Hi Everyone. This is my first, and likely third to last post. (I can only think of two other things I might want to say at some point, unless it turns out I want to clarify something that I did not communicate well the first time.)
An interesting area for study. For the experiment suggested above, I would also suggest adding a variety of other sounds to the list. If they all give the same effect as the suggested "O-O-O-O-Oh" it would tend towards a different conclusion than if there are a variety of effects or degrees of the effect. How about vowel sounds in general as apposed to consonants or mixing the two in different ways, etc.
Terry Dobson used to talk about various exercises in sound while practicing under O Sensei. I don't recall him talking about it at Bond Street but he probably did. At that time, Sensei Paul Kang of Bond Street specified various particular sounds to be made with various specific movements and different sounds on attack versus defense. Sensei Kang is not one to volunteer much spiritual advice beyond "continue to practice" so I never got much explanation from him about the why and wherefore of it.
Terry Dobson on the other hand, did a fair amount of "preaching". At SUNY Purchase, he talked about this a fair amount, but did not give much direction in terms of specific sounds. None the less, we used to practice on our own some exercises he described as given to him by O Sensei.:
1) Practicing KiAi while sitting in seiza in front of a bucket of water. The idea is to make the surface of the water ripple without straining your voice.
2) A variation I made up at the time and worked for me. On overcast days in an open field - shout up towards the sky in as relaxed a manner as possible, with proper breathing. When you get the right sound, coming from the right place in your body, you get a ringing echo back from the sky. This one can fill your whole body with energy and make the world look bright. I believe it works as a kind of purification.
3) Various singing like sounds, with a relaxed throat carried through the full movement of a technique.