I have taken a bunch of measurements using a Behringer ECM8000 and the REW software.
It's good to see you back again, Mike!
But you have a problem. A big problem. Your REW data is not valid, because you have a serious mains hum issue. Take a look at your spectrogram:
REW-double-hum.jpg
See those spikes? They never die away, or even change in intensity. They are always there, very powerful, continuous.
See the frequencies? Australia is 50 Hz, and your spikes are at 50, 100, 150, 200 etc Hz. All the way up the spectrum. You can see them crystal clear on the waterfall plots too,
Strangely enough, you somehow managed to get 60 Hz hum in there as well! 60, 120, 180, 240 Hz... all of the harmonics are there. I guess you must be running a dual power system, with both 220V/50Hz and also 110V/60 Hz: Not sure why, but both frequency sets are there.
That hash is absolutely overpowering any acoustic data, so the entire data set is no use.
My guess would be that you either have a faulty mic cable, or you have a faulty mic (it wouldn't be the first time I've heard of an ECM-8000 having a ground fault on it: in fact, it seems to be quite common: Behringer quality control and all that, I guess).
So first you need to identify that problem and get it fixed, then you'll have to re-do your REW tests, but you need to do them right this time. I VERY much doubt that you did your tests 140 dBC, as shown by the graphs
so I'm assuming you did not actually calibrate REW properly with a hand held sound level meter, and you did not set up your system so that each individual speaker produces 80 dBC by itself, which will automatically give you the 86 dBC reference calibration level.
Therefore, after you have found and fixed your massive mains hum problem, calibrate REW using your hand-held sound level meter, then run the tests again. This time, run three tests with the mic positioned precisely in the middle of your head (!), or rather, in the middle of where your head will be when you are mixing, exactly on the room center line, with the tip and exactly 1.2m above the floor, and the mic angled upwards at about 60°. Do one test with just the left speaker, one with just the right speaker, and one with both speakers. Do not adjust anything between tests! Don't even touch the system at all, except to turn of and on the speakers.
Next, your way of looking at the data is not very useful at all: A graph that runs from 2 Hz to 30 kHz and -160 dB to + 180 dB shows you nothing useful about the response of the room. Zilch. You cannot draw any useful conclusions at all from that.
You need to look at the correct parts of the spectrum: First and foremost, 15 Hz to 500 Hz, and 35 dB to 100 dB (assuming you calibrated the system correctly to 86 dB). That will clearly show you how your low end is doing, which is the most critical part of the spectrum. Then you can choose other parts of the spectrum and other ranges.
Your RT60 graph is also pretty useless: You have the range set 1 to 10 seconds, which would be fine if you were measuring the RT-60 time of the space shuttle hanger at NASA, but for a small room you pretty much never need to set the top scale more than 1 second (unless the room is completed untreated, maybe). And while smoothing your RT60 to 1 octave is OK for showing nice flat graphs to impress your friends and neighbors, it does not show you anything useful at all! Set it to 1/3 octave, and 1 second max, range 50 Hz to 10 kHz, to see what the time domain response really looks like.
- Stuart -
