String stiffness and flexibility

As we have already mentioned in our introductory article, variations in the waves formed on a string are what makes one string sound different to another.  And as you might expect, the stiffness of a string will affect the wave and thus the way energy transmits to the rest of the instrument. If perfectly stiff and rigid, no wave motion is generated which means the string won't sound at all.  You absolutely must have some flexibility. 

From a sound perspective, the reason all this matters is because it has been shown that changes in the bending stiffness of a string impact the balance of harmonic and inharmonic frequencies.  Ie stiffness influences the frequency output and by doing so, changes our perception of whether the string is warm, metallic or dull, or any other idiom we wish to assign the frequency pattern we hear.  Specifically, the stiffer the string, the lessprominent the higher harmonics.

So stiffness would be hugely useful variable when comparing strings.  But there's a catch - measuring it is not as easy as determining the string's tension.  You need specialist equipment to get accurate readings.  And even if you had it you would need to standardise the bowing motion applied so that readings are consistent.  Even the bow and rosin used would affect the results.  So unfortunately we need to resign ourselves to the fact we aren't going to get this information from manufacturers soon.  A pity, as it would be a lot more useful from an acoustic point of view than tension.