String noises revisited

[Ed Sutton]

Allen-

We need protocols to diagnose longitudinal mode and agraffe noise.

If I understand Jim Ellis' book, in a 7 foot grand piano, longitudinal mode noises will tend to occur in octave 3, and they will tend almost always to be at or near the frequency of the 15th partial. There will probably be a slight delay after the attack and before the sound develops. If you make slight changes in the pitch of the string, the longitudinal mode sound will not change pitch, but will disappear when the pitch has changed such that the modes that excite the longitudinal mode are outside of its resonance band.

Since the longitudinal mode is excited by the combined energies of the 7th and 8th partials, if you can excite the string at the 1/8th or 1/7th point of its length, the longitudinal mode should be significantly less.

For agraffe noises, I've found that inserting  a screwdriver between the strings behind the agraffe, and turning it slightly, will sometimes make the sound clear up, in which case shoving a little wedge of hard leather between the strings can clear up the noise.

There must be some other agraffe diagnosis techniques short of replacing the agraffe to see if it makes it better.

Ed Sutton
  ----- Original Message ----- 
  From: Allen Wright 
  To: Pianotech List 
  Sent: Friday, July 11, 2008 7:02 PM
  Subject: Re: String noises revisited


  this line of thought is very interesting to me, as agraffes was what I first wondered about with this noise, but didn't do anything about. I considered changing one to see if it would make any difference. I guess it wouldn't hurt to do that...this only makes sense if the theory is that there's something operating with agraffe problems in the tenor region (plain wires) that's not happening elsewhere? It seems a bit odd to me that so many B's would have an agraffe-related problem in the same few notes. 


  I just returned from a short trip away, doing some damper troubleshooting in a very nice 4 year old Hamburg B outside Glasgow. After finishing up the day with tuning and some voicing, the owner was quite happy with the improvement. But as he played up the scale he immediately noticed the same high ringing we're discussing here - on the D#3 - and pounced on it. I couldn't believe this same phenomena was haunting me again! I basically said, "sorry - this is something common to the B's and I'm afraid I can't help you with it (now, at least) except for a bit of voicing. Hopefully you won't notice it in actual musical contexts". Which is probably largely true; but still, I'd like to figure out what this is and be able to make it go away. People notice this sound; that one small section jumps out as having a different quality.


  Allen




  On Jul 10, 2008, at 8:14 PM, Kazuo Yoshizaki wrote:


    I recently had this problem with an Essex grand although I don't know
    if this is the problem that Allen is facing now. It had a noticeable
    jing with forte. I loosened the strings and 'dressed' the inside of
    the agraffes by tweaking the strings with a string hook, and the noise
    was gone.


    On Thu, Jul 10, 2008 at 1:33 AM, <BobDavis88 at aol.com> wrote:




      Allen, I'm still thinking about this, and, although I don't know if it
      relates to the Hamburg pianos, there was a run of New York pianos in the
      seventies that had a poor agraffe profile. That is to say, the shape of the
      inside of the agraffe did not make a good termination. I have a couple of
      D's that exhibit this in the tenor. We restrung one, changing the agraffes,
      and it really cleared up the high metallic whistle. Inspecting the old and
      new agraffes under magnification really showed up the difference.


      On the other D, increasing the draft angle slightly by putting a center pin
      under the string (on the counterbearing felt) made a big improvement,
      although we'll still eventually want to replace the agraffes.


      Let us know when you find out for sure what it is.


      Bob Davis




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  Allen Wright
  London, UK


  http://www.broadjam.com/akwright






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