"You mentioned using a calibrated RTA, but both screenshots say differently. "
That is because I used a different RTA. My original measurements were done with an Audio Control SA-3051 which is a calibrated RTA/mic combo. The TrueAudio makes it easier to post pics online and can also do a lot finer measurements then the 1/3 octave AC.
"comparative results are the best you can expect"
Which is what I was going for here. The mic is the mic/pre-amp combo from ETF Acoustics.
"Unless your soundcard requires otherwise, you'll get the best results with in/out set to the same sampling rate, too. "
I was not using the TrueAudio noise. I was using the built in pink noise generator from the Audio Control and feeding the 288 directly.
"If so, the results can be really bad, as few even have a hard sound card. For remote stuff, I use an external (Extigy), and with it, get good enough results with slow sampling."
I am using an external SB sound card as the built in sound card had far too high of a noise floor to get anything useful from it.
"It's pretty unlikely your 30-pound driver is ringing, but after you get calibrated,"
It isn't the whole driver that would be ringing, it would be the diaphragm that rings. That is a fairly common trait of metal cone drivers... probably isn't a big stretch that diaphragms may do that too. I checked the noise source into my FFT (Spectral Dynamics SD-380) last night and it certainly didn't have any boost at 25kHz like that.
"verify the protective screen has no loose threads, and that the phase plug isn't loose. Same for loading cap, terminals, etc. Coil rubs from poor centering or over-tightened screws are usually very audible (read; nasty!). I found a "floating" tangerine once, but that too, is rare. "
I don't think any of that is an issue. You will note that the bad diaphragm (in another 288) is also showing the spike at 25kHz... just at a lower level.
Shawn
