Hi sofus, You're quick to agree with the concept that the tongue and its effect on the oral cavity has no effect on air speed. Try this simple experiment. Take a piece of unused toilet paper (I had to add "unused" so some clown wouldn't ask!!) about a foot long and hold it out from your face about a foot. Now, blow "super softly" into the paper and slowly whistle a scale and notice the effect on the paper as your tongue lessens the oral cavity. Be sure NOT to change the shape of your aperture. Just air and the tongue softly whistling a scale. It should take a few tries before you can get a comfortable conclusion. Then do the same thing but whistle a low long note followed by a long high note and octave higher without changing your aperture. What do you notice?