Belly rail crown - Why???

[Ron Nossaman]

>Regarding planing/cutting a rise into the belly rail mid-section. Is it 
>not even more pertinent whether there is a rise cut into the concave curve 
>(as viewed from the outside of the case) of the case in the mid-treble 
>area? In this area the same question would apply, but the geometry would 
>be even more exasterbated. My understanding is that some manufacturers put 
>a rise in this area and some don't. What are thoughts about this?

I wouldn't consider it necessary. Most of these rim contouring concerns 
tend to fall around the killer octave area of the scale.


>Regarding the plywood filler in the cut-off area. I wonder, would there be 
>any benefit to using MDF or some other material that would offer the 
>support you are looking for, but perhaps have more desirable acoustical 
>properties. I know very little about acoustics. My thinking for posing the 
>question is the preference for MDF in stereo speaker 
>cabinets/installations over plywood for acoustic reasons. Thoughts?

I don't think it would matter a whole lot. The cutoff bar is the new 
perimeter rather than the rim. Screwed and glued to the beams, it should 
adequately define the board termination.



>And lastly, what do you do/think about bevel angles on rim components when 
>rebuilding/remanufacturing. 1) Change all angles to match new soundboard 
>(Yikes!)? 2) Leave original components (rim) as they were, but bevel new 
>components (cut-off bar) to match soundboard? Or 3) leave original 
>components (rim) as they were, and don't worry about putting any bevel in 
>new rim components (install the cut-off bar on a plane with the rest of 
>the inner-rim-top)?

3.


Ron N