Tweeter positionning ?

Hello !

I'm rather a fullrange disciple, but a friend of mine asked me to design him a fullrange TQWT with a supertweeter.

For info, I will use Supravox 165GMF and Fostex FT17H, but I think it doesn't matter.

I have played with phase adjustment between different speakers and realize that it has a Huuuuuge importance in the reproduction clarity !

I thought it would be better to post this here.

I have heard that the tweeter had to be placed in phase with the main driver. OK, but when I'm not in the axis of the speaker, the waves coming out from the tweeter won't be in phase anymore won't they ??

I have also heard that placing the tweeter the nearest possible from the main driver allowed to have a more coherent source, near from the ideal point source radiation.

But many High-end speakers on the market have the tweeter out of the baffle !! Even Fostex sells their high-end tweeters with a support to put on the top of the enclosure.

On my design, the center of the woofer is at 260mm from the top (10") of the enclosure.

So, my question is : what is the most suitable place in my case to put the tweeter in ? Is it worth not placing it on the vertical axis of the baffle ? Is it worth not placing it in the baffle ?

Thanks !