Rocking bridges

John Delacour JD@Pianomaker.co.uk
Sun, 23 Dec 2001 22:51:55 +0000


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The phenomenon of the piano bridge rocking and of this bodily rocking 
motion of the bridge contributing to the transfer of the note 
produced by the string to the soundboard has been put forward 
repeatedly by Ron N., Ron O. and Del.

I would like to consider this interesting and undocumented theory at 
a very basic level.



To simplify things I thought it would be a good idea to eliminate as 
far as possible any impediment to the bridge's rocking, such as the 
tension of the other strings and the fixing to the soundboard, so the 
drawing above shows a string (s) of some material stretched between 
two pins (p) and passing over a bridge (b) that is curved at the 
bottom to allow it to rock and roll. The string (s) cannot slide over 
the bridge top.  Out of the top of the bridge comes a needle (n) that 
ends in a pointer (a) running round a scale (d).  Clearly if pressure 
is applied to the string at s or anywhere, the pointer (a) will move 
clockwise as the bridge (b) rocks and will return to zero when the 
pressure is released.  The base can be considered anything fairly 
rigid and is not pertinent to the design; it is in no way to be 
considered a representation of a soundboard.

I will describe the device in more detail once it is accepted as a 
realistic schematic representation of a stringed instrument with a 
bridge that is more than usually free to rock.

JD

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