JBL RMC User Manual

RMC™ Room Mode Correction

User Guide

Table Of Contents

RMC™ Room Mode Correction System 3 - 5

What Is RMC 3

What is Included in the RMC Calibration Kit 4

How To Use The RMC Kit 4 - 5

Speaker Placement 6 - 7

Where To Place The Loudspeakers 6 - 7

- Smooth Response

6

- Mounting Options 6

- How Close Should The Loudspeaker Be To The Listener 7

- What About Setting Up In Small Spaces 7

Boundary Compensation 7

Calibrating Your System 8 - 13

I. LSR6328P System 8 - 13

Taking Measurements

8 - 9

Analyze Your Measurements

10 - 11

Adjusting The RMC System 12 - 13

II. LSR6328P Systems with LSR6312SP Subwoofer 14 - 17

Taking Measurements

15

Analyze Your Measurements 16 - 17

Adjusting The RMC System 17

III. LSR6332, or Other Passive, Systems with LSR6312SP Subwoofer 18 - 19

Method One

18

Method Two 19

IV. LSR25P Systems with LSR6312SP Subwoofer 19

V. Surround Systems 20

VI. Multi-Channel Systems with Bass Management 21 - 22

JBL Professional Contact Information 24

2

The Room Mode Correction™ System

What Is RMC?

Developed by JBL Professional, RMC™ is a system designed to calibrate and correct low
frequency (LF) response in typical listening rooms and production facilities. The LSR6328P
full range monitor and LSR6312SP Subwoofer contain a single section parametric equaliz­er that can be adjusted to compensate for the major low frequency response peak caused
by standing waves in a particular listening space. The LSR6332, LSR25P and other sys­tems can experience the benefits of RMC when an LSR6312SP is used in the system.

The RMC process allows you to optimize the low frequency response of your system in
your work environment. Using the tools provided in the RMC Kit, simply follow the instruc­tions step-by-step and allow approximately 30 minutes to perform the adjustment process
for a stereo system. You will experience a noticeable improvement in the sound quality of
your system.

What are Room Modes? Room modes are low frequency resonances caused by standing
waves involving the geometry of the room and its boundary surfaces. The most prominent
modes are the ones that occur between opposite surfaces. If response peaks due to these
modes are not corrected, your mixes may be bass-shy, because you will tend to overcom­pensate for what may sound like too much bass in the program. Response peaks due to
room modes can be accurately removed by introducing a carefully-tailored inverse
response, which RMC provides. You may also encounter response dips, which are due to
local reflections and interferences between the loudspeaker and listening position. The
most common reflections are from the floor. You should be aware that no system of equal­ization can correct for a response dip. Dips can only be compensated for by repositioning
loudspeakers and/or listeners in the playback environment. Figure 1 illustrates the typical
situation as it exists in most production rooms. The measured response at the listener is
shown in the right portion of the figure. In most rooms, the response rise due to the domi­nant mode will usually be in the range from about 40 Hz to 60 Hz, and the response dips
due to floor reflections will be seen in the range from 50 Hz to about 90 Hz.

RMC provides a method for equalizing the peak shown in Figure 1, but the dip, if it is
severe, must be corrected through rearrangement of loudspeaker and listening positions.
In most cases however, "floor bounces" are not problematic.

Mode Structure

3

Figure 1

Null

Listening Position

Peak Due to Axial Mode

dB

Peak

Speaker Position

Peak

dB

Most Modes: Most Floor Dips

25 - 60 Hz

Dip Due to Floor Reflection

Frequency (Hz)

65 - 90 Hz

What Is Included In The RMC Calibration Kit

• Specialized Sound Level Meter

• Calibration CD

• User Guide

• Measurement Chart Paper (make additional 1-to-1 copies for future use)

• Width Template

• RMC Adjustment Tool

• RMC Remote Bypass Control

• 9 Volt Alkaline Battery

How To Use The RMC Kit

Using the calibration CD, warble tones spaced approximately on one-tenth octave centers
are played over the speaker systems, and the room response is measured and plotted
point-by-point on chart paper. The center frequency of a response peak is identified, and,
using the Width Template, the width of the peak is determined. The height of the peak in
dB is also measured. These three values are then entered into the RMC equalizer section
located on the rear electronics panel of the LSR6328P or LSR6312SP and, using a look-up
table in this manual, an inverse frequency response curve is introduced into the system.

The RMC Meter

: Two views of the RMC sound level meter are shown in Figure 2. The
meter has a press and hold switch to incease battery longevity. Full-scale on the meter
corresponds approximately to a sound pressure level of 86 dB. The meter's scale covers a
range of 16 dB, the same as that of the chart paper you will use to record your measure­ments. Here is a list of meter status indications:

• Power-On/Low Signal: This is indicated by the
illumination of any LED on the bar graph. If
the sound level in the listening space is below
the measurement range of the meter, a green
LED near the bottom of the bar graph will light.

• Overload: If the sound level in the listening
space exceeds the range of the meter, 0 dB
through -5 dB will all light simultaneously.

• Normal Measurements: When the sound level
is within the range of the meter, the green LED
will be off and one of the red LEDs on the bar
graph will be illuminated, indicating the relative
sound level in decibels (dB).

• Low Battery: When the battery voltage is too
low for accurate measurements, an LED at the
bottom of the bar graph will be illuminated. At
this point, replace the battery. (We recommend
that you keep a spare battery on hand.)

Side

Figure 2

4

-1

-2

-3

-4

-5

-6

-7

-8

-9

-10

-11

-13

-15

-18

U-R

Ball

Power

Front

Chart Paper: As you play test tones on the CD through the system, you will plot the read­ings on the chart paper. A calibration procedure will ensure that the signals you read will
fit within the window of the meter. Any signals that appear below -16 dB will simply be
entered along the bottom edge of the chart. We recommend you make photo copies of the
chart paper for your use, and keep the original master for future duplication. When dupli­cating, do not enlarge or reduce the size of the chart.

A view of the chart is shown in Figure 3, with the level scale at the left and the frequency
scale at the bottom. Below the chart are areas for you to enter your collected data:
Frequency (Hz), Level (dB), and Width (%).

The 9-V

olt Battery: should be installed in the Sound Level Meter prior to use.

The RMC Remote Bypass Control

: when connected to an LSR6328P or LSR6312SP, allows
you to bypass the RMC system from the listening position for before-and-after compar­isons. You may use mono (tip-sleeve) 1/4” cables such as guitar cables to make the con­nections as shown below.

-

-

-

-

-

Figure 3

5

0dB

-1 dB

-2dB

-3dB

-4dB

-5dB

-6dB

-7dB

-8dB

-9dB
10dB
11dB
12dB

14dB

16dB

57

20Hz

22 24 25

Frequency

31 35 41 45

28

26

Hz

47

50

Level dB

62 68

53

76 85

90

95 105

Width

115

126

%

Y-Cable

Y-Cable

1/4" Cable

Connect to RMC Bypass Control

1/4" Cable

RMC™

Y-Cable

1/4" Cable

Y-Cable

1/4" Cable

Speaker Placement

Where To Place The Loudspeakers

A basic question is “where should I place my loudspeakers in the room?” Here are some
pointers for you.

A. Smooth Response

: Place the loudspeakers where their frequency response will be the
smoothest and most uniform. The best locations are fairly close to a wall (no more than
about 10 inches from the wall), or out in the room and positioned on ear-height loudspeak­er stands. Figure 4 and Figure 5 show options for both stereo and surround setups.

Boundary surfaces create reflections from the loudspeakers that will, to some extent, inter­fere with the direct sound from the loudspeaker to the listener, and these will cause peaks
and dips in response, primarily in the mid-bass range and lower (roughly 250 Hz and lower).

When the loudspeakers are placed within about 10 inches of the wall, the reflected sound
at mid and low frequencies will be largely in phase, or in step, with the direct sound from

the loudspeakers, and interferences will be reduced.

L

C

R

LR

RR

L

C

R

LR

RR

Figure 4

Figure 5

6

Near The Wall

Free-Standing Loudspeakers

Generally, the best place to locate a subwoofer is on the floor against a wall, or within a few
inches of the wall. You should avoid the center of the wall, and you should also avoid placing
the sub directly in a corner. What you are looking for is response that is generally uniform and
free from a severe dip or a pair of peaks, and even slight side-to-side adjustments (6 or 8 inch­es) can materially affect these. A single peak of course you can adjust through RMC, resulting
in the flattest possible LF response.

Alternately, when loudspeakers are placed on stands well out into the room, the path traveled
by the reflected signals from the walls will be much longer than the direct path from the loud­speaker to the listener, and the level of the wall reflections will be much lower than direct
sound. The result is less interference.

B. Mounting: When positioning loudspeakers on a wall, always follow mounting recommenda-

tions provided by the manufacturer of the mounting hardware and aim the principal axes of
the loudspeakers at the primary listening position. If your loudspeakers have ports on the
back, make sure that there are at least 3 to 4 inches between the port opening and the wall.

Caution:

Unsafe mounting or overhead suspension of any heavy load can result in serious injury and equipment
damage. Mounting of speakers should be done by qualified persons in accordance with all applicable local safety and
construction standards. Be certain to follow the instructions providied by the manufacturer of the mounting bracket,
be certain that it is capable of supporting the weight of the speaker to be mounted.

Space your loudspeakers so that the listening angle is symmetrical with the listening posi­tion. For stereo, the normal included angle between loudspeakers and listener should be in
the range of 35 to 50 degrees. For surround sound applications, follow the recommendations
as shown in Figure 5.

C. How Close Should The Loudspeakers Be To The Listener: Ideally, the loudspeakers should be

far enough away from the primary listening position so that normal head movements don’t
interfere with stereo or surround imaging. Also, the loudspeakers should ideally be placed
up to 8 feet away from the listening position, which would be ideal. If space is not well
damped, you may be required to operate in a “near-field” environment with the loudspeak­ers no greater than about 4 feet away.

D. What About Setting Up In Very Small Spaces: The first thing you should do in a very small

space is ensure that it is as acoustically “dead” as possible. Problems will arise both from
boundary reflections as well as from standing waves in the room, and the more heavily
damped the room is, the better it will sound. You may also be forced to place your left and
right channel loudspeaker virtually at the corners of the space, which compounds
response problems. This leads us directly into the next section on boundary compensation.

Boundary Compensation

Your LSR6328P loudspeakers are designed to operate most effectively in relative free space ­away from the walls of a room. Internally, they have been equalized to produce the flattest
low frequency (LF) response under this free-standing condition. When you move the loud­speaker toward the wall, the LF response below about 150 Hz will rise, reaching a boost of
about 3 dB. If you move the loudspeaker toward a corner (the intersection of two walls), the
LF response will build up even more. There are two DIP switches on the back panel of the
LSR6328P that engage various values of LF attenuation and compensate for these LF build­ups of response, and graphic below shows the settings you should use in order to make
these changes. The general rules are as follows:

Free-Standing 0 dB attenuation
Near A Wall 1.5 to 3 dB attenuation
Near A Corner 3 to 4.5 dB attenuation

Use no more attenuation than required to reduce any tendency for the system to sound
boomy or bass-heavy. This adjustment should be made before you proceed with the RMC
equalization process.

7

I. LSR6328P System

If your CD player has an output volume control, we strongly recommend that you patch
directly from one output of your CD player to the input of the LSR6328P system.

If your CD player does not have an output volume control, patch into a console fader then
go directly from the console output to the LSR6328P, bypassing any further controls or
functions. These options are shown in Figure 6.

The loudspeakers will be measured one at a time. Set the DIP switches on the back panel
of the system to the OFF position. If you are using boundary compensation setting
Switches 5 and 6, leave these settings on. Make sure that all controls are set to their
counter-clockwise position and that the RMC ENABLE switch is in the OUT position and
that the GREEN RMC “Active” LED is OFF.

Calibrating Your System

Volume

Figure 6

+

+

p.

Figure 7

8

Taking Measurements

1. Place your speakers in the desired position and wire the system together. For assis­tance with wiring, see the LSR6300 Series owners manual. Connect the RMC Remote
Bypass control to each speaker using “Y” adaptors supplied with each LSR6328P and
LSR6312SP. Turn on the speakers.

2. Setting the reference level: Hold the RMC Meter vertically in front of you at ear level
with display facing you and microphone facing the speakers. Press and hold the ON
button. Play Track 2 on the test CD, adjusting the CD program source level so that the
wide-band noise signal will read -7 on the sound level meter. The purpose here is to
establish a reference level baseline for your measurements.

LSR6328P

Control

out

CD Player

LSR6328P

CD Player

out

Console:

Direct-to-Fader In/Out

out

Input T rim Active

4 dBu Input Sensitivity

8 dBu Input Sensitivity

VLF Protect Off

HF Level +1 dB (2 kHz - 20 kHz)
HF Level -1 dB (2 kHz - 20 kHz)

-3.0 dB

-1.5 dB

-4.5 dB LF Boundary Com