Scruffing -was - Over-Strike vs Under-Strike

[Frank Emerson]

> What does scruffing do to the sound?
I think there are two questions here.  What does shank flex do to the
sound, and what does scruffing do to the sound?  Regarding the first, if
you have a shank made of rubber, as you might suspect it were, from the
slow-motion photography, there is a huge amount of energy lost that would
otherwise transfer into a more powerful sound.  Regarding scruffing, it
broadens the "strike point" into a "strike range," damping upper partials.
 
> If the hammer did not scruff, would the piano sound different?
I expect so.

> How hard do you have to play to have significant scruffing in a vertical?
I did not conduct the study, so I do not know what the controls were for
the forces applied to the key.  I think there was a fairly wide range of
forces, representative of normal playing.  I suspect that if the key is
struck with enough force to produce a sound, there is some flex, and some
scruffing. Significant   .... I don't know.

> Is it more significant in a particular range?
The heavier the hammer, the more inertia will influence the flex of the
shank.  On the other hand, the longer the string the less, proportionately,
the "strike range" deviates from the "strike point."  Another consideration
is that as the strings progressively move to a greater angle to the action
motion, ... well, who knows what effect that has.

Hey, I never said I had answers.  I do better at raising more questions.

Frank Emerson

> -----Original Message-----
> >From: Frank Emerson <pianoguru at earthlink.net>
> >Sent: Nov 25, 2006 1:00 AM
> >To: Pianotech List <pianotech at ptg.org>
> >Subject: Re: Scruffing -was - Over-Strike vs Under-Strike
> >
> >It's been a while since I have seen the slow-motion photographic study,
but to the best of my recollection, the shank flexing due to impact with
the strings seems to overpower other considerations.  Uprights could
certainly benefit from more substantial shanks.  I said that my drawing was
exaggerated, but not by much.  It is amazing how an upright hammer flops
around before coming to rest.  
> >
> >Frank Emerson
> >pianoguru at earthlink.net
> >
> >
> >----- Original Message ----- 
> >From: Steve Fujan 
> >To: Pianotech List
> >Sent: 11/25/2006 12:02:22 AM 
> >Subject: Re: Scruffing -was - Over-Strike vs Under-Strike
> >
> >
> >Wow Frank, great sketch!  
> >
> >Hmm......
> >So, if the shank flex causes upward scruff, and the offset axis causes
downward scruff, then could they be "tuned' to cancel each other out?
> >
> >Intuitively, it seems like scruffing and flex are both power and clarity
robbers.  Could super stiff shanks help minimize both? 
> >
> >Steve Fujan
> >
> >
> >
> >
> >On 11/24/06, Frank Emerson < pianoguru at earthlink.net> wrote:
> >How can scruffing occur unless the hammer shank flexes?  It does flex,
and it does scruff, but always upward.  As the flagpoling of the shank
reverses, the hammer begins to scruff downward just as it is rebounding
from the string.  The proximity of the axis of rotation to the string is
less significant than the length of the hammer bore from the strike point. 
This can be seen in slow-motion photograph of action movement.  It is
amazing how much an upright shank flexes.  You would think it would break
before flexing as much as it actually does.  A grand shank flexes also, but
not nearly so much.  The drawing below is simplistic and exaggerated, but
illustrates the point. 
> >Frank Emerson
> >pianoguru at earthlink.net
> >
> >
> >----- Original Message ----- 
> >From: Steve Fujan 
> >To: joegarrett at earthlink.net;Pianotech List
> >Sent: 11/24/2006 12:47:45 PM 
> >Subject: Re: Over-Strike vs Under-Strike 
> >
> >
> >Shifting slightly to the concept of scruffing...    The hammer contact
will always "scruff" towards the hammer pivot axis (unless the pivot axis
could somehow lie in the plane of the string).   The closer the pivot axis
is to the string, the less "scruffing" will occur. 
> >Steve Fujan 
> >
> >
> >On 11/24/06, Joseph Garrett < joegarrett at earthlink.net> wrote: 
> >Upon reading the follow-ups of Jons query, I'd like to wonder which is
> >which. I've always considered "Over-Strike" as the Downward angle of the 
> >hammer, which would put the hammer Beyond Perpendicular. ??? Am I
correct 
> >on that? If so, then, "Under-Strike" would be, where the hammer does not
> >achieve Perpendicular, on contact?? The "Over-Strike" hammer, (on an 
> >Upright), would "scruff", (for lack of a better word), downward, at
impact. 
> >The "Under-Stike" hammer would therefore "scruff" upwards.
> >Do I have all of this backwards? Confused minds need to know what the 
> >consensus is.<G>
> >
> >
> >Joseph Garrett, R.P.T.
> >Captain, Tool Police 
> >Squares R I
>
>