An Introductory Guide to Subwoofers 
Using the Behringer Feedback Destroyer 
A tutorial with the freeware program Room EQ Wizard
This page is under construction
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Using Room EQ Wizard to make measurements requires a computer with a full duplex sound card (these can both record and playback at the same time). If you're using a laptop that only has a microphone input, you need a USB soundcard. The lowest cost USB sound card is the USB SoundBlaster MP3+ External Soundcard. 

This combined with the RS SPL meter becomes one of the lowest cost measurement systems available.

For information about the equipment needed to use a measurement microphone with Room EQ Wizard or other software based measurement systems click HERE
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Room EQ wizard, (REQW) is designed to be used to take measurements, generate plots and then model the response of various EQ filter settings using the BFD. Doing that requires quite a bit of test equipment and the knowledge to use it. (Don't worry we'll get into that later).

What's interesting is that REQW can also be used as a tool to model the effects of the filters using only the measurement numbers from your RS SPL meter testing. 

Also one can simply 'invent' a plot using a .txt file, then use REQW to see the effects filters would have on those abstract plots. This is how the 'example' filter plots (shown on the Understanding EQ and Equalizers page) were generated.

The only short coming to REQW is that it doesn't not allow one to overlay multiple plots.
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To make either a real or invented plot you need to make a WordPad .txt file that contains the frequency and the SPL separated by a comma.

For example......

16,85
18,84.4
20,85.3
22,85.3
25,87.7
28,84.7
31.5,78.5
36,84.1
40,84.4
45,81.1
50,77.7
56,61
63,72.2
80,78.2
89,75
100,78.2
111,75

Give this file an appropriate name such as ListeningPostion.txt or NearfieldTest.txt 

Now save the file to a folder named RoomEQtesting or something similar. 
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1) Open the Room EQ Wizard program. Toward the lower right side you'll see tab with the names of the different speakers used in a surround sound system. Click on the 'Sub' tab. 

2) Next click on 'File' at the top left hand corner and click on 'Import Measured Data'. A dialog box will open asking "Which loudspeaker was the data measured from"? And you'll see 'Sub' in the box. Click on 'Ok'.

3) Chose the 'Files to be imported" option and box will open. Go to the folder where you saved your .txt file and click on the name of the .txt file to load your data.  

4) A dialog box will open asking of you want to reverse the effects of the RS meter's "C" weighting. Click 'Yes' if you wan to do that.

5) The program will load your data. 
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NOTE: Room EQ Wizard has the ability to utilize calibration files. If you're using the RS meter download the .cal file HERE. If you're using the Behringer ECM8000 mic download the .cal file HERE.
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This is a screen shot of the data in my example above. I chose this example specifically because it will be very problematic to fix.

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Just to get started and understand a bit about the program, clink on the "Find Peaks" button, then click on the "Assign Filters" button
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Now go down to the lower right quadrant where the text says  DSP1124P. You'll see a column of 12 'Controls' in the default mode all say "auto". 

Click on the arrow beside on box then chose the "Manual" setting. 

Beside 'Control', click on the arrow next to the "None" box and choose "PA". When this is done filter setting will open. 

To find a specific frequency on your plot place the curser on the spot and click. A blue line will appear, at the bottom of the line you'll see the exact frequency where you placed the curser.

In the example below you can see the null is centered at 56.02Hz

Now this is a deep room null so correcting it will be problematic. The best solution is to cut the frequencies around it.
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Choosing a filter centered at 94Hz with a bandwidth of 11/60 and -11dB of cut provides the new plot you seen in the screenshot below.

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