I did that with two layers of 3/4" plywood to create 90 degree conical waveguides using a version of the 25 watt Electro-Voice 1.5" phenolic "Super-Dome" tweeter, as used in the EV 100S and other 1980's era cabinets.
Response was reasonably consistent with pattern control down to ~3000 Hz, the waveguide providing around +3dB gain. One could use as many layers of material as wanted to increase the size and depth.
I've also used a 45 degree router bit to extend the Eminence APT 80 tweeter horn, rear mounting it on a 3/4" baffle.
The recessed mounting brought the driver closer to time alignment with the woofer, and extended pattern control a bit lower.
Smoothing over the exit profile with a file and sandpaper reduces the hard edge diffraction.
Art
Please post measurements of the APT 80 if you have them with additional curved baffle. I have been tempted to do the same at times with mine.
I did it on an old luxor tweeter which had a rising response in the high frequencies. I tried a few thicknesses of mdf and found one that made it very nice and flat. Rounding the transition to the baffle also helped.
This is on my list to do soon. I think the issue with it is that waveguides often need a different taper to work well. But it would depend on the tweeter's characteristics and how it interacts with the waveguide. Obviously, measurements are necessary for both on and off-axis response.
Yeah, I'm a little puzzled as to why I haven't seen it done much. Conical expansion with a small roundover at the throat and mouth seems very common.
This is also very close to the contours of an OS waveguide from what I can see.
This is also very close to the contours of an OS waveguide from what I can see.
The Hornresp software can be used to model this before you build anything.
As an introduction to the measurement, the speaker baffle and rear mounted 8" drivers near the extended APT80 horn would change the response compared to the Eminence measurement using a 2ft x 2ft baffle built into the wall of a 270 cu. ft. chamber with fiberglass on all six surfaces (three with custom-made wedges).
The blue trace "Mon APT raw" is the raw response of the APT80 with the 45 degree extension in the wedge monitor cabinet depicted above, "APT new X" with it's passive crossover.
The APT80 extension appears to have lifted the midrange to a similar level of the 90x90 Bi-Radial APT200.
That said, none of the eight APT drivers in those monitors response match each other.
If I recall correctly, the driver measured above was somewhat "average" 😉
I matched pairs as close as possible, and always used them on the same monitor mixes so they could share the same corrective equalization.
Art