Ok, I need the 101 basic course here.
This is now a solved problem. Good controlled directivity speakers, with decent output capacity, placed properly.
Can you give some examples or, at least, some specific characteristics of such speakers ?[/QUOTE]
I can try to show which properties affect speech clarity, and then how a speaker affects this.
Speech clarity - in the meaning how easy it is to understand words and sentences - is important in acoustics, for design of auditoriums and such, there are defined standards for acoustic properties of such rooms, standards that defines how to measure and how to interpret and compare what was measured, and how the numbers relate to speech clarity. Decay rate is an important parameter, and this is the one that is important for hifi/home theater reproduction, because frequency range, noise and distortion can be assumed to be within acceptable limits.
Early reflections and too much early energy can be seen as noise that obscures and disturbs the original signal, and this noise makes it more difficult to understand speech. So we want to keep early reflection level below certain limits.
We can look at C50 in REW, from REW description:
"The early to late energy ratio in dB, using sound energy in the first 50 ms as the 'early' part. C50 is most often used as an indicator of speech clarity."
One speaker is like this:
A different speaker in the same room is like this:
And this last speaker in a different room:
So we see that both speakers and room can create different results.
Now, this is a quite lean and crude analysis, if we look at the IR - impulse response, we can see a better imsage of what is going on very early in time. The first speaker:
The other speaker, in the same room:
This other speaker in the other room:
Now we see that the speaker has more influence early in time, compared to the room.
This second speaker has a much better directivity control, which gives a huge reduction in early reflected sound. This again, gives this speaker better speech clarity.
From this one may conclude that the speaker with very narrow radiation is the best. But a speaker with laser-like radiation will not sound nice, and you would need to sit exactly on-axis. So the best radiation pattern is something that covers as much of the room as possible, and at the same time avoids sending sound into boundaries that causes early reflections.