That Japanese science thing is very similar to what I have heard from years ago and what Duke has talked about as well.
Image focus comes almost entirely from the direct sound. Reflected sound affects this differently depending on the amount of delay. Within a window of about 3-5ms it is too close in time and imaging suffers. Sound travels about 1ft/ms. This is where the advice to place speakers several feet from walls comes from. Beyond about 5ms reflected sounds contribute to a perception of space. This is where the sense of envelopment comes from.
That is of course far from the whole story. That is just one aspect of it. The initial wave front. Really accurate low bass is associated with large spaces and is another factor in envelopment. Then there is the spectrum of direct sound to the reflected, diffuse sound. And more. They all go together.
These are all closely related and similar. There is more difference in the language being used to describe them and from what point of view than anything else.
Image focus comes almost entirely from the direct sound. Reflected sound affects this differently depending on the amount of delay. Within a window of about 3-5ms it is too close in time and imaging suffers. Sound travels about 1ft/ms. This is where the advice to place speakers several feet from walls comes from. Beyond about 5ms reflected sounds contribute to a perception of space. This is where the sense of envelopment comes from.
That is of course far from the whole story. That is just one aspect of it. The initial wave front. Really accurate low bass is associated with large spaces and is another factor in envelopment. Then there is the spectrum of direct sound to the reflected, diffuse sound. And more. They all go together.
These are all closely related and similar. There is more difference in the language being used to describe them and from what point of view than anything else.