This is an iPhone app from Studio Six Digital called AudioTools. It's actually a very powerful tool with a ton of options that I've barely scratched the surface of.
These apps were previously just play toys, but this thing is legit. Used to be that the internal mics were just "guessing" below ~ 250hz and there were large differences from one mic to the next. But Studio Six has figured out how to bypass the phone's internal processing and/or filters to bring us a pretty awesome suite of tools.
Anyway, I decided to put it up against the Dayton EMM-6 using Room EQ Wizard (REW). This is a very popular DIY combo for the SQ crowd. The mic has been calibrated. My phone is utilizing the default calibration (meaning, I didn't do shit).
Top pic is the Dayton+REW (laptop based). Bottom is the $20 app on my iPhone6 using the internal mic. Both in 1/12 octave.
If you're not seeing much difference... that's the point I'm trying to make. And the only anomaly I can really see is the peak ~ 4khz on mine. And that very well may be the difference between FFT and RTA or a resonance between my headrest and the phone case.
Either way... we all know RTA is only part of the story, but it's a great way to *see* what you're hearing and I highly recommend this app to anyone who gives a shit what their system sounds like.
Also... here's the stock system in the Fiesta. Suck it.