[pianotech] even touch to test ppp

[peter sharp]

Interesting. Perhaps I could offer a few ideas about the variation in your strike weights of up to 6 grams.
What sort of numbers did you get for strike weight? One less gram sounds intriguing for no strike! 
Regardless of friction eveness and regulation, the variation in component masses within the action key would vary the effort at the key front, and therefore the required strike weight for each key.
For instance, if the ratio is, say, 5.0 at one key, then a variation of 6 grams in strike weight represents a change of less than 1 gram at the hammer, allowing for inefficiences due to friction and internal loads within the action, such as the weight of the whippen assembly.
Therefore, any small discrepancies in hammer mass are magnified at the key front more than five-fold. Similarly for variations in key out-of-balance mass, including leading and position of the backchecks.
A slight variation in action ratio between keys (have you measured half a dozen?) will also contribute to a variation in mechanical advantage, again regardless of eveness of friction values. 
Jack movement across the knuckle would also be a suspect here, and is a big factor in the ratio change as the key is pressed. Because of the non-linear, or accelarated, action displacement, any given strike weight will result in different hammer velocities, albeit difficult to measure and very slight.
In the end, my bet is that you might be expecting just a little too much from the piano mechanics.
Another thought is that the slow drop test you are using tends to give more an indication of the static friction within the action, whereas when the piano is being played, even slowly, the friction characteristic will change to a dynamic value.
I tend to rely on finger touch to feel if the pianissimo control is even, including hammer after-strike position, since the hammer will not be checking at such low dynamic. The pianist may be playing his ppp anywhere on the key, not just at the front, so we must also recognise his ability to adjust his touch as he plays. (read "his/her" for any "his" above :) )
Peter Sharp







________________________________
From: Gene Nelson <nelsong at intune88.com>
To: pianotech at ptg.org
Sent: Tue, 26 January, 2010 12:24:54 PM
Subject: [pianotech] even touch to test ppp

Just curious if anyone does more than rely on their hands to judge how evenly the entire piano responds at the softest possible playing.
In an action that is well regulated and balanced with friction +/- 0.5g from key to key and hammer strike weights evenly graduated using a Stanwood curve - I do not have confidence in my touch while playing chromatic scales to judge ppp playing evenness. Sometimes a key will not hit the string and it is not consistent, it will vary across the piano so I blame my lack of even touch.
I used Spurlock gram weights, set on key ends (like when measuring down weight) and let it free fall in a controlled manner, adding or taking away weight to zero in on a number that could mean something, like how many grams to get the hammer to contact the string.  One gram less gets no sound. Did this with and without sustain pedal.
Suprised to find discrepancies of up to 6 grams and the discrepancies stay about the same with or without the sustain pedal.
Any opinions here - am I splitting hairs? Does the above sound like a valid test?
Also, I am a bit puzzled about how to account for the discrepancies. As all pinning and key frictions are very close, it could only be a mass thing?
Any thoughts on this.
Gene 



      __________________________________________________________________________________
See what's on at the movies in your area. Find out now: http://au.movies.yahoo.com/session-times/
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100125/a2123460/attachment.htm>