What's the average directivity range of a typical 6" cone?

[bzfcocon]

That is completely wrong. RT does not depend on directivity but the rise of the reverberation field will. While it is true that the build up and decay in terms of individual reflections are the same, the initial conditions are completely different and as such the results will be completely different.

I see it in the same way. D/R ratio at a certain position will depend on two factors:

1. directivity-dependent initial conditions: loudspeaker directivity + very early strong reflections, which govern how much energy is being "pumped" into the room to excite the build-up of the diffuse reverberant field

2. directivity-independent room RT which governs the build up/decay of the diffuse reverberant field

As Earl seems to be advocating using a more directional system in a less well damped room, it isn't clear how that differs from using a normal speaker in a normal room.

David

Griesinger's papers suggest that localization ability is mainly governed by D/R (which, as you pointed out, can be controlled in a number of ways: directivity, listening distance, RT) while spaciousness is predominantly related to RT only.

So, from this perspective, the two situations are different:
- increasing D/R by means of directivity leaves RT alone, while decreasing RT by adding more damping, well, decreases RT...not the same thing.
- adding damping to counter strong early reflections will also reduce room RT, while using a high directivity loudspeaker will not.

I think Earl also suggests that the delay in the build up of reverberant field plays a role. Not sure which tho.

 

[speaker dave]

So, from this perspective, the two situations are different:
- increasing D/R by means of directivity leaves RT alone, while decreasing RT by adding more damping, well, decreases RT...not the same thing.
- adding damping to counter strong early reflections will also reduce room RT, while using a high directivity loudspeaker will not.

I think Earl also suggests that the delay in the build up of reverberant field plays a role. Not sure which tho.

As I mentioned you can deal with the early reflections by damping or by reflectors. I am currently sitting in front of a system where I reduced the first major reflections via 4 simple reflectors. Not only did the first reflection reduce considerably but the impulses response shows some later bounces that have dropped as well. They must have been strong double bounces. The impulse examples are in a post above.

So you don't have to reduce RT if you don't want to.

As a comment on the direct to reflected ratio, my test system lets me directly play with this ratio. The front speakers are fairly close to the listener and fairly directional. Secondary radiators are highly reverberant. Any combination of the two components can be set with independent EQ, plus additional delay for the reverberant component if desired.

I am hearing all the spaciousness addition that you would expect, but it takes a pretty strong amount of reverberant field to get to a significant difference. If the total reverberant curve is lower than the direct curve by more than a few dB then switching it on and off makes no significant difference in spaciousness. (Is virtually inaudible.) If it is equal or a few dB higher than the direct component then it becomes easily obvious.

This suggests that sitting at the critical distance or a little closer (whatever your speaker directivity or room constant) is enough to get the room to minimal contribution. Added spaciousness will required a greater distance than that.

David