Steinway Sustain

[Delwin D Fandrich]

----- Original Message -----
From: "Tony Caught" <caute@optusnet.com.au>
To: <pianotech@ptg.org>
Sent: April 17, 2001 2:07 AM
Subject: Re: Steinway Sustain



> > My question to the more experienced people, ( Del, where are you?)

A short trip to China.



> > is what effect does too much downbearing have on tone?  Wouldn't that
make
> > the board so high that it would transfer the energy more quickly than we
would
> > like?

Excessive downbearing (i.e., excessive string downforce against the bridge
and soundboard) makes the soundboard somewhat stiffer than it otherwise
would be. Picture an overly compressed spring; the more you press against
the spring the stiffer it becomes and the more resistance you feel. This
raises the mechanical impedance of the soundboard, affecting the rate of
energy transfer from the strings. Especially to the lower frequencies
present in them (i.e., the fundamental). In theory, this should increase
sustain, but in practice this may not be all that noticeable since there
isn't all that much energy in the strings through this region -- that is,
the killer octave region -- to begin with and there are other places for it
to go.

(At least this is what usually happens. Some piano designs are such that
considerable distortion can be introduced in the soundboard/rib structure as
humidity causes the soundboard panel to swell. The relative height of the
bridge stays about the same -- string deflection doesn't change much -- but
that portion of the soundboard between the bridge and the inner rim bows up.
>From the side and along the ribs the soundboard takes on a slight 'S' curve
shape. In these cases it is anybody's guess as to what will happen to the
sound during periods of high humidity. Generally both power and sustain
suffer.)



> I have always figured that when a string is struck and the energy is
> transferred to the string, the string then passes the energy onto the
> soundboard. Now energy = sustain/volume. If the volume is high the sustain
> will be short. If there is too much downbearing the sustain will be short
> and the sound loud. A piano will low down bearing will have long sustain
but
> only medium volume and vici versa. Got to be a balance somewhere.

Usually just the opposite takes place. A piano with low downbearing (i.e.,
little string downforce against the bridge and soundboard) will have a
somewhat percussive sound. A lightly loaded soundboard -- whether it has
crown or not -- will not be as stiff as one more heavily loaded and its
impedance to energy at lower frequencies will also be on the low side.
Whether this piano will be 'loud' -- in addition to being percussive -- will
depend on the characteristics of the hammers, the stringing scale, the
design of the string terminations, etc. Sustain will be on the short side
since most of the energy in the strings goes into that initial percussive
attack sound.

This is a common problem with pianos using compression-crowned soundboards.
For a variety of reasons -- refer back to the articles I wrote for the
Journal for a more complete explanation -- soundboard crown dissipates more
quickly through this critical region than it does through the other parts of
the board. Since there are also a couple of other common design flaws
through this region (in addition to the method of obtaining soundboard
crown) the result is the very typical loss of sustain -- hence our reference
to this region as the 'killer octave' -- you have found with this piano.

You can sometimes make the problem less bad by all of the regulating and
voicing techniques offered by other posts on this subject, but the real
problem lies with the soundboard and until that is dealt with none of the
other repairs will be all that helpful.

I might add that the common idea of hardening the hammers through this
region generally only makes the problem worse. Acoustically what is
happening is that the fundamental energy within the strings is being drawn
off very rapidly into a soundboard that is not as stiff as is desirable.
Hardening the hammers decreases the amount of fundamental energy excited in
the string making the resulting sound ever more 'bright' and harsh sounding.

You can also sometimes make the problem less bad by adding some weight to
the bottom of the soundboard along the bridge line. While this is not as
effective as replacing the soundboard with one having the proper amount of
stiffness, it may help. Adding mass will increase the soundboard impedance
somewhat more with the higher partials which you don't really need, but it
will also have some effect on the fundamental frequencies involved through
the killer octave region. Start with about 100 grams located as close to the
center of the worst area and go from there.



Then Kevin wrote:

> Remember what Del said about soundboards. Today they are all made too
thick
> (not shaped in the bass), makes the board stiffer, requires harder/heavier
> hammers to excite the strings, lots of volume but no sustain.

In general this is true. However, soundboards can also be made regionally
too thin. This is especially in the upper tenor and treble. And even more
especially if these boards are compression-crowned. Excessively thin
compression-crowned soundboards have a habit of de-crowning themselves very
rapidly even without being exposed to high humidity climates.



> wouldn't mind
> betting that if you cut the soundboard clear of the rim in several
sections
> (as Ron Overs did in the Yamaha G2 in one section) then put Abel hammers
on
> you could have a decent sounding piano.

We've been doing this regularly on a variety of different pianos for some
years and now have a considerable backlog of experience with the technique.
(It was also standard along the bass of our U122 upright.) It won't help
through the killer octave region however. Here the problem is already a loss
of stiffness and cutting the soundboard free would only reduce the stiffness
further.

Regards,

Del