JBL LSR4312SP, Owner'S Manual

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Appendix A: About Surround Sound
The term “surround sound” generally refers to any multichannel audio confi guration – that is, any
setup that consists of more than a single stereo pair of speakers. The most common surround sound
confi guration is 5.1, consisting of fi ve full-range main speakers (Left, Right, and Center, positioned in front
of the listener, and Left Surround and Right Surround, positioned behind the listener) plus a subwoofer
(the “.1” channel, so-called because it usually contains only 10% of the frequency bandwidth as
compared to the main speakers).
Other surround confi gurations requiring a subwoofer include, 6.1 which adds a rear center channel to a
standard 5.1 confi gurations and 7.1 which adds left-of-center and right-of-center speakers to a standard
5.1 confi guration. Addition of a subwoofer can be used for bass management in these and other surround
system confi gurations.
The LFE Channel
Another term for the “.1” channel is LFE, short for “Low Frequency Effects.” This term originated in the
fi lm world, where the subwoofer is typically employed to provide extra low frequency reinforcement,
generating rumbles and the sounds of explosions, etc. In music applications, the LFE channel usually
contains only low frequency instruments such as bass, bass drum, and synthesizer elements. The LFE
low-pass fi lter in the LSR4312SP allows you to monitor the LFE channel as it will sound after it has been
mastered, without fi ltering applied or fi ltered (at 50Hz, 80Hz, or 120Hz), allowing you to reproduce the fi nal
product as it is intended.
+10 dB Gain
Because low frequencies require more energy than high frequencies to be perceived at the same
loudness, bass content can easily overload a recording system, especially when using media with limited
dynamic range. For this reason, some cinematic systems employ a scheme in which the LFE channel is
recorded 10 dB below reference level, with the signal then boosted by the same 10 dB upon playback.
Although this practice has largely been abandoned with the rise of modern digital recording media, having
provision for this 10 dB of boost allows legacy soundtracks to be played back as they were originally
intended. This is precisely the function of the “+10 dB GAIN” switch on the rear panel of the LSR4312SP.
Note that setting this switch to the ON position boosts only the LFE channel (regardless of whether analog
or digital inputs are being used), not the overall subwoofer level; when bass management is turned on (see
next page). This switch does not affect the other channels being reproduced.
Bass Management
“Bass management” is a term that refers to the practice of using a subwoofer to reproduce the bass
frequencies of all main channels, in addition to the function of reproducing the independent LFE channel.
Because of the physiology of the human ear, low frequencies are largely nondirectional: given an adequate
listening distance, we can’t easily tell where bass signals are coming from. Thus, it makes little or no
difference to the listening experience whether the bass component in a sound comes from the originating
speaker (which may be off to your left or right, or even behind you) or from a dedicated subwoofer which
is better equipped – and better positioned in the room – to reproduce low frequencies than even a full-
range monitor. For that reason, you may want to use your LSR4312SP subwoofer to reproduce all the
bass frequencies in your mix. That’s the function of the Bass Management button on the front panel:
When ON, not only will the LSR4312SP reproduce the bass component (that is, all frequencies below the
set crossover [X OVER] frequency) of all channels connected to its analog inputs and, if DIP switch 5 is
set to the “Bass Management” position, its digital inputs, but all networked LSR4300 studio monitors will