Killer Octave & Pitch Raise

[Dean May]

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Structurally, it seems to me that the bridge would be least likely to
roll at the greatest point of curvature. Consider a piece of steel, 1"
wide, 1/8" thick, 2 feet long, welded to a thin piece of sheet metal on
edge. This is our bridge on the soundboard, easy to rotate forward and
backward. It has no support behind or before it. 
 
Now imagine the bar stock bent into an L shape welded on edge on the
sheet metal. Near the bend, the corner of the L, the bar stock will be
very strong and resistant to rolling. It has the leg behind it to
support the direction of the loading. But as force is applied closer to
the ends of the legs it will loose strength and rotate easier in that
local area. 
 
Dean May

-----Original Message-----
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On
Behalf Of Terry
Sent: Friday, February 11, 2005 5:23 PM
To: pianotech@ptg.org
Subject: Killer Octave & Pitch Raise


When I raise the pitch of a piano, typically I find that I need to pull
an area of the treble, commonly around the sixth octave or so, a bit
extra so that area does not end up flat when the pitch raise is
completed. I use typical pitch raise overpulls - 20% in bass, 25% in
tenor and 33% or so in treble - but that one octave or so in the treble
needs to go a little further - maybe 35 or 38%. I find this to be true
on most pianos.
 
My understanding is that one factor that may conspire to produce a
killer octave (low volume and/or short sustain) in a piano is the fact
that the killer octave area is also the area the long bridge is curved
most - rather than having the downbearing supported in part by a
straight (or nearly so) bridge (like in the tenor), the curved part of
the long bridge in the killer octave area is more prone to rolling - I
know, not rolling - actually soundboard deformation - but I'm trying to
point out that it can rotate in this area more easily than other areas.
 
My question is - might these two phenomena be related? Is the killer
octave area more prone to going flat because the bridge is rotating (I
suppose in part due to soundboard not having enough support in that
area)?
 
Thanks for any thoughts.
 
Terry Farrell


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