Qsc audio DCA ACCESORIES User Manual

Cinema Accessories

for DCA Series amplifiers

USER MANUAL

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XC-3 LF-3 SF-3

Two-way crossover with delay

Low-frequency filter with delay

Subwoofer filter

*TD-000079-00*

TD-000079-00

Rev. A

Products, Inc.

CINEMA ACCESSORIES FOR DCA AMPLIFIERS

I. Introduction

This manual covers setup and operation of cinema crossover accessories for QSC DCA Digital Cinema Amplifiers. These accessories comprise three models: the XC-3 crossover, the LF-3 low frequency filter, and the SF-3 subwoofer filter. Together with DCA amplifiers, they allow you to assemble any type of cinema sound system, mono or multi-channel.

Ch. 1

full-range audio

audio plein registre

Vollbereichaudio

audio de gama llena

Using the XC-3 in a simple two-way system. In many speaker systems, a passive mid/high combination will handle the higher frequencies, creating essentially a three-way system.

full-range audio

audio plein registre

Vollbereichaudio

audio de gama llena

XC-3

2-way crossover

XC-3

2-way crossover

DCA amplifier

Ch. 2

Ch. 1

DCA amplifier

Ch. 2

Ch. 1

LF-3

low-frequency filter

DCA amplifier

Ch. 2

full-range audio

audio plein registre

Vollbereichaudio

audio de gama llena

Using the XC-3 and LF-3 in a stereo three-way system

Using the SF-3 with a discrete subwoofer channel

XC-3

2-way crossover

SF-3

subwoofer filter

Ch. 1

DCA amplifier

Ch. 2

Ch. 1

DCA amplifier

Ch. 2

Each accessory mounts directly to the back of the amplifier, from which it also draws its power. It has its own input and, if necessary, output connectors. A male HD-15 connector conveys the audio signals into the amp through its DataPort.

Frequency and delay parameters are user adjustable by inserting selected 8-pin SIP resistor networks (included with each unit) into sockets on the underside of the accessory. A DIP switch permits selection of functions such as delay and high-frequency boost.

II. Description of Functions

XC-3 This accessory is a two-way crossover, with the low frequency

band fed to channel 1 of the amplifier and the high frequencies to channel 2. An all-pass filter on the low frequency band delays the audio signal, permitting time alignment of a cone driver with a high-frequency horn. A selectable high-frequency boost circuit provides several increments of compensation for screen loss or constant-directivity horn equalization. A HF trim control provides 0 to 20 dB of attenuation for matching levels between frequency bands.

The XC-3 can be used by itself with one amplifier for a 2-way system (shown top left), or with the LF-3 and an additional amplifier for 3-way systems, as shown at left. The XC-3 has a pass-through output in parallel with the input for distributing the audio signal to the LF-3. The filter circuitry uses a 4thorder Linkwitz-Riley alignment with 24 dB/octave slopes.

LF-3 Used in a system with the XC-3, the LF-3 performs the low-

frequency crossover functions in a 3-way system as shown at left. Unlike the XC-3, though, it is a device with two discrete channels; one LF-3 with an amplifier will support two other amplifiers with two XC-3 accessories, as shown. The 4th-order Linkwitz-Riley low-pass filters have 24 dB/octave slopes.

Each channel also has an all-pass filter providing delay for time alignment. Frequency and delay parameters

for both channels are set individually, although in all but a few applications they would be set the same. Each channel also has a trim control providing 0 to 20 dB of attenuation to facilitate matching levels

among the various frequency bands.

SF-3 This subwoofer filter accessory has two summed inputs and a bandpass filter that defines the frequency

range of the subwoofer program. The frequencies of the 2nd-order high-pass and 4th-order Linkwitz-Riley low-pass filters are both user-defined. The high-pass filter also has a switchable low-frequency boost feature: switched on, it provides a 6 dB bump at the selected high-pass frequency, useful for extending the low-end response of some speaker systems; off, the response is a flat Butterworth curve that is 3 dB down at the selected frequency. The output is parallel, feeding the same signal into both channels of the amplifier. The SF-3 has no delay function. A level trim control provides 0 to 20 dB of attenuation.

The SF-3 can be used to derive subwoofer-range program from full-range audio, or it can be used with a discrete subwoofer channel in cinema sound systems.

III. Configuring the accessories

Configure each accessory before you mount it to the amplifier. If an accessory is already mounted to an amplifier, always turn the amp off before changing switch settings or input or output connections, or detaching the accessory.

Use the tables on the following pages to determine the correct resistance for the desired frequency and delay settings. Use the diagram at the top of the opposite page to identify the values of the resistor networks. A flowchart for each model will assist you in setting the various parameters, and the chassis label on each accessory also details the correct DIP switch

2-way

settings. An appendix in the back of this manual lists manufacturerrecommended crossover frequency and delay settings for various popular

3-way

cinema speaker systems. The purpose of the delay functions in the XC-3 and LF-3 is to correct for time

misalignments between different types of speaker driver in the overlap region between adjacent frequency bands. These time misalignments occur when

the acoustical source points of the drivers for the adjacent frequency bands are physically at different distances from the listener(s). A delay compensation of 1 millisecond represents approximately 1.13 ft (13.5 in), or 34.4 cm.

NOTE: Even if you don’t use a particular filter or delay feature on an accessory, put an unused SIP resistor network of any value into its socket to ensure circuit stability when it is powered up.

The SIP resistor networks have no polarity and therefore do not need to be

LF boost

inserted in a certain direction. Make sure all eight pins are inserted properly into the sockets holes, and then gently but firmly press the network into the socket until it is fully seated. If a SIP resistor network is difficult to remove

LF flat

Low pass filter off

Low pass filter on

with your fingers, use a small screwdriver, prying gently first at one end of the SIP and then the other, until it is loose.

Configurable functions of the three accessory models

+10 dB +7.5 dB +5 dB +2.5 dB

XC-

LF delay

LF-3

Delay

SF-3

+ 8 hidden pages