During my technical course on hammer voicing in Stuttgart with Renner company, I honed the complex and essential technique of voicing to achieve a perfect sound.
The process starts with raw wool, which is expensive due to its long fibers that enhance the quality of the felt during processing. Raw wool has a curly structure that is then compacted through a massive washing machine that blends different types and sizes of wool.
Next, the fibers are carded in the same direction, both horizontally and vertically, to determine the grain of the felt. The wool is then pressed and goes through a machine that steams the felt, causing the fibers to expand and obtain a hard and flexible material. This felt is further pressed to achieve the necessary hardness for the hammers.
The optimal elasticity and flexibility of the final hammer contribute to an excellent sound and require less work during voicing compared to a less flexible hammer. The felt is washed with special soaps to make it soft and then prepared for gluing with wood, obtaining the desired shape through a press. To restore elasticity, the hammer fibers are needled during voicing.
Voicing alters the sound quality and affects the horizontal equalization of the keyboard, coordinating the harmonics and refining the sound of individual notes vertically. It has an impact on the overall tone of the piano. If the hammers are of good quality, the tone can be modified to suit the expressive needs of the pianist.
After piano usage, the shape of the hammers undergoes slight changes. As some hammers are used more than others, tone differences develop over time among individual notes. Some hammers harden more than others. These increasing differences make the tone inconsistent and difficult for the pianist to control, limiting its potential. Voicing corrects these disparities, restoring consistency both horizontally and vertically. The piano technician intervenes on the hammers and strings to achieve a uniform sound response with the same key strike.