13
LFE Input
LFE (Low-Frequency Effects) refers to the “.1” channel of a “5.1”
channel recording. Normally, all signals will come to the active
towers via the normal speaker-level inputs. However, your Snell
XA Towers include an alternative line-level input for bass signal
connection. If your processor allows you to feed all five-channel
bass to the front left and right channels, and by so doing leaves
only the LFE (.1 channel) at the processor’s subwoofer output,
then a coaxial lead can be run to each tower’s LFE input.
To understand its use, a little background about multichannel
formats is in order. Dolby® AC-3 and other 5.1 systems are
configured as five full-frequency range channels and one addi-
tional bass-only channel dubbed the .1 channel. Since the five
channels are full range, there is no restriction of what type
of signals can go into each. Certainly, the bass frequencies of
the background music of a movie will be sent to each channel
in line with all other components of the musical mix.
Explosions and sound effects are another story. It evolved in
movie cinema practice that theater owners wanted a separation
of normal soundtrack material from explosions and effects.
This separate track became known as the LFE or Low Frequency
Effects channel (later the .1 channel). Theater owners could then
decide if they wanted to invest in large theater subwoofers. If
they decided not to invest, they knew that explosions and such
would not be overloading the main system because they were
on a separate channel that could be ignored.
In order to have adequate headroom for effects, Dolby specifies
that, after decoding and D to A conversion, the “.1” channel
should be boosted 10dB. Whatever level the other five channels
can achieve, the .1 channel has the headroom to play up to
10dB louder. Hopefully, the recording engineers will use this
extra headroom sparingly. Unfortunately, the recording of the .1
channel seems to always be recorded at its maximum level. This
can lead to problems of balance with a normal home theater
system for the following reason: If small speakers are used with
a subwoofer, the subwoofer does double duty by reproducing a
combination of the bass from the five channels (music and dia-
log) and the .1 effects channel. For the music to sound full and
balanced, an exact setting of subwoofer level is required. This
might be a gain setting that often reproduces the .1 channel
(potentially 10dB louder) at too high a level, causing overdrive
or at least an excessive effects level.
Some processors are now giving setup options that allow trim-
ming of the LFE from Dolby-specified full gain (+10dB) down to
a lesser level. The music and cinema XA Towers also allow you
to set LFE level if you use a separate LFE input with its own level
adjustment potentiometer. This control is calibrated relative to
a processor with the Dolby-required +10dB LFE gain. That is,
setting it to 0 will give the same overall level. Setting it to -8
would be 8dB less than ”normal,” which is in fact 2dB of gain
relative to other channels. (The LFE gain calibration marks
assume your power amplifier has a voltage gain of about 26dB.)
This will allow you to control the LFE level independently of
other bass. When the LFE mix-level knob is set to 0dB, LFE mate-
rial will be reproduced at the full Dolby-specified mixed level.
Settings less than 0dB will change the proportion of the effects
level (explosions and the like) to music bass levels. This is best
set by finding a disc with a preponderance of LFE energy and
setting the knob until the balance between explosions and the
rest of the soundtrack seems “realistic.” Hint: One way of deter-
mining a good level is to set it to give (at a typical loud listening
level) a bit of gut feel to the explosions and gun shots. Extreme
settings will become fatiguing over time.
The above procedure is by no means mandatory. If you do not
wish to use separate connections for LFE, most processors will
send it to any channels designated “Large” with a configuration
choice of “no subwoofer.” In all cases, it is important to consult
the processor manual because some manufacturers have differ-
ent interpretations of what these designations mean.
To Next Page
Loading...
