Reduction of Choilam

This past Shabbos, I davened in Rabbi Shapiro's shul and noticed that the baal shacharit pronounced all his cholams as /oy/. Which is Oykay by me. But then I noticed that he pronounced some of his cholams as /o/. For example, he said ledor vador and be`or panecha.

I came up with a few incorrect hypotheses to attempt to explain this - perhaps early on he pronounced these words as cholam rather than choilam, they go reduced to kamatz (which was about how he was pronouncing them), which now prevented realization of them as choilam.

But then Rabbi Shapiro davened mussaf, and I noticed that he did exactly the same thing, in the same places. (In fact, the baal shacharit was a grandson of Rabbi Shapiro.) And the kid who sang Adoin Oilam did the same. So, it is not an error so much as a consistent pattern.

The answer seems to be that there is a phonological reduction of choilam to cholam where it is followed by resh in a closed syllable. (A closed syllable is one that ends with a consonant.) Why? Well, try saying be`oir or ledoir. Based on the configuration of the mouth for each sound, there is an automatic sheva insertion to allow pronunciation of the resh. Thus, it would have to be pronounced le-doy-er and be-oy-er. With conscious effort, one can avoid this, but otherwise, it is automatic. This is somewhat like patach ganuv in Hebrew, where a final chet or ayin is introduced by a leading patach. (Or the diphthong ay as in the English word "mile," which most people I know pronounce as one syllable, but which Dr. Suess clearly pronounced as one, as you can see by his meter.)

The alternative to insertion of shwa, which is in effect transforms the syllable into two syllables,
one can reduced the diphthong-ness of the diphthong, thus changing the choilam into a cholam.

This appeared to be true only in closed syllables, but in open syllables, the resh could begin the next syllable and so their was no reduction. Thus, be-or (which is closed), but oirois (where the first oi is open, and the resh begins the next syllable.)

I noticed the Rabbi Shapiro had similar reduction, though not total reduction, in the presence of other closing consonants. Something to pay attention to in the future (besides of course for the semantic meaning of the words ;) .