AFAIK a short "ä" is always pronounced /ɛ/ in German, but is there a consensus among native German speakers about the pronunciation of a long "ä" ? Different sources say different things about it:
"ä" is always pronounced /ɛ:/, a longer version of the phoneme of the letter "e" in the English word "bed" (US pronunciation in IPA syntax: /bɛd/)
"ä" is always pronounced /e:/, a longer version of the first phoneme of the letter "A" in the English word "April" (US pronunciation in IPA syntax: /ˈeɪ.pɹəl/)
However, the pronunciation I hear in different German words is not consistent with any of those two rules. Example: in http://joycep.myweb.port.ac.uk/pronounce/vowelae.html , "Mädchen" is pronounced /ˈmeːtçən/ , "kläglich" /klɛ:gliç/ , "wählen" /ˈvɛːlən/ and "Währung" /ˈveːʁʊŋ/ . Is it a regional difference?