What would happen if I took a 1" exit compression driver...

[freddi]

gittin' there! - how would it sound at this point with EQ?

 

[kenpeter]

Now that plot seems well within reason to be equalized flat...
You may need lots of treble boost, since you havn't the usual
narrowing dispersion pattern.

 

[kenpeter]

Here was mine...
http://www.diyaudio.com/forums/multi-way/153831-styrofoam-smith-horn.html

 

[Patrick Bateman]

Denim insulation around top and bottom edge, not very neatly applied:

A dip at 4800hz is indicative of a reflection about 0.7" from the diaphragm. Basically the sound is traveling 0.7", hitting something, then being reflected back into the diaphragm out of phase.

Would it be possible to see if there's something in the way? Or is it simply a reflection off of the radial baffle?

If it's the latter, you might stick a little cone of wood into the throat of the compression driver to scatter the reflection.

 

[dumptruck]

Well, that feature is the only one that vanishes if you remove the top circle and moves with the distance to the top circle, so I think that makes it pretty certain it's the latter? I suppose if I were using a bolt-on driver instead of one with the threaded part...

 

[Pano]

The Denim seems to have worked a treat. Ultratouch brand? I was going to suggest felt, but this seems to work well.

 

[dumptruck]

Yep, I've got two big garbage bags of it. It is really handy for any time "what if there was a lot absorption here?" comes up.