I understand that rhoticity and rhotic are terms
applaied to consonant phones that become an [r] phone
(rhoticity) and to vocalic phones that have added some
[r] like sound. And it seems that articulatorily the English
rhotic vowels are related to a retracted tongue root.
Also i have read that rhotic vowels are acoustically
characterized by a lower third formant, but as i have made some
spectrograms with my own pronunciation of them -for example
pronouncing a rhotic [a´]- the third formant is seen in what
looks more a higher position than a lower...
So my query is that if you know how are vocalic rhotic phones
accoustically defined please let me know.

In another sense i understand that when speaking of consonants
the word "rhotic" is not used, an instead retroflex would be the
proper. If you have any comment on this also would be wellcome.

And the last, if you know a good manual of general phonetics
(i mean by "general" not debvoted to the phonetics of just a
particular language or familly of languages) that you think worthy to
recommend i please to tell me it.

Yours cordially,