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Below is a chart that I use for soundboard analysis. Measurements are taken
before and after taking the tension down. Crown sections are measured
between the ribs using a string stretched as far as possible and a wedge
gauge (very low tech). I try and correspond the measurement of the crown
with the downbearing measurements in terms of location. An analysis of the
soundboard rib design can also be made using the rib dimensions-I haven't
done that yet. Downbearing measurements are Lowell gauge readings. Note
that .0175 corresponds to about 1 degree.
I won't tell you what my conclusion was about this soundboard but you might
be able to guess. (Steinway AIII)
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? Also note (not included in the data below) that when
measuring the change in distance from the struts to the bridge in the upper
end of the piano (from about rib #6 to the top) the average change was about
1 mm (the board rose about 1 mm).
BTW this board had received a lot of shimming perhaps with the idea of
restoring crown??? What do you think?
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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