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AV123 Onix R-DES Rocket Digital Equalization System

Part II

September, 2006

John E. Johnson, Jr.

 

In Use

To configure the R-DES, you need to measure how your subwoofer performs in your home theater, so that you can use the R-DES software installed on your computer to make some EQ curves.

To accomplish this, R-DES supplies a pink noise soundtrack, along with an entire set of low frequency test tones, on the CD that you used to install the software.

You will also need an SPL meter, such as made by Radio Shack.

Now, open the R-DES program. You will see the following window. On the left, you will see four numbered curve labels, all saying "Default" (the window shown below has my corrected curves listed, which I will explain shortly).

The default curves look like the one shown in the right portion of the window. They are flat to about 40 Hz, then begin to roll off, depending on which button under "Crossover" you have selected and which frequency you choose for the low-pass.

There are five EQ bands, each with a circular rotating dial to adjust "dB" (the amount, or height, of the adjustment), the "Hz" or frequency for that band, adjustable from 20 Hz to 120 Hz, and the "Q", which is the width of that band, i.e., the spread around the chosen frequency that you want the band to operate.

Highlight each of the default curves one at a time and click the up arrow at the top of the program after you highlight each curve. This will upload the default curves to the R-DES box. Now, push the Select button on the R-DES box to highlight LED number 1.

Connect the subwoofer output of your receiver to the left RCA input on the R-DES box, and the left RCA output of the R-DES box to your subwoofer.

Since you don't want the other channels to interfere with the measurements, you need to disconnect all of the speakers except for the subwoofer. Also, turn the subwoofer's crossover off if you can (in your receiver's bass management menu, set the subwoofer crossover frequency as high as it will go - you can turn it back to the original number after you have completed the R-DES curves).

So, with the CD in your player, and your SPL meter on the chair where you sit when watching movies, click on the Graph Paper icon on your laptop computer's desktop, which opens the following window.

On the left are the frequency tones that are on the CD, next to a column where you type in the SPL readings that you get when you play the tones.

At the top, select whether you need any correction factors. Choose either "None" if you have a reference microphone, or "RS" if you are using the Radio Shack SPL meter. With the Radio Shack meter, set the response on the meter to "Slow" and "C-Weighting".

Next, turn down the volume on your receiver, then sit in your chair with the SPL meter and your laptop, and play the Noise track on the CD. Using your remote to control the volume on the receiver, adjust the loudness to 85 dB. Type 85 in the Noise SPL line in the graph paper window.

Then, play the various test tones (sine waves) on the CD and record the SPL in the respective places in the graph paper window. Once that is done, the graph paper window will look something like this:

I used a calibrated professional microphone rather than the Radio Shack SPL meter, so I selected None in the Correction menu. Part of my graph went below the bottom line, but all you have to do is change the Noise SPL number to a lower value (such as 70), and that will move the graph up.

So, now you have your subwoofer's room response plotted, going through the R-DES, but without any EQ correction.

Then what I did was right-click on the first default curve, and selected "Rename", and I named that curve "Curve 1 Lab Corrected", referring to the correction for a subwoofer in our lab.

Next, I used the rotary dials to in the R-DES program to compensate for the dips and peaks in the uncorrected room response for the subwoofer.

Here is what the curve looked like when I was finished.

Notice that this curve is the "opposite" of the uncorrected room response, so as to result in a flat - or as flat as possible - response when the R-DES curve is applied.

Here is the room response, plotted before (using the Bypass path on the R-DES)and after correction (using memory bank 1, with the Curve 1 Lab Corrected data uploaded to that memory bank on the R-DES box).

In the Bypass mode, the response is highest between 35 Hz and 70 Hz, but rolls off on either side. Application of Curve 1 Lab Corrected data flattened the response to between 20 Hz and 70 Hz. I use a low-pass crossover of 50 Hz, and what I wanted was the flat response between 20 Hz and 50 Hz.

Click Here to Go to Part III.

Copyright 2006 Secrets of Home Theater & High Fidelity

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