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MultiWay Conventional loudspeakers with crossovers 

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5th November 2017, 05:07 PM  #21 
diyAudio Member
Join Date: Apr 2011

Something like that. Here is a rough idea of how to go about it. Its harder to describe than to do, given some familiarity with a 3D CAD tool.
Draw a square on the surface of the horn a short distance in from the apex. Now draw an arc that is tangent to the CD's exit cone at one end and tangent to the horn wall at the midpoint of one side of the square at the other end. (This is the hard part, you may need to reposition the square or the horn wall to satisfy both constraints.) Once you have that arc, rotate it around the circle defining the CD exit to create a 3D surface. (In SketchUp, use the follow me tool.) Now the 3D surface touches the square you drew at just 4 points. Draw additional lines to fill in the corners smoothly emulating the process with modelling clay I described earlier. Ultimately you will define a surface and underlying structure to be milled or printed but you still have to decide how to integrate it with the horn. Lots to keep you busy until after Christmas. 
5th November 2017, 07:40 PM  #22 
Old guy with soldering iron
diyAudio Member

MR. Oil,
If you use Fusion 360 to make your 3D printed designs, you can import tables of numbers into it. With a spreadsheet, you can use the Oblate Spheroid formulas to generate the needed tables. See attached Excel file for one I used  but, sorry, can't answer many questions about it, as I don't remember well what I was doing then, and didn't keep notes!. But I used a radius for the last third or so of the curve and tweaked values to get the curves to meet. front.png Then export the table (trim it down to maybe 15 or so values, with most detail at the throat end) as a csv file. Fusion 360 can import the table(s) as spline curves (it smooths out between the provided points), and with those you can rotate them for a round horn shape; or use them as "guides" for lofting between a circle and whatever mouth (or adaptor) shape you are looking for for nonround shapes.
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[W9MJE] Horn spreadsheet SynergyCalc/; SmallSyns SmallSyns; Crossover design Xsim; Depot diffusor supereasy diffusors Last edited by bwaslo; 5th November 2017 at 07:43 PM. 
5th November 2017, 09:22 PM  #23  
diyAudio Member
Join Date: Jul 2017
Location: Hamburg

Quote:
I can't understand what you are saying (not my mother tongue), but I have an idea on how this thing could look like... (atached) Is this correct? Greetings 

5th November 2017, 10:10 PM  #24 
diyAudio Member
Join Date: Apr 2011

Its a start. What you have there, with a few more lines added, could do the round to rectangular conversion. Just draw lines from each junction of the polygon that approximates the circle down to the nearest corner of the square. This will do the corner fill. (But it doesn't do the CD exit angle matching.) I actually got a 3D print of such a structure once but never used it in a project because by that time I had something working with modelling clay.
here is what I came up with for the 3d printing or milling: Throat profile 14 degrees 1 inch exit_11.jpg It matches a 14 degree exit angle and does round to square for a 60x60 horn. I plan to CNC mill it into two layers of 18 mm BB plywood plus .25" of CD mounting plate. The front part of in, grey, is the corner fill for the round to rectangular converstion. The back part is the exit angle matching for a BMS4550. BWaslo and I were talking about how to generate that curve. He from a xY table that approximates an ideal Oblate Spheroidic expansion, me from simpler criterion. Once you have such a curve, you can use Sketchup's "followme" tool to move it around a circle to create the needed expanding pipe, which you then edit into your horn drawing. That expanding pipe is what you see in the back half of my drawing above. I got my curve graphically by starting with the Charles Hughes whitepaper on quadratic throat waveguide and then added the exit angle matching criterion to it. There is a figure (see below) in the white paper which should get you started. I hesitate to say more if there is a language barrier between us. You really need to work your way through the process yourself as there are several of design decisions you need to make along the way. CEHughes fig.jpg 
6th November 2017, 01:00 AM  #25  
diyAudio Member
Join Date: Mar 2011
Location: Rochester, MN

Quote:


12th November 2017, 06:57 PM  #26 
diyAudio Member
Join Date: Jul 2017
Location: Hamburg

Hi,
Back working at this after a busy week... @nc535 I was wondering if the exit angle matching needs to be a curve... (can't see it on the 1st pic) In the case of the 2nd picture the exit angle would be 0°, right? Also how would you implement such a curve in Hornresp? Thanks for your help! 
12th November 2017, 07:47 PM  #27 
diyAudio Member
Join Date: Apr 2011

Yes, the exit angle matching requires a curve; otherwise its simply an extension of the straight conic section (assumed to be) inside the CD and there will still be an abrupt change of slope that will cause diffraction and reflection where the line meets the horn.
Right, the picture from the Charles Hughes white paper is for a 0 degree exit angle. It would be more accurate to say they weren't addressing the need for exit angle matching. That curved throat section can't be modeled in HR. HR gives you choice of conical, parabolic, and exponential for each segment of the horn and some ability to model a throat chamber but that isn't sufficient. Most likely you would need to model both the CD and the waveguide in something like ABEC3 to see the beneficial effect. 
12th November 2017, 08:06 PM  #28  
diyAudio Member
Join Date: Apr 2011

Quote:
I googled "Importing XYZ data from Excel into Sketchup" and found this link Importing geometry from Excel or text files  Ruby API  SketchUp Community Now that I know its possible in Sketchup also, I guess I'll have to try it. Thanks for the push, even though its sure to make my brain hurt Jack 

12th November 2017, 11:12 PM  #29 
diyAudio Member
Join Date: Mar 2011
Location: Rochester, MN

Jack  thanks for the link. Now if I can figure out how to create points along an arbitrary spline for export to AxiDriver I will be in business.
To keep this ot MrOIL  I wouldn't worry much about simming the throat of the wg for the hf portion on your Synergy. To be honest I've never paid it much attention, only using it to figure out midrange ports which are going to be unaffected by a radius at the cd entrance or not. That radius will create a change of distance but I would think for our purposes it would be negligible. 
27th December 2017, 11:46 AM  #30 
diyAudio Member
Join Date: Jul 2017
Location: Hamburg

I worked a bit here and there and I think that I'm finished now...
I had a little problem regarding the throat adapter; I now have the round to square adapter before the exit angle matching, because I use an asymmetric dispersion (60*90). When i was finished i just wanted to try to remove the expansion change in the horn and the results were almost the same (see pics). Should I remove the expansion change? Are there any errors I made and what do you think of the results? The dip around 11kHz is from the mid ports acting as a helmholtz resonator I would suspect. Is this correct? Thanks in advance! 
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