RMC™ Room Mode Correction User Guide
Table Of Contents RMC™ Room Mode Correction System What Is RMC What is Included in the RMC Calibration Kit How To Use The RMC Kit Speaker Placement Where To Place The Loudspeakers 3 4 4-5 6-7 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 Boundary Compensation Calibrating Your System I.
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.
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.
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.
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.
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.
Calibrating Your System 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.
3. Now advance to Track 3. This track contains a set of warble tones beginning at 126 Hz, moving downward to the lowest frequencies. As this track is played, keep your eye on the meter. If none of the tones on Track 3 causes an over-reading, draw a horizontal line on the chart paper at a level of -7 dB. (See Figure 3) This will be your baseline reference level. 4. If any of these tones causes an over-load reading on the meter, stop the CD player and adjust the CD source volume downward slightly.
Analyze Your Measurements Most of your measurements for LSR6328P systems will fall within one of the six examples which follow. Here are detailed descriptions of each example: Example A: Absence of a floor interference dip indicates the loudspeaker was probably mounted against a wall in a well-damped room, and not too far away from the monitoring position. You may proceed to equalize the LF room mode for flat response.
Example D: This is a near-ideal case, and the recommendation is to do nothing. Your system will be fine as it is. Variations Within ±3 dB 0dB -1 dB -2dB -3dB -4dB -5dB -6dB -7dB -8dB -9dB -10dB -11dB -12dB -14dB -16dB 20Hz 22 24 25 26 28 31 35 41 45 47 50 53 57 62 68 76 85 90 95 105 115 126 Example E: Two interference response dips; no peaks due to room modes. This pattern may be seen in small spaces where two different delay paths are evident, such as from the floor and a wall.
Adjusting The RMC System When you have identified the peak you wish to equalize, 1.) enter its center frequency in the space provided at the bottom of the chart paper; 2.) in the space provided, enter the level of the peak which is the distance in dB between the peak value and your baseline; finally, in the space provided, enter the width as determined by the width template. Figure 10a PULL Figure 10a shows the Width Template. To adjust, pull the tab at the top of the width template.
4.) Enter your tabulated values into the LSR6328P RMC equalizer using the table below: Data Entry in RMC Equalizer Table: Control Position Width (%) Frequency (Hz) Depth (dB) 0 (CCW) 4.5 24 0.0 1 5.0 25 0.0 2 7.5 26 0.0 3 10.0 28 0.5 4 12.5 31 1.1 5 16.5 35 1.9 6 20.5 41 2.9 7 23.0 45 4.4 8 26.0 47 6.4 9 28.0 50 7.9 10 29.5 53 8.3 11 31.0 57 8.9 12 34.0 62 9.5 13 39.0 68 10.2 14 41.5 76 11.0 15 43.5 85 11.7 16 45.0 90 12.7 17 46.5 90 13.1 18 48.0 95 13.5 19 49.0 95 13.9 20 (CW) 50.
II. LSR6328P Systems With LSR6312SP Subwoofer First, make sure that you have completed steps for a stereo LSR6328P system. Signal for the left and right LSR6328P speakers should be fed through the main LSR6312SP unit and the calibration of the left and right LSR6328P units must have been done with the LSR6312SP powered off or in Bypass mode (See LSR6300 owner’s manual). Now, to calibrate the RMC system of the LSR6312SP, power up the unit and make sure the Bypass is not active.
Feed one channel from the CD player into the left or right channel input on the rear of the LSR6312SP and proceed with the following steps: 1. Set both the LSR6328P and LSR6312SP to the same input sensitivity, using the DIP switches on the back panels of each unit, as shown in Figure 14. Make sure that the gain trim pot on the LSR6312SP has been disabled.
Analyze Your Measurements Because of the extended LF response of the LSR6312SP system and its normal location at the intersection of floor and wall, you may see a variety of response conditions, such as the ones shown in Figures 15 and 16.
A very sharp dip adjacent to a peak: Figure 16 shows a peak at 41 Hz with an adjacent sharp dip at 57 Hz. A deep response dip such as this is caused by destructive interference, and such peaks can occur either above a dominant or strong response peak, as shown here, or below a response peak. Sometimes, moving the test microphone a short distance will virtually eliminate the dip. (Actually, you are not eliminating the dip, but merely moving away from it.
III. LSR6332 Or Other Passive Systems With LSR6312SP Subwoofer Many engineers will want to use the LSR6312SP subwoofer in stereo or surround activities using passive loudspeaker systems such as the LSR6332. There are two ways you can do this: Method One Feed the Left, Center and Right channel power amplifiers through the three sets of signal inputs and outputs on the rear panel of the LSR6312SP, as shown in Figure 17.
Method Two Many engineers are quite happy with the response of their existing stereo or surround loudspeakers. They may only want to add a subwoofer to their system for more extended bass. In this case, the hookup shown in Figure 18 should be used. You can get a subwoofer feed by sending a parallel or “multed” feed of the LCR front channels - or by using the Direct In to the subwoofer if your signal source has a SUB or 0.1 (point-one) output.
V. Surround Systems Figure 20 shows a setup in which 3 LSR6328P units and one LSR6312SP unit comprise the front channels. The rear channels are completely independent of the front set and may even be different loudspeaker models. For example, a pair of LSR25s may be used in the rear. The front channels and subwoofer have been discussed earlier in this User Guide. If you choose to use a pair of LSR6328Ps for the rear channels, treat them as discussed in Section II on page 14.
IV. Multi-Channel Systems With Externally Provided Bass Management If you are using your LSR6300 system to monitor discrete multi-channel audio, and want to simulate the listening chain of the theater or home theater environment, you may choose to set up your system this way. See Figure 22 below. Right R in L in Center C in Left Figure 22 L out Source out RR out LR out C out Bass Management R out System Sub out Sub Direct in RR in LR in Left Rear Subwoofer Right Rear 1.
3. Turn all speakers on and perform level calibration of all channels. • To conform to cinema standard used to playback movies and DVDs, an input signal -20 dBFS (Full Scale) should produce 85 dB SPL from each individual satellite and 95 dB SPL from the subwoofer. A +10 dB gain switch is provided on the LSR6312SP SUB DIRECT IN which can be used to conform to this gain structure.
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