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<DIV><FONT face=Arial size=2>Hi Don, hi Isaac,</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>With actual hammer shape, it is only =
possible to
catch the center of percussion (as Don said "the line of action where =
the string
strikes the hammer to pass through the hammers center of percussion")
if the tail of the hammer has more mass than actually most hammers =
have. (I
don´t know the new Yamaha hammers yet but if they introduced them =
recently they
surely worked on the same subject)</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>So i agree also with Isaac =
that one
effect of those hammers is a reduced loss in he center pin =
(more
stable at impact) and therefore more rejected energy that he can "feel" =
in the
key. (And hear, sound is more "free")</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=oleg-i@noos.fr
href="mailto:oleg-i@noos.fr">oleg-i@noos.fr</A> ; <A =
title=pianotech@ptg.org
href="mailto:pianotech@ptg.org">Pianotech</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Saturday, January 17, =
2004 2:23
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>Hi Isaac:</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The center of percussion should only =
come into
play when the hammer strikes the string. Ostensibly you would =
want the
line of action where the string strikes the hammer to pass through the =
hammer's center of percussion. This would result in no =
force at the
pivot due to impact. If you don't strike at the center of =
percussion
some small amount of energy is lost to the pivot. Only =
a small
portion of the kinetic energy of the hammer is imparted to the =
string,
the rest goes into deforming the felt, the leftover kinetic =
energy
when the hammer bounces back and vibrational energy imparted to the =
wooden
parts of the action, particularly the hammer shank.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>The "touch" of the keys is really =
independent of
this. There are two independent parts.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>There is a static balance: this is =
what you feel
if you partially depress the key and stop...you will feel a force =
upward
against your finger. This is what the lead weights added to the =
key can
adjust. The more lead, the less static force against your
finger.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Then there is dynamic inertia: =
this is what
you feel when you try to *accelerate* the key downward.
The quicker you accelerate the key, the more reaction force =
you will
feel back from the key. The dynamic force is added to the =
static
one to equal the total force you feel with your finger. The =
dynamic
force depends on how fast you depress the key; the static force is =
there all
the time and doesn't change.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Think of it as if you are holding a =
20 lb.
dumbell in your hand. If you just stand there it will pull down =
on your
arm with a force of 20 pounds. If, however, you jerk it suddenly =
upwards
you will feel more than 20 lbs. pulling downward, due to =
inertia.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>The dynamic behaviour of the action =
is changed by
modifying the moment of inertia of the rotating parts. This can =
also
be changed by moving/adding/removing leads, but the =
balance may be
affected as a result.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Hope this helps!</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Don A. Gilmore<BR>Mechanical =
Engineer<BR>Kansas
City</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV>----- Original Message ----- </DIV>
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<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>
<A title=oleg-i@noos.fr href="mailto:oleg-i@noos.fr">Isaac sur =
Noos</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, January 16, =
2004 6:23
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: Cockeyed hammers =
/ Don
Gilmore</DIV>
<DIV><FONT face=Arial size=2></FONT><BR> </DIV>
<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>
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2px solid; MARGIN-RIGHT: 0px">
<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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