Killer Octave Question

[Ron Nossaman]

>I'm just following along on this discussion and don't have much to
>contribute in terms of whether the bridge does or doesn't support crown.
>But, assuming that it doesn't, the question that comes to my mind is
>whether or not you could build a bridge that does support crown, and,
>assuming you could, would there be any benefit.

Big question. I don't know. As it is, I consider the bridge something that 
ties the panel and rib set together into a controlled stiffness unit. I 
want the bridge stiff enough to disburse load between adjacent ribs, not to 
act as a rib itself. I want the ribs supporting the load and controlling 
diaphragm response.


>In addition,  I recall
>reading a few days (at least) ago a comment by Del in which he mentioned a
>piano in which the original bridge had tapered down to a relatively reduced
>height was being replaced by a bridge of fuller height (in the treble) that
>would add stiffness in the upper area and that he expected it to improve
>sustain--assuming my memory is serving me well here, which it may well not
>and I am open to being corrected.  If that's true, and if the bridge can be
>made of stiffer material, or supported in some manner, why would you not
>want to use the bridge to support crown and, while your at it, have the
>thickness of the bridge increasing as it goes up the scale (rather than
>tapering down) to add stiffness and better impedance characteristics to the
>treble section.

Requirements for bridge stiffness are also dependent on ribbing, as he 
mentioned. With more ribs, or stiffer ribs, the assembly doesn't need as 
stiff a bridge.


>   Anyway,
>the basic question is, is there any benefit to considering manufacturing a
>bridge of materials, shape that will support crown and/or contribute to the
>kind of impedance characteristics we're looking for whether in the short or
>long term.
>
>David Love

Maybe, but I wouldn't expect much. You'd need a straight bridge, like the 
banana piano. A curved one would and does just rotate when you load it. 
Take a straight maple bridge 40mm wide by 35mm tall and 150cm long with a 
7mm crown (40 meter radius, since a 60' (18M) radius would make a 15.5mm 
crown and you would have some difficulty attaching a rib set to it). 
Supported at the ends, it only takes a 40 pound center load to push that 
bridge flat. Ah, but the load isn't concentrated in the center, nor is a 
bridge supported only at the ends. True. The bridge is supported by each 
rib throughout it's length, which means that the bridge isn't supporting 
crown. It's just connecting and disbursing load between adjacent ribs - 
much like the curved bridge we have now. Where's the gain? Then there's the 
minor problem of cutting different crowns in all the ribs to correspond to 
the bridge profile and getting the profiles of the ribbed panel and bridge 
to match. A straight bridge would certainly eliminate some of the load 
distribution problems inherent in the current design, but that doesn't have 
anything to do with crowning the bridge.

Ron N