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Harp Myth 9
Laminates & Composites
This article is the ninth in an extended series of articles addressing issues and myths surrounding traditional harps and their construction. This iteration is the fifth of five which deals with materials. The use of composites, be they laminated woods or synthetic materials are not traditional but are ever more common.
The "P" Word
Almost inevitably, this brings us to the "P" word... plywood. Plywood is, depending upon the wood, glue and ply angles, up to ten times stronger than a solid wood of the same thickness. When plywood is made, adhesive is applied between the layers and then the whole sandwich is pressed together. The pressure crushes the precious cellular structure of the wood while the cross grains of the ply layers and the glues impose a stiffness in all directions. All of this means that a plywood soundboard cannot move in the same manner as one of solid wood the voice of the instrument is effected.
Plywood, we personally prefer the term "laminate", can be made to resonate nicely when enough active force is applied but it lacks the sensitivity to a full range of frequencies. Laminated woods of all kinds lose clarity in the high range and harmonic in the low range. Laminates are most sensitive to midrange frequencies, a trait shared by the human ear. It is, in fact, due to this shared characteristic that plywood pedal harps derive additional benefit. The pedal harp's range of greatest projection is the ear's range of optimal hearing, giving the harp the advantage of additional "bang for it's buck"/perceived loudness for it's projection. The accompanying disadvantage is that the voice of instruments containing laminates does not mature as the instrument ages. A thirty year old Martin guitar (all of which are solid wood) sounds richer, bigger and brighter than a one year old Martin. A thirty year old laminate guitar sounds just like it did when it was one year old.
The good news about laminates is that the trade-off can be well worth the price. As discussed above, the added strength of laminations are of use in pedal harp construction. Traditional harps also benefit from the use of laminates. Laminates are easier to handle and quicker to build into harps so harps with laminated tonewoods are generally less expensive. This is certainly of advantage to students and those who play primarily for themselves because the decreased entry level price makes it possible for more people to learn and to play harps. Additionally, laminates can be made to produce an extremely warm sound and this is a voice preferred by many players both amateur and professional. Finally, for those who travel extensively with their harps or those who live in extraordinarily dry environments, laminates are less likely to develop significant cracks.
So Shines a Good Soundboard in a Weary World
There are good reasons to use composites. Instrument composites are synthetically generated combinations of graphite (carbon/carbon), an epoxy resin matrix with additives to enhance the acoustic properties and, sometimes, polyesters. Composites are durable and dimensionally stable. They can be formed into shape and, of particular importance, are of low weight and high stiffness. Composites are also not sensitive to humidity, which is interesting in and of itself. In guitars, Ovation has long been using composites for guitar backs while Turner, Moses, Wampeter and others have been fabricating necks, fingerboards and other components for many years.
While our lutherie is continuing to experiment with composites in structural bracing, we are not proponents of composites in soundboxes as primary components. Our reasoning is most clearly defined in words taken from a piece of literature distributed by a composites manufacturer:
In general, composites can be designed to be a consistent medium for sound propagation. Woods have hard and soft parts within the material, inconsistencies which can produce a variety of sonic and structural effects. In wood, long continuous fibers produce the most powerful sound. Fibers in a longitudinally-oriented composite achieve the same goal. Composites, properly produced, do not have pockets, splits, non-uniform density and non-cohesive materials altering their internal structure. Such discontinuities can alter the speed and quality of transmission of a sound wave. Properly designed composites also do not produce frequency peaks and dead spots associated with wood and some other materials. They are not susceptible to variations in humidity.
- Moses, Inc.
In other words, instruments built of composites do not sound like instruments built of wood. They do not have the harmonic character that individual woods bring to a great instrument. They take away the disadvantages of woods and the glories as well. As we understand it, the great Antonio de Torres, father of the modern classical guitar, made a guitar with one of his standard soundboards but a paper mache body. Those who heard the guitar said it sounded good. So shines a good soundboard in a weary world.... We believe that composite-backed instruments are a ringing endorsement of the importance of the soundboard woods. We like woods because they are not perfect. We believe it is those very imperfections which add a grace and life we find precious.
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