[CAUT] Wire Stretch

[RicB]

Hi JD..

Sorry... typo there, good eyes you spotted a problem right off.  The 
string length should have read 100 for speaking length, not 150.

A 150 length with 0.8 wire (all else same scenario) would result in 
frequency of around 1371 hz undeflected and 1484 hz when deflected 5 mm. 
Tension would jump from 176 lbs to 202 lbs and bearing on the deflection 
point would be around 23 lbs.  With 0.9 wire I get 1218 hz to  1345 hz 
and a tension increase from 182 lbs to 214 lbs and a bearing at the 
deflection of  24 lbs.

Please note these string parameters are not necessarily real life.  The 
spread sheet takes string speaking length, back length, wire size and 
undeflected tension as input parameters, and then calculates undeflected 
frequency and changes in tension and frequency for given deflection 
lengths.  I could plug in some pretty bizarre input parameters if I 
wanted to... :)

Cheers
RicB


    at 11:37 pm +0100 3/5/07, RicB wrote:


     >For a 0.8 mm ¯ string of 150 mm long speaking length, 50 mm back
     >length... and tension at 150 with zero deflection, a 5 mm deflection
     >will increase tension to 189 lbs, cause a frequency change of 248 hz
     >(from 2057 to 2305) and impose a 28 lb bearing force on the point of
     >deflection.

    Well I calculate that to have a 13.5 wire of 150mm in length (a very
    rare occurrence) you would need to have it about note 69 to get a
    tension near 150lbs and the frequency of note 69 is 1396.91 cps.  You
    seem to be saying that you can get a frequency of 2057 cps. from
    150mm. of 13.5 mwg. wire (in other words about note 76) and I say
    that would produce roughly 350lbs of tension and the string would
    break before any upward deflection was imposed on it, let alone 5mm,
    which is inconceivable at any rate at this point of the soundboard.

    Have I misunderstood your numbers?

    JD

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