Fig 3Hammer and voicingClick or 1–6 to throw · V to voice the feltas made · ready
The hammer head, and the newest force pulseTop felt, underfelt and maple molding, seen on its sideLoad cell signal: 1 ms and 25 N a divisionHammer felt gets stiffer the harder it is squeezed. Its force grows as compression to the power 2.5, so a faster blow is shorter as well as harder. Here an 8.7 g C4 hammer hits a rigid anvil: at 1 m/s the felt gives about 1.2 mm and pushes back with 13 N for about 4 ms. At 5 m/s it gives 3.0 mm and peaks near 126 N for about 2 ms. A shorter pulse excites more high partials, which is why loud notes are brighter as well as louder. Voicing changes the felt itself: needling the shoulders softens it (lower stiffness, longer and rounder pulses, a darker tone), and lacquer hardens it. The felt also pushes back less than it was pushed (hysteresis), so the hammer leaves at about four-fifths of its speed. On a real string the contact lasts a little longer, because the string gives way too.