Tonewood
Tonewood refers to specific wood varieties that possess tonal properties that make them good choices for use in woodwind or acoustic stringed instruments.
Varieties of tonewood
As a rough generalization it can be said that stiff-but-light softwoods are favored for the soundboards or soundboard-like surface that transmits the vibrations of the strings to the ambient air. Hardwoods are favored for the body or framing element of an instrument. Woods used for woodwind instruments include African blackwood,, also known as grenadilla wood, used in modern clarinets and oboes. Bassoons are usually made of maple, especially Acer platanoides. Wooden flutes, recorders, and baroque and classical period instruments may be made of various hardwoods, such as pear wood, boxwood, or ebony.Softwoods
- Spruces are often used in the sound boards of instruments from the lute, violin, oud, mandolin, guitar, and harpsichord families; as well as the piano. Spruce is particularly suited for this use because of its high stiffness-to-weight ratio. Commonly used varieties are Sitka spruce, Adirondack spruce, Engelmann spruce, and Picea abies.
- Cedars, particularly Western Redcedar, have since the 1950s been used in the tops of flamenco guitars, classical guitars and to a less degree in steel string acoustic guitars.
- Yew was once widely used for lute bowls.
- Other softwoods, such as redwood and Douglas fir have been used to a limited degree. Redwood is not used commonly for guitars with steel strings, but has been used for Spanish guitars.
Hardwoods
- Maple is traditionally used for the backs and sides of violin family instruments. It is also frequently seen in acoustic guitars and mandolins. Most Fender electric guitars feature maple necks. Hard-rock maple is commonly used for wooden tripods for its vibration damping properties. Variations of maple are used on the tops of electric guitars for aesthetic purposes. The very sturdy frame of the modern piano is usually made of maple or of beech.
- Mahogany may be used in the tops of some guitars as well as the back, sides, and necks of instruments of the mandolin and guitar families. Mahogany may also be used for the solid bodies of electric guitars, such as the Gibson Les Paul. Due to lack of availability other similar woods are used as mahogany replacements, such as toona, khaya, meranti, Agathis, nato wood and sapele. Some of these alternatives are Mahogany family timbers.
- Rosewoods are often used in the back and/or sides of guitars and mandolins and fretboards on guitars. The most sought-after variety, Brazilian rosewood, Dalbergia nigra, has become scarce and expensive due to severe trade restrictions, scarcity and demand. However, in August 2019, CITES announced an exception for rosewood used in musical instruments. The most widely used rosewood used now is east Indian rosewood, often paired with a spruce top for steel string guitars and with spruce or cedar for classical guitars.
- Koa is traditionally used for ukuleles. Koa is also used for steel string guitars mostly due to its beauty and compressed dynamic range.
- Ebony is also often used in many types of instruments for fingerboards, tailpieces, tuning pegs, and so forth due to its attractive appearance, smoothness to the touch, hardness and wear resistance. Several varieties of ebony are used. Ebony is often dyed to make it appear more uniformly black than the natural wood, which sometimes shows brown streaks.
- Cocobolo used in upper-end clarinets and guitars.
- Paubrasilia, commonly called pernambuco or Brazil wood, is the most sought-after material for the bows of classical stringed instruments, because of its effects on the tones they produce.
- Blackwood.
- Walnut is often used for the backs and sides of guitars and mandolin family instruments.
- Ash, alder and basswood are commonly used for the bodies of electric guitars for their stiff properties.
Mechanical properties of tonewoods
| Wood species | ρ Density kg/m3 | J Hardness N | E Modulus of flexure GPa | ? Poisson’s strain ratio | F Flexural strength MPa | C Compress strength MPa | S Shrink Volume % | R Sound radiation coefficient | D Rigidity ⅛″ plate Pascal · m3 |
| Balsa | 150 | 300 | 3.71 | 0.229 | 19.6 | 11.6 | 8.5 | 33.2 | 10.4 |
| Paulownia | 280 | 1330 | 4.38 | 37.8 | 20.7 | 6.4 | 14.1 | ||
| Northern White Cedar | 350 | 1420 | 5.52 | 0.337 | 44.8 | 27.3 | 7.2 | 11.3 | 16.6 |
| Western Red Cedar | 370 | 1560 | 7.66 | 0.378 | 51.7 | 31.4 | 6.8 | 12.3 | 23.8 |
| Obeche | 380 | 1910 | 6.69 | 60.8 | 29.3 | 8.7 | 11.0 | ||
| Engelmann Spruce | 385 | 1740 | 9.44 | 0.422 | 62.2 | 31.5 | 11.0 | 12.9 | 30.6 |
| Sugar Pine | 400 | 1690 | 8.21 | 0.356 | 56.6 | 30.8 | 7.9 | 11.3 | 25.1 |
| Eastern White Pine | 400 | 1690 | 8.55 | 59.3 | 33.1 | 8.2 | 11.6 | ||
| Norway Spruce | 405 | 1680 | 9.70 | 63.0 | 35.5 | 12.9 | 12.0 | ||
| Basswood | 415 | 1824 | 10.07 | 0.364 | 60.0 | 32.6 | 15.8 | 11.9 | 31.0 |
| Redwood | 415 | 2000 | 8.41 | 0.360 | 61.7 | 39.2 | 6.9 | 10.8 | 25.8 |
| Sitka Spruce | 425 | 2270 | 11.03 | 0.372 | 70.0 | 38.2 | 11.5 | 12.0 | 34.1 |
| Okoume | 430 | 1790 | 8.47 | 75.0 | 36.2 | 12.2 | 10.3 | ||
| Red Spruce | 435 | 2180 | 10.76 | 66.0 | 33.6 | 11.8 | 11.4 | ||
| Western White Pine | 435 | 1870 | 10.07 | 0.329 | 66.9 | 34.8 | 11.8 | 11.1 | 30.1 |
| White Poplar | 440 | 1820 | 8.90 | 0.344 | 65.0 | NA | 8.4 | 10.2 | 26.9 |
| Red Alder | 450 | 2620 | 9.52 | 67.6 | 40.1 | 12.6 | 10.2 | ||
| Yellow Poplar | 455 | 2400 | 10.90 | 0.318 | 69.7 | 38.2 | 12.7 | 10.8 | 32.2 |
| Catalpa | 460 | 2450 | 8.35 | 64.8 | 18.9 | 7.3 | 9.3 | ||
| Port Orford Cedar | 465 | 2620 | 11.35 | 0.378 | 84.8 | 41.9 | 10.1 | 10.6 | 35.3 |
| Primavera | 465 | 3170 | 7.81 | 70.5 | 40.4 | 8.6 | 8.8 | ||
| Spanish Cedar | 470 | 2670 | 9.12 | 70.8 | 40.4 | 10.2 | 9.4 | ||
| Swamp Ash | 481-538 | ||||||||
| European Alder | 495 | 2890 | 8.99 | 75.9 | 42.2 | 14.0 | 8.6 | ||
| Alaskan Yellow Cedar | 495 | 2580 | 9.79 | 76.6 | 43.5 | 9.2 | 9.0 | ||
| Douglas Fir | 510 | 2760 | 12.17 | 0.292 | 86.2 | 47.9 | 11.6 | 9.6 | 35.5 |
| Kauri | 540 | 3230 | 11.87 | 86.6 | 42.3 | 11.3 | 8.7 | ||
| Black Ash | 545 | 3780 | 11.00 | 86.9 | 41.2 | 15.2 | 8.2 | ||
| Sycamore | 545 | 3430 | 9.79 | 69.0 | 37.1 | 14.1 | 7.8 | ||
| Bigleaf Maple | 545 | 3780 | 10.00 | 73.8 | 41.0 | 11.6 | 7.9 | ||
| Limba | 555 | 2990 | 10.49 | 86.2 | 45.4 | 10.8 | 7.8 | ||
| Black Cherry | 560 | 4230 | 10.30 | 0.392 | 84.8 | 49.0 | 11.5 | 7.7 | 32.5 |
| Western Larch | 575 | 3690 | 12.90 | 0.355 | 89.7 | 52.6 | 14.0 | 8.2 | 39.4 |
| Lacewood | 580 | 3740 | |||||||
| Honduran Mahogany | 590 | 4020 | 10.06 | 0.314 | 80.8 | 46.6 | 7.5 | 7.0 | 29.8 |
| Red Maple | 610 | 4230 | 11.31 | 0.434 | 92.4 | 45.1 | 12.6 | 7.1 | 37.2 |
| Black Walnut | 610 | 4490 | 11.59 | 0.495 | 100.7 | 52.3 | 12.8 | 7.1 | 40.9 |
| Koa | 610 | 5180 | 10.37 | 87.0 | 48.7 | 12.4 | 6.8 | ||
| Sycamore Maple | 615 | 4680 | 9.92 | 98.1 | 55.0 | 12.3 | 6.5 | ||
| Nyatoh | 620 | 4760 | 13.37 | 96.0 | 54.4 | 8.7 | 7.5 | ||
| Myrtle | 635 | 5650 | 8.45 | 66.9 | 38.9 | 11.9 | 5.7 | ||
| English Walnut | 640 | 5410 | 10.81 | 111.5 | 50.2 | 13.0 | 6.4 | ||
| Green Ash | 640 | 5340 | 11.40 | 97.2 | 48.8 | 12.5 | 6.6 | ||
| Australian Blackwood | 640 | 5180 | 14.82 | 103.6 | 41.0 | 11.9 | 7.5 | ||
| Norway Maple | 645 | 4510 | 10.60 | 115.0 | 59.0 | 6.3 | |||
| Teak | 655 | 4740 | 12.28 | 97.1 | 54.8 | 7.2 | 6.6 | ||
| Sapele | 670 | 6280 | 12.04 | 109.9 | 60.4 | 12.8 | 6.3 | ||
| White Ash | 675 | 5870 | 12.00 | 0.371 | 103.5 | 51.1 | 13.3 | 6.2 | 37.1 |
| Yellow Birch | 690 | 5610 | 13.86 | 0.426 | 114.5 | 56.3 | 16.8 | 6.5 | 45.2 |
| Pear | 690 | 7380 | 7.80 | 83.3 | 44.1 | 13.8 | 4.9 | ||
| Red Oak | 700 | 5430 | 12.14 | 0.350 | 99.2 | 46.8 | 13.7 | 5.9 | 36.9 |
| Hard Maple | 705 | 6450 | 12.62 | 0.424 | 109.0 | 54.0 | 14.7 | 6.0 | 41.0 |
| American Beech | 720 | 5780 | 11.86 | 102.8 | 51.1 | 17.2 | 5.6 | ||
| African Padauk | 745 | 8760 | 11.72 | 116.0 | 56.0 | 7.6 | 5.3 | ||
| Black Locust | 770 | 7560 | 14.14 | 133.8 | 70.3 | 10.2 | 5.6 | ||
| Zebrawood | 805 | 8160 | 16.37 | 122.8 | 63.5 | 17.8 | 5.6 | ||
| Ziricote | 805 | 8780 | 10.93 | 113.1 | 63.9 | 9.8 | 4.6 | ||
| Ovangkol | 825 | 5900 | 18.60 | 140.3 | 64.2 | 12.1 | 5.8 | ||
| East Indian Rosewood | 830 | 10870 | 11.50 | 114.4 | 59.7 | 8.5 | 4.5 | ||
| Brazilian Rosewood | 835 | 12410 | 13.93 | 135.0 | 67.2 | 8.5 | 4.9 | ||
| Pau Ferro | 865 | 8710 | 10.86 | 122.4 | 60.9 | 9.9 | 4.1 | ||
| Wenge | 870 | 8600 | 17.59 | 151.7 | 80.7 | 12.9 | 5.2 | ||
| Bubinga | 890 | 10720 | 18.41 | 168.3 | 75.8 | 13.9 | 5.1 | ||
| Purpleheart | 905 | 11190 | 20.26 | 151.7 | 83.7 | 10.6 | 5.2 | ||
| Jatoba | 910 | 11950 | 18.93 | 155.2 | 81.2 | 12.1 | 5.0 | ||
| Gaboon Ebony | 955 | 13700 | 16.89 | 158.1 | 76.3 | 19.6 | 4.4 | ||
| Boxwood | 975 | 12610 | 17.20 | 144.5 | 68.6 | 15.8 | 4.3 | ||
| Brazilwood | 980 | 12540 | 17.55 | 179.4 | 13.3 | 4.3 | |||
| Mora | 1015 | 10230 | 19.24 | 155.5 | 82.4 | 17.7 | 4.3 | ||
| Bloodwood | 1050 | 12900 | 20.78 | 174.4 | 98.7 | 11.7 | 4.2 | ||
| Cumaru | 1085 | 14800 | 22.33 | 175.1 | 95.5 | 12.6 | 4.2 | ||
| Cocobolo | 1095 | 14140 | 18.70 | 158.0 | 81.3 | 7.0 | 3.8 | ||
| Ipe | 1100 | 15620 | 22.07 | 177.0 | 93.8 | 12.4 | 4.1 | ||
| Katalox | 1150 | 16260 | 25.62 | 193.2 | 105.1 | 11.2 | 4.1 | ||
| Lignum Vitae | 1260 | 19510 | 14.09 | 127.2 | 84.1 | 13.0 | 2.7 | ||
| African Blackwood | 1270 | 16320 | 17.95 | 213.6 | 72.9 | 7.7 | 3.0 | ||
| Carbon-fiber/Epoxy | 1600 | 135 | 0.30 | 1500 | 1200 | 0 | 5.7 | 396 | |
| Aluminum Alloy | 2700 | 70 | 0.35 | 0 | 1.9 | 213 | |||
| Steel Alloy | 8000 | 200 | 0.30 | 0 | 0.6 | 586 |
Carbon-fiber/Epoxy added for comparison, since it is sometimes used in musical instruments.
Data comes from the Wood Database, except for ?, Poisson's ratio, which comes from the Forest Product Laboratory, United States Forest Service, United States Department of Agriculture. The ratio displayed here is for deformation along the radial axis caused by stress along the longitudinal axis.
The shrink volume percent shown here is the amount of shrinkage in all three dimensions as the wood goes from green to oven-dry. This can be used as a relative indicator of how much the dry wood will change as humidity changes, sometimes referred to as the instrument's "stability". However, the stability of tuning is primarily due to the length-wise shrinkage of the neck, which is typically only about 0.1% to 0.2% green to dry. The volume shrinkage is mostly due to the radial and tangential shrinkage. In the case of a neck, the radial shrinkage affects the thickness of the neck, and the tangential shrinkage affects the width of the neck. Given the dimensions involved, this shrinkage should be practically unnoticeable. The shrinkage of the length of the neck, as a percent, is quite a bit less, but given the dimension, it is enough to affect the pitch of the strings.
The sound radiation coefficient is defined as:
where is Young’s Modulus of flexure in Pascals, and ρ is the density in kg/m3, as in the table.
From this, it can be seen that the loudness of the top of a stringed instrument increases with stiffness, and decreases with density. The loudest wood tops, such as Sitka Spruce, are lightweight and stiff, while maintaining the necessary strength. Denser woods, for example Hard Maple, often used for necks, are stronger but not as loud.
When wood is used as the top of an acoustic instrument, it can be described using plate theory and plate vibrations. The flexural rigidity of an isotropic plate is:
where is Young’s Modulus for the material, is the plate thickness, and is Poisson’s ratio for the material. Plate rigidity has units of Pascal·m3, since it refers to the moment per unit length per unit of curvature, and not the total moment. Of course, wood is not isotropic, it's orthotropic, so this equation is at best an approximation.
The value for shown in the table was calculated using this formula and a thickness of ⅛″=3.175mm.
When wood is used as the neck of an instrument, it can be described using beam theory. Flexural rigidity of a beam varies along the length as a function of x shown in the following equation:
where is the Young's modulus for the material, is the second moment of area, is the transverse displacement of the beam at x, and is the bending moment at x. Beam flexural rigidity has units of Pascal·m4.
The amount of deflection at the end of a cantilevered beam is:
where is the point load at the end, and is the length. So deflection is inversely proportional to. Given two necks of the same shape and dimensions, becomes a constant, and deflection becomes inversely proportional to —in short, the higher this number for a given wood species, the less a neck will deflect under a given force.
Selection of tonewoods
In addition to perceived differences in acoustic properties, a luthier may use a tonewood because of:- Availability
- Stability
- Cosmetic properties such as the color or grain of the wood
- Tradition
- Size
Preparation
For most applications, wood must be dried before use, either in air or kilns. Some luthiers prefer further seasoning for several years. Some guitar manufacturers subject the wood to rarefaction, which mimics the natural aging process of tonewoods. Torrefaction is also used for this purpose, but it often changes the cosmetic properties of the wood. On inexpensive guitars, it is increasingly common to use a product called "Roseacer" for the fretboard, which mimics Rosewood, but is actually a thermally-modified Maple. "Roasted" Maple necks are increasingly popular as manufacturers claim increased stiffness and stability in changing conditions.