A tone bar grommet is a rubber grommet that is inserted between a tone bar and the harp of a Rhodes piano. Its function is to dampen vibrations between these two parts. There are two grommets in each tone bar assembly.
Function:
The grommets work alongside the tone bar screws, and the tone bar springs. Therefore there are two of each of these per tone bar along with a washer that sits between the head of the screw and the grommet. One for the escapement screw, and one for the voicing screw. Being made of a dense rubber, the grommet sits between the screw and tone bar. When the hammer tip strikes the tine, the tone bar vibrates. The grommets are designed to prevent this vibration from moving through the tone bar screw into the harp. This allows decay and sustain of the note to be longer, and the note clearer.
On some later Mark I and Mark II pianos, there is only one tone bar screw, grommet, and spring in the top octave or so. This is because the tone bars have poor sustain, and removing the escapement screw aids in improving this. With no screw there is no need for a grommet or spring either.
Restoration:
When undertaking a Rhodes piano restoration it is common practice to replace the tone bar grommets, along with the screws. This is because the screws can lose their resonant properties as they corrode, and the Philips head itself can become stripped. The grommets crucially are also replaced as they become hard and brittle and allow more vibration to transfer to the harp, reducing sustain. Replacing the springs is optional, but can aid in an improvement of the sound. For the majority of Rhodes pianos, replacement of these will make a positive change to the instrument.
