JBL LSR4312SP, Руководство пользователя

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32
Reference - RMC
™
Room Mode Correction
RMC™ Room Mode Correction
When loudspeakers or subwoofers are placed in any work space, they and the room behave as a system
which, for better or worse, acts as the reference point for creative decisions. When a room has inadequate
acoustic treatment, “room modes” (sometimes called “standing waves”) can produce, producing low
frequency resonances that give a misleading impression of bass response and therefore make it diffi cult to
achieve a proper mix balance. Also, when a speaker is placed in close proximity to a boundry wall, corner
or work surface, the response of the system is affected.
The LSR4312SP subwoofer (and all LSR4300 studio monitors) utilizes a revolutionary JBL technology
called RMC™ (short for “Room Mode Correction”) that is designed to correct the problem. RMC analyzes
the frequency response of all speakers and subwoofers at the mix position and automatically applies
corrective fi lters to dramatically minimize low frequency resonance or minimize the effect of boundries.
Because room modes create resonance at specifi c frequencies with very narrow bandwidths (sometimes
called “Q”), the on-board analyzer has the intelligence to identify the specifi c frequency and Q and apply a
corrective parametric fi lter to only the component of the signal that causes the problem.
When the RMC analysis is initiated, the onboard analyzer in each LSR4300 speaker and subwoofer emits
a reference tone that is measured at the mix position using a calibration microphone. The computer mea-
sures the response received via the microphone and compares it with the original tone being emitted. It
determines which if any conditions should be corrected, and then calculates and applies a corrective fi lter.
The entire process takes only a few seconds per speaker.
During the RMC calibration process, the computer trims all speaker and subwoofer levels in fi ne* incre-
ments so that all monitors in the system produce equal SPL (sound pressure level) at the mix position.
This ensures that all speakers are balanced and is particularly useful in surround sound applications where
space limitations often prevent optimum speaker placement. For example, if the center speaker is closer
to the mix position than the other main speakers, attenuation must be applied so your mix balances are
correct. Without this correction, your end product will sound unbalanced on a properly calibrated play-
back system. RMC also automatically adjusts the polarity of the LSR4312SP subwoofer so it sums prop-
erly with the main speakers.
When using an LSR4312SP subwoofer, it is important to carry out RMC calibration with the subwoofer set
to the mode it will most often be used in. For example, if you plan on using bass management most of the
time, carry out RMC with the LSR4312SP bass management turned ON and with the bass management
crossover set to the desired frequency. If after performing RMC calibration the bass management settings
are changed, RMC will automatically be bypassed and the front panel RMC button will be illuminated. To
enable RMC, return subwoofer to prior settings or perform a new RMC calibration. If you don’t plan on
using bass management most of the time (i.e., if you plan on using the LSR4312SP solely to reproduce
the LFE channel), make sure it is turned OFF before performing an RMC calibration. For more information,
see Appendix A on page 34 in this manual.
X
RMC calibration can only be carried out when the LSR4312SP is networked with one or more LSR4300
speakers. Refer to the LSR4328P / LSR4326P owner’s manual for a step-by-step description of the RMC
calibration procedure.
* LSR4328P, LSR4326P: level trim resolution is ± .25dB. LSR4312SP: level trim resolution is ± .5 dB.