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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 tonewoodEdit

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, (Dalbergia melanoxylon), 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 (Pyrus species), boxwood (Buxus species), or ebony (Diospyros species).

SoftwoodsEdit

  • 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 (or Alaskan) spruce (Picea sitchensis), Adirondack (or red) spruce (Picea rubens), Engelmann spruce (Picea engelmannii), and Picea abies (variously known as Norwegian, German, Alpine, Italian or European spruce).
  • Cedars, particularly Western Redcedar (Thuja plicata, not a true cedar), have since the 1950s been used in the tops of 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.

HardwoodsEdit

  • 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 (it is one of the hardest and most stable tonewoods, so it is often used in the neck because of its ability to withstand high string tension). Hard-rock maple is commonly used for wooden tripods for its vibration damping properties. Variations of maple (commonly maple wood with flamed or quilted grains) 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 (embargo and CITES), scarcity and demand. However, in August 2019, CITES announced[1] 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.[2]
  • Blackwood (Tasmanian/Australian).[3]
  • 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 tonewoodsEdit

Some of the mechanical properties of common tonewoods, sorted by density.

Wood species ρ

Density

kg/m3

J

Hardness

N

E

Modulus of flexure

GPa

𝜈

Poisson’s strain ratio

T

Tensile strength

MPa

C

Compress strength

MPa

S

Shrink

Volume

%

R

Sound radiation

energy

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
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
Red Spruce (Adirondack) 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
Douglas Fir 510 2760 12.17 0.292 86.2 47.9 11.6 9.6 35.5
Lacewood 530 3160
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
Honduran Mahogany 590 4020 10.06 0.314 80.8 46.6 7.5 7.0 29.8
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
Nyatoh 620 4760 13.37 96.0 54.4 8.7 7.5
Green Ash 640 5340 11.40 97.2 48.8 12.5 6.6
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
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
Gaboon Ebony 955 13700 16.89 158.1 76.3 19.6 4.4
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
Carbon-fiber/Epoxy 1600 135 0.30 1500 1200 0 5.7 396

Carbon-fiber/Epoxy added for comparison, since it is sometimes used in musical instruments.

Data comes from the Wood Database[4], except for 𝜈, Poisson's ratio, which comes from the Forest Product Laboratory, United States Forest Service, United States Department of Agriculture[5]. 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[6]. The volume shrinkage is mostly due to the radial and tangential shrinkage. In the case of a neck (quarter-sawn), 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 energy coefficient is defined[7] as:

 

where   is Young’s Modulus of flexure in Pascals (N/m2, i.e. the number in the table multiplied by 109), 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 (R = 6 vs. 12).

When wood is used as the top of an acoustic instrument, it can be described using plate theory. 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 (equivalent to N·m), 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 (defined as  ) 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 (in m4),   is the transverse displacement of the beam at x, and   is the bending moment at x. Beam flexural rigidity has units of Pascal·m4 (equivalent to N·m²).

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 (i.e. from the strings).

Selection of tonewoodsEdit

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 (Some instruments require large pieces of suitable wood)

SourcesEdit

Many tonewoods come from sustainable sources through specialist dealers. Spruce, for example, is very common, but large pieces with even grain represent a small proportion of total supply and can be expensive. Some tonewoods are particularly hard to find on the open market, and small-scale instrument makers often turn to reclamation,[8][9] for instance from disused salmon traps in Alaska, various old construction in the U.S Pacific Northwest, from trees that have blown down, or from specially permitted removals in conservation areas where logging is not generally permitted.[10] Mass market instrument manufacturers have started using Asian and African woods, such as Bubinga (Guibourtia species) and Wenge (Millettia laurentii), as inexpensive alternatives to traditional tonewoods.

The Fiemme Valley, in the Alps of Northern Italy, has long served as a source of high-quality spruce for musical instruments,[11] dating from the violins of Antonio Stradivari to the piano soundboards of the contemporary maker Fazioli.

PreparationEdit

Tonewood choices vary greatly among different instrument types. Guitar makers generally favor quartersawn wood because it provides added stiffness and dimensional stability. Soft woods, like spruce, may be split rather than sawn into boards so the board surface follows the grain as much as possible, thus limiting run-out.

For most applications, wood must be dried before use, either in air or kilns.[12] 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.

ReferencesEdit

  1. ^ "Music to your ears: CITES CoP18 moves towards strengthened regulations for tropical trees, as well as cautions exemptions for rosewood musical instruments". CITES.
  2. ^ "Saving the Music Tree". Smithsonian Magazine. Retrieved 2017-11-07.
  3. ^ "Alternate Woods - Jeffrey R Elliott - Guitars hand crafted by Jeffrey Elliott". Elliottguitars.com. Retrieved 2016-11-05.
  4. ^ "The Wood Database". The Wood Database.
  5. ^ "Wood Handbook: Chapter 4: Mechanical Properties of Wood" (PDF). Forest Product Laboratory. 1999.
  6. ^ "Dimension Shrinkage". The Wood Database.
  7. ^ Roest, Max (August 17, 2016). "Design of a Composite Guitar, section 5.2.3". TU Delft.
  8. ^ "Acoustic Guitar Central: Recycled Tonewoods". Michelettiguitars.com. Retrieved 2016-11-05.
  9. ^ "Adrian Lucas. Luthier Interview. MP3. | Guitarbench Magazine". Guitarbench.com. 2009-02-10. Retrieved 2016-11-05.
  10. ^ "The Lucky Strike Redwood. Tonewood profile. | Guitarbench Magazine". Guitarbench.com. 2009-11-04. Retrieved 2016-11-05.
  11. ^ See article posted by National Public Radio: [1], as well as the web site of Ciresa, a tonewood company based in the Fiemme Valley.
  12. ^ "Archived copy". Archived from the original on 2011-05-03. Retrieved 2011-04-12. Cite uses deprecated parameter |deadurl= (help)CS1 maint: archived copy as title (link)

External linksEdit