David, Just a few more words on the subject of hammer weight. In terms of producing the loudest tone from a piano the hammers weight within the parameters you have suggested may be a relatively unimportant factor. It would be helpful to keep in mind the force equation of Newton second law; force is equal to the mass times the execration. A light hammer moving at a faster speed could have the equivalent force upon impact with the string as a heavier hammer moving slower. An example of this is that a penny dropped from the empire state building can do as much damage as a cannon ball dropped from the second story (not including the mezzanine). Another aspect related to the force of impact of the hammer and the string is the energy applied to the key by the player and how much of the energy will be lost in the action before the hammer arrives at the string. After all you cant magically produce more energy; you can only waist it less and use it wisely. The losses in this regard can be enormous as must of us know and the action should be designed to allow the player to deliver a forceful blow without making the action unsuitable for controlled playing at other dynamic ranges. This is probably why the key depth has been established in the 3/8 range. Proper action design and regulation can only minimize the losses of energy in the action. Another problem with producing a powerful sound is the tremendous loss of energy as the hammer flexes upon impact. Felt of any quality or density is very inefficient at storing potential energy. Most of the energy applied to compressing the felt will be lost to internal friction. This is particularly true of too soft felt. This is the point I was trying to make before about the differences between cold-pressed and hot-pressed hammers. Cold-pressed hammers need to be reinforced with hardeners to bring the felt to a point of stiffness that will minimize the energy loss while hot-pressed hammers will already be at this point out of the box. Manufacturers have found this aspect to be convenient but using these heavier hot-pressed hammers can needlessly complicate rebuilding older actions; forcing the technician to more extensive action modifications than would otherwise have been done. I can personally attest to the fact that more problems have been created by using heavier hammers in the rebuilding process than by using too light a hammer. One aspect of producing a powerful tone is the efficiency of the soundboard. It seams from my experience the soundboards condition plays a dominant role in the success of performance instruments. Soundboards that are inadequately crowned, too thick, insufficiently tapered and with incorrect bearing are often to blame for a week tone. Getting the action to work as well as possible is important but that is only halve of the problem. John Hartman
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