Piano Voicing (Tone Regulation)
The goal of voicing is to give the piano a tonal palette that is even across the keyboard and offers a controllable range of dynamic expression, from delicately clear and singing pianissimos to brash and full fortissimos. Voicing can be thought of as a final step that follows regulation and tuning towards the goal of optimizing a piano's touch, control and tone. A lot of voicing issues can be addressed simply by making sure the piano is regulated well and in good tune. But in the case that the piano is regulated well and freshly tuned, and you still don't like the sound of the piano, there are certain things that can be done. Before we get started, there are a few indicators that can help you determine if your piano might need voicing. If you've noticed that your piano:
•Sounds noticeably different than when you first bought it,
•Has a limited tonal range compared to when you first bought it,
•Still sounds harsh even after tuning,
•Is harder to play quietly,
•Sounds uneven (some notes stick out as brighter/mellower/louder/softer)
Then your piano most likely needs voicing. The most often and most visible symptom of a piano that needs voicing will be excessively grooved hammers. In general, the hammers on your piano should have a smooth, rounded surface with little to no string grooves at the crown (tip) of the hammers. Over time (this will depend on how often and how hard the piano is played), the strings will create grooves in the hammers. These grooves will harden over time, and will generally cause the tone of the piano to become brighter (or sharper) and more metallic sounding. This can be remedied by removing a few layers of felt on the hammer, which will get rid of the hardened grooves and restore the smooth rounded surface of the hammer. Also, if the hammers are misshapen, or unevenly shaped, that will also affect the tone, and will be something that reshaping the hammers will help fix.
Sometimes the hammers may be shaped well but are too hard, which will also lead to a bright sound. If the sound is too bright for you, a technician can soften the hammers, most often by needling the felt in targeted places. If the hammers are too soft, the tone is often described as muffled, woolly or dead. This can be remedied either by removing some of the outer felt, polishing the felt with high-grit sandpaper, and/or using chemical hardeners to harden the felt in strategic areas.
In some cases, especially on older pianos that have seen lots of playing, it may simply be that the hammers are just too worn to "bring back to life," so to speak, and it would be best to replace them with a new set. Depending on the piano, there are certain types of hammers that will work best with the given design, but there are several independent hammer makers operating today that offer the technician a wide variety of options to address the tonal desires of their customers.
As you can see, there are lots of options for changing the tone of a piano, but in general, each piano, based on its structure, scaling and hammer design, will have its own tonal parameters where it will operate best, and from there the technician can adapt the tone to suit the owner's needs. For even more information on this topic, read the Piano Technician's Guild bulletin on Voicing/Tone Regulation.