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

1

© Copyright 1998 QSC Audio Products, Inc. All rights reserved.
“QSC” and the QSC logo are registered trademarks, and “DCA” and “DataPort” are trademarks, of QSC Audio

Products, Inc.

2

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

LF

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

HF

MF

HF

DCA amplifier

Ch. 2

Ch. 1

DCA amplifier

Ch. 2

L

Ch. 1

LF

LF-3

low-frequency filter

LF

DCA amplifier

Ch. 2

R

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

MF

HF

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.

3

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

3

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

f

HP

f

XO

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

f

XO

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

f

f

HP

LP

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

4

Use only these three digits to

determine resistance code.

Disregard the other

numerals and letters.

RESISTANCE

2.7K

3.9K

4.7K

5.6K

6.8K

8.2K
10K
12K
15K
18K
20K
22K
27K
33K
39K
47K
56K
68K

CODE

272
392
472
562
682
822
103
123
153
183
203
223
273
333
393
473
563
683

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4.0K6.5

3.0K7.4

Use these tables with the XC-3 and LF­3 to determine the correct resistor
values for the crossover frequencies
and delays you need. The shaded
values are for the LF-3 and the high­pass frequency (fHP) of the XC-3).

Identifying SIP resistor networks

Setting up the XC-3

This procedure involves setting the DIP switches, as well as selecting
and inserting SIP resistors into the appropriate sockets. Set switches
2, 9, and 10 to ON. The flowchart on the next page takes you through
all the steps necessary before mounting the accessory to the amp.

The illustration on the next page shows the locations of the sockets for
the SIP resistor networks. The resistor networks have no polarity or
directionality and therefore do not need to be inserted in any particular
way, as long as each network pin goes into its own hole in the socket.

Use the tables at the top of this
page to select the correct resistor
networks for the settings you need.
The SIPs supplied with the XC-3
provide a selectable frequency
range for fXO of 80 Hz to 1.5 kHz, and
delay settings from 0.3 to 1.8 mil­liseconds, plus
contact QSC’s Technical Services
department if your application re­quires different settings.

bypass

(no delay);

10

9
8
7
6
5
4
3
2
1
0

-1

-2

-3

-4

-5

-6

500

1k

2k 4k

Effects of high frequency boost on frequency response (crossover frequency

= 500 Hz). A boost of +10 dB is most common for compensating for screen loss

(attenuation of high frequencies as sound passes through screen perforations)

XC-3 controls and switches

3k 30k6k 9k10k5k 50k20k15k

7k700

and for constant-directivity horns.

HF boost = 10 dB

HF boost = 7.5 dB

HF boost = 5 dB

HF boost = 2.5 dB

HF boost = OFF

40k8k

5

J1

2- or 3-way?

Switches 7 & 8 =

ON

Switches 7 & 8 =

OFF

Select fXOand fHP;

install appropriate

SIPs in J1 (f

XO

) and

J7 (f

HP

)

Select fXO; install

appropriate SIP in J1

2-way3-way

Need LF

delay?

YesNo

Select delay; install

appropriate SIP in J2

Switch 1 = OFF

Switch 1 = ON

Need HF

boost?

10 dB (CD horn)

No

Switches 3–6 =

OFF

Switch 3 = ON;
Switches 4–6 =

OFF

Switch 4 = ON;
Switches 3,5, 6

= OFF

Switch 5 = ON;

Switches 3,4, 6

= OFF

Switch 6 = ON;
Switches 3–5 =

OFF

7.5 dB

5 dB

2.5 dB

Yes

Install SIP (any

value) in J7*

Install SIP (any

value) in J2*

*To ensure circuit stability

Attach to amplifier

(f )

XO

J2

(LF delay)

J7

(f )

HP

Locations of SIP sockets on the XC-3

When using the XC-3 in a three-way system in conjunction with the LF-3,
the lower frequency (fHP) should match the crossover frequency of the
LF-3 (fXO). The SIPs supplied with the XC-3 allow a selectable frequency
range for fHP of 80 to 500 Hz.

FACTORY SIP SETTINGS

f

XO

LF delay 1.8 ms (27K SIP resistor in J2)
f

HP

FACTORY SWITCH SETTINGS

Bi-amp mode (switches 7 & 8 = ON)
LF delay active (switch 1 = ON)
HF boost defeated (switches 3 through 6 = OFF)
Switches 2, 9, & 10 = ON

500 Hz (12K SIP resistor in J1)

80 Hz (68K SIP resistor in J7)

RECOMMENDED AMPLIFIER SETTINGS WITH THE XC-3

Clip limiters ON, both channels
Stereo mode
High-pass filter ON, both channels
High-pass frequency 30 or 50 Hz, both channels

Setup flowchart for the XC-3

6

Setting up the LF-3

)

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J8

(Ch. 1 f )

J6

(Ch. 2 f )

J2

(Ch. 2 delay)

Locations of SIP sockets on the LF-3

Switches 1 & 10 = OFF

Install SIPs (any

value) in J1 and J2*

J1

XO

(Ch. 1 delay

XO

Select f for Ch.1 and Ch. 2;

XO

install appropriate SIPs

in J8 (Ch. 1) and J6 (Ch. 2)

Need LF

delay?

This procedure involves setting the DIP switches, as well as selecting and inserting SIP resistors into
the appropriate sockets. Set switches 2 and 4 through 9 to OFF, and switch 3 to ON. The flowchart
below takes you through all the steps necessary before mounting the accessory to the amp.

The LF-3 is typically used in a system in conjunction with
the XC-3 crossover. For example, a stereo three-way
system will require three DCA amplifiers, two XC-3
cinema crossover accessories, and one LF-3 low­frequency cinema accessory, as shown on page 2. The
typical input signal is full-range audio taken from the male
XLR connector labeled “OUTPUT (TO LF-3)” on the XC-3.

The illustration to the left shows the locations of the
sockets for the SIP resistor networks. The resistor net­works have no polarity or directionality and therefore do
not need to be inserted in any particular way, as long as
each network pin goes into its own hole in the socket.

Use the tables at the top of page 5 to select the correct resistor networks for the crossover

frequency (fXO) and delay settings you need. The SIPs supplied with the LF-3 provide a range

of frequency selections from 80 Hz to 500 Hz, and delay settings from 0.3 to 1.8

YesNo

Channel 1: Switch 10 = ON

Channel 2: Switch 1 = ON

Select delay ;

for Ch.1 and Ch. 2

install appropriate SIPs

in J1 (Ch. 1) and J2 (Ch. 2)

LF-3 controls and switches

milliseconds plus bypass (no delay); contact QSC’s Technical Services department if

your application requires different settings.
When using the LF-3 in a three-way system in conjunction with the XC-3, the crossover

frequency of the LF-3 (fXO) should match the lower high-pass frequency (fHP) of the XC-3.

*To ensure circuit stability

Setup flowchart for the LF-3

Attach to amplifier

In most circumstances, the LF-3 would be used with an amplifier in stereo mode. But

if two amp channels are needed for one low frequency signal, you can use the Channel 1 input

of the LF-3 and parallel the inputs of the amplifier (using the amp’s DIP switches).

FACTORY SIP SETTINGS

f

XO

Delay 1.4 ms, both channels (22K SIP resistor in J1 & J2)

FACTORY SWITCH SETTINGS

Delay active, both channels (switches 1 & 10 = ON)
Switches 2 and 4 through 9 = OFF; switch 3 = ON

350 Hz, both channels (18K SIP resistor in J6 & J8)

RECOMMENDED AMPLIFIER SETTINGS WITH THE LF-3

Clip limiters ON (both channels)
Stereo mode; parallel mode in applications requiring dual LF amp channels with one source
High-pass filter ON (both channels)
High-pass frequency 30 or 50 Hz, depending on speaker (both channels)

7

Setting up the SF-3

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This procedure involves setting the DIP switches, as well as selecting and inserting SIP resistors into
the appropriate sockets. First, set switches 1 through 6 and 10 to OFF. The flowchart on the opposite
page takes you through all the steps necessary before mounting the accessory to the amp.

The bottom right illustration details the locations of the two SIP sockets used on the SF-3. The resistor
networks have no polarity and therefore do not need to be inserted in any particular way, as long as
each pin goes into its own hole in the socket.

The mono subwoofer program can be derived from summing and filtering stereo or mono full-range
audio, or it can come from a discrete mono subwoofer channel, such as in a 5.1, 6.1, or 7.1 cinema
surround system. If the subwoofer program is to be derived, use the SF-3’s low-pass filter to set the
high end of the subwoofer passband. If the subwoofer program source is a discrete channel, as in most cinema
systems, we recommend that you bypass the low-pass filter.

The SF-3’s two inputs are summed together, so you can use one or both, depending on your system
needs. The outputs to the two amplifier channels are monaural and in parallel, unlike the XC-3 and
LF-3. Thus, SF-3 is the only DCA accessory that can be used with the amplifier in bridged mono mode,
when necessary.

Use the table at right to select the correct resistor networks for the SF-3’s filter frequency settings.
An identification chart for SIP resistor networks is on page 5. The SIPs supplied with the LF-3 provide
a selection of three low-pass frequencies: 80, 150, and 250 Hz; and six high-pass frequencies from
20 to 50 Hz. Use the speaker manufacturer’s recommended filter settings.

SF-3 controls and switches

The low-frequency boost switch selects the Q of the high-pass filter: 0.707 for flat (Butterworth),
or 2 for “boost,” which adds a 6 dB peak at the filter’s selected frequency. Some speakers require
this boost to extend the low-frequency response.

FACTORY SIP SETTINGS

f

HP

f

LP

30 Hz (27K SIP resistor in J2)
250 Hz (22K SIP resistor in J1 & J2)

FACTORY SWITCH SETTINGS

Low-pass filter OFF—”cinema” setting (switches 7 & 8 = ON)
LF flat (switch 9 = OFF)
Switches 1 through 6 and 10 = OFF

RECOMMENDED AMPLIFIER SETTINGS WITH THE SF-3

Clip limiters ON (both channels)
Stereo or bridged mono mode, as the application dictates
High-pass filter OFF (both channels)

8

Use this table to determine the correct

resistor values for the SF-1 filter frequencies.

J6

(f )

LP

J2

(f )

HP

Locations of SIP sockets on the SF-3

high-

low-

pass

pass

Derived
by filter

Turn low-pass filter on

Switches 7 & 8 = OFF

Select low-pass freq. (f );

install appropriate SIP in J6.

Select high-pass freq. (f );

install appropriate SIP in J2.

L P

HP

Is subwoofer

Is subwoofer

program derived or

program derived or

discrete?

discrete?

high­pass

From discrete

subwoofer

channel

Turn low-pass filter off

Switches 7 & 8 = ON

Select high-pass freq. (f );

install appropriate SIP in J2.

Install SIP (any

value) in J6*

HP

Need LF

boost?

Switch 9 = OFF Switch 9 = ON

*To ensure circuit stability

Attach to amplifier

Setup flowchart for the SF-3

IV. Mounting the accessories

An accessory may be mounted with the amplifier either in or out of the rack, even if the
amp is installed with rear rack ears.

1. Turn off the amplifier before installing the accessory.

2. Make sure the SIP resistor networks are installed properly and no SIP sockets are empty.

3. Line up the HD-15 connector on the accessory with the amplifier’s DataPort, then press the
accessory onto the back of the amplifier so that the HD-15 connector inserts into the DataPort.

YesNo

4. Use the three screws supplied to secure the accessory to the amplifier chassis, as shown
at left. Two long screws go into the holes near the DataPort, while the short screw goes
through the hole in the tab on the right edge of the accessory. Do not overtighten the
screws.

5. Attach the input and output cables to the appropriate connectors on the accessory. Use
the amplifier’s normal output connectors for attaching speaker and monitor cabling.

9

V. Setting up the DCA accessories in the cinema sound system

Setting up the DCA accessories in the B chain of the cinema sound system primarily involves setting the trim
levels on the XC-3, LF-3, and SF-3. This requires the pink noise source in the cinema processor and a real-time
acoustical spectrum analyzer.

1. Set up the analyzer microphone in the center of the cinema audience seating area or in another recommended location.

2. Set the gain controls wide open for all the DCA amplifiers, and check the HF boost settings on the XC-3 accessories.

3. Apply a pink noise test signal from the cinema processor to the left channel XC-3 input. Watch the frequency
response on the analyzer and use the HF trim control on the XC-3 and the LF trim on the LF-3 to balance the
levels of their frequency bands to that of the the mid-frequency band, within specifications. If the shape of
the HF response is not correct, use a boost setting that better corrects the deficiency; turn the amplifiers
off before changing the switch settings.

4. Repeat this process for the center and right screen channels and any surround channels that are bi- or tri-amped.

5. Follow the processor instructions for setting sound pressure level outputs of all the channels, including the
subwoofer.

If you are unable to obtain a satisfactory frequency response or SPL on a channel, carefully check the wiring and
connections. Some likely causes are reversed speaker polarity on one or more drivers; loose or broken wiring or

connections; or blown or damaged speaker drivers.

DCA

5.1

Cinema

Processor

L
C
R
LS
RS
Sub

XC-3

XC-3

XC-3

1

2

1

2

1

2

1

2

DCA

DCA

DCA

Left
MF

Left
HF

LF-3

Center
MF

Center
HF

LF-3

Right
MF

Right
HF

SF-3

Left
Surround

Right
Surround

DCA

1

2

DCA

1

2

DCA

1

2

Left
LF

Center
LF

Right
LF

Spare

Sub

Sub

A typical 5.1 surround system with DCA amplifiers and accessories

10

APPENDIX

Crossover and delay settings for popular cinema loudspeaker systems

Consult your speaker documentation. Some data has not yet been determined. Also, the high-frequency horn
of some of the systems listed have multiple mounting positions, so the desired delay settings will depend on
the positioning chosen. Check the QSC website (http://www.qscaudio.com) for information updates.

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12

© Copyright 1998 QSC Audio Products, Inc. All rights reserved.

“QSC” and the QSC logo are registered with the U.S. Patent and Trademark Office.

QSC Audio Products, Inc., 1675 MacArthur Boulevard Costa Mesa, California 92626 USA

PH: [phone] FAX: [phone]