- Thread Starter
- #241
Did a little experimenting with sweeps and RTA tones for distortion measurement. I'm not sure we can get there from here.
With both I found moving the Umik 1 even a few inches could alter the distortion significantly. Sometimes 20 db for RTA use. Just for instance using a 780 hz tone and RTA several feet from speakers, I could get .134 % 2nd and .454 3rd, move it six inches resulting in 2.55% 2nd and 6.34% 3rd. Going 6 inches further gave a result of .444% 2nd and .874% 3rd. Obviously at least two are wrong for what the speaker is doing and probably all of them. Peaks and dips for standing waves are a problem.
Similar problems though of smaller magnitude with sweep based distortion measures. And whether you get a lower resulting distortion with long, short or medium length sweeps depended upon where in the room you put the microphone. Getting close to the speaker also didn't seem to help.
Or am I doing this all wrong?
Pretty much the same thing happens when you measure frequency response. For that reason I think maybe it would make sense to move mic while doing RTA as it needs to be done when measuring freq response.