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 75LE’s include an alterna-
tive line-level input for bass signal connection. If your
processor allows you to feed all fi ve-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 mul-
tichannel formats is in order. Dolby® AC-3 and other
5.1 systems are confi gured as fi ve full-frequency range
channels and one additional bass-only channel dubbed
the .1 channel. Since the fi ve channels are full range,
there is no restriction of what type of signals can go
into each. Certainly, the bass frequencies of the back-
ground 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 own-
ers 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
specifi es that, after decoding and D to A conversion, the
“.1” channel should be boosted 10dB. Whatever level the
other fi ve channels can achieve, the .1 channel has the
headroom to play up to 10dB louder. Hopefully, the re-
cording 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 fi ve
channels (music and dialog) and the .1 effects channel.
For the music to sound full and balanced, an exact set-
ting 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 al-
low trimming of the LFE from Dolby-specifi ed 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
if you use
if you use
separate LFE input with its own level adjustment poten-
tiometer. This control is calibrated relative to a processor
with the Dolby-re10dB 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 amplifi er 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 material will be reproduced at the full Dolby-speci-
fi ed 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 fi nding 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
Hint:
Hint:
determining 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 confi guration choice of “no subwoofer.”
In all cases, it is important to consult the processor
manual because some manufacturers have different
ºinterpretations of what these designations mean.
