(40) Soft Pedal: Hammer Voicing
Grand pianos: The soft pedal (the left pedal) is used to change the mood (timbre, tone) of the sound from percussive to more gentle. It is not designed to produce softer sounds, a fact many pianists do not know. Thus "soft pedal" is a misnomer for grands — in order to play pianissimo, you must simply learn how to play softly. You can produce almost as loud sounds with the soft pedal depressed as without. One difficulty with the soft pedal is that it (una corda, or more correctly due corde for the modern grand) is often not indicated, so the decision to use it is left to the pianist. Another problem is that too many teachers do not teach how to use it correctly.
In grands, the soft pedal causes the entire action (including the hammers) to shift to the right so that the hammers miss one string in the three-string section when it is fully depressed. The amount of shift should be the distance between adjacent strings in the three string section so that the two struck strings will hit the grooves of adjacent strings; otherwise, the sounds will not be even. The main requirement is that the unstruck string should completely miss the hammer.
The unstruck string acts as a reservoir into which the other two strings can dump their energy; the struck strings will drive the unstruck string into vibration. Since the vibration of the unstruck string is in anti-phase with the struck strings (a driven string is always in anti- phase with the driver), it takes the edge off the initial prompt sound and at the same time, excites more horizontal vibrational modes than when all three are struck in unison. The horizontal vibrations transfer energy less efficiently to the sound board and produces a softer sound with longer sustain.
When the soft pedal is depressed, only two strings can produce the prompt sound but eventually, all three strings contribute to the after-sound because the three strings are coupled. This reduces the prompt-sound so that the sound is less percussive.
In the double and single string sections, the strings have much larger diameters, so when the action moves sideways, the strings hit the side walls of the grooves, thus giving them a horizontal kick and increasing the after-sound by increasing the horizontal string vibrations. Thus the change in timbre is similar to that in the three string section. This mechanism is fiendishly ingenious!
Pianists not educated in the use of the grand's soft pedal will often use partial soft pedals and claim that it softens the sound. That is certainly true, but the effect is unpredictable from piano to piano and from note to note on the same piano. It is impossible for the piano technician to align all hammers and strings so accurately that the unstruck string will miss the hammer at the same pedal travel for every three string note. Thus the partial soft pedal effect will be uneven and non-reproducible from note to note. This is why a partial soft pedal is not a correct pedal usage; it is not a design feature of grands.
With experimentation, it is possible to use a half soft pedal in which the strings are shifted half way so that they hit the soft "hills" between grooves, producing very soft sounds. This might be one way to play PPP. It might be a way to play softly on a piano that needs voicing badly. Thus, with increasing pedal travel, the sound changes from normal to very soft to slightly soft and change in timber. Every student must be taught the correct use of the soft pedal on a grand, which is to either depress it all the way, or release it completely. What kind of sound does it produce? When do you need it? The only way to correctly play softly on a grand is to make sure that the hammer is properly voiced.
The mistaken use of partial soft pedals with grands is so common because it works for uprights and digitals, and most students begin their lessons on them. In most uprights, the soft pedal causes all the hammers to move closer to the strings, thus restricting hammer motion and decreasing the volume; it is a true soft pedal, and a partial soft pedal works. Unlike the grands, loud sounds cannot be produced on an upright when the soft pedal is depressed. It has only a minor effect on timbre. There are a few upscale uprights in which the soft pedal works similarly to that of the grands.
Hammer voicing: If it is necessary to close the grand lid in order to play pianissimo, the hammer almost certainly needs voicing [re-shaping, needling, etc., (78) Polishing Capstans, Hammer Voicing]. Grands are designed to be played with their lids open. Students should practice with the lid open because they will perform with the lid open, and it is the only way in which you can hear the true sound of a grand, including PP and FF. With properly voiced hammers, you should be able to control soft playing to any desired degree with a open grand. With worn, compacted, hammers, playing PP is impossible. Too many students had never practiced PP because it was impossible on their pianos.
A compacted hammer transfers its energy to the strings during an extremely short time interval at impact and the hammer immediately bounces off the strings. This high efficiency of energy transfer gives the feeling of a very light action. That is why there are old grands that feel feather light. Softer hammers will make the action feel heavier. This is because, with the softer impact point of the hammer, it stays on the string longer, so that the string is pushed out of its original position before all the hammer energy is transferred to the string. The energy transfer becomes less efficient and the pianist must use more force to produce the same volume of sound. Thus voicing can change the apparent key weight more than lead weights. The piano technician must strike a compromise between voicing the hammers sufficiently soft so as to produce a pleasant tone and enable pianissimo, but sufficiently hard so as to produce adequate sound. For all except the highest quality pianos, the hammer needs to be on the hard side in order to produce enough sound and to make the action feel nimble, which makes such pianos difficult to play PP. This in turn can "justify" use of the soft pedal when it should not be used. The majority of practice pianos are not voiced often enough especially because uprights don't produce enough sound to begin with, and they are effectively closed pianos, unlike grands. Voicing the hammers would further reduce the sound output.
The action should also be regulated in order to enable PP (the let-off properly minimized, etc., Reblitz, Arthur,). Piano owners who know nothing about voicing can make the piano tuner's job difficult because, after the hammers are properly voiced, the owner will complain that the action is too heavy to play. In reality, the owner had become accustomed to playing a feather light action and never learned how to play with real power to generate that gorgeous piano sound. Compacted hammers, when played FF, will produce a harsh, unpleasant sound that can damage the ears [(61) Hearing Loss]. Piano owners should make sure that their tuners can voice hammers because many tuners do not routinely voice hammers.
The fact that a partial soft pedal should not be used on a grand should not be controversial but often is, because even some advanced pianists mistakenly think that (1) the soft pedal is for producing softer sounds and (2) if a full soft pedal gives a certain effect, a partial soft pedal should give a partial effect on a grand. Anecdotal accounts indicate that use of partial soft pedal on a grand is widespread. One might think that we should be able to use a partial soft pedal with reproducible results by a very slight soft pedal, in which case all the strings in the 3-string section will hit the sides of the grooves in the hammer. When the strings just miss their grooves, the sound will be softer because this area of the hammer had not been compacted by previous playing. Even this scheme will not work, because it will affect only the 3-string section, resulting in a jarring transition from three string to the two string section. Also, nobody has enough foot accuracy to control such a small pedal action.
In summary, "soft pedal" is a misnomer for the grand. Its main effect is to change the timbre of the sound. A loud sound played with the soft pedal depressed will be almost as loud as without the soft pedal, because roughly the same amount of energy was transferred to the strings. Of course, the sound will change, because its timbre has changed. Provided that the piano is regulated and the hammers are voiced, PP will be possible without the soft pedal. A partial soft pedal will produce unpredictable, uneven effects. A partial soft pedal works on most uprights and digitals, but a partial soft pedal habit cultivated while practicing on uprights and digitals can produce unexpected results when performing on a grand.