Killer Octave Question

[Delwin D. Fandrich]

----- Original Message -----
From: <A440A@aol.com>
To: <pianotech@ptg.org>
Sent: Wednesday, April 09, 2003 5:43 PM
Subject: Re: Killer Octave Question


> Greetings,
>    The killer octave is usually supported by the section of belly rail
that
> is farthest from buttressing.  The normal connection of the plate to the
> belly rail at the plate's "horn" provides resistance to outward movement,
and
> the rails connection to the case at the treble end, likewise.  However,
the
> ribs that must support crown under the killer octave bear against the
> bellyrail at its greatest unsupported span and it just might be one reason
> that this section of the piano loses its bearing first.  (The rib under
the
> C5 on a Steinway O meets the bellyrail approx. halfway between the plate
horn
> and the treble end of the rail).
>    Many other reasons could go into the equation, too.
>


While I agree that the belly bracing of most so-called "modern" pianos
leaves much to be desired, this placement does not have anything to do with
the fact that compression-crowned soundboards lose their crown very rapidly
through this section. The ribs of the soundboard do not function as
structural arches. Wood is too compliant, the crown radius is too great and
neither end (belly rail or rim) can be made rigid enough (with or without
proper placement of the rim braces.) See my articles on the problems of
piano soundboards in the Journal. One of them has a section dealing
specifically with this issue.)

To understand why tone quality--specifically sustain--dissipates so rapidly
through this region you have to consider all of the factors that affect the
overall stiffness of the soundboard assembly and its support system. These
include (but is probably not limited to):
    -- the crowning technique,
    -- the type and placement of the ribbing,
    -- the grain orientation of the soundboard panel and orientation of the
ribs relative to this and then the orientation of both to the bellyrail,
    -- the physical characteristics of the wood used (specifically its
propensity toward perpendicular-to-grain compression-set)
    -- the compliance of the rim and the bellyrail assembly,
    -- the physical size of the soundboard through this region,
    -- the off-center placement of the bridge,
    -- the stringing scale (including both the frontscale and the
backscale),
    -- the plate configuration,
    -- the mass, compliance and shape of the hammers
    -- etc.

Understanding the "killer octave" is not one of those issues that can be
resolved with simplistic answers: "There is not enough downbearing," or,
"The soundboard has lost its crown." While both of these are probably true
they do not explain why there is not enough crown or why the soundboard has
lost its crown. Nor do they explain why the piano with "good" string bearing
and "good" soundboard crown might still have a lousy killer octave.

All of these factors interrelate to form a whole. Many, if not most, of them
have been discussed on this list and/or in various PTG Journal articles.
They have also been a part of many Convention classes--including my own. And
I'll use this opportunity to invite one and all to Dallas this July where I
(and a whole bunch of others) will attempt to shed light on this and many
other equally complex issues.

Del