[brad944911]

  Hi all, first time on this board and hope I can get some help/direction like on the Open Baffle site.  I have a small-ish room (about 200 ft2) and I initially toyed with a 4 way open baffle with almost no directivity hoping it would scratch the itch for great sound and impact.  It sounded great to me but at the cost of off axis imaging and a small, rapidly deteriorating sweet spot moving off axis.  So I began looking into constant/controlled directivity designs.  The CD horns and drivers worked great when applying Geddes' toeing guidance, but the 10 inch mid-bass/midrange are being driven well past their beaming range I think.   
  So what exactly am I looking for?  The horns I am using have a 90 degree horizontal dispersion and I want to know what frequency that equals for different size drivers; 6.5-12's mostly.  I've seen so many papers that say use the circumference divided by wavelength to get an answer while others say a frequency that is half the diameter is the max...etc.  Does anyone have firm guidance? 
Thanks in advance,
Brad   

[bwaslo]

You can use Jeff Bagby's "PCD" for this:  http://audio.claub.net/software/jbabgy/PCD.html

Just use flat files for woofer "FRD" and "ZMA", set a few meters distance and the "Horizontal Panning" to your waveguide's angle.   Make the "crossover" essentially nothing (first order, with just a fraction of a mH seriesi inductor).





The above is for a 12" woofer (piston diameter about 0.8x12"), as sensed from a 45 degree angle offset.

Here are some "flat" response (FRD) and impedance (ZMA) files:
http://libinst.com/Xsim/FlatFRD.FRD 
http://libinst.com/Xsim/8ohmZMA.ZMA

[brad944911]

Well that is a pretty useful tool, thanks man!  BTW, do you still mess around with the Unity, Synergy horns?  Anything new?  I was kinda looking into building one.  Thanks, Brad

[bwaslo]

Hi Brad,

Yes, still playing with those kind of designs.  Latest have been some "miniaturized" versions, which are built around a commercial waveguide (with a midrage ported in to its side) and a spaced pair of woofers ported just below to extend the directivity down a little lower in frequency -- works really well if I do say so myself.    There's a build thread on these over at DIYaudio -- (http://www.diyaudio.com/forums/multi-way/292379-small-syns.html).

About to build the third iteration of these, same drivers and (probably) crossover, but in a shallower but taller ported box.