[CAUT] Scientific study - Stainless wire (Help!)

[Jim Busby]

Thanks Ric.

Juan and I have talked about this (the science of wire) many times and
while his web site does have a lot of technical data there are more
basic questions I'm after. More practical & down to earth. Maybe "Wire
101" or "Wire for dummies"... (That would be for me)

Maybe you're right (most the science is already there) and I need to
(also) pursue a more subjective and less scientific study as well. It's
fun to be at the start of such things, but, as in writing papers, etc.
the hardest thing to do is to narrow the topic and nail down a thesis.

I wish I understood the math (below) and such as you do.

Now, back to study your post...

Regards,
Jim


-----Original Message-----
From: caut-bounces at ptg.org [mailto:caut-bounces at ptg.org] On Behalf Of
Richard Brekne
Sent: Tuesday, August 28, 2007 6:45 PM
To: caut at ptg.org
Subject: [CAUT] Scientific study - Stainless wire (Help!)

Hi Jim

Sorry to be in late on this, and perhaps this has been covered by some 
of the others already. But a few points just so.  First check out Juans 
own website on these questions. He actually has some of the answers for 
you already.. at least as far as physical properties are concerned.   
Stainless steel wires density is different to standard steel, which 
needs to be plugged into any and all formulas dealing with string 
characteritics. As an example,  McFerrin gives the following basic 
formula (in metrics) for Tension (page 26). T = f^2 * L^2 * d^2 * ((Pi *

7.85 gm)/ 981)  The 7.85 is the string density value for standard piano 
wire.  981 is the acceleration of a freely falling body in a vacum... 
actually 981 centimeters per second per second.  A bit of physics in 
there... but the point is that the resulting Tension for standard steel 
wire all else being equal will be different then Stainless because the 
7.85 is no longer the same value.  For Stainless this value is 7.90  
Actually, average density figures are a bit dodgey in real life... but 
they serve well as a general rule.  Maclom Rose wire is just under 7.8 I

believe just in case that is of interest.

So.. basically what this means is that  the tension on a Stainless steel

wire for the same frequency, length and diameter as a regular wire will 
be higher, and this explains why its breaking tension is reached 
quicker.  Breaking tension has become understood to be a key factor in 
governing piano sound.  Too  low and the string gets tubby... rubber 
bandish perhaps ?..  To high and it gets harsh and tends to break 
quickly... :)  Inharmonicity can be said to be related to a strings 
stiffness... which in turn is among other things governed by how much 
tension is on it and the elasticity of the material used.  Juan claimed 
to me on the phone that inharmonicity of his pure sound in real life 
scaling is generally lower if I remember that conversation right... 
struck me as a bit odd considering that given equal frequency, length 
and diameter a pure sound string would have higher tension on it.... but

then I dont really know how the rest of it all works in.

Bass strings with Pure sound wire will no doubt sound different (again, 
all else being equal) because the core wire has a different average 
density and so the overall average density of the wound string will be 
different.  This will affect all wire sound characteristics.

Pure sound can be used very successfully for low tension instruments... 
indeed one should be able to quite successfully design a lower tension 
instrument then is seen at all in modern piano making I would imagine.d

One thing to keep in mind... is that most of the formulas used for 
strings contain quantities that dont really lend themselves all that 
poifectly to real life strings... and as such must be kept in 
perspective.  Especially the formula for Inharmonicity is a bit dodgey.

It utilizes two quantities that you can find alllll sorts of various 
values for.  Youngs modulus (elasticity) and average density.  Breaking 
strengths and breaking % are ball park figures and will vary 
significantly from delivery to delivery of string material... all 
depending on the the exacting conditions at the time each bunch was
drawn.

You can figure a lot based on math models that will line in general up 
with real life situations.  But in the end you cant take all the guess 
work out of how a piano will sound before you actually get it built.  In

fact I'd estimate that those that buy into the predefinable school quite

overestimate what they can predict... but thats just my opinion and I am

by no means an accomplished designer with 50 years of experience under 
my belt.  I have on the other hand talked to quite of few, and their 
consensus is clear.

This doesnt provide any new questions for you to ask... but perhaps it 
might serve to stimulate you to a few new ones of your own.

Cheers
RicB


    List,

    We (BYU) finally are ready to do some scientific studies of
stainless
    wire. This will be conducted by Physics professors/students here at
BYU.
    Could any of you help me pose some "questions", "queries" or
whatever
    you want to call it, for these studies? 

    One of our student piano technicians is doing his senior project and
his
    professors (who we've bugged for years) are just now getting excited
    about this.

    Here are some things I've thought of;


    1.    What are the actual differences in sound between stainless and
    Mapes or Roslau? (Spectrum, etc.)
    2.    What are the differences in inharmonicity between the two?
    3.    (how?) Do bass strings with stainless core sound different
than
    other core?
    4.    etc....