[pianotech] Soundboard Analysis

[David Love]

I think it was more that there was negative crown but once I saw there was
no positive crown with the string test I didn't pursue trying to determine
if the crown was actually negative nor by how much.  When I took pressure
off the board by letting down the tension and saw an increase in bearing
(soundboard rise) and a change in the distance between the bridge and the
struts (which I didn't include below), and then crawled under to check the
crown it was still not positive.  The board had risen but not enough to turn
negative crown into positive crown.  The board was flat to begin with.  BTW
this piano had been restrung at least once before.  

 

Also note that the bearing measurements in some sections were more negative
after the board was loaded than they were positive to start out with.  The
bridge transmitting the load between ribs from higher settings in adjacent
areas pushed those areas lower then otherwise they could be by themselves.
Nothing earth shattering there, just an observation.   But it is a reminder
that both when you design the rib array or set bearing on an existing board
you want try and insure that the load on the ribs distributed equally.  You
don't one are a set of ribs doing more work than another.

 

David Love

www.davidlovepianos.com

 

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Gene Nelson
Sent: Thursday, June 23, 2011 9:38 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Soundboard Analysis

 

 

 

  _____  

Question to ponder:  Why would it be that although there is a positive
change in downbearing when the tension comes off there is no apparent change
in measured crown?  

 

*** Bridge rotation?

 

Gene

 

 

 

 

Rib#                       Crown                              DB w-ten/wo
Rib L    H        W  (mm)

Or section           w-ten/ wo-ten

 

1                              2/2
.006/.015                             600         17           28

 

2                              2/2
.006/.015                             790         20           27

 

3                              2/2
.009/.012                             940         20           27

 

4                              1.5/2.5
-.006/.003                            1040       20           27

 

5                              0/.5
-.003/.003                            1080       22           27

 

6                              0/0
-.009/.006                            1120       21           27

 

7                              0/0
.006/.018                             940         21           26

 

8                              0/0
.006/.021                             660         20           25

                                                                

9                              0/0
.006/.027                             560         20           18           

 

10                           0/0
.018/.042                             390         18           23

 

11                           0/0
.022/.045                             340         17           23

 

12                           0/0
.025/.050                             270         16           23

 

 

David Love

www.davidlovepianos.com

 

 

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