[ the craft of the guitar maker ]By TREVOR SEMPLE
3. Soundboard MaterialsPLAYERS often express strong preferences for cedar or spruce soundboards. Makers, too, often prefer one or other material to work with. Last time we looked at the origins of both timbers, and now it may be interesting to compare their qualities for instrument soundboards.
Both are, of course, perfectly valid structural materials for instruments, along with a whole host of others, like plastic, metal, animal skin or ceramics. Strength alone is not the test of a good soundboard. Other rather unexpected qualities of the material's structure colour the sound.
Stringed instrument notes usually have very complicated waveforms - individual notes look nothing like sine waves because so many higher harmonics get mixed in with the fundamental. Every material will act as a filter to these harmonics, letting some pass more easily than others. This the ear will perceive as tone. Apart from tone, the density of the material will be a major factor in determining the attack. The degree of damping caused by the very structure of the material will control the sustain: high internal damping loses string energy as friction. Instead of moving your eardrums, the vibrating strings just make the soundboard hotter! Together, these factors create an 'envelope. In conjunction with what we may broadly call 'tone', the sound now has a distinct fingerprint to our cars.
Animal skin is a very different material from wood, so a banjo becomes recognisable for what it is, even when we cannot see it. Metals have very different properties again, so when the resonator is made of spun aluminium, it sounds like it! A Dobro does not sound like a classical guitar.
Let us now return to cedar and spruce. In the scheme of things, the differences between them are quite small. They are, after all, both wood. They are also fairly close in structure, as the various timbers go. Cedar is a less dense timber than spruce. It is also less strong, but very straight grained because the trees grow on a slower spiral than spruce trees, and extremely stable. When you tap a piece of cedar it clearly sounds a little different from spruce. The first time you hear that sound you think you have the most perfect soundboard on earth. Cedar has a fabulous ring, with fast, brilliant harmonics and long, ringing sustain. Unfortunately, it seems to be rather the same disappointment as with ground coffee the smell often promises more than the taste delivers!
I believe that the reason for this is to do with the interaction between so many parts of a finished instrument. Apart from the qualities of the soundboard, the final tone comes from the strings, the air cavity, the back, the bridge and so on. The difference in soundboard tone has to be quite substantial before it becomes really audible.
Some cedar guitars do sound noticeably different from their spruce-topped counterparts, but this is not just to do with the cedar. The majority of Spanish makers have pioneered a particular way of working with cedar that is significantly different from the way most of us use spruce. The sound is generally quite powerful, rich and lively. The other side of the coin is that it tends also towards being rather mushy, erratically balanced and with penetrating wolf notes.
Makers in Northern Europe were looking for a new identity in their preference for spruce. So not only did they choose a soundboard material, but at the same time a whole style of building to go along with it. At its best, this can give a clean, rather clipped treble, basses that do not overpower the treble, and adequate though never massive power. At its worst the guitar can sound thin, unresponsive and rather feeble.
The possibilities here for the maker are very exciting. There is so much room to drift the sound of an instrument in any particular direction. The important thing is to have a really clear concept of what you are aiming for, and the courage to develop bold and sometimes unorthodox ways of coaxing a particular sound from a sometimes stubborn piece of wood. All down the line, you are forced to make highly subjective judgements about this desirable sound you carry round in your head. The maker tries to enhance those qualities that are felt desirable, and suppress the undesirable ones. A flexible approach like this can give vibrant personality to an instrument, which can be very exciting for the player, too.
Unfortunately, this rich spectrum of possibilities has often been overlooked. Attitudes have sometimes become polarised around one stereotype or the other. There is very little mileage in this sort of argument. If you decide that red is the only colour for a proper sports car and your friend is equally adamant about green, there is not a lot more to be said.
©1990 Trevor Semple
"Classical Guitar Magazine", October 1990
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