This PVC Romanian caval has inner diameter 20 mm and Lenghth/bore ratio L/B=74 cm/2 cm=37. Therefore it is in the category (see post 199 or 248 ) of the upper registry flutes and not overtone flutes. In other words it can play with the 1st harmonic the 1st octave decently but the 2nd harmonic it plays easier the 2nd octave.
We remind the reader that in the online notes here we call a sequence of 7 interval that sum-up to 12 semitones a mode and all cyclic permutations of it as the scale that the mode belongs. Thus any cyclic permutation of the 2-1-1-3-1-1-3 is considered again as the parachromatic Byzantine scale but at a different mode of it.
See also the post about the parachromatic Byzantine flute (3rd chromatic Byzantine minor scale) post 235 and post 242 about how to convert a Romanian caval to play both the harmonic minor and double harmonic minor
Other very well known 7-notes Byzantine scales but different from the parachromatic or 3rd Byzantine chromatic minor , also in the chromatic family are the harmonic minor or 1st Byzantine chromatic minor (https://en.wikipedia.org/wiki/Minor_scale#Harmonic_minor_scale ) and double harmonic minor or 2nd Byzantine chromatic minor (https://en.wikipedia.org/wiki/Double_harmonic_scale).This PVC Romanian Caval has a thumb hole and it is also tunable . Normally without the tump hole the 2+3 front holes in Romanian Caval flute with fipple plays the A4-B4-C5-D#5-E5-F5 in semitones 2-1-3-1-1-4 The tump here plays the note G#5 thus all the A4 double harmonic minor scale 2-1-3-1-1-3-1 is playable.
The fipple is from an Irish Low D4 whistle, with rather thin corridor to Blow air and a sound hole of size 15 mm (vertically to the tube) and 7 mm or 10 mm longitudinally.
The size of the lowest 2 holes is only 7 mm which allows the fipple to play also the 1st octave with the 1st harmony quite well and in stable way without being necessary a special buzzing embouchure : A3-B3-C4-D#4-E4-F4-G#4-A4. If the flute would be made from 16.5 inner diameter PVC tube the 1st octave by the 1st harmonic would be playable only with the special buzzing embouchure mm, but the 3rd and 4th harmonic would be payable only by overblowing and without partial opening of the thump hole.
But the sizes of the rest of the 3+1 holes is 10 mm which gives more benefits. The benefits are that the 3rd hole that normally plays D#3 or D#4 can very easily with partial holing play also D3 or D4 thus having the scale A3-B3-C4-D4-E4-F4-G#4-A4 or in semitones 2-1-2-2-1-3-1, which is the A3 harmonic minor. Some caval flute add a hole between the 2nd C4 and the 3rd D#4 to do that, This is necessary only when the holes are small size. With 10 mm size holes this is easily done with partial holing.
Also the thumb hole which is again 10mm size can easily play by partial holing the G4 , thus together with the D3 play the natural minor A3-B3-C4-D4-E4-F4-G4-A4.Because the bore is quite large (20 mm) and the lower holes also large size, the higher overtones require something more than overblowing.
The 2nd overtone requires simply overblowing. But the 3rd and 4th overtones require partial opening of the thumphole to help them.
We see this efficient PVC Romanian caval in A3 with thump hole in the next photos
VERSION OF THE FLUTE IN DOUBLE HARMONIC MINOR WHICH IS CLOSED OR INVARIANT TO THE 3RD OVERTONE
Nevertheless, the 3rd harmonic and on the same holes in such a flute (and on the original 6-notes Romanian Caval too) will not give notes inside the double harmonic minor as it does say in a major mode flute . The double harmonic minor has a mode, the 5th mode which is symmetric to shift higher by an interval of 5th and in interval structure it is 1-3-1-2-1-3-1. Therefore if we open holes for this 5th mode of the double harmonic minor we will get again a flute in double harmonic minor which has the additional advantage that the 3rd overtones on the same holes gives again notes of the same scale.
E.g. if the flute starts again from a, the notes that we should open holes are the
All holes closed gives a4
1st hole open gives a#4
2nd hole open gives c#4
3rd hole open gives d5
4th hole open gives e5
5th hole open gives f5
6th thumb hole gives g#5
This scale is a mode of the d5 double harmonic minor . By partial holing on the 2nd hole and on the 6th hole we may play also the d5 simple harmonic minor and natural d5 minor .
