Keyframe Bedding

[David Skolnik]

Hello Andre, List -
Hope you're well.  Sorry to likely miss you in 
Vancouver in July.  I'd be glad to buy the DVD.
Note: With regard to recent discussion about 
extraneous material, I left Andre's post intact, 
for reference.  I apologize if it seems unnecessary.


There are a few reasons why I don't think the 
tuning fork analogy  applicable to the concept of 
stressing the frame.  For one, the objective in 
the case of the tuning fork is exactly to 
transfer energy to the solid surface, in order to 
magnify its audibility.  In the case of the key 
frame, the objective is to reflect, or minimize the energy transfer.

>The shock, and thus the transfer of energy, causes the other child to
>hop up a little into the air.

While the shock is certainly perceived, it is 
inertia that makes the little critter fly up in the air.

Whatever the weight of the load, it would seem 
that the ratio of energy transfer to energy reflection would be
determined by the mass and rigidity of the 
supporting structure - keys, keyframe, 
keybed.  While stressing a keyframe might be a 
byproduct of assuring a positive interface with 
the keybed, I don't see how the issues of 
developing internal stresses, such as has been 
discussed in relation to soundboards, can apply 
here, since those stresses would impact upon the 
way in which the board responds to the energy 
transfer, whereas we don't want to see such transfer into the key frame.

>The key frame, supported in the middle by posts, the glide bolts,
>carries the weight and automatically transfers the energy onto the key
>bed, which is a part of the 'basic' construction of the 'basis' of the
>instrument.

The weight of the action is supported by the 
front and back rails, and stabilized by the glide 
bolt.  The bulk of the weight remains on the 
front and back.  The better the construction, the 
less energy transfers to the frame and bed.

>So, if the contact between the glide bolts and the key bed is so so...
>the transfer of energy is 'so so' as well.
>If however the contact is firm, so will the transfer of energy be,
>resulting in a louder tone.

I certainly agree that a faulty interface between 
glide bolt and key bed will compromise the energy 
transfer to the string, but I don't see how 
putting additional pressure on a well-set glide will improve things.

Actually, I can see how stressing the newer, more 
flexible frame would add to its own rigidity, 
which, in turn would better reflect the 
energy.  Even if accurately bedded by traditional 
standards, the floppier construction probably 
absorbs a considerable amount of energy.  I would 
still be concerned about friction and compromised 
back rail bedding, but, maybe you persons are correct.

David Skolnik
Hastings on Hudson, NY






At 03:16 PM 7/8/2008, you wrote:

>On Jul 8, 2008, at 8:10 AM, David Skolnik wrote:
>
>>I'm not sure that Andre's tuning fork analogy is operational here.
>>I would need to hear a more thorough explanation.
>
>Hi David, and list,
>
>The principle applied here is the 'transfer of energy', nothing else.
>I always use the analogy of the sea saw, used by children :
>two children on a sea saw and they go up and down fast...
>One child goes down. The sea saw hits the ground (the consistency of
>the ground is important ... remember the endless pro's and con's about
>white conical front punching ? brrrr....)  and the shock of hitting
>the ground is transferred along the sea saw to the end of the sea saw
>and, to the other child going up.
>The shock, and thus the transfer of energy, causes the other child to
>hop up a little into the air.
>The energy is transferred along the balancier (the lever) of the sea
>saw, but also into the post that supports the lever.
>The combined weight of the sea saw lever, the children, and the shock
>of impact of the lever hitting the ground is supported by the post
>that supports the lever, the balancier.
>The heavier the weight of the lever and the heavier the weight of the
>children, the more energy is transferred into the post, and thus into
>the 'ground'.
>
>This is my explanation of what happens to keys and an action, resting
>on a key frame, which rests on the key bed.
>
>The keys (the balancier) and the action (the children sitting on the
>sea saw) represent the combined weight of the balancier and the
>children.
>The key frame, supported in the middle by posts, the glide bolts,
>carries the weight and automatically transfers the energy onto the key
>bed, which is a part of the 'basic' construction of the 'basis' of the
>instrument.
>
>The heavier the weight of the lever(s) and action, the more energy is
>transferred into the ground, the structure of the piano.
>More energy input will cause the structure to respond (re-sound).
>
>So, if the contact between the glide bolts and the key bed is so so...
>the transfer of energy is 'so so' as well.
>If however the contact is firm, so will the transfer of energy be,
>resulting in a louder tone.
>
>If you put energy into a tuning fork by hitting it on a solid object
>and you then bring it into contact with a 'sounding board', the energy
>of the vibrating tuning fork will be transferred into the board.
>The quality of the board of course determines the transfer, but the
>final output it is also determined by the weight (down bearing) of the
>'sea saw and the children'.
>
>In other words :
>More wieght/pressure results in this case in a louder tone.
>
>
>We find analogies everywhere. A good example is the shock absorber of,
>for instance, a car, and, of course, a piano hammer head, or anything
>that transfers/absorbs energy.
>
>
>friendly greetings
>from
>André Oorebeek
>
>Antoni van Leeuwenhoekweg 15
>1401 VW Bussum
>the Netherlands
>
>tel :   0031 - 35 6975840
>gsm : 0031 - 652388008
>
>concertpianoservice at planet.nl
>www.concertpianoservice.nl
>
>"where music is,
>no harm can be"
>
>
>
>
>
>
>
>
>--
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