Phonetic differences between ɑ and ɒ in English and American pronunciation standards

Question

First, I should state I'm a native U.K. English speaker from the West Midlands.

With 44 Phonemes present in English, I'm having trouble deciding when I should use ɑ and ɒ, from this website we can an example for ɑ with father. Both American and British pronounce this the same I believe.

But on Collins dictionary, for which I am referring to, as they have IPA phonetic representations for both British and American English, the following words follow a similar trend (I could give more but you will get the idea):

1. honest
2. gone
3. robot
4. hot
5. body
6. lot

The trend, is that in all cases, the British IPA would use ɒ, while American would use ɑ. Now from my perspective, this is correct, Americans tend to elongate and turn it into more of an "aw" sound, while British English tends to keep it sharper.

BUT, my problem is that I would like to find examples of words where the British and American IPA of a word, both contain the same ɑ, OR the same ɒ, so I can note the differences between two different speakers, if any.

I was quick to come to the conclusion that they are equal because the British always use ɒ, while Americans always use ɑ, but the entry of father disproves this conclusion.

So how can I find words like father, where both American and British IPA representations use the discussed IPA symbols, and what is the true difference between the two discussed IPA symbols?

Phonetic questions are inherently difficult to describe, if there is any part unclear, please let me know and I will do the appropriate edits.

Answer 1

The most common transcription systems for the most commonly transcribed American English accents don't use the symbol /ɒ/ at all. In its place, you will often see /ɑ/ (as you have found), or in certain contexts /ɔ/, or possibly /o/ (only in the sequence /or/).

The set of words where the sound /ɑ/ occurs in both accents is a bit problematic. The largest, most stable category would be words with /ɑr/ in American English, and /ɑː/ or /ɑːr/ in British English. For example: star or starry. The American English sound actually could be analyzed as a rhotic vowel phoneme /ɑ˞/, although I usually see it transcribed as a vowel-consonant sequence.

There is also a fairly small, heterogeneous class of words where /ɑ(ː)/ occurs in both British English and American English without a following /r/ sound. Some of these words have an unstable vowel quality, though: for example, even though father has the sound /ɑ/ in "RP" British English, it may have other qualities in other British dialects. The linguist John Wells chose the word palm to exemplify this class of words, but this turned out to be a somewhat unfortunate choice because this is another word with a fairly unstable vowel quality: many American English speakers use /ɔ/ (with or without a following /l/) here, and there is some evidence that this might be traced back to historical variation between different British English accents. I think the clearest/stablest examples of words in this class are monosyllables borrowed from other languages that end in the letter "a": bra, spa, and the note names fa and la.