Below are some measurements I made in my home theater using my ETF/ECM8000/MobilePre setup. Each time I do a set of measurements I first do a new baseline set (what is shown below) before making changes and measuring the impact of the changes. I also measure at least the six marked positions along the main sofa for the baseline and each change. This takes a little bit of time, but isn’t too bad and provides a lot more information than measuring at a single point only.
The first measurement shows the frequency response at each of the six points along the main sofa starting toward the center of the room and working toward the wall (see www.bradjudy.com/audioblog/2005/08/07/the-room/ for the room diagram).
As you can see, the response holds mostly steady at some frequencies as the measurements move and I suspect this is because the measurements are in a straight line parallel to one set of walls. However, at other frequencies, the response changes significantly along the sofa. The extreme of this change is highlighted in the graph with exact values on the right-hand side.
This is a waterfall graph for one of the middle (sub3) positions fromt he same set of measurements:
And here is a time slice view of the same sub3 measurement. The author of ETF suggests using the time slice graph method over the waterfall for displaying information on decay.
As you can see from these two graphs, there is a significant ‘ringing’ of a room mode around 23.5Hz as well as a smaller one around 32Hz. Fortunately, most of the 10-100Hz frequency range doesn’t exhibit much ringing.
