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Harp Myth 3
Flat, Staved and Round Backs
This article is the third in an extended series of articles addressing issues and myths surrounding traditional harps and their construction.
Arch Nemesis
As beautiful as staved-back and round-back folk/traditional harps are, unfortunately, they represent one of those cases when physics works in opposition to the eye. In acoustic terms, the myth is that every frequency, no matter what direction it travels when it leaves the inside of the soundboard, will have a properly aligned portion of the back to actuate. Theoretically, this is true but it is only part of the story.
In virtually all stringed instruments, the back and the front (the soundboard), are meant to work in conjunction with one another to generate the voice. As the soundboard is activated by a string, its movement serves to compress and express tonal frequencies in complex patterns which then excite the inside of the back of the instrument. When the back resonates, frequencies to which it has responded are altered and themselves expressed, some returning to the inner face of the soundboard in an even more complex array. This interaction is what gives an instrument depth and life and some of the color in its voice. In simplest terms, the back of a stringed instrument needs to be able to move as freely as possible.
Now, think mechanically. An arch is a mechanically stronger structure than a plane. Meaning, all other things being equal, it takes a greater amount of force of frequency to generate movement in an arched surface than in a flat one. A flat back can be activated by a string more efficiently, yielding potentially greater sensitivity than the same force applied to a rounded back. Staved backs also suffer some of the problems of an arched surface. While each stave is, itself, a plane, the nearness of every point on the plane to a joint serves to generate losses in sensitivity. Joints contribute to losses due to the glues embedded in the fibers and the juxtaposition of grain direction, one stave to another. Additionally, staves are narrow pieces of wood and are unable to produce the frequencies that a large flat area can produce. This is the same reason that soundboards are not this narrow. It is also the same reason that a big speaker has an advantage over a small speaker - it moves more air and is sensitive to a larger range of frequencies.
Think about it in terms of other instruments with which you are familiar like the Ovation guitar or a Neapolitan ('taterbug) mandolin. Ovation has marketed themselves extremely well but, with rare exceptions, players, performers and builders agree that the Ovation sound is heavily mid-range. Usually, it is the sound of an excellent piece of soundboard wood bouncing off of plastic. It tends to lack the subtleties and harmonics that are the trademarks of fine guitars. This is not to say that there are not lots of folks who enjoy the Ovation sound. It is to say, however, that no one would confuse the voice of a Martin or Gibson or Taylor or Santa Cruz or a Somogyi for an Ovation. The same is true of the Neapolitan mandolins. When Gibson introduced their flatter mandolin, the little bowl backs were blown out of the arena by the larger, richer, brighter Gibson voice.
The exception in staved backs is the lute. The lute was compensated for its rigid mechanical structure by making the wood of the back so thin (1.5mm thin) that the soundboard was able to easily activate the back. The downside is that significant tuning and re-tuning is necessary. To top it all off, the thin woods can not move enough air so lutes always have comparatively soft voices. [It is worth noting here that there are many modern luteshaped objects which classical luthiers refer to as "Galutes". They are lute shaped but the woods are the thickness of guitar woods so they are not at all comparable in voice to real lutes.] Harps cannot mechanically tolerate an extremely thin back without other tradeoffs.
There are many harps with round or staved backs that have beautiful tone. The point is, that all other things being equal, a flat back can be controlled by a luthier to voice a wider range of expressed tones. The joy is that the hand of every Master luthier takes these unchangeable Laws of Physics, wraps around them the art of their own personal work and lends the gift of diversity to this most ancient of strings.
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