Toroidal Output Transformers Provide Full Electrical Isolation and Meet Worldwide Safety Agency Approval Automatic Two-Speed, High Efficiency Fan CoolingFor Quiet Normal Operation with Maximum Cooling on Demand Rear-to-Front Air FlowKeeps Equipment Racks Cool Front Panel Status LEDsIndicate Clip, Protect, Power and Signal Presence Rear Panel Detented Gain Controls For Security and Resetability Open Input ArchitectureFlexible Input Options Detachable Euro-Style Barrier Strip InputEasy and Economical Connections
he CX6T amplifier is ideal for use in any permanently installed sound system. Designed to meet the specialized needs of high power, high quality audio systems, the CX6T offers the features requested most by contractors and installers from around the world. The CX6T resides in a rugged three rack-space steel chassis approximately 17.9 inches deep. With high quality internal isolation transformers, the CX6T features built-in capability for driving 25, 70 or 100 volt distributed sound systems as well as direct output voice coil loads. Versatile design allows a 25, 70 or

Stereo (W/Ch)

volts 70 volts 100 volts 200 watts 300 watts
100 volt connection on one channel and a direct connection on the other channel. For maximum flexibility, you can even drive a distributed line and a low impedance load on the same channel at the same time! The CX6T features a built-in 45 Hz subsonic filter that reduces saturation of speaker transformers caused by excessively low frequencies. High output power, versatile loading options, high thermal capacity and rugged reliability make the CX amplifiers ideal for any high quality sound system installation.
OUTPUT POWER (Isolated Outputs)

1 kHz, 0.1% THD

Stereo, Bridge, or Parallel Operating ModesSwitch Selectable Double Thickness Rack EarsFor Extra Strength Covered Barrier Strip Output ConnectionsMeets Safety Agency Requirements Simple Barrier Strip Connection Determines Output Mode25 V, 70 V, 100 V and Direct Outputs Available Simultaneously Built-in 45 Hz Subsonic Filter Prevents Speaker Transformer Saturation With Minimal Effect on Program Material
OUTPUT POWER (Direct Outputs)
45Hz-20kHz, 0.1% THD 1kHz, 1% THD
220 watts 350 watts 450 watts*
200 watts 250 watts 250 watts 400 watts 600 watts 440 watts 700 watts 900 watts* 400 watts 500 watts 500 watts

*typical

Mono-Bridged
volts 140 volts 200 volts
1675 MacArthur Boulevard Costa Mesa, California 92626-1468 USA Phone: 714/754-6175 Fax: 714/754-6174

CX6T Specifications

POWER OUTPUT Direct output, watts per channel, both channels driven 8, 45 Hz-20 kHz, 0.1% THD 8, 1 kHz, 1% THD 4, 45 Hz-20 kHz, 0.1% THD 4, 1 kHz, 1% THD 2, 1 kHz, 1% THD* Isolated outputs, watts per channel, both channels driven 70V or 100V, 1 kHz, 0.1% THD 25V, 1 kHz, 0.1% THD Direct Outputs, bridged mono 8, 45 Hz-20 kHz, 0.1% THD 4, 1 kHz, 1% THD* Isolated outputs, bridged mono 50V, 1 kHz, 0.1% THD 140V, 1 kHz, 0.1% THD 200V, 1 kHz, 0.1% THD DISTORTION
ARCHITECTS AND ENGINEERS SPECIFICATIONS
The amplifier shall contain all solid-state circuitry, using complementary silicon output devices in a Class AB output circuit. The amplifier shall operate from 50-60 Hz AC power, with internal taps for selecting voltages 100,120, or 220-240 VAC. The amplifier shall operate from a normal household AC outlet, drawing less than 580 VA when driven with random program material at 1/8 rated power into four ohm loads. The amplifier shall be supplied with a single molded AC cord having an appropriate AC plug for the intended operating voltage. The amplifier shall employ forced-air cooling with a two speed fan for minimum acoustic noise. Air flow shall be from rear to front to avoid temperature rise inside the rack. Rack mounting shall be possible without clearance necessary between amplifiers for ventilation. The amplifier shall be capable of continuous operation at 1/8 power, into four-ohm loads, for ambient temperatures up to 104 F (40 C). The amplifier shall contain two independent channels, with separate AC transformer secondaries, power supplies, and protection systems. All protection systems shall be self resetting upon removal of fault, and the remaining channel shall continue to operate. Each channel shall have independent protective circuitry against open circuit, short circuit, or mismatched loads. Each channel shall monitor temperature of its heat sink and power transformer, and shall trigger fan speed boost, and if necessary, signal muting to prevent excessive temperature rise. Each channel shall have on-off muting, acting for three seconds after turn-on, and within 1/4 second after turn-off or loss of AC power. Each channel shall have DC fault protection for the load, consisting of a load-grounding relay with fault fusing to interrupt power. Fault fuses shall be adequately large to prevent nuisance blowing at any output power the amplifier is capable of delivering. Each channel shall have the following controls and displays: A rear panel Gain control and Bridge/Stereo/Parallel mode switch, front panel displays consist of a green LED power-on indicator; one yellow LED signal indicator, triggering at -30 dB; a red LED showing true amplifier clipping; and a red LED which indicates muting when illuminated. The output connectors for each channel shall be shrouded barrier strip connectors. The input connector shall be mounted on a removable panel to permit upgrades. The standard input panel shall provide detachable Euro-style header connections for each channel. Inputs shall be electronically balanced, with a minimum impedance of 10 kilohms per side, and a common mode rejection of at least 50 dB from 20 Hz to 20 kHz. The standard input panel shall contain switches for mono-bridging and parallel inputs, and solder patterns for input isolation transformers, gain reduction resistors, and firstorder high and low pass filters. The input panel shall have enough space behind it to contain a circuit board measuring up to 5.9" wide by 4.1 deep. The multi-pin connector to the amplifier circuitry shall supply positive and negative DC supply currents, and for each channel, balanced input signals, output signal, and clip/protect signal. Optional XLR and 1/4 RTS input connectors may be installed in place of a standard blank panel, mounted above the standard input panel. Internally-mounted toroidal output transformers shall provide electrically isolated output taps for 25, 70, and 100 volt distributed lines. The direct amplifier output shall also be available to drive voice coil loads. The use of voice coil and distributed line operation is independent on each channel. It is possible to use both the direct and isolated outputs simultaneously on a single channel, as long as the total power rating of the amplifier is not exceeded. A built-in 45 Hz, third-order subsonic filter shall be provided to reduce saturation of speaker transformers, due to excessive low frequency program material. The filter is non-defeatable and affects all outputs. Each channel shall be capable of meeting the following performance criteria with both channels driven: Sine-wave output power of 200 watts into eight ohms, and 300 watts into four ohms, 45 Hz to 20 kHz, with less than O.1% THD. Frequency response at 3 dB below rated power shall be 3 dB at 45 Hz and -0.2 dB at 20 kHz. The voltage gain shall be 40, equivalent to 32 dB, and the input sensitivity shall be 1.02 Vrms. The signal to noise ratio over the range of 20 Hz to 20 kHz shall exceed 100 dB. IHF damping factor shall exceed 200 for the direct outputs. Output regulation, of the isolated outputs, shall not exceed 1.0 dB at 100 volts, 1.1 dB at 70 volts and 2.0 dB at 25 volts. The amplifier chassis shall occupy three rack spaces, with provision for securing the rear corners. Depth from mounting surface to tips of rear supports shall be 17.9" (45.5 cm). 3.3 A 4.8 A 7.2 A 4.5 A 0.6 A 0.6 A 0.6 A 0.6 A Weight shall not exceed 55 Ibs. (25 kg). The amplifier shall be the QSC Audio Products Model CX6T.

SMPTE-IM, less than 0.05%, direct outputs
FREQUENCY RESPONSE Direct outputs: -3 dB @ 45 Hz*, -0.2 dB @ 20 kHz Isolated outputs: 45 Hz*-16 kHz, +0, -3 dB * Low frequency response is limited by 18 dB/octave 45-Hz high-pass filter. DAMPING FACTOR OUTPUT REGULATION NOISE VOLTAGE GAIN @ direct outputs 200 (@ direct outputs) 100V1.0 dB; 70V1.1 dB; 25V2.0 dB 100 dB below rated output (20 Hz to 20 kHz) 40x (32 dB)

FPO/BACK

INPUT SENSITIVITY, VRMS for rated power, 8 1.02 INPUT IMPEDANCE 10K unbalanced, 20K balanced
CONTROLS Front: AC Switch Rear: Parallel/Stereo/Bridge Switch, Ch.1 and Ch. 2 Attenuator Knobs (11 detents: 0, -2, -4, -6, -8, -10, -12, -14, -18, -24, off) FRONT PANEL/INDICATORS (per channel) PROTECT: Red LED CLIP: Red LED SIGNAL: Yellow LED POWER: Green LED REAR PANEL/CONNECTORS (each channel) Input: Euro-style detachable header Output: Covered barrier strips COOLING 2-speed fan, with back-to-front air flow
AMPLIFIER PROTECTION Output Averaging short circuit protection, open circuit, ultrasonic, RF, thermal muting Stable into reactive or mismatched loads LOAD PROTECTION OUTPUT CIRCUIT TYPE POWER REQUIREMENTS: Turn-on/turn-off muting, DC-fault load grounding relay with internal fault fuses Class AB complementary linear stage 100, 120, 220-240 VAC, 50/60 Hz
POWER CONSUMPTION Normal operation: 1/8 power @ 4 per channel Worst case continuous program: 1/3 power @ 2 per channel Maximum: full power @ 2 per channel Multiply current by 0.5 for 220-240 VAC operation
Channel Load AC Current, Full Power AC Current, 1/3 Power AC Current, 1/8 Power AC Current, Idle
8 + + + 2 25V, 70V, 100V DIMENSIONS Faceplate Width Chassis Depth Faceplate Height WEIGHT 7.7 A 12.5 A 18.8 A 11.2 A 4.9 A 7.4 A 11.0 A 6.7 A
Standard 19" (48.3 cm) Rack Mounting 17.9" (45.5 cm) deep (to rear support ears) 5.25" (13.3 cm) Shipping62 lb; 28 kg; Net55 lb; 25 kg

CX Series

USER MANUAL

CX4 CX4T

Rev. B *TD-000057-00*

*TD-000057-00*

Table of Contents
PART 1CX SERIES USER MANUAL
I. Warning Notices..... 2 Speaker Damage..... 3 Speaker Output Shock Hazard.... 3 Rack Mounting Precautions..... 3 II. Overall Description..... 4 III. Inputs..... 6 Input Sensitivities..... 6 IV. Outputs..... 6 V. Controls & Displays..... 8 AC Power..... 8 Operation..... 8 Troubleshooting..... 9 Open Input Architecture Level I..... 10 Parallel, Stereo, or Bridged Operation... 11 Maximum Long-Term Output Power.... 13 AC Current Consumption..... 13 Heat Emissions..... 14 Protection Circuits..... 15 VII. Specifications..... 16 VI. Operation...... 8
PART 2CX APPLICATION GUIDE....19
VIII. Distributed Lines..... 19 IX. Designing the Distributed Sound System... 20 Loudspeaker Coverage and Placement... 20 Determining Power Levels..... 22 Selecting the Amplifier.... 23 Using Components with Different Voltages.... 24 X. How Many Speakers?..... 25 Speaker Transformer Saturation.... 26 Connecting Both a Distributed Line and a Direct Loudspeaker on One Channel.. 26 Wire Loss...... 27 AC Current Consumption..... 29 Heat Emissions..... 29 XII. Address & Telephone Information.... 30 XI. Other Design Considerations.... 26
EXPLANATION OF GRAPHICAL SYMBOLS
The lightning flash with arrowhead symbol, within an equilateral triangle, is intended to alert the user to the presence of uninsulated dangerous voltage within the products enclosure that may be of sufficient magnitude to constitute a risk of electric shock to humans. The exclamation point within an equilateral triangle is intended to alert the users to the presence of important operating and maintenance (servicing) instructions in the literature accompanying the product.

CAUTION

RISK OF ELECTRIC SHOCK DO NOT OPEN
CAUTION: To reduce the risk of electric shock, do not remove the cover. No user-serviceable parts inside. Refer servicing to qualified service personnel. WARNING: To prevent fire or electric shock, do not expose this equipment to rain or moisture.
RISQUE DE CHOC LECTRIQUE NE PAS OUVRIR
EXPLICATION DES SYMBOLES GRAPHIQUES
Le symbole clair avec point de flche lintrrieur dun triangle quilatral est utilis pour alerter lutilisateur de la presence lintrieur du coffret de voltage dangereux non isol dampleur suffisante pour constituer un risque deltrocution. Le point dexclamation lintrieur dun triangle quilatral est employ pour alerter les utilisateurs de la prsence dinstructions importantes pour le fonctionnement et lentretien (service) dans le livret dinstruction accompagnant lappareil.
ATTENTION: Pour eviter les risques de choc lectrique, ne pas enlever le courvercle. Aucun entretien de pices intrieures par lusager. Confier lentretien au personnel qualifi. AVIS: Pour eviter les risques dincendie ou dlectrocution, nexposez pas cet article la pluie ou a lhumidit.

VORSICHT

GEFAHR EINES ELEKTRISCHEN SCHLAGES. NICHT FFNEN!
ERKLRUNG DER GRAPHISCHEN SYMBOLE
Der Blitz nach unten zeigendem Pfeil in einem gleichseitigen Dreieck weist den Benutzer auf das Vorhandensein einer unisolierten, gefhrlichen Spannung im Gehuse hin, die stark sein kann, einer Person einen elektrischen Schlag zu versetzen. Das Ausrufzeichen in einem gleichseitigen Dreieck weist den Benutzer auf wichtige Betriebs- und Wartungs- vorschriften in den beiliegenden Unterlagen des Gertes hin.
VORSICHT: Um das Risiko eines elektrischen Schlages zu vermindern, Abdeckung nicht entfernen! Keine Benutzer Wartungsteile im Innern. Wartung nur durch qualifiertes Wartungspersonal. WARNUNG: Zur vermeidung von Feuer oder elektrischen Schlgen, das Gert nicht mit Regen oder Feuchtigkeit in Berhrung bringen!

Lift safety shroud. Loosen screw terminals. Insert wire connectors under screws. Tighten screw terminals. Lower safety shroud.
If your application calls for connecting an 8-ohm speaker and a distributed line to the same amplifier channel, the CX4T, CX6T and CX12T can do that. However, since most of the audio power is drawn by the direct-connected speaker, you must derate the distributed line; the distributed line should have a total power load of no more than one-fourth the amplifiers normal distributed line power rating. Make sure the direct-connected speaker can handle the 8-ohm power rating of the amplifier. See Applications Notes section for more details.
Output connections for CX, bridged mono mode. Output connections for CX, parallel or stereo mode.
Output connections for CXT, bridged mono mode.
Output connections for CXT, direct low impedance
Output connections for CXT, 25 volt line.
Output connections for CXT, 70 volt line.
Output connections for CXT, 100 volt line.
Output connections for CXT, bridged mono mode, 140 volt line.
Output connections for CXT, bridged mono mode, 200 volt line.
V. Controls & Displays

CX4 AND CX4T

The channel attenuator controls, labeled in dB of attenuation , are located on the rear panel. They have 11 detents, adjustable from 0 dB (full gain) to (full attenuation). The LED displays for each channel function as shown at right.
LED Display for CX4 and CX4T:
CX6, CX6T, CX12, AND CX12T
LED Display for CX6, CX6T, CX12, and CX12T:

VI. Operation

AC POWER
The amplifier is available for 100, 120, or 220-240 VAC, 50 or 60 Hz operation. Unless it is specially ordered otherwise, each amplifier is configured for the line voltage in the market it is sold in. For example, those sold in Japan are 100 VAC; for North and Central America, 120 VAC; for Europe and most of Asia, 220-240 VAC. The power cord has a plug for connecting to a standard AC source. For 120-volt operation, the plug is a standard 15-ampere grounded NEMA fitting; it meets safety agency requirements for current consumption of less than 12 amperes during normal operation, but peak current draw under heavy usage can be higher. Models built for 220 to 240-volt use have a standard Schuko (continental Europe) connector on the power cable.

OPERATION

CX4 and CX4T
When first powering up, start with the gain controls off until proper operation is verified (upon turning on the AC switch, the POWER LED should come on, and after three seconds, the muting will stop and sound can be heard). The amp should now be working. Gain should be kept in the upper half of its range for full performance. POWER LED indicators are provided to monitor the operation of each channel. Each channel has a red CLIP indicator that will show any distortion in the amplifier. The mute circuit should cut the sound off as soon as you turn off the amp, and mute for three seconds before restoring power to the speakers. This blocks turn-on and turn-off thumps.
CX6, CX6T, CX12 and CX12T
When the amplifier is first turned on, the red PROTECT LED on each channel will light for about two or three seconds, during which the output relays will stay open to mute the speakers. After the turn-on muting interval, the PROTECT LEDs turn off, the green POWER LEDs light, and the output relays close to enable the speaker outputs. Even during the muting interval, the yellow SIGNAL and red CLIP LEDs operate normally if there is a signal present. If the CLIP LED is on while the amplifier is muted, cut the gain back immediately to avoid a full-power blast of sound when the output relays close. If a channel stays muted with PROTECT lit, or if its SIGNAL or CLIP indicators light up when the gain is turned all the way down, it may be defective; see the troubleshooting segment for more information. The SIGNAL LED indicates signal levels that are -30 dB (referenced to full rated output power) or higher. Whe the amplifier is shut off, the amplifier should mute both channels virtually instantaneously, with the PROTECT indicators lit until the power supplies are discharged.

TROUBLESHOOTING

Problem: Channel will not come out of muting
If reducing the gain control to attenuation does not release muting, the channel is defective or overheated (see Overheating, below). If reducing the gain releases the muting, raise the gain back up slowly while you watch the SIGNAL and CLIP indicators; the problem may be an abnormal signal (with excessive ultrasonic energy, for example) that could otherwise damage your speakers.
PROBLEM: No sound (CX6/CX12)
Is the channel muted? (If the PROTECT indicator is lit, the channel is muted; see below.) Is the SIGNAL LED lit or flashing? (If so, the speaker is open or blown, there is an open circuit in the speaker wiring, or there is an open circuit in the internal output wiring of the amplifier.) If the SIGNAL indicator is dark, there is probably not enough signal, or even none at all. Try turning up the rear panel attenuators or boosting the signal level at the input. If the SIGNAL indicator shows little or no activity but the CLIP LED is lit or flashing, there is probably a short circuit in the speaker wiring, especially if the PROTECT indicator starts flashing. It is also possible, but less likely, that the channels output relay is defective and will not open, thereby shortcircuiting the channel output and producing the same symptoms.

BRIDGED-MONO MODE CAUTION: ALL MODELSOutput voltages as high as 160 volts rms are available between the CX amplifiers bridged terminals (200 volts at isolated outputs). CX4T, CX6T and CX12T (140V and 200V operation)Fully insulated CLASS ONE wiring must be used to connect the amplifier to the loudspeakers
MODE BRIDG MONO: ATTENTION TOUT LES MODLES Des tensions de sorties aussi leve que 160 volts rms sont disponible aux bornes du amplificateur CX en mode bridg mono (200 volts aux sorties isols). CX4T, CX6T ET CX12T (opration 140V et 200V)On doit utiliser du cblage entirement isol de CLASSE 1 pour relier lamplificateur aux haut-parleurs.
VORSICHT BEI MONOBRCKENBETRIEB: ALLE TYPENZwischen den Ausgangsklemmen der CX-Verstrker knnen Ausgangsspannungen bis 160 Volt RMS anliegen (200 Volt bei isolierten Ausgnge). CX4T, CX6T UND CX12T (140V- u. 200VBetrieb)Der Anschlu mu vom Verstrker bis zum Lautsprecher mit vollisoliertem Kabel erfolgen.
PRECAUCIN PARA EL MODO MONO PUENTE TODO LOS MODELOS Voltajes de salida de hasta 160 VRMS existen entre los terminales de puente del amplificador CX (200 voltios a las salidas aisladas). CX4T, CX6T Y CX12T (operacin 140V y 200V)Utilice cableado de CLASE UNO totalmente aislado para conectar las altoparlantes.
Instructions for bridged operation
CX4 and CX4T 1. To engage the bridged mono mode, jumper the barrier strip inputs on the rear, in accordance with the diagram printed under the barrier strip inputs. Connect the amplifier input to channel 1 only, with the jumpers as shown to channel 2. Channel 1 and channel 2 gains must be matched. A 4, 8, or 16 ohm speaker load can be connected across the two red speaker terminals, using the red binding post of channel 1 for + or hot.
CX6, CX6T, CX12 and CX12T 1. 2. Set the switch to the Bridge position. Connect the signal to channel 1s input only. Do not connect an input signal to channel 2. However, as a convenience for routing the same signal to multiple amplifiers without using Y connectors, the mode switch connects the channel 1 and channel 2 inputs in parallel. Therefore, you can use channel 2s input terminals to pass the audio signal on to other amplifiers. 3. Use only channel 1s gain control to set the level. Both channels SIGNAL and CLIP indicators should flash identically when the amplifier is operating. 4. Connect the single speaker load across the + amplifier outputs as shown in the Outputs chapter. The positive speaker wire goes to channel 1, and the negative to channel 2.

VII. Specifications

POWER OUTPUT Direct output, watts per channel, both channels driven 8, 20 Hz20 kHz, 0.1% THD 8, 45 Hz20 kHz, 0.1% THD** 8, 1 kHz, 1% THD 4, 20 Hz20 kHz, 0.1% THD 4, 45 Hz20 kHz, 0.1% THD** 4, 1 kHz, 1% THD 2, 1 kHz, 1% THD* Isolated outputs, watts per channel, both channels driven 70V or 100V, 45 Hz16 kHz, 0.25% THD** 25V, 45 Hz16 kHz, 0.25% THD** Direct Outputs, bridged mono Hz20 kHz, 0.1% THD 8, 45 Hz20 kHz, 0.1% THD** 4, 1 kHz, 1% THD* Isolated outputs, bridged mono 50V, 45 Hz16 kHz, 0.25% THD** 140V, 45 Hz16 kHz, 0.25% THD** 200V, 45 Hz16 kHz, 0.25% THD**

*typical

270 350

350 450

700 900

175 150

250 200

500 400

450 700

600 900

1200 1800
DISTORTION SMPTE-IM, less than 0.05% FREQUENCY RESPONSE** CX4, CX6, CX12: CX4T direct outputs: CX4T isolated outputs: CX6T, CX12T direct outputs: CX6T, CX12T isolated outputs:
20 Hz20 kHz, 0.2 dB -3 dB @ 50 Hz, -0.2 dB @ 20 kHz 50 Hz16 kHz, +0, -3 dB -3 dB @ 45 Hz, -0.2 dB @ 20 kHz 45 Hz16 kHz, +0, -3 dB
**Low frequency response on T versions is limited by 18 dB/octave 45-Hz high-pass filter. Low frequency response on CX4T versions is limited by 12 dB/octave 50-Hz high-pass filter. DAMPING FACTOR 200 (@ direct outputs) OUTPUT REGULATION 100V 70V 25V NOISE 100 dB below rated output (20 Hz to 20 kHz)

1.0 dB 1.1 dB 2.0 dB

1.1 dB 1.2 dB 2.0 dB
VII. Specifications (cont.)
VOLTAGE GAIN @ direct outputs: INPUT SENSITIVITY, VRMS for rated power, 8 ohms INPUT IMPEDANCE 10K unbalanced, 20K balanced CONTROLS Front: AC Switch Rear: Parallel/Stereo/Bridge Switch (except CX4, CX4T) Ch.1 and Ch. 2 Attenuator Knobs (11 detents: 0, -2, -4, -6, -8, -10, -12, -14, -18, -24, off) FRONT PANEL/INDICATORS (per channel) PROTECT: Red LED (except CX4, CX4T) CLIP: Red LED SIGNAL: Yellow LED (except CX4, CX4T) POWER: Green LED REAR PANEL/CONNECTORS (each channel) Input: Euro-style detachable header Output: Covered barrier strips COOLING 2-speed fan, with back-to-front air flow AMPLIFIER PROTECTION Output Averaging short circuit protection, open circuit, ultrasonic, RF, thermal muting. Stable into reactive or mismatched loads. LOAD PROTECTION Turn-on/turn-off muting, DC-fault load grounding relay with internal fault fuses. OUTPUT CIRCUIT TYPE CX4, CX4T, CX6, CX6T: Class AB complementary linear stage CX12, CX12T: Class H complementary linear stage, with 2-step high-efficiency circuit POWER REQUIREMENTS: 100, 120, 220-240 VAC, 50/60 Hz

35 (31 dB) 35 (31 dB) 40 (32 dB) 40 (32 dB) 56.5 (35 dB) 56.5 (35 dB)
POWER CONSUMPTION (see chart on page 13)
Normal operation: 1/8 power @ 4 per channel Worst case continuous program: 1/3 power @ 2 per channel Maximum: full power @ 2 per channel Multiply current times 0.5 for 220-240 VAC operation
Model CX4, CX4T Channel Load 8 + + + 2 25V, 70V, 100V 8 + + + 2 25V, 70V, 100V AC Current, Full Power 5.7 A 9.2 A 13.3 A 8.7 A 7.7 A 12.5 A 18.8 A 11.2 A AC Current, 1/3 Power 3.4 A 5.2 A 7.4 A 5.0 A 4.9 A 7.4 A 11.0 A 6.7 A AC Current, 1/8 Power 2.3 A 3.5 A 4.9 A 3.3 A 3.3 A 4.8 A 7.2 A 4.5 A AC Current, Idle 0.4 A 0.4 A 0.4 A 0.4 A 0.6 A 0.6 A 0.6 A 0.6 A

8 + + + 2 25V, 70V, 100V

14.7 A 23 A 33 A 21 A
8.4 A 12.4 A 16.5 A 10.9 A

4.5 A 6.1 A 8.0 A 5.7 A

0.8 A 0.8 A 0.8 A 0.8 A
DIMENSIONS Faceplate Width Chassis Depth Faceplate Height
Standard 19" (48.3 cm) Rack Mounting 17.9" (45.5 cm) deep (to rear support ears) CX4 & CX4T: 3.5" (13.3 cm) CX6 & CX6T; CX12 & CX12T: 5.25" (13.3 cm) CX4 CX4T CXlb; 16.4 kg 42 lb; 21 kg 49 lb; 24 kg 27 lb; 13.6 kg 37 lb; 18.2 kg 42 lb; 20 kg CX6T CX12 CX12T 62 lb; 28 kg 58 lb; 26.3 kg 75 lb; 34 kg 55 lb; 25 kg 50 lb; 22.7 kg 67 lb; 30.4 kg

WEIGHT Shipping Net

Part 2CX Series Application Guide

power levels.

ith the helpful advice and input from contractors and consultants around the world, engineers at QSC designed the CX Series amplifiers to be a versatile and reliable foundation for high-quality installed sound systems.
This applications guide will help you design your sound system properly and utilize your CX amplifier(s) effectively.

VIII. Distributed lines

The best way to distribute audio power from a common amplifier among numerous relatively low-powered loudspeakers is to use a distributed line, whether all the loudspeakers are meant to receive the same or different
A distributed line is usually referred to by its maximum voltage25-, 70-, 100-, or 140-volt lines are most common. An amplifiers power rating is determined by how much current it can put out at a standard voltage level; a low-power 70-volt amp has less current capability than a high-powered 70-volt amp, even though they can both put out the same voltage. The high-powered amp can drive more speakers and at higher power levels than the lower-powered one can. This is somewhat analogous to AC electrical distribution, where you might have circuits rated for 15A, 20A, 30A, etc., at 120 or 240 VAC, and you can connect any number of appliances to them as long as you dont exceed the circuits current capacity.

1.2W 2.5W 5W 4 COM

1.2W 2.5W 5W 10W COM 4 COM
Example of a loadspeaker connected to a distributed line through a transformer
Loudspeakers on a distributed line use tapped transformers to match their power requirements to the line. A loudspeaker with a 70-volt transA

70V Amplifier 0

10W COM
former tapped at 2 watts, for example, will receive that amount of power when the amplifier puts out 70 volts on the distributed line. Trans4 COM
1.2W 2.5W 5W 10W 0.5W 1W 2W SPKR COM
former taps are usually set at 3 dB intervals, i.e.,
each successive tap is twice the power level of its predecessor. An example would be a transformer tapped at 0.5, 1, 2, and 4 watts. This allows you to select a power level that is most appropriate for the situation while still retaining the versatility of configuring other loudspeakers on the same line for different power levels.
Example of a 70 volt distributed line
IX. Designing the Distributed Sound System
There are several main steps in designing a distributed sound system: Determining loudspeaker coverage and placement Determining power levels for each loudspeaker Choosing the right amplifier
LOUDSPEAKER COVERAGE AND PLACEMENT
The goal in placing the loudspeakers in a distributed system is to acoustically cover the required area effectively but economically. An effective coverage would be one where the sound from the systems loudspeakers is not only audible, but intelligible, over all of the area. An economical coverage would be one that achieves the goal with the fewest loudspeakers necessary. A loudspeaker in a partially or fully enclosed area produces two sound fields: the direct field, which is sound coming directly line-of-sight from the loudspeaker; and the diffuse field, which is sound from the loudspeaker which has reflected off of surfaces in the area, such as floors, walls, tables, ceilings, etc. The direct sound field decreases with distance from the loudspeaker; every time you double the distance, the sound pressure level drops 6 dB. This is called the Inverse Square Law because the result of a 6 dB sound pressure level decrease is the same as 1/4 of the sound intensity (i.e., the sound power per square centimeter), which varies inversely with the square of the distance. Even though it too is subject to the Inverse Square Law, the intensity of the diffuse field is more difficult to predict, especially with multiple acoustically reflective surfaces. The problem is that moving away from one surface may also be moving closer to another. Controlling the diffuse field often involves architectural planning as well as acoustical treatment with absorptive surface materials. To maintain intelligibility, maximize the ratio of direct field to diffuse field; this generally involves placing the loudspeakers as close to the listeners

0.1 0.2 0.5 20.0 18.0 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 -10.0
Decibels referenced to 1 watt

dB(ref1watt)

Power(Watts)

Distance from speaker

Power increase in dB; referenced to loudspeaker sensitivity rating (1 watt @ 1 meter)

EXAMPLE

A loudspeaker (sensitivity: 94 dB @ 1W, 1 meter) in a busy office covers an area with an ambient noise of 72 dBA, measured at a seated persons ear position at the desks. The client wants superb intelligibility, so your goal is to provide an SPL of 97 dB (72 plus 25) to the intended listeners. The ceilingmounted speaker is about 6 feet, or 1.8 meters, above the listeners ears. The dB figure from the inverse square law conversion guide for that distance is 5.2 dB; this means that the loudspeaker would have to produce 102.2 dB (97 plus 5.2) at a distance of 1 meter to achieve 97 dB at a distance of 1.8 meters. The loudspeaker will require a power level 8.2 dB (102.2 minus 94) greater than 1 watt; this works out to 6.6 watts. The speaker transformer taps are 0.5, 1, 2, 4, and 8 watts; the closest choice would be the 8-watt tap, which turns out to be only 0.8 dB higher than the design ideal.

SELECTING THE AMPLIFIER

After youve determined the power taps for each loudspeaker transformer, add them up. The sum will be what you determine your amplifier requirements from. If you have 16 loudspeakers tapped at 2 watts, seven at 1 watt, and eight at 10 watts, the total audio power the loudspeakers want is 119 watts. Thanks to a transformer phenomenon called insertion loss, though, your amplifier needs to provide more power than the loudspeakers will draw. High-quality speaker transformers typically have an insertion loss of about 1 dB, meaning that it takes about 1.25 watt going into the transformer to put 1 watt into the loudspeaker. A lowerquality transformer may have a loss of 2 dB, which requires approximately 1.6 watts for every watt that the loudspeaker receives. Poor-quality transformers may have even higher losses, but they will probably degrade the systems audio performance severely even if there is adequate amplifier power to overcome the losses. To compensate for the insertion loss, add a corresponding percentage to the sum of the transformer power taps. For transformers with a 1 dB loss, add about 25%; in the example above, that would increase 119 watts up to 149 watts. Next, it is a good engineering practice to add another 25% to the figure. This allows a margin both for dynamic audio headroom and for some future adjustments to the systeman added speaker or two, a few transformer tap changes, etc. That would bring the total power requirement for the example system up to 186 watts. This would be the minimum power rating for the amplifier you choose.

INSTALLATION TIP: Once the sound system is installed and operational, turn the amplifier off and take an impedance measurement across the distributed line at the amplifier output, using an audio impedance meter (not an ohmmeter). Record the measurement for later use. If you ever have to make a service call on the system, measure the impedance again and see how it compares to the recorded figure; its a quick and easy way to see if anything in the distributed line system has been changed. Likewise, measure the impedance anytime youve changed a transformer tap, added or removed a loudspeaker, or made any other adjustment to anything on the distributed line.
USING COMPONENTS WITH DIFFERENT VOLTAGES
Sometimes it may be practical to use a transformer or loudspeaker/transformer combination with a different voltage system from what it was originally intended. For example, a 70-volt transformer could be used in a 25volt system, although you would have to derate the power taps similarly. Never use a transformer with a higher voltage than what it is designed for, though; i.e., you couldnt use that same transformer on a 100- or 140-volt line. To properly derate the transformer tap power levels, locate the column with the voltage the transformer is rated for in the table below, then locate the row with the system voltage you want to use it in. The table will indicate the dB reduction to use with the derating chart below it.
You have a 70-volt transformer with taps labeled 0.6, 1.2, 2.5, and 5 watts. What power points will those taps provide on a 50-volt line? The table shows that 50 volts is 3 dB less than 70 volts. The chart confirms that the taps will provide 0.3, 0.6, 1.25, and 2.5 watts, respectively.

X. How Many Speakers?

How many loudspeakers can you connect to the distributed line? The amplifier itself determines the amount of audio power available to the line, and from that figure you must compensate for insertion loss in the speaker transformers and for headroom when you determine how much power is available

1.56 watts

+25% for headroom. approx. 1/4 watt more to compensate for transformer insertion loss*
for the speakers. For example, lets suppose you have an amplifier rated at 500 watts into a 70-volt line, and your speaker transformers each have an insertion loss of 1 dB, which is

1.25 watts

typical. The losses in the transformers mean that they will draw 25% more audio power than they deliver to the speakers. For headroom, as mentioned before, you add at least another 25% to the total amount of power drawn from the amplifier. The additional 25% headroom is optional but highly recommended. It will allow for future additions to the system and reduce the stress on the power amplifier. 1.25 x 1.25 = 1.5625

CONNECTING BOTH A DISTRIBUTED LINE AND A DIRECT LOUDSPEAKER ON ONE CHANNEL
The T versions of the CX amplifiers have simultaneous direct outputs (for loudspeakers) and 25-, 70-, and 100-volt isolated outputs (for distributed lines). This adds a measure of versatility that few other amplifiers can match: being able to drive both a loudspeaker and a distributed line on a single channel at the same time. Setting up such an arrangement is simple, but it requires some precautions: Use an 8-ohm speaker for the direct connection. Make sure it has an adequate power rating (150 watts for use with the CX4T, 200 watts for use with the CX6T; 400 watts for the CX12T). Connect it across the low impedance outputs. The distributed line must not be loaded any higher (sum of transformer taps plus allowance for insertion loss plus allowance for headroom) than 40 watts for the CX4T, 60 watts for the CX6T, or 125 watts for the CX12T. Connect it across the appropriate transformer terminals. The directly connected speaker will constitute most of the load on the amplifier channel, so it will receive considerably more power than the distributed line. If you adjust the amplifier gain controls to vary the sound level from the directly connected
speaker, it will affect the sound level from the distributed lines speakers also, possibly altering them from your intended levels. An alternate method is to attach an 8-ohm speaker across the 25-volt outputs. This provides up to approximately 80 watts to the speaker and makes more power available to the 70V or 100V connections: up to 75 watts for the CX4T, up to 150 watts for the CX6T; up to 400 watts for the CX12T.

WIRE LOSS

Even the highest-quality copper wire has a small amount of resistance to electrical current flow, and the wires resistance is inversely proportional to the cross-sectional area of its conductor. Therefore, to minimize the power lost to speaker cable resistance, you should use the largest stranded (always stranded) copper wire that is practical for the job. This is especially important with direct low-impedance speaker connections; e.g., a halfohm wire resistance would not affect a lightly-loaded 100-volt line noticeably, but it would reduce the amount of power going to a 2-ohm load by 36%, a 1.9 dB drop. It would also reduce the damping factor to no better than 4. If an amplifier could drive a speaker load through theoretical zero-resistance wire, no power would be lost in the speaker cables. In the charts below well compare the power delivered through real-world speaker cables with the theoretical zero-resistance ideal and express it as a ratio called the power transfer coefficient. It is determined by the formula POWER TRANSFER COEFFICIENT = [RLOAD/(RWIRE + RLOAD)]2 Lets say you have an 8-ohm speaker load. With that imaginary zero-resistance wire, all the power would be delivered to the load, so the power transfer coefficient would be 1. If you then substituted wire with 0.2 ohm of resistance, the load would only get 95.2% of the power it got with the zero-ohm wire, so the power transfer coefficient would be 0.952 (a loss of 0.2 dB, by the way).

A major objective in the design of the CX Series amplifierseven the higher-powered modelsis to permit their operation from readily available, standard AC power sources. Normal conditions in power amplifier rating means operating with a random program source (pink noise), using pink noise as a source, at an average power level equal to one-eighth of maximum power. This is recognized by most of the worlds safety agencies as the loudest you can play music through an amplifier and still keep the incidence of clipping to a reasonable minimum. An amplifiers peak current draw at full output power into 2 ohms is several times what the normal draw is, but its various protection circuits will prevent this condition from lasting more than a minute or two. When you plan the AC power hookups for your amplifiers, use the following table to predict the current requirements per ampli-

AC Current Consumption

fier. You can use the one2
FULL 1/3 POWER POWER 1/8 POWER

FULL 1/3 POWER POWER

1/8 POWER
4 or Distributed Line FULL 1/3 1/8 POWER POWER POWER 10A 13A 24A 4.5A 7.5A 12A 3.8A 5.0A 6.5A
eighth power figures to predict the normal continuous current draw, then add a safety margin to allow for occasional crescendos.
CX4, CX4T 0.4A CX6, CX6T 0.9A CX12, CX12T 1.0A

6.0A 7.9A 15A

2.8A 4.3A 8.6A

2.5A 3.2A 5.1A

15A 19A 33A

6.8A 10A 17A

5.6A 7.0A 8.5A
Essentially, a power amplifier draws electrical energy from the AC mains, converts it to DC, and then converts it again into an analog of the input signal to send out to the loudspeakers. Any AC power that enters the amplifier through the power cord and does not exit through the speaker outputs turns into heat, which the amplifier must rid itself of by exhausting it to the outside. In indoor use, multiple amplifiers may present a sizeable challenge to a buildings air conditioning system. Use the table below to predict the heat that will be emitted by your amplifier. Use one-eighth power for normal, continuous usage.

Heat Emissions

Btu/hr
4 or Distributed Line FULL 1/3 1/8 POWER POWER POWER 1360 343

1530 386

945 238

2230 562

CX4, CX4T

(preliminary)

kcal/hr Btu/hr

kcal/hr Btu/hr kcal/hr

XII. Address & Telephone Information

Address: QSC Audio Products, Inc. 1675 MacArthur Boulevard Costa Mesa, CA 92626-1468 USA
Telephone Numbers: Main Number (714) 754-6175 Sales Direct Line (714) 957-7100
Sales & Marketing (800) 854-4079
(toll-free in U.S.A. only)
Technical Services (714) 957-7150 (800) 772-2834
Facsimile Numbers: Sales & Marketing FAX (714) 754-6174 Technical Services FAX (714) 754-6173
World Wide Web: http://www.qscaudio.com BBS/World Group: QSC OnLine Technical Support 1200-14400 bps; 8N1 (714) 668-7567 (800) 856-6003 CompuServe: GO QSCAUDIO ID: 76702,2635
1675 MacArthur Boulevard Costa Mesa, California 92626 USA PH: (714) 754-6175 FAX: (714) 754-6174
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