Horn and U-frame

[Tytte71]

Dear all

Recently I ordered two JMLC-350 horns from Autotech to test with 1,4" compression drivers. I have also ordered four TD18H+ from Acoustic Elegance (arriving sometime near Christmas I hope). The woofers are intended to be used as future subs, but for now I would like to test them in another setup. Nice to have something to do during Christmas holliday

Allthough I am confident that the TD18H+ performs great as a (low) midrange unit I have yet to find good/usable measurements for them (such as off-axis response, CSD, distortion and large signal measurements) .

As I read many others also have experienced, OB dipoles couples better to the room than traditional boxed cabinets - for me the statement includes a 15"/waveguide combo that I've tried. I believe this is due to the dipole's CD. Must add I've never tested U- or H-frames. Playing with the thoughts of finding something easy and nice to test the woofers with, it stroked me - what if I use the TD18H+'s in cardioid U-frames? That could maybe maintain ideal dispersion and at the same time improve the low frequency capacity over OB dipole.
As John k... shows; one 18 inch woofer in a U-frame have the capacity equal to a similare specified 36" woofer in an OB dipole.

The woofers could be mounted inside a boxed frame with inside diagonal bracings (forming a two octagons) leaving the open back area close to driver Sd. The back should be stuffed with appropriate type and amount of damping material

I am not sure about the crossover frequency since I don't know the TD18H+'s off axis response, but I was thinking of crossing the higher 18" at some place between 550-700Hz (used a Faital driver spec. as guidance). The second woofer is just to add capacity at the lowest octaves.

The bass should extend down to 30Hz and be able to play relatively loud. My living room eats subbass for breakfast so no help to get there. The TD18H+ have a Qts of 0,22 which is also a drawback with regards to lower extension / power needed - but that is subordinate in this testing context I believe. By the way - I will run an active crossover setup.

Must admit I am on real thin ice here and feel there are many pitfalls to the design. And, I haven't found any software/tools that can help me with simulating U-frames.

Therfore, I would appreciate your advices and tips for the design, i.e. the ideal size for this U-frame, special concideration... and ehh... maybe I should just leave it as a stupid thought?

Best regards