Contact Ratio

Mensurix 5 and MiniMens Simulator introduced the new parameter “Contact Ratio”.

It is a ratio between the time the hammer touches the string and the time the wave traveling along the string from the strike point to the bridge and back to the strike point.

If this two time are equal, one have a ratio of 1. This means that the hammer moves away from the string as the string wave returns from the bridge and gives therefore the maximum of energy into the first harmonic. This contact ratio is highly dependent of the string tension and of the hammers stiffness. Assuming a smoothed stiffness in the hammer set will show any differences in the scales strike point stiffness.

Unfortunately strike point stiffness of the strings of a note (K) can not be taken in correlation to contact time (and therefore contact ratio) on the break from bichords to trichords, since the hammers damping loss is different if there are 2 or 3 strings. So any theoretical calculation of contact time with static formulas go too far off from whats happen real.

With the dynamic model of Mensurix one can measure a realistic contact time.

The Reference Graph allows you to make a sound classification of two different instruments.

Or you can use the contact ratio to set your string diameters at the breaks to achieve a better sound balance.

On the graph below, the Example 1 curve is from a Hamburg grand piano, and Example 2 is from a Vienna grand piano. One can see, that around the break the contact ratio of the Hamburg piano lies nearly on a straight line indicating a well balanced sound that will keep its line also if the hammers intonation becomes lost in time.

A relative sound classification can be seen in the Graph 2 (with Hamburg as grey curve in reference) directly since around the break and the upper bass region on the Hamburg model the contact ratio is higher (with a more bass pronounced sound), wheras on the Vienna model has less contact ratio resulting in a more harmonics pronounced sound in the bass region. This must not be a question of quality, but shows the instrument specific sound characterization.

 

The blue line in the graph marks the break, (on the keyboard the red marker)

Graph 1

Graph 2

copyright (c) 1988-2004 Bernhard Stopper