How is the pronunciation of r before th? Specific case: "north"
Some consonants such as n,d,t are usually alveolar in English, except that they are replaced by dentals when they are before dental fricatives (th): tenth, said this, in the….
What about "r" before "th"?
- Arthur: BrE /ɑ:θəʳ/, AmE /ɑ:rθɚ/
- north: /nɔ:θ/, AmE /nɔ:rθ/ ; northern
My conjectures are:
- a or o are lowered in the mouth so that we have /ɑ/ or /ɔ/.
- the mouth becomes less tensed
- the r is very loose
- n in north becomes dental!
The point of constriction in retroflex consonants per se tends to be alveolar/postalveolar. I'm afraid I don't know of any actual data off hand, but I dare say it would not be surprising to find that the point of articulation of /r/ is very slightly fronted before dental consonants (but still within the alveolar region).
On the other hand, while I guess physiologically possible, I think it would be hugely unusual for the articulation of a retroflex to be so far fronted as to warrant being called "dental". On the other hand, I believe some languages such as Hindi-Urdu have retroflex and dental /r/ sounds contrasting with one antoher.
(And I would be very keen to stand corrected if anybody knows otherwise.)
P.S. You might want to listen to how speakers pronounce "for the" in the sample recordings in the Speech Accent Archive (the link is to one speaker, but several have been recorded).
Let me take your conjectures one at a time:
- a or o are lowered in the mouth so that we have /ɑ/ or /ɔ/.
This may be true, but I suspect that it's subject to quite a lot of dialectal variation and varies wildly depending on the other surrounding segments. All English dialects neutralize some contrasts before /r/, but the exact number and nature of the mergers vary a lot.
In my idiolect, the primary difference in articulation before /r/ is actually monophthongization. Taking the gnome/norm minimal pair, gnome has a diphthong which is approximately [əʊ], while norm has a monophthongal [o:].
- the mouth becomes less tensed
I'm not sure what you mean by this. Less tense compared to what?
- the r is very loose
"Loose" is too vague for me to comment on. The /r/ clearly does not become dental. In rapid speech, the /r/ may become very brief, to the point that its presence is largely marked by the preceding vowel allophone.
- n in north becomes dental!
This definitely does not happen. Dental/alveolar place agreement never intervenes across vowels.
Apparently there are 2 common articulations of /r/ in American English, one retroflex, and the other dorsal. For me (AmE speaker), /r/ is dorsal, not coronal, so there's no such assimilation. This phone is called the molar or bunched r. It can be described roughly as a back-palatal or pre-velar approximant that's somewhat bunched up along the left-right axis. Approximate transcription: [ˈnoʉ̯˞θ]. John Laver transcribed this sound using the symbol [ψ].
For speakers that use the retroflex articulation, it's possible to slide from a retroflex [ɻ] through [ɹ] to [θ] in one smooth motion, so I don't expect any special assimilation of /r/ other than this.
I do assimilate /n/ to interdental when it immediately precedes /θ/ or /ð/. However, the /n/ in north is separated from the /θ/ by two segments, during both of which the tongue's corona retracts from the alveolar ridge; there's no reason at all for it to assimilate. (During articulation of [oψ] I think the tip of my tongue is below the alveolar ridge away from the teeth, roughly at the level of the lower teeth.) I see no difference between either the /n/ or /r/ in north vs. Norse.
About the pronunciation of /ɔ(w)/ in north, or in gnome vs. norm: I exhibit the same monophthongization of /ɔw/ to [o] as JSBձոգչ noted. Alternatively you can think of the /r/ as a semivowel that replaces the /w/-offglide of /ɔw/. Also the initial vowel in the resulting diphthong [oψ] (as in norm [noψm]) is distinctly raised, not lowered, and also more rounded, relative to /ɔw/ (as in gnome [nɔʊm]). In Arthur, the vowel /a/ doesn't seem to be changed by the following /r/.
In my dialect (fairly generic AmE), your premise is not true. There is no difference in the pronunciation or the articulation of the 'n' between "tense" and "tenth".
Likewise, there is no difference in the pronunciation or articulation of the 'r' between "normal" and "north".