"double striking" problem

[Jim]

Hi Avery:

You did a lot of the right things.  The most usual cause of this
problem however is the close let-off.  I also like to use the
closest let-off possible, BUT, it is important to test the blow
with a very soft blow using a vertical stiff finger.  Pianists are
able to play much softer than we mere mortals. While standing,
play each key with a very soft touch (almost to the point of
failure) and you will catch the double bouncers.  What is
happening is that in this type of playing, the key does not reach
the bottom of the stroke, therefore, there is no let-off or after
touch. Increasing the after-touch still will not solve the problem.
Only increasing the let-off will.  All the other things you did were
good, the checking, making the springs right with minimum bounce
at the top etc.

Jim Coleman, Sr.

On Wed, 12 Feb 1997, Avery Todd wrote:

> List,
>
>    I had a problem yesterday with our Hamburg D. One of our piano faculty
> gave a recital last night and had been talking to me about notes "double
> striking" (his term) on very soft playing. It was a VERY soft, but
> noticeable, double strike on some notes (hammers not going into check and
> bouncing back into the string), primarily notes in the middle third of the
> piano.
>    I was able to solve the problem to his satisfaction but I don't *really*
> understand what caused it in the first place so it was pretty much a trial
> and error kind of thing. I just now talked to him on the phone and
> everything worked out very well. He said he felt very comfortable with the
> piano. So, I guess all's well that end's well, but I need to understand
> what causes this type of thing so I can prevent it from happening in the
> future.
>    It's very difficult to explain this problem in words, but here are some
> questions and some things I did to try & solve the problem.
>
>    What really controls how much upward "throw" (I can't think of a better
> term) the hammer does when adjusting the repetition? Is it strictly how high
> the hammer catches on the backcheck? Does the amount of let-off or drop
> affect it also? I know that key dip would also affect where the hammer is
> caught in relation to the strings, of course.
>    The repetition spring tension is what "seemed" to be causing the problem.
> I had to play at least mp to get the hammer to go into check but most
> hammers had very little lift at all. Certainly not strong enough to cause
> any kind of bounce at the top. I even had to increase the tension the
> smallest amount possible to ensure repetition without getting a bounce back
> on very soft playing. I brushed the hammer tails with a suede brush to get
> any residue out the grooves on the tails to try to improve checking.
>    Also the backchecks. They're Hamburg backchecks, about 1-1/2 yrs. old,
> having been replaced when new hammers, shanks and flanges were installed. I
> regulated them as high as possible without getting a rub on the hammer tail
>
> on a hard blow. This also seemed to help some.
>    I even increased the aftertouch a little by raising the hammer line
> slightly, trying to insure that the jack was completely escaping from under
> the knuckle. Yes, I lubed them, too. I did notice that the knuckle leather
> is starting to get slightly loose around the core, so I guess I'll have to
> do that correction as soon as I can put the piano out of commission for a
> bit. Could that looseness have any affect on this?
>    I normally regulate with a very close let-off, especially on our
> performance pianos and have never had a problem. This time, I increased the
> let-off and the drop, very slightly, to see if this would help stop the
> hammers from bouncing back into the strings but I would like to put the
> let-off back at 1/16" without having this problem recur. The bedding was
> also checked.
>
>    Sorry this is so long but I'm trying to give all the information I can
> in hopes someone can explain this to me. I hope I've explained it clearly
> enough for you to understand what I'm talking about. Any comments to help
> me understand the "whys and wherefores" of this problem would be greatly
> appreciated. Thanks.
>
> Avery
>
> _____________________________________
> Avery Todd, RPT
> Moores School of Music
> University of Houston
> 713-743-3226
> atodd@uh.edu
> _____________________________________
>
>
>