Since I had access to this fairly large space on a one time basis I decided to repeat the frequency/magnitude meausrements as done outdoors during the "Day 1" measurements in John's backyard. The space is 40 feet long, 25 feet wide and 20 feet high. The RD 75 was suspended from the ceiling. Bottom of the driver motor was 44" above floor level. The microphone was placed at 80" above floorlevel. Measurements were taken at 1, 2, 3 and 4 meter.
The 3 and 4 meter plots show some FFT artifact ripples since the data interval between impulse and first echo got smaller as distance to the driver increased. Interesting to see how there is "breating" in the curves as distance to the driver increases.
The graphs below belong to a RD75 on a baffle suspended 34" high. Microphone was placed 72 inch high. It is pretty obvious that the baffle is affecting the magnitude over a wide range.
Although the results of these distance measurements correlate better than the earlier meausrements taken outdoors, a repeat in a "really big" space is warranted. All reflection echoes were taken out, but the shorter data window on longer throw distances makes that the accuracy in the low end of the spectrum might be impaired. The data window at 4 meter was only 13 milliseconds anymore, which should be "good" down to 80 Hz. FFT windowing will "eat" in the data however, casting some doubt on the accuracy in the low end of the spectrum.