TL;DR
/ɜ/, /ɛ/ and /ɝ/ are significantly different vowels. /ɜ/ and /ɝ/ are virtually the same vowel sound; both are central, the only notable difference is that the latter is being influenced by a following [ɹ]. /ɛ/ is a front vowel i.e. the highest point of the tongue is positioned relatively in front in the mouth.
Explanation
Vowels vary enormously from speaker to speaker. Also, different dictionaries use different systems to represent pronunciation; some use IPA, some use other systems.
Here's the vowel chart to begin with:
From Wikipedia
How this chart (vowel quadrilateral) works is explained in detail by Patricia Ashby in Understanding Phonetics:
What the four-sided (‘quadrilateral’) figure shows us is a schematization of two dimensions of tongue movement, demarcating the boundaries of the vowel articulatory space within the oral cavity. The slanted left-hand line marks vertical displacement of the front of the tongue, showing us different degrees of open approximation. The top line, which we call close (as in ‘near to’), represents a position just wider than the degree of stricture required to generate friction. The jaw aperture is narrow and to reach this height, close, the front of the tongue is bunched up in the sort of position that also associates with the approximant consonant [j] (much like the sound at the beginning of English yet).
(p87)
In a nutshell, there are two main types of vowels based on the openness of the mouth:
- Open vowel: as the name indicates, the mouth is open and the tongue is positioned far from the roof of the mouth e.g. [a ɑ] (as in ᴛʀᴀᴘ and ᴘᴀʟᴍ, respectively)
- Close/high vowel: the tongue is positioned close to the roof of the mouth (but not creating any constriction because there's no constriction in vowels) e.g. [i u] (as in ꜰʟᴇᴇᴄᴇ and ɢᴏᴏsᴇ, respectively)
- Other vowels such as near-close, close-mid, mid, open-mid, near-open etc., lie in between open and close vowels.
The horizontal lines represent another feature of vowels called 'vowel backness'. It means whether the highest part of the tongue is positioned in the front or the back of the mouth. The same book (Understanding Phonetics) says that: "Vowels are made well back in the vocal tract, using only the body of the tongue – the front, centre and back. In terms of place of articulation, therefore, they are located between palatal and velar" (p84). On the basis of backness, vowels are primarily divided into three main categories:
- Front vowel: the highest part of the tongue is located relatively in front in the mouth e.g. [i e æ ɛ]
- Back vowel: the highest part of the tongue is position relatively back in the mouth as in [u ɑ ɔ ʌ]
- Central vowel: the tongue is positioned halfway between front vowels and back vowels as in [ɜ ə ɐ]
There's another feature called vowel roundedness which means whether or not the lips are rounded during vowel production. In the chart, some vowels occur in pairs such as [i, y], [ɨ, ʉ], [ɛ, œ] etc., the ones to the right side are rounded whereas those to the left side are unrounded.
Here are some transcriptions for scary from dictionaries that use IPA:
- Scary → /ˈskɛːri/, /ˈskɛəri/, /skɛri/
it can either be pronounced with a long vowel /ɛː/ or a short one /ɛ/ (the only difference is 'vowel length', not 'vowel quality'), or even with a diphthong /ɛə/ (it involves a change of position of the tongue i.e. from /ɛ/ to /ə/). /ɛ/ is called open-mid, front, unrounded vowel: it's a front and unrounded vowel. In articulating [ɛ], the tongue is positioned one-third of the way from an open vowel [a] to a close vowel [i].
- Scurry → /ˈskʌri/, /ˈskɝːi/, /ˈskɜr.i/
Scurry, on the other hand, can be pronounced with /ʌ/, /ɜ/ or /ɝ/, depending on the variety of English:
- the one with /ʌ/ is mostly used in British English
- the one with /ɜ/ can also be found in British English and in some American accents
- the one with /ɝ/ is only found in rhotic accents such as General American
There's a significant acoustic difference between /ʌ/, /ɜ/ and /ɝ/:
- /ʌ/ vs. /ɜ/: The difference between /ʌ/ and /ɜ/ is 'vowel openness' in English; /ʌ/ is a bit more open than /ɜ/. In English, /ʌ/ is usually centralised. Another distinction is that /ʌ/ is usually shorter in length than /ɜ/.
- /ɜ/ vs. /ɝ/: /ɝ/ is called a 'rhotacised' vowel and is mostly found in rhotic accents such as General American. As explained in A course in phonetics by Ladefoged and Johnson, /ɝ/ "does not fit on the chart because it can't be described simply in terms of high-low, front-back and rounded-unrounded"; it is an r-coloured or a rhotacised vowel. It involves another feature known as 'rhotacisation'. As Ladefoged and Johnson explain: "rhotacization describes an auditory property, the r-coloring, of a vowel". Rhotacisation occurs when certain vowels are followed by [ɹ]. R-coloured vowels can be articulated in two distinct ways, depending on the speaker [also from A course in phonetics by Ladefoged and Johnson (p94)]:
- Some speakers have the tip of the tongue raised, as in a retroflex consonant
- Others keep the tip down and produce a high bunched tongue position
Here's a clear illustration of both from A course in phonetics by Ladefoged and Johnson:
[the encircling is not a part of the original illustration, it's mine]
Notes
- Don't confuse /ɜ/ and /ɛ/; /ɜ/ is the vowel in 'bird', and /ɛ/ in 'bed'
- The vowel /ʌ/ is the vowel in CUT, TUT, STRUT, HUT, SHUT etc.
- The rhotacised vowel /ɝ/ is only found in rhotic accents of English (chiefly American).
- The rhotacised vowel /ɝ/ is just a vowel, having been strongly influenced by a following R, just like nasalised vowels. Non-rhotic accents such as Southern Standard British English don't have rhotacised vowels.
- The difference between /ˈskɝːi/ and /ˈskɜr.i/ is that the vowel in the former has a rhotacised vowel i.e. it's a vowel, having been controlled by a following [ɹ] while the vowel in the latter is a central vowel followed by a consonant [ɹ].
