Mouth hole shape?

[cokekola]

I found following explanation of different mouth hole sizes and shapes on the page http://www.markshep.com/flute/Finding.html :

"The two basic shapes used for the mouth hole are the oval and the rounded rectangle; either one is acceptable. The size of the mouth hole, however, should not vary too much from the average. A large mouth hole will favor the low notes at the expense of the high, while a small mouth hole will favor the high notes at the expense of the low."

The difference of different mouth hole size sounds trivial. But there is no explanation of the effect of the mouth hole shape. Are there some significant differences in embouchure with rounded rectangular and oval mouth holes?

[fluteguy18]

From what I've heard a rounded embouchure hole produces a consistent sound whereas a rectangular hole allows for a wider array of tone colors. I don't know if that's true. I have however come to favor rectangular holes more and more as I've started experimenting with tone color.

[Zevang]

I have the same opinion of Fluteguy. Though I must add that the real secrets behind mouth hole design and its effects in our individual sound did not reside in the visible part of it, that is if its shape is rounded or rectangular, but instead it is mostly a function of the way the makers work at the "undercut". This is covered by a mist that is passed generation after generation of flute makers and supposedly is never made public nor widely known for obvious reasons.

Maybe that's the reason we have so much written about this or that cut, material or shape. There are always many words, rather confusing, to describe what you will get from a type of headjoint or flute. In my opinion, this is such an individual matter that only when you actually experiment and/or practice with a particular type of instrument you are able to certify yourself about any allegation about this or that quality or characteristic of a given design.