Compression ridges was :Do you dry the ribs, along with the board, prior to gluing ?

[Dean May]

Ric,

I don't think what we are saying is all that different (I know, it's
happened before), except you are adding that there is a minimum threshold of
mass desirable for the bass and a minimum threshold of stiffness desirable
for the treble. I would just like to explore what those minimum thresholds
are. 

You are saying stiffness is more important in the bass and mass is more
important in the treble. By inference then mass is less important in the
bass and stiffness less important in the treble. That is basically the same
thing I remember Del saying. 

Dean

Dean May             cell 812.239.3359 

PianoRebuilders.com   812.235.5272 

Terre Haute IN  47802

 


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of ricb at pianostemmer.no
Sent: Friday, February 01, 2008 6:13 PM
To: pianotech at ptg.org
Subject: Compression ridges was :Do you dry the ribs, along with the
board,prior to gluing ?


Hi Dean

Spent a long time looking for this exact post below... one from
Nossaman I rememebered.  I wanted to make sure I had it right. 
Several other posts I rant into from Del went along the same lines...
and I almost settled on one of those.  

As I understand these posts... what is said is that in the high
treble (assuming enough stiffness to begin with) the amount of mass
is critical... more critical then added stiffness to the sound. And
in the bass stiffness is more critical... once there is enough mass.  

Now I can be wrong... have been many times. But I dont think this is
the same thing as saying you want lots of mass and low stiffness in
the treble, and lots of stiffness in the bass and low mass.

Rons post is just below. Its from April in 2003.  It also mentions
what I told Thumpy just a day or two ago... about figuring support
for down bearing based on scale demands.  A lot said in a few words
in that post.

Cheers RicB



Exactly, no. Roughly, yes - in a rib crowned board. Rib stiffness is 
>computed with a standard beam deflection formula, like the rib was a 
>center loaded beam. The rib scale is calculated from the stringing
scale, 
>with stiffness requirements being determined by tensions and bearing
load. 
>You're trying to tailer the impedance of the soundboard assembly at
any 
>specific point in the scale to requirements of the string scale and 
>bearing at that point. Stiffness control is the more critical in the 
>bottom half of the scale, and mass control more important in the top
half. 
>Positioning is determined by bridge type and placement, case shape,
string 
>scale, and whatever else you want to take into account like panel 
>thickness, grain angle to the belly rail, rib to panel grain angle,
cutoff 
>bars, number of ribs, etc. Lots of decisions to make