xkcd

Thank you for reminding me of this channel, I'd forgotten about it.

Interesting about the merging. Schwa has always been weird for me because in my dialect it can be many sounds. I grew up saying "obstruction" as [ʌbstɹʌkʃɪn] like those around me. Then I hit grade school and was told by a straight-faced teacher that both the first and last syllables in this and similar words were schwas while pronouncing them differently :)

The point about stress is interesting. I've been playing with pronouncing the phrase, and almost everything tends toward [ɐ] when I speak the syllables one at a time, even the ones I marked with and pronounce as a schwa in normal speech. The notable exceptions are the final schwas in "obstruction" and "onions", which tend toward [ɪ], and the -nel of "tunnel", which is something like [nɫ] (vocalic ɫ) ~ [nəɫ].