15 May 2008

First go at Room EQ

Last week we had a first go at trying to improve the acoustics in my studio. As I stated before my friend Hanz heard some nasty peaks in the low end of the sound. I bought a Behringer FBQ2496 to solve these problems. The FBQ2496 is basically a very precise equalizer. You can set filters to lower the level of the problem frequencies.

We hooked up a Behringer measurement microphone to the fireface 800 on my mastering PC. This was the easiest way since this microphone needs phantom power. After that we downloaded the Room EQ Wizard software from: http://www.hometheatershack.com/roomeq. Surprisingly this software is free to use. And it is widely used by audiophiles and professionals around the world.

After setting up the software and adjusting the right position and input levels for the microphone, we did a couple of measurements. In the picture on the left you see the result. The blue line is the ideal situation, and the red line is the actual situation. As you can see we only focussed on the low end up to 200 Hertz.
As you can see there is a big dip around 100 Hertz and quite a big peek after that. This has to do with room resonances. Also between 40-50 and 80-90 there are some peeks. After measuring the software calculates the filters it has to set to compensate for the peaks. Unfortunately this is the only thing you can fix a bit. The dip is not fixable Hanz explained to me because it is caused by reflections that cancel each other out in the room. If you make them louder they still will cancel each other out and it will have the same result.

In the picture in the right you see some new lines. Again the same blue ideal line but now another light blue line is added. These are the actual filter calculations that the software did. One nice feature of room EQ is that you can transmit these values over midi to the FBQ2496. Unfortunately though this didn't seem to work. So we entered the values manually in the equalizer. Next time we will spend some more time figuring out why the midi transmit didn't work. The red dotted line you see in the picture now is the curve that Room EQ wizard now predicts to be actual in the room. We did not have time to measure again. So we will have another go somewhere in the future. We did do some listening tests with the FBQ2496 running and put it in bypass mode a couple of times and we could hear the difference. It was subtle but the low end definitely got more definition (less muddy). So the technical side works. Now we have to try to improve it a bit more. Off course the best way to solve these problems would be to treat the room with acoustic materials, but that is not going to happen anymore in this studio. I will be starting a very exiting new project that I will tell you about soon :)

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