[pianotech] Tuning the duplex sections

[John Delacour]

At 19:05 -0700 14/03/2011, David Love wrote:


>Why would that be a surprise?

David, I don't think you can have read my message very carefully.  I 
contrasted two opposite cases, one there the pedal causes the tone to 
'blossom' and the other where it causes it to wither.  If the same 
cause produces opposing effects in two different cases, surely one of 
these effects must be a surprise.

>If you go to the piano, lift the dampers and then simply clap your 
>hands over the strings you'll get some excitement of the strings. 
>That certainly comes from the change in air pressure that follows 
>the clapping of your hands.

No argument there, except that I think it's important to repeat that 
without the soundboard and bridge you would hear almost nothing. 
Your clapping does not excite the strings directly; it produces sound 
waves in the air that impinge on every square inch of the soundboard 
and produces flexural waves in the board that are transferred through 
the bridge to the strings and cause them to vibrate.

>...The front duplex by the same token probably receives some energy 
>from the changes in air pressure from the surrounding air.  The 
>difference is that the front scale is not attached directly to a 
>flexible diaphragm as the soundboard but rather the plate which is 
>acoustically dead, in effect.  Doesn't that make sense?

I'd say, as I think others have recently said, that the vibration of 
the front section of a string comes from direct mechanical 
transmission of stress in the speaking length of the same string 
across the front bridge by what has been called a 'rocking' motion or 
see-saw effect and that any direct excitation by the sound waves in 
the air is infinitesimal.  And this can quite easily be demonstrated 
by experiment.

So my question (and my surprise) remains.  Why does good piano x 
bloom when I lift the dampers and good piano y wither?

JD