[pianotech] rcs design considerations

Gene Nelson nelsong at intune88.com
Fri Aug 6 22:51:12 MDT 2010


Thanks so much for the replies. Yes Dale, I am a bit confused.
The piano is an 1880's Hallet and Davis 8'9"
The belly bracing is substantial with several beams crossing eachother as 
they go in two directions. I do not think stiffness is an issue within the 
limits of the softwood it is made with so low mass or low impedence would be 
the issue.
It sounds like if I increase the rim impedence then a board design can lean 
toward the typical board desing that I am familiar with. If I do not then a 
thicker board and shallower grain angle relative to the belly rail would be 
reasonable?
The thicker board is always counterintuitive to me for this reason: Strings 
displace the board assembly and it is the ribs that respond by returning to 
their original position. If a board is thicker it is more massive and would 
cause the assembly to return slower, making the lower firquencies more 
predominate. But we tend to thin the board in the bass.
The 12 foot piano in southern california has a 12.5mm board and David has a 
difficult time getting higher partials.
My scale is yet to be determined and I will be making a new bridge so I just 
do not know where the tension will be yet.
Gene
----- Original Message ----- 
From: "Ron Nossaman" <rnossaman at cox.net>
To: <pianotech at ptg.org>
Sent: Thursday, August 05, 2010 8:49 AM
Subject: Re: [pianotech] rcs design considerations


David Love wrote:
>  Ron mentioned beefing up the rim which in effect then changes the rim 
> mass in order to be able to use what would be the same basic design.

Both mass and stiffness. This is most critical in the top half
of the scale, where the higher frequencies produced need a
high impedance boundary. By the time you've added a big cutoff
bar, a fish, and belly rail bracing and mass, you've
essentially replaced the top half of the soundboard perimeter
with high impedance material and can design accordingly
without needing new sets of rules.


> That’s another approach.  I think the question though is given a soft wood 
> rim without altering the mass what changes must be made to accommodate the 
> difference.

Mass wasn't mentioned in the original question, but building
with a lower density softer material will also decrease mass.

Ron N 



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