Thanks Romy and Paul for your comments.
Romy wrote : "...I personally would probably go for a monopod frame above the upper bass horn (merging it in middle) as I feel it make the architecture more elegant, more airy and visually less demanding..."
Yes, perhaps a frame with a single mast would have been more orderly. It certainly would have been possible. My logic in going with parallel masts is as follows:
Option 1 : Single mast - Frame passes up under the 180Hz horn.
In this case, the horizontal member of the support would have eaten into valuable vertical space for the tweeter.
Option 2 : Single mast - Frame passing behind the driver and up over the 180Hz horn.
I now know what the 180Hz horn does (and really love it), but at the time I did not, and wanted to leave space for both deeper and more shallow horns; I did not want for example, the forward end of a horizontal member dictating horn geometry or placement (yes, there are ways around this problem) and by extension placement of all other horns of that channel.
Of the two options, this is the better choice. However, it must also be born in mind that the 180Hz horn + S2 is nearly as deep as the upper bass horn, and weighs 135 lbs, most of which are concentrated toward the big end of the horn, and that passing a central mast behind the S2 (leaving space for driver removal and time arriving adjustment) would mean holding all the horns weight in pure cantilever.
To summarize, because it is less restrictive with regard to horn placement, and because it is less solicited in terms of load (cantilever) I elected to go with a parallel mast configuration.
If however I were to put these things into production, I would nail down the variables and reconsider using a single mast, as the advantages it represents in simplicity of fabrication alone are enough to justify such an approach.
"...Horn installations are ugly from female perspective..."
Yes, and this type of woman is, from my perspective, as interesting as your average cabbage. However, last night I had a female visitor who commented (without being prompted) that she found the installation to be "beau"... I said "What?... Say that again please... Does this make you a lesbian?"
Anyway, the horns are not the only objects in the place which others might consider as aesthetically offensive elements. Most likely due to professional deformation (my DAY JOB), I have developed an aversion to all styled objects; I won't buy them, and can't stand living with them. By contrast, I find horn installations to be visually fascinating, because like weapons, they are so expressive of their function.
Paul S wrote :
"...So, you used to be:
tool and die guy
mold maker
brain surgeon..."
My background is in automotive styling (cringe!). Plaster working skills were learned by watching the French and Italians make automotive prototypes... I was lucky enough to witness the last of their breed in action... The best were veritable artists... We now do everything via CAD and CNC milling. Along with waiting tables, motorcycle mechanics and metal fabrication skills were all acquired in past lives.
About fifteen years ago, as a remedy to the effects of said DAY JOB, I undertook an ambitious personal project (its finally done!) which called for, among other things, a basic knowledge of structural engineering and metallurgy; I this from books.
BTW, one of my favorite books ever written happens to address the subject of structural engineering (along with quite a few other subjects... Not what you'd expect).
It is : "Structures, or Why Things Don't Fall Down", by J.E. gordon.
http://www.amazon.com/Structures-Things-Dont-Fall-Down/dp/0306812835
jd*
How to short-circuit evolution: Enshrine mediocrity.