Front Duplex

[Overs Pianos]

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Kevin,

>    This is a Steinway M from 1995. Looks brand new; no string 
>grooves to speak of, knuckles perfect, case perfect, I suspect it 
>saw light playing infrequently for most of it's life. Wasn't Susan's 
>article about an SD-10?

Susan's article was about an SD-10, but front duplex problems are the 
same regardless of the manufacturer. There are pretty new pianos out 
there which don't sound too pretty, with noises aplenty.

Duplex bars which are:
* larger radius
* softer than the wire
* close to in-tune with a harmonic of the speaking length
* too long
are all factors which contribute to string noise.

Ideally the front duplex should be:
* a small radius (these days we are setting to 1mm or slightly less)
* harder than the wire (when rebuilding we harden the cast in bar)
* shorter, 40 mm is too long, under 30 is preferable though often 
impossible to achieve.
* set to a detuned length, ie. to a length mid way between two harmonic lengths
* set to a height for a string approach angle of not greater than 15 
degrees (or the wire will be cut by the non-deforming small-radius 
duplex bar).

The 'glue on the duplex length' trick (thank you Jim Coleman snr), to 
increase mass and therefore to detune, is a very effective on the 
road fix.

We nickel plate our front duplex bars (after hardening) to improve 
string rendering and to prevent corrosion.

Ron O.
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        OVERS PIANOS
Grand piano manufacturers
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Web:   http://www.overspianos.com.au
Email: mailto:ron@overspianos.com.au
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