Alpine 3672 - Theory of Operation; Crossover Network Fundamentals; Input Selector and Subwoofer Modes

—
21. REMOTE-ON: INDICATOR:
An LED gives visual confirmation of whether or not the unit
is in operation. Helps system troubleshooting.
22. SUBWOOFER OUTPUT UPPER: CUTOFF
FREQUENCY. ADJUSTMENT. CONTROL:
This continuously: variable: control: adjusts the low-pass
corner frequency: of the: subwoofer output independently
fromthe CH.1/2 and CH 3/4 Low outputs. Itis variable from
-50 to 120 Hz.
23.. SUBWOOFER MODE SWITCH:
Selects. a Non-fading, Front-fading,. or Rear-fading sub-
woofer output when using.a head. unit with.two pre-outs
and a built-in pre-amp fader.
Inthe
Non-fading
position.
(marked.CH.
1
—
4),
the
sub-
woofer
output
will
be
present
regardless
of
the
position
of
the
head
unit’s
fader
control.
Always
use
the
CH
3/4
Non-Fading
position
when
a
single
input
is
used
and
the
1-INPUT
mode
is
selected.
24. 2/1 INPUT SELECTOR SWITCH:
When the 2-input mode is selected, the CH 1/2 and CH 3/4
inputs
are
isolated
from
each
other.
This
allows
the
use
of
a
head
unit
with
separate
front
and
rear
pre-outs
while
retaining its front to rear fading capability.
The
1-Input
mode
combines
the
front
and
rear
inputs
so
that
a
head
unit
with
a
single
pre-out
can
be
used.
Front-
to-rear
fading
is
not
possible
in
this
mode.
In
the
1-input
mode,
only
CH
3/4
inputs
can
be
used.
CH
1/2
inputs
will
be
disabled.
| 3672
Theory of Operation
CROSSOVER NETWORKS:
Acrossover network divides the audio spectrum into different
segments. This segmentation is based on the frequency of
the signal. The crossover network actually employs filters that
pass a certain range of frequencies and block the rest. This
way, the signal can be separated into a set of signals with
different frequency response ranges.
1 Cineal
Audie signe To Tweeters
To Midrange
Drivers
OX@XOX®
Crossover Network 7@\
Mid-Bass
To Mid-Bass
Drivers
To Subwoofers
The lowest frequency appreciably present with at least half
the magnitude of the frequency with the highest output level
(3 dB down) in that segment, is called the Lower Cutoff or
the High-Pass Crossover point.
The highest frequency present in that segment which is also
at most’3 dBs lower than the frequencies with the highest
output in that region, is called the Upper. Cutoff or the
Low-Pass Crossover point of the network.
Increasing Frequency
A crossover network section does not necessarily have both
the lower and higher crossover frequencies:
1. LOW-PASS CROSSOVERS: Filters with only an upper
cutoff frequency. Subwoofer outputs are generally low-pass.
2. HIGH-PASS CROSSOVERS: Have a lower cutoff fre-
quency only. Tweeter (High) outputs are generally high-pass.
3. BANDPASS CROSSOVERS: Have both lower and upper
crossover points. These filters are made by adding a Low-
pass and a High-pass crossover together in series. Midrange
crossovers are generally bandpass.