Latest version: 26th September 2015
Rhenish instrument makers devised a very simple hammer mechanism during the 1760s that would adapt their clavichord designs to create an affordable pianoforte. It consisted in fixing a pear wood pivot block [Kapsel] to the back of the key, slotted to support a hammer in the form of a 2-armed lever. The one shown left is typical of many. As the finger presses the front of a key the distal part is lifted till the back of the hammer (here covered with white leather) strikes the underside of an overhanging shelf, also functioning as a hitchpin block. [See drawing below.] There is no agreed name for such actions in old documents but in the 20th century German scholars termed this Prellmechanik (implying a 'flip action') as first proposed by Walter Pfeiffer, c.1935. A cut-away view shows how this works:As you press the key the tail end is lifted, so that the distal end of the hammer hist the underside of the overhanging bar, flipping the hammer head up to sound the strings [not shown]. The arrangement shown here is the most frequent form, in which the hitchpin block and the flip bar [Ger. Prelleiste] are combined in one piece.
A serious disadvantage of such mechanisms is that the hitchpin block is weakened by the necessity for it to overhang its support structure. Also, the hammer heads must be tall enough to reach beyong this structure to contact the strings. (Observe that there is no nut for the strings to bear down upon and that if the hitchpin block were made thicker, for strength, the hammers would have to be even taller.) There is a further disadvantage, noted by Schiedmayer & Dieudonne in their Kurze Anleitung des Forte-pianos, 1824. If the musician holds down the keys, as it were tenuto, the hammer follows the intended path to strike the correct strings, but should he play staccato the key will have fallen back, so the hammer follows a different path and may make an unintended half strike on the next semitone above. This, argues Schiedmayer, is a very strong recommendation for the so-called 'English action' in which the hammers are attached to a fixed rail. In such actions the path of the hammer head is always the same, regardless of how you strike the keys.[Note that this problem does not arise with 'grand' pianos because the strings are parallel with the key and hammer.]
Nevertheless, owing to its simplicity, the above action, simple retro-oriented Prellmechanik, remained in use in south Germany, north Italy (Sud Tyrol), northern Spain (Catalonia), and among emigré German craftsmen in north America. Most of their instruments are either of C—f3 compass, later FF—f3. However, there is a very late 6-octave example in Nazareth PA, made by one of the Moravian Brethren named Anton Meyer, dated 1839 showing that provincial or inexperienced craftsmen continued with the concept long after more accomplished makers had abandoned it. Another 6-octave [FF-g4] specimen was made by Geronimo Bordas in Barcelona c.1830 (National Music Museum, Vermillion SD).
In 18th century examples the touch is usually very shallow, which suited hands accustomed to the clavichord, but the concept was capable of improvement, making the touch more even and manageable by inserting an under-lever as shown here. [Pfeiffer named this Prellmechanik mit Treiber]. It is not clear when this was invented but it is often seen in the 1790s.
This 2-lever type can be set up so there is very little lost motion and, if so desired, it can be designed to give a higher velocity ratio, but the main advantage is that the touch is more regular and even. Pianos with this action, like the single lever type, often have no separate keyframe, the balance rail being fastened to the bottom board as in so many clavichords. An example of this type is the instrument by John [Johann] Huber in Easton Pennsylvania. There are many more in German museums.
NOTE: It is NOT a distinguishing mark of German 'square piano actions' that the hammers should be turned to face the player [Retro-oriented as I have designated it]. It is perfectly possible to design a Prellmechanik, or flip action, with the opposite orientation of the hammers. However, for the basic single lever type it is necessary to insert a flip rail, or Prelleiste, above the keyboard, which must be removed before any key can be extracted. There is such an instrument in the store rooms of the Germanisches Nationalmuseum, Nuremberg, catalogue number MIR1153. But this is not an impressive specimen; it may be a converted clavichord, though it seems to have an unusually helpful amount space under the strings, suggesting that it was always intended for hammers.
A better solution is found in the work of Ignaz Senft of Augsburg, who devised an intro-oriented Prellmechanik with an under lever projecting to the rear, and it was very successful technically, but perhaps not very robust and durable. Only a few examples survive. Senft's action has been cited in many specialist reference books, but its arrangement seems to befuddle the minds of most commentators, who seem unable to classify it: it is certainly a Prellmechanik, with intermediate lever, but intro-oriented. Notice that here there is no need for a tall hammer head. In fact Senft's action is very responsive, and very ingenious.
Other variations on the basic Prellmechanik theme are conceivable. Examples with an escapement pawl, as used by Stein in flügel-form pianos, do not appear in Tafelklaviere before c.1795. Design constraints mean that you must either have very short hammers, or a weak hitchpin block. At Finchcocks there is a neat little single-strung specimen by Anton Walter which overcomes these problems, partly because its compact design with bass note C makes the structure more rigid, and partly because with only half the number of strings it places a much reduced strain on the case structure. It is a delightful instrument, provided that you can dispense with the bottom half octave.
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