Steve's Corner - Upper Notes with Low Sustain
There are occasions when the upper notes of the piano either do not sustain or lose their sustain over a period of years. This can be traced to a change in the apparent mass or loss of "freedom of vibration" of the tone bar/tine assembly.
The tine/tone bar assembly is a tuning fork with unequal legs. One leg (the tine) vibrates more than the other leg (the tone bar), but at the same frequency. Both parts are tuned for that specific frequency. The tone bar is gross-tuned by its length; the tine is gross-tuned by its length and fine-tuned by the spring, which acts like an adjustable weight. This concept is similar to the pendulum of a grandfather clock or a mechanical metronome. Any change in the apparent mass of the tine/tone bar assembly causes a shift in the frequency it was tuned for, hindering its sustaining properties. This is more important to the upper notes than it is to the lower notes.
The tine/tone bar assembly is intended to "float" on its adjusting tone bar springs, isolated from the mass of the tone bar screws by the rubber grommets that mount into the tone bars. Sometimes the tone bar springs crimp the inside of the grommet and allow the tone bar screw to come in contact with the tone bar: the result is a loss of sustain. After a number of years with the grommet being crimped, the grommet becomes permanently deformed. At this point you can do two things to improve or restore the sustain: either replace the grommet or force the grommet to reset. You can attempt to get the existing grommet to reset by removing it and loosening it up by rolling it vigorously between your fingers. By doing this, you are trying to get it to reform to its original shape. This can be helped by soaking it in Armor All (a protectant sprayed on car tires) before you roll it between your fingers.
Another thing that has caused the grommet to fail as an insulator is one of the types of tone bar screws that were used for a period of time. Originally the tone bar screw (#8x 11/2) was not threaded all the way up its shank: the 5/8" portion under the head was smooth. Then, for a while, a fully-threaded screw was used. Initially there was no difference, but over the years the grommet oxidizes and the threads dig into the grommet, helping to harden it. Insulation is lowered and sustain is affected. Massaging the grommet as previously mentioned plus filing down the threads of the tone bar screw should result in an improvement. Only file the threads down (not off) that are under the screw head and that go through the grommet, for about 1/2" of length.
- Chapter 2:
The RHODES Modular Action
- Chapter 4:
Dimensional Standards and Adjustments
- Chapter 8:
Early Design RHODES Pianos - Action (Prior to 1975)
- Chapter 10:
Early Design RHODES Pianos - Dimensional Standards and Adjustments