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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.