Tonewood

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 Tonewood: some general thoughts

  A musical instrument built from wood is almost a living thing. It is not a static thing, (affected by use, temperature and humidity), and it is not exactly like any other, (as no two pieces of wood are exactly the same). Its very nature depends upon the wood used in its construction, as each type of wood has different properties.

   There are several types of wood needed to build an instrument, because of the nature of the properties required by the different parts of the instrument. The soundboard must generate vibrations; the neck must resist bending; the back and sides will affect the tone; the struts and tone bars will affect the sound; the fingerboard must be hard; and certain woods must be flexible enough to make bindings, linings, and so on.

   Tonewood: this is the term used for wood that will generate the instrument's sound. Typically two different types of tonewood are used, one for the top, and the other for the back and sides. The types and combinations of these, together with the shape of the instrument, are largley but not wholly responsible for its characteristic sound. The choice of woods, however,  is an extremely complex area with many subtleties. Hopefully the following pages will shed some light on thisa area, for mandolins and other instruments as well.

   A word of warning here, as I am sometimes asked to identify exactly what woods are used in a given instrument.... within each species, there is as great a variety between boards as there are trees!! Ebony for example varies from light grey to black. Trying to identify woods by colour alone is almost impossible! Even the suppliers can't do it.... Frank Ford has a an interesting stroy...

  •    'Tom Humphrey, the well known classical guitar builder, was talking to one of the spruce suppliers and describing how he had selected the Adirondack spruce (also known as red spruce) tops he'd bought earlier. I asked the vendor about his spruce, "Do you know why it's called 'red' and how can you distinguish it from other spruce." He told me," I really don't know. I can't tell it apart from other species. I just have to take the word of the man who brings me the logs. He says it's red spruce."'

Choosing Tonewood

   The common grading scale for tonewoods is A, AA, AAA, and AAAA (or master grade). This grading scale is used by most retail sellers of tonewoods but is very subjective. 

   Grade A is clear of knots, swirls, and holes and has fairly straight grain. It may have uneven color, streaks, and wide apart/uneven grain lines. It will probably not be perfectly quartersawn. The piece of wood will also probably have runout. There will be little cross-grain figure.

   Grade AAA has even overall color, even and close grain lines, perfectly quartersawn along the whole width of the board, with minimal runout. Grain lines will probably be closer than 12 lines per inch. Cross-grain figure, also called silking or bearclaw will be visible.

   Grade AA is somewhere between the two.

  Grade AAAA - Master grade has no color variation, very pronounced cross-grain figuring, in addition to being perfectly quartered with minimal runout and close and even grain lines.

   (NB 'runout' is where the grain does not run parallel to the length of the board  for all its length.)

Top Thickness

   A general range of thickness of guitar tops is between 0.130" - 0.095". The stiffer a board is, the thinner it can be and still be structurally adequate.
The same thing applies to bracing. The stiffer the brace wood, the smaller the braces can be and still provide adequate structural support. A general range of brace size is not more than 5/16" wide and not more than 3/4" tall.
   The thinner soundboard and smaller bracing translates to less mass. Less mass in a soundboard translates to a more responsive and louder instrument.

   The stiffness of a wood beam is measured by how far the beam deflects when a certain amount of pressure is applied to it, or how much pressure must be applied to make the beam deflect a certain distance. A formula has been derived that measures the stiffness of a sample (MOE).

Species MOE(x10^6 in/lb^2) Weight(lb/ft^3) Top thickness?
redwood 1.34 28  
Western red cedar 1.11 23 .130"
yellow cedar 1.42 31  
englemann spruce 1.30 23  
white spruce 1.43 28  
red spruce 1.61 28 .110"
sitka spruce 1.57 28  
Indian rosewood 1.78 53  
African mahogany 1.31 32  
ebony 1.43 45  
Honduras mahogany 1.42 30  
Brazilian rosewood 1.88 47  
bigleaf maple 1.45 34  
black walnut 1.68 38

Topwood

Backwood

   Top tonewood, is usually either spruce (in the mandolin family) or cedar (in guitars) chosen because they promote vibrations very well. Spruce is number one on the list of strength-to-weight ratio for all the woods in the world, and cedar the second. Spruce is a little crisper and more powerful, whilst cedar is a little mellower.

   A wide grain top will tend to produce stronger bass response, because there are fewer stiff grain lines so the top is more flexible. From the flexibility comes a lower natural resonant frequency and more easily produced bass notes. A narrow grain top will tend to have comparatively stronger treble and more subtle bass, because lots of hard grain lines, is much stronger and has a higher natural vibrating frequency.  

   The backs and sides of virtually all guitars are made of hardwood. Strange as it may seem, softwoods just don't bend well and are more difficult to form into guitar sides.

   Sides just don't enter into the vibrations nearly as much as tops and backs. They define the body shape and support the top and back, but the back is very significant. The size and positioning on struts and tonebars is as crucial here as on the top.

   Mahogany is the most commonly used hardwood for guitar backs because it's relatively economical, durable, attractive, easy to work and resonant. For the mandolin family it is either maple or rosewood. Mahogany is probably the least dense hardwood, and rosewood one of the most dense.

Click on the wood grain photo for a larger picture, and the hyper-linked name for more informatioon.

englemann_spruce.jpg (23363 bytes)

western red cedar.jpg (70671 bytes)

European_Maple.jpg (7433 bytes)

East_Indian_Rosewood1.jpg (20916 bytes)

Englemann spruce

Western Red Cedar

European Maple

Indian Rosewood

Neckwood

Other backwoods