A piano hammer (the wool mallet that strikes the strings) has a significant role in the tone of a piano. When we speak of tone, we are not simply speaking of sound production. The tone is how soft or how harsh the sound is that is produced. It also is defined by how full the sound is and how long it lasts when left to ring. Each of these items can be adjusted by making alterations to the shape of the hammer and by hardening and/or softening different areas of the hammer.
The basis of proper hammer function is proper shape. Hammers have a shape that is similar to an egg. The top of an egg is round, not flat. Having a round crown on the hammer is vital to creating proper tone that is not harsh. To illustrate, hold your left hand in front of you with your palm facing up. Then, using your right hand with the palm facing down, strike your left palm (simply put, clap your hands). You probably heard the typical clap that you are used to hearing when you strike your palms together. Now, hold your left hand in front of you again with your palm facing up. Then, strike your left palm with your right hand in “karate chop” fashion. You will hear a sound, but it is much quieter than clapping your hands.
How does this apply to the piano hammer? New piano hammers have rounded crown because it reduces the surface area that is contacting the strings (think “karate chop”). Over time, piano hammers develop grooves and are worn flat, increasing the surface area that contacts the strings (think hand clap). As the surface area of the hammer’s strike point increases, so does the harshness of the tone that is produced. This is because there is a larger surface striking the string which causes excess ringing in the sounding strings. Some people call this harsh tone “bright” or “brassy”. Whatever you call it, it is not a pleasant tone.
Often, when a piano hammer becomes compacted and grooved, a trained piano technician can reshape the hammer to restore the proper strike point and improve the tone of the piano. This is done by filing the hammer to remove some of the felt and restore the rounded egg shape. This on its own can do wonders for the tone production of the piano. Mating the hammers to the strings and voicing the hammers (both topics are covered in a previous blog article) are critical steps that follow shaping the hammers. However, reshaping the hammers is sometimes all that is needed to get the piano’s tone back to bearable.