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<DIV><SPAN class=749381900-17012004></SPAN><FONT face=Arial><FONT
color=#0000ff><FONT size=2>H<SPAN =
class=749381900-17012004>ello</SPAN><SPAN
class=749381900-17012004>Getting back at that old post, I noticed that =
Yamaha
hammers that have more wood on the tails side than many, seem to be =
better
balanced and more stable in time, we also feel something while playing =
like if
the hammer where thrower more naturally than on other kind with thinner
keys.</SPAN></FONT></FONT></FONT></DIV>
<DIV><SPAN class=749381900-17012004><FONT face=Arial color=#0000ff =
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=749381900-17012004><FONT face=Arial color=#0000ff =
size=2>Is it
the percussion point that is involved (I still did not get it really) or =
does it
have to do with the actual center of gravity of the hammer/shank system
?</FONT></SPAN></DIV>
<DIV><SPAN class=749381900-17012004><FONT face=Arial color=#0000ff =
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=749381900-17012004><FONT face=Arial color=#0000ff =
size=2>Thanks
in advance</FONT></SPAN></DIV>
<DIV><SPAN class=749381900-17012004><FONT face=Arial color=#0000ff =
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=749381900-17012004><FONT face=Arial color=#0000ff =
size=2>Isaac
OLEG</FONT></SPAN></DIV>
<DIV><SPAN class=749381900-17012004><FONT face=Arial color=#0000ff =
size=2></FONT></SPAN> </DIV>
<BLOCKQUOTE dir=ltr
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<DIV class=OutlookMessageHeader dir=ltr align=left><FONT =
face=Tahoma
size=2>-----Message d'origine-----<BR><B>De :</B>
pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org]<B>De la =
part
de</B> Bernhard Stopper<BR><B>Envoyé :</B> vendredi 19 =
décembre 2003
01:02<BR><B>À :</B> Pianotech<BR><B>Objet :</B> Re: =
Cockeyed hammers
/ Don Gilmore<BR><BR></FONT></DIV>
<DIV><FONT face=Arial size=2>Don/Sarah,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>To design a hammer so that its =
pivot
coincides with the center of percussion is THE way to get a free sound =
and the
maximum of energy transfer to the string. it also allows the hammer to =
reject
the fastest way possible because oscillations in the pivot =
produce
friction and slow down hammer movement at contact point.
</FONT></DIV>
<DIV><FONT face=Arial size=2>i did several simulations with =
software called
pro/mechanica and reshaped hammers after results found. one could say =
that
actual hammer with heavy felts have their center of percussion much =
far away
from the pivot than lighter hammers have. putting a small lead in the =
tail of
the hammer can make them come closer to that point. center of hammer =
mass
should ly on a line along the center of the hammer shank and =
the
center of percussion is at distance x from pivot that can be =
calulated by
the formula x=I/(m*y) with I= moment of inertia, m=mass, =
y=distance to center
of mass</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>regards,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Bernhard</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>
<A title=eromlignod@kc.rr.com =
href="mailto:eromlignod@kc.rr.com">Don A.
Gilmore</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A =
title=pianotech@ptg.org
href="mailto:pianotech@ptg.org">Pianotech</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, December 19, =
2003 12:22
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Cockeyed hammers =
/ Don
Gilmore</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>
<DIV><FONT face=Arial size=2>Well, I didn't mean to imply =
that the
impulse at the pivot is all absorbed; but it is all lost as far as =
the
string is concerned.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The center of percussion is one of =
those
counter-intuitive phenomena in dynamics. For the multitude of =
college
students that only take a semester or two of physics, the concept of =
forces
on a free body acting at the center of gravity is a paradigm that is =
hard to
dislodge. For an object in free space or translating in a =
straight line, which comprises most situations, the center of =
gravity
is always used. But for an object pivoted at some location =
other than
its c.g., all bets are off. The most publicized version of =
this is a
baseball bat's "sweet spot" as you described.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Think of a wooden board hung from a =
pivot point
at its top. If you strike the board up near the hinge, the pin =
will
experience a force coming from the direction of the strike. =
But if you
strike the board at the bottom, the pin will experience a force in =
the
opposite direction as the board tries to spin about its =
center. There
is a point in between these two where the pin force is neither =
positive nor
negative and the pin will actually see <EM>no</EM> force. This =
is the
center of percussion and is <EM>not</EM> located at the centroid of =
the
board. It's not usually even particularly close.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>It would seem to be a good =
idea to design
the hammer so that the string contact point of the head passes =
through
the center of percussion. That way the maximum amount of
energy would be transmitted to the string...like dropping a =
ball on
it. But I'm not sure if they actually design them that
way.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV>Don A. Gilmore<BR>Mechanical Engineer<BR>Kansas City</DIV>
<DIV> </DIV>
<DIV></FONT>----- Original Message ----- </DIV></DIV>
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