stretching wire -- a preliminary test

[John Delacour]

At 21:00 -0500 10/4/08, William R. Monroe wrote:

>I think the point for me is that there are other factors to consider 
>re: pitch drops in pianos than long-term elastic deformation of 
>wire, and they shouldn't be dismissed without due diligence.

Certainly not, but they can be eliminated in tests.

The test I am about to describe is very basic and not satisfactory to 
me, but if there had been no pitch drop from this test I would have 
waited longer before devising a more decisive test.

A length of 17.5 (1 mm) Röslau polished wire was stretched between 
two 7mm wrestpins knocked very tightly into a solid mahogany tapered 
piano leg about 42cm apart so that the wire was only slightly above 
the surface of the wood.  The coils were well knocked down and the 
wire pulled firmly sideways while it was tuned to G-392.  This 
requires a tension of about 150 lbs, which is roughly half the 
"elasticity limit" of the wire --300 lbs (Röslau advertises 395 lbs. 
as the breaking strain of this size).

Over the space of an hour the string was pulled and plucked 
repeatedly and made to hold its pitch exactly under repeated plucking.

During the day of the set-up there was no significant change in the 
pitch of the  note.

Humidity and temperature remained practically constant.

When plucked about 24 hours later a fall in the pitch of the note of 
4 or 5 cents was noted.

48 hours later the note is 9 or 10 cents flat.

We shall see.

The main objection to this test is that the unlikely but not excluded 
possibility of movement in or of the wood is not excluded.  The next 
tests will eliminate this weakness.

JD