REED LONGEVITY; from ELASTIC to PLASTIC by Rick Epping
Hello Harp Techs
Rick Epping retired from Hohner USA in 2005, but his research and body of work continues to serve the harmonica community. Reprinted here is Rick Epping's paper on "REED LONGEVITY; from ELASTIC to PLASTIC":
Why do harmonica last year is for some players yet others wear them out in a short time? What causes a harmonica reed to wear out and what can the player do to improve a harmonicas longevity? A look at the reed material, and the activity going on in response to force may hold the answers.
Breath pressure applied to reed during normal playing causes it to swing, or flex back-and-forth in an elastic manner, with the extent of the reeds swing determined by the force of the breath pressure. The manner in which the reed changes it's shape during this process of flexing is called elastic deformation.
Like a spring, a flexed reed will return to its original shape upon cessation of breath pressure. There is, however, a limit to the degree to which a reed can be flexed where it will resume its original shape. Strained beyond those elastic limit through excessively hard playing, the reed undergoes plastic deformation, where it's structure is permanently altered.
How does plastic deformation take place? Looking microscopically at the reed, we find that it is made up of closely packed crystalline grains. These crystals are neither perfectly regular in shape nor pure in elemental makeup (refer to figure A).
Within the atomic lattice of each grain of metal we find irregularities in the form of incomplete layers of atoms, called dislocations, shown below as a vertical line of black dots. Stress on the reed can cause gradual slipping along lattice planes ordering these dislocations, resulting in a permanent alteration of the crystals shape (figure B).
Dislocations and other defects in the atomic lattice are plentiful in all natural crystals. They do not necessarily cause an adverse effect on the material; in fact, they play an important role in strengthening the reed and may offer an explanation to the question of how a harmonica reed is "broken in".
As numerous dislocations move throughout the material in response to continue stress, they meet, entangle and block each other's further movement. In addition, dislocations create exposed slip planes in the grains surfaces that help lock the grains together and resistance movement between them. The result is strain hardening, where the material strength is increased as is ductility is decreased. Strain hardening is utilized in the process of cold working metals to produce a desired strength or stiffness of the material.
Minor variations in thickness along the length of a new read will mean that some areas will be thinner and more flexible than others. If a new harmonica is play gently and softly for the first week, as Hohner recommends for breaking in, these more flexible various in the reed may have an opportunity to become strain hardened and thereby distribute some of the work of flexing to nearby, thicker areas of the reed. Giving a reed the chance to develop an even flexibility along its length (through gradual strain hardening of the more flexible areas), greater volume or stress levels that remains safely within the elastic limit of the entire read maybe possible.
Some of the stress – related changes in the atomic structure of the reed develop at a constant rate; That is, they cannot be Exceller rated by an increase in the amount of stress. If they knew her Monica is subject to the high stress levels associate it with loud or hard playing before it is given a chance to break in, the thinner, more flexible areas of the reed may undergo excessive plastic deformation.
A further point to consider is that a reed elastic limit is affected by temperature. A cold reed is more brittle and more susceptible to fracture propagation then is a warm reed. If there is no opportunity to permit a cold harmonica to reach temperature gradually,The player should at least spend a moment playing gently to allow the reeds a chance to warm up with breath. Warming a chromatic harmonica before playing also helps prevent the accumulation of breath condensation on the replacements, a common cause of sticking and popping windsavers.
In conclusion, the key to reed longevity may be twofold; first, break their harmonica in gently and, second continue to play with the breath pressure that keeps the reeds within their last limit. Moderate pressure should be sufficient to produce both good tone and volume as well as ensure a good life for the harmonica.
In the words of that little label inside your harmonica box, "so that your new Hohner harmonica will continue to give you many years of music full satisfaction, we suggest you follow these rules: (one) handle it carefully (two) always keep it clean (three) keep it covered in this special box". Truer words were never spoken.
Thank you Rick Epping
Your Harpsmith, Kinya
