QSC Audio Speaker SF 1 User Guide

SF-1  
Subwoofer  
Filter  
FPO  
Rev. A  
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SF-1 SUBWOOFER FILTER  
INTRODUCTION  
The SF-1 Subwoofer Filter is an upper slot accessory for QSC MXa Series amplifiers, which feature Level  
One Open Input Architecture. The accessory mounts in the back of the amplifier above the standard input  
panel.  
Ideal for adding subwoofer amplification to an existing full-range system, the SF-1 offers adjustable and  
selectable low-pass filtering for both channels of the amplifier, in addition to adjustable high-pass subsonic  
filtering. The filter slopes are 12 dB per octave, and the filter frequencies are programmable via provided  
SIP resistor networks.  
A slide switch, SW1, allows you to configure the SF-1 with a low-end “boost” which provides a suitable  
equalization for use with B6 speaker enclosures. A 10-position DIP switch, SW2, affords you the versatility  
of setting the accessory in many different configurations, such as mono summing and single channel  
bypass. The configuration process is detailed below.  
The use of the SF-1 for cinema subwoofer installations can reduce the chance of speaker damage by digital  
soundtracks. Low frequency information, below the box tuning frequency, can destroy speakers at power  
levels far below their rated capacity. The SF-1 can remove these damaging frequencies and also provide  
the needed equalization to flatten and extend the response of popular cinema subwoofers. These include:  
Electro-Voice models TL880D, TL550D, TL3512, TL440 and JBL 4645 and 4645B.  
Existing cinema surround systems typically have limited low frequency response. New digital surround  
formats now have full-range surround channels that extend frequency response much lower than previous  
optical surround formats. The SF-1 may be used to protect surround speakers from damage, due to  
excessive low frequency operation. It is desirable, however, to eventually upgrade the capability of the  
surround systems to handle the increased power and low frequency response requirements of digital  
soundtracks.  
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Figure 1  
Figure 1 shows where the pertinent switches, resistor networks, and connectors are located on the SF-1  
board.  
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CONFIGURATION  
SETTING THE SUBSONIC FILTER FREQUENCY  
The subsonic (highpass) filter on Channel 1 cannot be bypassed, and Channel 2 should only be bypassed  
inthebridgedmonomode. Plug-inSIPresistornetworkRN3setsthehigh-passfrequencyforbothchannels  
1 and 2. Table 2 shows the resistor value to be used for the frequency you desire. Typical subsonic  
frequencies available with the provided SIP resistor networks are 20, 25, 32, 35, 40, 50, 63, and 80 Hz.  
Consult your subwoofer manufacturer if you are unsure of what frequency to use.  
Ifyoudesirea6-dBboostatthelowendofthesubwooferfrequencyrange, settheslideswitchSW1toON”;  
otherwise set it to “OFF.” Such a boost is popular with users of Electro-Voice B6 subwoofer enclosures.  
TABLE 2  
Frequency  
Resistor Network Value (RN3 or RN4)  
20  
25  
32  
35  
40  
50  
63  
80  
100  
135  
160  
200  
250  
82K  
68K  
56K  
47K  
39K  
33K  
27K  
20K  
18K  
12K  
10K  
8.2K  
6.8K  
Factory set for RN3  
Factory set for RN4  
SETTING THE SUBWOOFER UPPER FREQUENCY LIMIT  
The low-pass filter sets the upper limit of the subwoofer frequency range. Plug-in SIP resistor network RN4  
sets the low-pass frequency for both channels 1 and 2. Table 2 shows the resistor value to be used for the  
frequency you desire. Typical frequencies available with the provided SIP resistor networks are 100, 135,  
160, 200, and 250 Hz. Consult your subwoofer manufacturer if you are unsure of what frequency to use.  
Whatever frequency you choose should be higher than that of the subsonic filter.  
SETTING DIP SWITCH SW2  
Determine the configuration you desire and set the DIP switches as described below.  
Positions 1 through 4 and 9 and 10  
First, decide whether you need “Mono Sum” or “Stereo” operation. This will determine the settings of  
positions 1 through 4 and 9 and 10 of DIP switch SW2.  
Mono Sum  
Because it is difficult for listeners to sense directionality of low audio frequencies, many subwoofer  
systems are set up for monaural operation, with both channels summed together. For mono  
summed operation, set the amplifier mode switch to “STEREO” and SW2 as follows:  
Position 1  
Position 2  
Position 3  
Position 4  
Position 9  
Position 10  
OFF  
ON  
ON  
OFF  
OFF  
ON  
Continue to “Positions 5 through 8” and set those switches to engage both channels’ low-pass  
filtering.  
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Stereo, Bridged Mono, and Parallel Mono  
If the two subwoofer channels are to carry different or independent program material, as in stereo  
or bridged mono, set the SF-1 for “Stereo” operation. Use this also for parallel mono operation from  
a single program signal source. For stereo, bridged mono, or parallel mono operation, set the  
amplifier mode switch to “STEREO,” “BRIDGED,” or “PARALLEL,” respectively, and SW2 as  
follows:  
Position 1  
Position 2  
Position 3  
Position 4  
Position 9  
Position 10  
ON  
OFF  
OFF  
ON  
ON if bridged mono, OFF otherwise  
OFF if bridged mono, ON otherwise  
Positions 5 through 8  
Next determine whether you wish to bypass the low-pass filtering on either channel for use with a full-range  
speaker system. This will determine the settings of positions 5 through 8 of DIP switch SW2.  
Channel 1: bypass or engage low-pass?  
If you’re connecting a full-range speaker to Channel 1, bypass its low-pass filtering. If you’re  
connecting it to a subwoofer, engage the filtering. Typical cinema subwoofers are an exception, the  
low pass filter should be bypassed in this application, as cinema processors typically perform this  
function.  
Position 5  
Position 6  
ON if bypassed, OFF if engaged  
OFF if bypassed, ON if engaged  
Channel 2: bypass or engage low-pass?  
Likewise, if you’re connecting a full-range speaker to Channel 2, bypass its low-pass filtering, and  
if you’re connecting it to a subwoofer, engage the filtering. Typical cinema subwoofers are an  
exception, the low pass filter should be bypassed in this application, as cinema processors typically  
perform this function.  
Position 7  
Position 8  
ON if bypassed, OFF if engaged  
OFF if bypassed, ON if engaged  
CAUTION: On DIP switch SW2, the switch pairs, i.e., positions 1 and 2, 3 and 4, 5 and 6, 7 and 8, and  
9 and 10, are complementary. That is, if position 1 is ON,2 must be OFFand vice versa; if 3 is  
ON,4 must be off, and so on. To prevent improper operation of the SF-1 and the amplifier, and  
possible damage that may result to the accessory, amplifier, or loudspeaker, check your switch  
settings carefully before you install the SF-1 in your amplifier.  
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INSTALLATION  
Before installing the SF-1, disconnect the amplifier’s power cable from the AC mains.  
1. Position the amplifier so that the rear panel is facing you. Locate the input panel and the blank  
accessory panel above it.  
2. Remove the four mounting screws—the two holding the blank panel and the two holding the  
standard input panel. Remove the blank panel (which the SF-1 will replace) and carefully pull the  
input panel out from the amplifier chassis (figure 2a).  
3. Disconnect the ribbon cable from the circuit board of the input panel.  
4. Position the SF-1 so that its component side faces the ribbon connector of the input panel card.  
5. Connect the included short ribbon interface cable from the SF-1 to the ribbon connector on the input  
panel card. The ribbon cable attaches to J4 on the SF-1 (figure 2b).  
Theconnectorsarekeyed;makesuretheylineupproperlyandtheribboncableisnottwistedbefore  
you carefully press them together. Be sure to press the connectors together firmly.  
6. Connect the ribbon cable from the amplifier (the cable you disconnected from the input panel card)  
to the SF-1 circuit board, using J3 (figure 2c). Make sure the cable is not twisted; the red stripe on  
the cable should be toward the right, from your point of view. Newer amplifiers have a keyed  
connector on the ribbon cable. Press the connectors together firmly.  
7. Tuck the interface ribbon cable neatly between the SF-1 and the input panel card. Insert the two  
cards carefully into the amplifier chassis and secure them with the four screws you removed in step  
2. Dont over-torque the screws (figure 2d).  
a
b
c
d
Figure 2  
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SPECIFICATIONS  
SIGNAL TO NOISE RATIO (22 Hz to 22 kHz):  
103 dB  
TOTAL HARMONIC DISTORTION  
CROSSTALK  
<0.1 %  
70 dB below rated power within passband  
better than 50 dB  
CMRR:  
FILTER TYPE  
second-order butterworth, Q=0.707  
(LPF and unboosted subsonic filter)  
second-order, +6 dB boost, Q=2  
(boosted subsonic filter)  
DIP SWITCH FUNCTIONS  
TABLE 3DIP SWITCH SW2  
Mode  
1
2
3
4
5
6
7
8
9
10  
Mono Sum  
Stereo  
OFF ON  
ON  
OFF  
ON  
OFF OFF ON  
Bypass Channel 2 (bridged mono)  
ON OFF  
OFF ON  
Engage Channel 2  
Bypass Channel 1 LPF  
Bypass Channel 2 LPF  
Engage Channel 1 LPF  
Engage Channel 2 LPF  
ON  
OFF  
ON OFF  
OFF ON  
OFF ON  
BLOCK DIAGRAM  
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APPLICATION NOTES  
For cinema surround channels and subwoofers that do not require an EQ boost, use the following switch  
settings.  
SW1 slide switch- BOOST OFF  
SW2 DIP switch  
Position 1  
Position 2  
Position 3  
Position 4  
Position 5  
Position 6  
Position 7  
Position 8  
Position 9  
Position 10  
ON  
OFF  
OFF  
ON  
ON  
OFF  
ON  
OFF  
ON if bridged mono, OFF otherwise  
OFF if bridged mono, ON otherwise  
The high pass filter frequency for non-boosted subwoofers, such as the JBL 4645 and Electro-Voice  
systems NOT being used in the step-down box tuning mode, should be selected at about 0.8 times the box  
tuning frequency of the subwoofer. A frequency of 20, 25, or 32 Hz will usually give the best results. Select  
an appropriate SIP resistor pack and install it in position RN3. Consult your speaker manufacturer for more  
details about your specific subwoofer system. Surround channels may benefit from the use of a high pass  
filter at 80 Hz, also installed in position RN3.  
For cinema subwoofers that require an EQ boost, use the following switch settings.  
SW1 slide switch- BOOST ON  
SW2 DIP switch  
Position 1  
Position 2  
Position 3  
Position 4  
Position 5  
Position 6  
Position 7  
Position 8  
Position 9  
Position 10  
ON  
OFF  
OFF  
ON  
ON  
OFF  
ON  
OFF  
ON if bridged mono, OFF otherwise  
OFF if bridged mono, ON otherwise  
The high pass filter frequency for boosted, B6 subwoofer alignments should be selected according to the  
recommendations of the speaker manufacturer. Select an appropriate SIP resistor pack, for the desired  
boost frequency, and install it in position RN3. Listed below are some suggested filter frequencies for  
popular subwoofers, consult your speaker manufacturer for more details about your specific subwoofer  
system. A variance of +/- 5% from the exact boost frequency will have very little effect on the performance  
of the system.  
Electro-Voice:  
TL880D  
TL550D  
TL3512  
TL440  
25 Hz  
32 Hz  
32 Hz  
32 Hz  
JBL:  
4645B  
25 Hz  
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APPENDIX A: WARRANTY & DISCLAIMERS  
DISCLAIMER  
QSC Audio Products, Inc. is not liable for any damage to speakers, amplifiers, or any other equipment that  
is caused by negligence or improper installation and/or use of the SF-1 Subwoofer Filter.  
PRODUCT WARRANTY  
QSC Audio Products, Inc. guarantees the SF-1 Subwoofer Filter to be free from defective material and/or  
workmanship for a period of three years from date of sale, and will replace defective parts and repair  
malfunctioning products under this warranty when the defect occurs under normal installation and use—  
provided the unit is returned to our factory via prepaid transportation with proof of purchase (sales receipt).  
This warranty provides that examination of the returned product must disclose, in our judgment, a  
manufacturing defect. This warranty does not extend to any product which has been subject to misuse,  
neglect, accident, improper installation, or where the date code has been removed or defaced.  
APPENDIX B: TECHNICAL ASSISTANCE & SERVICE  
Servicing your unit requires a trained technician capable of performing the type of service you need. There  
are no user serviceable components inside your unit and the danger of electric shock exists. Additionally,  
some of the components in your unit are QSC specific parts that require QSC replacements. Comprehen-  
sive service manuals for some models are available at QSC.  
TECHNICAL ASSISTANCE  
If you suspect that your amplifier is defective, check your system configuration and amplifier settings to  
determine the origin of the problem. In many cases, incorrect audio interfacing, poor cabling, or other  
system level impairments are the cause of problems in audio systems. For technical assistance beyond  
the information given in this manual, the QSC Technical Services department may be contacted.  
FACTORY SERVICE  
In the event that your amplifier does need factory service, you may reach the QSC Technical Services  
department for return instructions. A Return Authorization (RA) number must be obtained from the QSC  
Technical Services department. QSC may not account for products that are returned without a Return  
Authorization number.  
Product Return Guidelines  
1. Pack the product well for protection during shipment. QSC will provide the factory packaging free of  
charge upon request.  
2. Include a copy of the sales receipt, your name, return address, phone number, and defect description  
with your return correspondence.  
3. Call the QSC Technical Services department for a Return Authorization number.  
4. Mark the Return Authorization number on the outside of the packaging.  
5. Ship the product prepaid to QSC Audio Products. We recommend United Parcel Service (UPS).  
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QSC TECHNICAL SERVICES DEPARTMENT  
1675 MacArthur Blvd  
Costa Mesa, CA 92626  
Telephone: (800) 772-2834  
(714) 957-7150  
(714) 754-6175  
Fax: (714) 754-6173  
Bulletin Board:  
(714) 668-7567  
(800) 856-6003  
INTERNATIONAL SERVICING  
ForQSCproductsthatarepurchasedoutsideoftheUnitedStates, servicemustbereferredtothedistributor  
or dealer from where the product was purchased. There are numerous service centers in many countries.  
The service centers in your country may be located by your dealer, distributor, or by contacting QSC  
Technical Services.  
APPENDIX C: IMPORTANT ADDRESS AND TELEPHONE  
INFORMATION  
Factory address:  
QSC Audio Products, Inc.  
1675 MacArthur Boulevard  
Costa Mesa, California 92626-1468  
USA  
Factory telephone numbers:  
Main Number  
(714) 754-6175  
Sales Direct Line  
Sales  
(714) 957-7100  
(800) 854-4079  
(toll-free in U.S.A. only)  
Sales & Marketing FAX  
(714) 754-6174  
(714) 957-7150  
Customer Service  
Customer Service  
(800) 772-2834  
(toll-free in U.S.A. only)  
Customer Service FAX  
QSC OnLine  
(714) 754-6173  
(714) 668-7567  
(800) 856-6003  
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QSC AUDIO PRODUCTS, INC. 1675 MacArthur Blvd., Costa Mesa, CA 92626 USA Ph (714) 754-6175 Fax (714) 754-6174  
QSCand the QSC logo are registered with the U.S. Patent and Trademark Office.  
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