2 Electrical Precautions... 3 Electronic Control... 5 Equalization... 24 Equalization Settings... 21, 22 F F.R. High Pass Freq Switch... 9 F.R. Terminals... 10 Figure 1 - Front / Rear Panels... 8 Figure 2 - Audio Signal Chain... 13 Figure 3 - Protection Signal Chain... 14 Figure 4 - Sub Low Jumper Settings.. 16 Figure 5 - Full Range Jumper Settings.. 16 Figure 6 - Protection Threshold Jumper Settings. 16 Figure 7 - Connection Diagram... 18 Front Panel Indicators... 9 Full Range Only Operation... 20 Full Range Protect LED... 9, 23 Full Range Signal LED.. 9, 23 G General Description... 11 Ground Terminal... 10, 20 Grounding... 20 I In Case of Difficulty... 29 Indicator Lights... 23 Indicators, Controls And Connectors.. 9 Input.... 9 Input Signal Presence LED.. 9, 23 IntelliSense Operation.. 24 Interference - Hum And Noise... 20 Internal Jumpers... 10, 15 L Location In The Audio System.. 17 Loudspeaker Protection... 24 P Power Amplifier Gain... Power Amplifiers.. Power Connections... Power Input... 9 Power LED.... 9, 23 Protection Level Settings... Protection Signal Chain... Protection Switch... 9 Q Quick Start-Up... 7 R Rear Panel Connectors... 9 Rear Panel Controls.. 9, 21 Rear Panel Screw Terminals.. RS/VBS Settings... S Safety Information... 3 Sense Input Connections... Sense Line Fault Detection.. Setup And Operation... SLS/SBS Settings... Specifications... Sub Adjust Terminal.. 9. 22 Sub Gain Control... 9, 21 SUB High Pass Freq Switch.. 9 Sub Protect LED... 9, 23 Sub Sense Terminals.. Sub Signal LED... 9, 23 Subwoofer Only Operation... Subwoofer Polarity.. 22, 26 T Table 1 - RS/VBS Settings... Table 2 - SLS/SBS Settings.. Testing.... Transferable Warranty... U Unpacking And Inspection.. 6 Use Of SC21 With 8 Ohm Community Subwoofers.. Using Additional Subwoofers With The RSFB And SLS918. W Warranty Information / Service For Outside USA.. Warranty Information / Service For The USA.. Warranty Service.. 3 0