My next challenge on YouTube will be to present the central vowels. The difficulty is that not everyone agrees on what the central vowels are. I see four points that I must address:
1) /ɑ/ vs. /ɔ/
I’ve already explained to viewers in my video on back vowels that not all native speakers in the U.S. distinguish /ɑ/ from /ɔ/. I, for one, usually pronounce cot and caught the same way. However, my vowel sounds in cot and jaw are different. I’ve also noticed that when I’m using careful speech, I tend to make a difference between /ɑ/ and /ɔ/, but when I’m speaking fast and informally, I do this less. Am I the only one? If models are possible to give, I think students should hear the two distinct vowel sounds. One way is to use online recordings, such as those provided by The University of Iowa: Phonetics: The Sounds of English and Spanish. Most important for students to understand is that variations of /ɑ/ vs. /ɔ/ exist in North American English.
2) /ɑ/ – Central or Back Vowel?
Some sources, such as Rebecca Dauer’s Accurate English and the University of Washington’s Phonetics Resources, list this phoneme as a back vowel. Others, like Linda Lane’s Focus on Pronunciation, present the phoneme as a central vowel. The two views likely stem from the fact that variations in production exist. How you classify this sound depends on how you say it. Simply put, if the tongue is pushed backward, then it’s a back vowel. If the position is forward enough to differ from the position needed for /u, ʊ, oʊ/, then it can be grouped among the central vowels. Agreed?
3) /ʌ/ vs. /ə/
Is there a difference? Dauer and Lane agree there isn’t. The University of Washington states there is. I only see a difference in stressed versus unstressed sounds. If two separate symbols are needed for this, however, then we’d also have to create more symbols to deal such differences as the stressed /i/ in feed versus the unstressed /i/ in friendly, the “ee” being louder and longer than the “y”. I read that some actually use different tongue positions for /ʌ/ and /ə/, but since I don’t, my choice will be to present only /ə/.
4) /ɚ/ vs. /r/
Both Linda Lane and the camp at the University of Washington do not list /ɚ/ as a vowel. They address vowels followed by /r/ separately. In contrast, Rebecca Dauer in her book along with Gerald Kelly in his How to Teach Pronunciation not only include the “er” in “her” as a vowel, but also use two phonetic symbols to show its joining with a second vowel sound, which is much like the production of diphthongs. Kelly, in fact, lists the vowel sound in fear as a diphthong: /fɪə/. (He uses /ɜː/ for the “er” alone.) Dauer sticks with the label “vowels followed by <r>”, but follows the same practice with her symbols (fear = /fiɚ/). I find the use of two symbols helpful and think it’s helpful for students to view /ɚ/ (or /ɜː/) as a vowel and /r/ as a consonant.
 Dauer, Rebecca M. Accurate English: A Complete Course in Pronunciation. Prentice Hall Regents, 1993.
 Lane, Linda. Focus on Pronunciation: Principles and Practice for Effective Communication. Longman, 1993.
 Kelly, Gerald. How to Teach Pronunciation. Longman, 2000.