This [ʊ] sound is the vowel sound for words like hook, pull, and good. When I began to learn English a bit more seriously two decades ago, I used a book that taught me to pronounce it shorter and more relaxed than the long sound of [u], the vowel sound in words like pool, food, and cool. It also told me to round my lips too.
My pronunciation is fine (I hope, at least people around me seem to understand me perfectly), however I found a strange tendency in recent years, especially from Americans. (I can watch them on TV and video clips.) Many of them seem to not round their lips when pronouncing this [ʊ] sound.
The first time I noticed this was the time I heard an ESL teacher pronounced it with the [ɯ] sound (she is not a native English speaker, by the way). There is no [ɯ] sound in English, but there is one in Thai language. The [ɯ] sound, though being a close-back vowel, is always unrounded. So it sounds very strange to me at first, since [ʊ] is a near-back-near-close vowel, and I thought it is supposed to be rounded.
Wonder why she pronounced it that way, I started to watch native speakers on TV closely, and found that only some of them pronounce [ʊ] unrounded in normal speech. Most of them seem to round their lips a little (how much the little is little is another matter). But when they exaggerate the word, most of them don't round their lips, e.g., I saw one judge on a vocal-focused reality show exclaimed Good! for maybe three seconds long, and in that entire three seconds there was no lips rounding at all!
I consulted Wikipedia, and found that the matter of this rounding is unclear:
"Its vowel roundedness is generally rounded, which means that the lips are rounded to a greater or lesser degree, but is sometimes rather ambiguous. Because no language is known to contrast rounding with this place of articulation, the IPA has not created separate symbols to show this."
So which pronunciation is standard for the [ʊ] sound? Rounded or unrounded?
Best Answer
Certainly there is some rounding, but because roundedness is not phonemic in this position, there is also considerable variation in how much of it actually occurs in any given word and speaker.
For example, you will find that it is generally somewhat more rounded in pull and full than it is in put and foot respectively. That’s because having an r or an l right next to it rounds it off a bit — which is why it is a bit more rounded in root and rook than it is foot or cook. Same with rookie versus cookie, where the first version is a bit more rounded than the second. And of course, a w helps: compare how wool is even more rounded than full, and also moreso that wood.
I believe English has no words with [ʊw], as that seems redundant. However, it can occur in phrases, especially in some dialects, where something like I knew it full-well may approach that.
However, it is still perceived as the very same phoneme in all those words and cases I’ve just listed above.
Correction — or not
I said that I thought English had no words with [ʊw] in them. And at the end of the day, I still believe that. However, I have discovered that grepping the OED yields the apparent existence-proof counterexample of Rauwiloid, which means:
You also have compound words whose first element ends in [aʊ] (rather than [aw], as it is sometimes spelled) connecting to something that begins with [w], and which have in effect a “double w” in them, you expand the list to include such things as:
Finally, if you consider the sound in words like no and micro to be an [oʊ] diphthong rather than [ow], then you get all these, most of which were originally compounds of some sort:
For example, yeowoman theoretically yields /ˈjoʊwʊmən/, at least in North America. Still, there is a reasonably convincing argument to be made that that one is better written as simply /ˈjowʊmən/.
Slightly less uncommon is nowise, which is a compound of one word ending in a diphthong connected to another starting with a triphthong, so /ˈnoʊˌwaɪz/.
But I am still highly dubious of the existence of [ʊw], because I think it fuses into the semi-consonantal glide, [w]. After all, nowise and no eyes are homophonic, so I think this idea of [ʊw] is very hard to justify, and so I stand by my initial statement.
Even towel is usually pronounced with just one syllable, /taʊl/, thereby rhyming with cowl /kaʊl/. Even with folks who work very hard to put two syllables into that, with /ˈtaʊ.wəl/, I submit that you could write that /ˈtawːəl/ and avoid the whole controversy of whether a semi-vowel/semi-consonant/off-glide is really /ʊ/ or really /w/. However you write it, it seems like the same sound to me, such that bisyllabic towel just has a geminate [w]: /ˈtaw.wəl/.