QSC SC-424, SC-423C Owner's Manual

1675 MacArthur Blvd., Costa Mesa, CA, 92626 USA
Main Number [phone] Sales & Marketing [phone] or toll free (USA only) [phone]
Customer Service(714) 957-7150 or toll free (USA only) [phone]

Cinema Loudspeaker Systems User Manual

LF-4215 and LF-4215-8 Low Frequency Loudspeakers

Introduction

The LF-4215 dual 15” (381mm) low frequency enclosure is designed specifically for cinema
applications. Meeting cinema requirements for extended low frequency response differentiates
the LF-4215 from more conventional “rock-and-roll” woofer systems. The LF-4215 covers the
frequency range from 35 Hertz to 1000 Hertz, depending upon the high frequency system
requirements. Close Coupled Woofers (CCW), with its tight spacing between woofers, improves
coupling and keeps coverage angles wide over a greater frequency range than more widely
spaced designs. The LF-4215-8 is an 8 ohm version of the standard 4 ohm LF-4215.

The two custom 400 watt, 15” transducers were developed especially for cinema use. They fea­ture extremely large 4” (100mm) voice coils and a multi-vented pole piece to ensure cool opera­tion, even at high power levels. Cooler temperatures increase transducer lifespan and decrease
the problem of power compression at high power. An undercut pole piece ensures the voice coil
operates in a Symmetrical Magnetic Gap (SMG), reducing second harmonic distortion.

The enclosure is constructed of high quality MDF panels and features Single Woofer Chambers
(SWC, separate chambers for each transducer). In the rare event of a transducer failure, this
prevents over-excursion of the remaining transducer caused by improper box loading.

Mounting points for high
or mid-high system

Large, Fully Radiused Ports (FRP) ensure smooth air flow through the ports, especially at higher
power. This prevents potentially audible port turbulence noise. Both internal and external port
openings are fully radiused.

With Symmetrical Port Loading (SPL), bass ports are evenly spaced on each side of the trans­ducers, making internal pressure more uniform across the back surface of the transducer. This
prevents the cone from being displaced to one side or another by unbalanced forces, reducing
the chance of driving the voice coil out of the center of the gap at high power.

Three T-nuts in the top of the enclosure provide easy mounting of QSC’s HF-75 high frequency
system, or MH-1075 mid-high system.

Enclosure is not designed to be suspended, flown, or rigged. Do not suspend,
fly, or rig this enclosure.

This product is capable of producing sound pressure levels that can perma­nently damage human hearing. Always keep sound pressure levels in the lis­tening area below levels that can damage human hearing.

Install in accordance with QSC Audio Product’s instructions and a licensed,
professional engineer. Only use attachments, mounts, accessories, or brack­ets specified by QSC Audio Products, Inc. Refer all servicing to qualified per­sonnel. Servicing is required when the apparatus has been damaged in any
way.

WARNING! Before placing, installing, rigging, or suspending any speaker
product, inspect all hardware, suspension, cabinets, transducers, brackets
and associated equipment for damage. Any missing, corroded, deformed or
non-load rated component could significantly reduce the strength of the
installation, placement, or array. Any such condition severely reduces the
safety of the installation and should be immediately corrected. Use only hard­ware which is rated for the loading conditions of the installation and any pos­sible short-term unexpected overloading. Never exceed the rating of the
hardware or equipment. Consult a licensed, professional engineer when any
doubt or questions arise regarding a physical equipment installation.

*TD-000141-

© Copyright 2003, 2004, 2007, QSC Audio Products, I nc.

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

QSC® is a registered trademark of QSC Audio Products, Inc.

TD-000141-00 rev.F

Connections

Normal Connection

The LF-4215 has barrier strip screw termi­nals for connection. The terminals accept
up to #10 AWG stranded loudspeaker wir­ing. Use the largest wire size and shortest
wire length possible for a given installa­tion. Observe the polarity markings and
keep polarity consistent throughout the
system for best performance.

Normal Connection Example:

Parallel Connection of Second LF-4215

The terminals marker SPK2 may be used to
connect another LF-4215 in parallel. Con­nect the wires as shown in the illustration,
at right. Note: If the LF-4215’s internal wir­ing has been modified in any way, this may
not function. If this is the case, remove the
terminal cup and verify the presence of the
factory yellow jumper and blue jumper
wires; remedy as required or have the
loudspeaker serviced.

Individual Transducer Connection
(requires modification)

CAUTION! Requires removal of
terminal cup and cutting of
both the yellow and the blue
jumper wires that connect the
SPK1 and SPK2 terminals.

Parallel Connection Example:

Individual Transducer
Connection Example:

The transducers are wired in parallel
inside the enclosure. If individual trans­ducer connection is required, remove the
terminal cup and remove the yellow and
the blue jumper wires that are connected
between the SPK1 and SPK2 terminals.
Replace the terminal cup and mark the
enclosure with a note of the modification.