The paper by R. Skarnitzl and J. Volín Reference values of vowel formants for young adult speakers of Standard Czech (Akustické listy, 2012) provides vowel formant values for 75 university-level students (48 females, 27 males).
The figure shows formant fields on the ERB (psychoacoustic) and Hertz (objective) scales. The non-high short and long vowels – /e eː, a aː and o oː/ – manifest almost complete overlap. A qualitative difference in the close front vowels was desribed decades ago, hence the transcription /ɪ/ and /iː/. Our data showed a smaller degree of qualitative difference in the close back vowels, suggesting a sound change in progress – the difference between the short /u/ and the long /uː/ has already exceeded the just noticeable difference.
The following table summarizes rounded values in Hertz for male speakers.
|vowel||F1 (Hz)||F2 (Hz)|