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For this project I will be creating a high end 3 way floorstander using the Rival R176-P-08 paper cone 7 inch woofers and the Morel TM4055-8 tweet/mid's. These woofers were used by Ben in his Fenrir speakers and by Javad in his Rivalries with good results. The Morel drivers were used by Paul K in his Cornetta speakers (MWAF 2019) with very good results as well.
My plan is to mount the TM4055 in the center of a large 4 inch thick donut style baffle using a 4 inch radius roundover along the top 80% of the baffle. My drafting skills are not the best, so the drawing does not show the actual roundover (sorry). The radius will taper down to 3", then 2" and finally to 3/4" where it merges with the lower box. The lower box will have a 3/4" radius roundover (not shown). I am going to grind out the roundovers with my belt sander, forming the radius in stages using guide lines and cardboard templates. JR did a good job of rounding the corners and facets on his small bookshelf speakers a few years ago, using only a beltsander. Seems like a good plan and it should work as long as I develop a good spherical rhythm as I sand back and forth to reach my layout lines. I will, of course, be wearing an M95 dusk mask and using particle board instead MDF to keep the dust down.
What I am trying to do here is to reduce diffraction ripple above 1kHz as much as possible. Attached is a model of the expected diffraction using a square 13.625 baffle with 4 inch radius roundovers. I used Jeff B's BDS program to create this model. My baffle be round, but the results above 1kHz should be similar. The remaining lower frquency diffraction bumps should be easy to handle in the xover (approx 800Hz).
I'll be picking up lumber next week and will stop back here from time to time with pictures. As soon as the cabinets are done, I'll be running up a full set of measurements. Stay tuned and thanks for reading. Comments and feedback are always welcome.