>> Question: why does a shorter string contact time translate to a "sound richer >> in higher partials"? >> >>Michael Wathen >The hammer that stays on the string longer actually mutes partials that >would otherwise be vibrating while the hammer is on the string. If the >hammer stayed on the string 1 second it would be muting all vibration >(blocking). If it stayed on the string only 1 _micro_, second all audible >partials would be heard. Right?? >David M. Porritt, RPT >SMU - Dallas Yes [well, except for the ones which are multiples of the inverse of the strike point fraction -- i.e., if the string is struck at 1/7 of its length, the 7th, 14th, etc. partials will be missing]. It gets better, though ! Another interesting way of looking at it is via the _production_ of partials as well as their _attenuation._ Now, I'm not a physicist, so I'll do my best on this -- those of you who are jump in, but don't beat me up ! The hammer induces a particular shape into the string not just by the time it stays on the string but by the time over which it delivers its energy. This induced wave is a picture of the sum of all the partials produced by the string. For instance, you can picture that if the hammer were able to induce a long wave wherein the string vibrated only over its whole length, the string would be producing basically fundamental. If instead the wave looked more like ______/\_______ (or maybe ----^v-------, use your imagination), that would be representative of a tone with a greater proportion of high partials to low. Therefore, if the hammer can be made to deliver the same amount of energy over a longer time, a smoother or longer waveform results, and therefore a greater proportion of the tone is made up of fundamental and lower partials. Since the most desirable piano tone is weighted more and more toward the lower partials the farther up the scale we go, a full spectrum is not necessarily desirable, but we want to use all the available energy to produce a strong tone. This is where wool felt comes in -- it acts as an adjustable spring which stores energy, allowing it to transfer that energy to the string over a longer period of time. The stiffer the spring (hammer) the more quickly the energy is delivered, and the spikier the resulting waveform, which can be shown (by Fourier analysis) to be composed of more high partials. The important thing here is that the SAME amount of energy is delivered to the string in either case. Voicing is a matter of adjusting the stiffness of the spring, giving us the ability to shift energy from one part of the spectrum to another WITHOUT losing power. The other side of the coin is that it is possible for the hammer felt to be soft enough that it no longer acts as a spring but as a shock absorber (imagine covering a basketball with marshmallows). The same amount of energy is in the hammer, but is dissipated both as the hammer decelerates at the beginning of contact with the string, and by resorbtion of energy from the vibrating wire. This is why very little needling is done at the surface of the hammer's tip. I hope this makes sense ! Bob Davis, RPT University of the Pacific Stockton, CA
This PTG archive page provided courtesy of Moy Piano Service, LLC