Too many central vowels?

[Das Baron]

Potential vowel inventory:
[a e i o u]
[ɛ ɪ ɔ ʊ]
[ɨ ɪ̈ ɘ ɜ]

Having never used central vowels much in my conlangs, does this vowel inventory have an unrealistic number of them?

[Whimemsz]

No. It's kind of an odd selection of central vowels, though.

[Bob Johnson]

Let's reorganize a bit
Front: iɪeɛ
Cent: ɨɪ̈ɘɜ
Back: uʊoɔ
and /a/ goes somewhere.

A bit Englishy with all the ɪʊ business but it doesn't seem horribly imbalanced. You could probably make a case for it being real enough. The biggest problem I can see is the /ɪ̈/ and keeping a contrast with it and its 4 neighbors. Maybe spread it out a bit more to /ɨ ɘ ɜ ä/ in the center and have /a/ be very front. (Not very back; more back than front is impossible/very rare)

Also → C&CQ

[Rui]

@Bob: notice how Das Baron actually has them all in brackets, not slashes. I wonder if that was intentional?

[Wattmann]

I'll say that the point of having too many central vowels is when you cannot readily distinguish between them.
If you cannot make a difference between, say, /mɨˤkə/ and /mɘˤkə/, you'll probably interchangeably use "feces" and "candy" inside the language itself

[alice]

Swedish seems to manage fine with several central vowels, although one of our resident Swedes should really confirm or deny this.

[Skomakar'n]

And most of us don't even have a schwa.

[zompist]

Potential vowel inventory:
[a e i o u]
[ɛ ɪ ɔ ʊ]
[ɨ ɪ̈ ɘ ɜ]

The number, no. [ɪ ɪ̈ ɨ] seem awfully close together though.

(Also, if the grouping implies that [ɛ ɔ] are laxed, that's rather Englishy.)

[spats]

Potential vowel inventory:
[a e i o u]
[ɛ ɪ ɔ ʊ]
[ɨ ɪ̈ ɘ ɜ]

Having never used central vowels much in my conlangs, does this vowel inventory have an unrealistic number of them?

I think this is close to fine. It seems Germanic to me. Are there tense/lax or short/long pairs?

For example, if you grouped them thusly:

/i/ /ɪ/
/e/ /ɛ/
/a/
/o/ /ɔ/
/u/ /ʊ/
/ɨ/ /ɪ̈/
/ɘ/ /ɜ/

Then you'd effectively have German but with central instead of front rounded vowels. Adding a length, closed/open syllable, or tenseness distinction would help differentiate the series.

Another arrangement that's similar would be:

/i/ /ɪ/
/e/ /ɛ/
/a/ /ɐ/ (instead of /ɜ/)
/o/ /ɔ/
/u/ /ʊ/
/ɨ/ /ɪ̈/
/ə/ (instead of /ɘ/, unstressed syllables only)

If you're going for all monophthongs of the same length, then I think you're not likely to get much more complex than:

/i e ɛ a ɔ o u ɨ ɘ ɜ/

Most languages that I've seen that have the lax high vowels are the results of length/stress distinctions rather than part of the basic arrangement of vowels.