Piano Sound: The Rim

[Tony Caught]

Hi Gordon,

I try to look at this another way, I know that what you are saying seems to
be the general consensus but.

The original vibrations come from the strings, these vibrations are
transmitted along the bridge to other strings causing them to vibrate in
sympathy with the original strings and at the same time, to the soundboard.
Now the soundboard is vibrating in a very complex manner. It must be to
allow machines like Tunelab to pick up all the harmonics of a particular
note when other notes are sounding as well.

Now all these frequencies travel at different wave lengths and if they are
reflected back from the rim out of phase then they would cancel out the
frequency coming from the string.

Thus, IF the rim is reflecting the vibrations back into the soundboard the
resultant sound will vary in accordance to the pitch of the notes and key in
which they are played. I would prefer a sound that comes from the strings
without any rim echo.

The firmer the rim or the edging of the soundboard the better but my
thoughts are this.  If the rim is solid and rigid then the soundboard will
be held in a more exacting position. If it is solid it will also not
vibrate. Yes it will transmit the sound but it will not vibrate as the
soundboard does, thus the vibrations stop at that point.

Possibly in the ideal piano the rim should be rigid and solid, the
soundboard attached only by the ribs with the boards thickness varying from
1/4" in the bass to 1/2" in the treble with possibly the ribs becoming
closer as they progress to wards the treble. This way the rim cannot
possibly reflect the vibrations back and the board would be totally reliant
on the strings for the sound generation.

When the sound or vibrations are leaked to the case whether this is via the
rim or the pressure bar or the iron frame the energy is taken away from the
soundboard to the detriment of the tonal qualities of the piano.

A solid rim is ideal for holding the soundboard and thus the bridges
attached to the soundboard in an exact position. If the soundboard is
attached only via the ribs less restrictions are there to allow the
soundboard to vibrate freely. If soundboard is vibrating freely then there
is less energy lost. If the soundboard has more energy then the sustain will
be longer, the volume louder and the tone more harmonically rich.

Some manufacturers are heading this way but at a slow pace. But as you have
heard from Ron Overs and Del Fandrich  and and first you have to prove you
are right over 50 years to be accepted. There are many other aspects of
construction to be considered, maybe if this thread carries on they also can
be explored.

Now, what do you think. Lets see if we can build on this concept or should
it be cast aside.

Regards


Tony Caught
caute@optusnet.com.au



----- Original Message -----
From: "gordon stelter" <lclgcnp@yahoo.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: Monday, September 16, 2002 6:26 PM
Subject: Re: Piano Sound: was something else

>
> --- Tony Caught <caute@optusnet.com.au> wrote:
> > So you says that a rim  reflects or has to reflect ?. And why should it.
?



> Well, it WILL reflect some vibration back, regardless. The stiffer,
denser, and more rigid the rim is, the more vibrations will be relected back
into the board.  What is not reflected will be tranmitted to the case/rim,
and either carried back to the board somewhere else or dissipated as heat in
the rim wood fibers. I think it is optimal that this vibration be dissipated
by heat in the lampshades and curtains of the room the piano sits in, not
the piano itself.  In other words, as much of the pianist's finger pressure
as possible should be converted to sound and LEAVE the piano, before being
absorbed by soft materials. I believe the softer case woods in many modern
pianos,
 Asian or otherwise, largely contributes to their relatively impotent tone
when compared to high quality pianos from 100 years ago!!!
      That said, the relationship between stiffness and density will play a
vital role in the piano's tonal "personality". Some pianos ( Boesendorfer,
old Chickerings, Emersons, etc. ) use spruce for case and beams, so that
some of the energy transmitted to them will still be converted to audible
resonance. Spruce, while light, is still considered a "hardwood" as the
fibers between the rfesonant vacuous cells are tightly compacted. So it has
both high transmittal and resonant properties. But not the best reflective
properties when used in a case application, as it is not dense enough,
overall, to make extremely rigid structures.
      At the other extreme are old Knabes, which have the most "rock hard"
rims (and cases) I have ever seen! In these pianos a fast, loud, rather hard
tone is emitted, as vibrations are quickly kicked back to the board, which
is held very rigidly by massive rock maple cases.  I have seen many 100 year
old Knabes
 with excellent crown.  It should also be noted that these boards have a
heavy coat of finish, usually shellac, which is extremely stiff ( and
brittle ) when fully cured. This brittleness surely aids vibrations as they
travel across the face of the board. ( But I use 2 part "conversion"
varnish, as it also has this property but is more impervious to humidity,
and is inedible to the house crickets that live here. "Down side" is that it
emits formaldehyde fumes like crazy for several months as it cures. )
       On many old pianos the cases were also veneered with rosewood or
ebony. This was not just cosmetic, as these very dense woods transmited
vibrations around the case to where they could be re-absorbed by the board.
The builders new this.

>     Gordon Stelter