Hi
While I can’t speak to the new unit (TEF25), I have a 20 and have had a 12, 12 plus and the original TEF 10. If you have already downloaded the latest core updates and such and that didn’t fix it, try running it from a different computer. The only problems I have had were “something” to do with the computer communicating with the TEF.
I guess “IBM compatible” still covers a good deal of ground internally.
When you say “6 degrees of phase error in loop back”, do you mean it shows up at 20KHz? (possibly suggesting a very short time error).
So far as measuring subwoofers, I can make some suggestions so far as using the TEF 20.
You mention you have about 100 feet of open space outdoors, cool.
For A vs B comparisons it doesn’t matter so much but if you want to get real 1 Watt 1 Meter ground plane sensitivity, it is more involved.
You will want to be further than one meter from anything with the size of a subwoofer, in theory, the source is emanating from a hole on the ground (burring an array of subs in a parking lot would be a pain). You want to be far enough away so that the size of the boxes does not introduce too much error.
A distance of 10 meters is –20 dB from 1 meter so far as inverse square law and driving the system with 10 times the “1 Watt” voltage (+ 20 dB over 1 Watt) results in a 1 Watt 1 Meter equivalent.
This is a large enough distance so that the “error” from not doing it properly is insignificant.
While 10 meters makes the math easy, the down side is that all VC drivers begin to show the effects of heating when driven above about 1/6 to 1/10 rated power, depending on the system, 100Watts may be into that region.
Any other distance can be used too but the closer you are to the source, the greater the error is and the further away you are, the larger the reflected sound level.
The latter would not be a concern if you were in a big flat empty field.
Use your “speaker” icon to produce and set the test voltage at 60 HZ, most DVM’s are calibrated at 60 HZ.
Lets say you had a sub with a 40 HZ low cutoff.
In “parameters” set the upper and lower frequency limits (say 20 HZ to 200Hz) and select some small value for sweep time, like 3 seconds or so.
Click “best resolution”
Typically, depending how much detail you want to see, enter a resolution frequency value that is about 1/10 to 1/6 of the corner frequency.
For seeing “everything”. Set the resolution to about 1/10 the low frequency sweep limit.
Remember to keep the upper frequency limit to some reasonable limit, the higher it is, the longer the measurement will take.
Because of the TEF’s increasing resolution with increasing frequency, set the smoothing.
Your ear has about a 1/6 octave critical bandwidth so a smoothing factor of about 16% octave corresponds to what your ears could resolve under the right conditions so use more or less depending.
Also, being a ground plane measurement, you want to place the mic on the ground or really on some scrap of plywood etc.
Hope this helps, have fun.
Tom Danley
Danley Sound Labs