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Tonewood

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Tonewood refers to specific wood varieties used for woodwind or acoustic stringed instruments. The word implies that certain species exhibit qualities that enhance acoustic properties of the instruments, but other properties of the wood such as esthetics and availability have always been considered in the selection of wood for musical instruments. According to Mottola's Cyclopedic Dictionary of Lutherie Terms, tonewood is:

Wood that is used to make stringed musical instruments. The term is often used to indicate wood species that are suitable for stringed musical instruments and, by exclusion, those that are not. But the list of species generally considered to be tonewoods changes constantly and has changed constantly throughout history.[1]

Varieties of tonewood

As a rough generalization it can be said that stiff-but-light softwoods (i.e. from coniferous trees) are favored for the soundboards or soundboard-like surface that transmits the vibrations of the strings to the ambient air. Hardwoods (i.e. from deciduous trees) 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, used in modern clarinets and oboes. Bassoons are usually made of Maple, especially Norway maple (Acer platanoides). Wooden flutes, recorders, and baroque and classical period instruments may be made of various hardwoods, such as pear (Pyrus species), boxwood (Buxus species), or ebony (Diospyros species).

Softwoods

Hardwoods

  • Maple, especially Norway Maple, is traditionally used for the backs and sides of violin family instruments. Bosnian Maple is probably the maple used by the Italian violin makers Stradivari and Guarneri. Maple 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 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 Australian red cedar (Toona), African mahogany (Khaya), meranti (Lauan), Kauri (Agathis), mora (Nato), 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[3] 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 Brazilwood, is the most sought-after material for the bows of classical stringed instruments, because of its effects on the tones they produce.[4]
  • Blackwood (Tasmanian/Australian).[5]
  • Walnut is often used for the backs and sides of guitars and mandolin family instruments.[6]
  • Ash, Alder and Basswood are commonly used for the bodies of electric guitars for their stiff properties.

Mechanical properties of tonewoods

Some of the mechanical properties of common tonewoods, sorted by density. See also Physical properties of wood.

Wood species ρ

Density

kg/m3

J

Hardness

N

ELR

Flexural modulus

GPa

𝜈LR

Poisson's strain ratio

F

Flexural strength

MPa

C

Compress strength

MPa

S

Shrink

Volume

%

R

Sound radiation

coefficient

D

Rigidity

3mm plate

N·m

Balsa 150 300 3.71 0.229 19.6 11.6 8.5 33.2 8.8
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 14.0
King Billy Pine[7] 350 5.80 69.0 11.6
Sugi (Japanese Cedar) 360 1420 7.65 36.4 28.0 10.5 12.8
Western Red Cedar 370 1560 7.66 0.378 51.7 31.4 6.8 12.3 20.1
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 25.8
Black Cottonwood 385 1560 8.76 58.6 31.0 12.4 12.4
Sugar Pine 400 1690 8.21 0.356 56.6 30.8 7.9 11.3 21.2
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
American

Basswood (Linden, Lime)

415 1824 10.07 0.364 60.0 32.6 15.8 11.9 26.1
Coast Redwood 415 2000 8.41 0.360 61.7 39.2 6.9 10.8 21.7
Black Willow 415 1920 6.97 53.8 28.3 13.9 9.9
White Fir 415 2140 10.24 66.9 39.6 9.8 12.0
Noble Fir 415 1820 11.17 74.4 39.5 12.4 12.5
Sitka Spruce 425 2270 11.03 0.372 70.0 38.2 11.5 12.0 28.8
White Spruce 425 2140 9.07 59.6 32.6 13.7 10.9
Okoume 430 1790 8.47 75.0 36.2 12.2 10.3
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 25.4
California Red Fir 435 2220 10.23 71.5 37.3 11.4 11.1
Butternut 435 2180 8.14 55.9 35.2 10.6 9.9
White Poplar 440 1820 8.90 0.344 65.0 NA 8.4 10.2 22.7
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 27.3
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 29.8
Primavera 465 3170 7.81 70.5 40.4 8.6 8.8
Western Hemlock 465 2400 11.24 0.485 77.9 37.3 12.4 10.6 33.1
Spanish Cedar 470 2670 9.12 70.8 40.4 10.2 9.4
Australian Red Cedar (Toona) 485 3130 9.22 71.5 36.1 10.8 9.0
Swamp Ash 481-538
European Alder (Black Alder) 495 2890 8.99 75.9 42.2 11.0 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 29.9
Bald Cypress 515 2270 9.93 0.338 73.1 43.9 10.5 8.5 25.2
Silver Maple 530 3110 7.86 61.4 36.0 12.0 7.3
Mediterranean Cypress 535 2490 5.28 44.6 5.9
Kauri (Agathis) 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
American 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
Sweetgum 545 3780 11.31 0.325 86.2 43.6 15.8 8.4 28.5
Anigre 550 4380 10.95 83.0 47.7 11.8 8.1
Limba (Korina) 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 27.4
Cerejeira 560 3510 10.88 72.9 43.5 8.3 7.9
Queensland Maple 560 3620 10.83 81.0 47.0 15.0 7.9
American Elm 560 3690 9.24 81.4 38.1 14.6 7.3
Western Larch 575 3690 12.90 0.355 89.7 52.6 14.0 8.2 33.2
Avodiré 575 5180 11.13 106.2 51.7 11.3 7.7
Lacewood 580 3740
Honduran Mahogany 590 4020 10.06 0.314 80.8 46.6 7.5 7.0 25.1
Monkeypod 600 4010 7.9 65.7 39.9 6.0 6.1
Cuban Mahogany 600 4120 9.31 74.4 43.3 8.0 6.6
Peruvian Walnut 600 4250 7.81 77.0 45.2 11.4 6.0
Red Elm 600 3830 10.28 89.7 43.9 13.8 6.9
Red Maple 610 4230 11.31 0.434 92.4 45.1 12.6 7.1 31.4
Black Walnut 610 4490 11.59 0.495 100.7 52.3 12.8 7.1 34.5
Koa 610 5180 10.37 87.0 48.7 12.4 6.8
Sycamore Maple (EU) 615 4680 9.92 98.1 55.0 12.3 6.5
California Black Oak 620 4840 6.76 59.4 38.9 10.2 5.3
Nyatoh 620 4760 13.37 96.0 54.4 8.7 7.5
Oregon 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
African Mahogany (Khaya) 640 4760 10.60 91.0 49.0 10.0 6.4
Redheart 640 5380 10.32 98.7 46.2 10.6 6.3
Claro Walnut (California Black Walnut) 640 5030 10.7
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
Narra 655 5620 11.89 96.3 57.0 6.9 6.5
Iroko 660 5610 9.38 87.6 54.0 8.8 5.7
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 31.3
Dark Red Meranti (Lauan) 675 3570 12.02 87.7 48.8 12.5 6.3
European Ash 680 6580 12.31 103.6 51.0 15.3 6.3
Makore 685 5350 10.71 112.6 57.2 12.4 5.8
Yellow Birch 690 5610 13.86 0.426 114.5 56.3 16.8 6.5 38.1
Pear 690 7380 7.80 83.3 44.1 13.8 4.9
Field Maple 690 5110 11.80 123.0 6.0
Red Oak 700 5430 12.14 0.350 99.2 46.8 13.7 5.9 31.1
Hard Maple (Sugar, Rock) 705 6450 12.62 0.424 109.0 54.0 14.7 6.0 34.6
European Beech 710 6460 14.31 110.1 57.0 17.3 6.3
American Beech 720 5780 11.86 102.8 51.1 17.2 5.6
Afrormosia 725 6980 11.83 102.9 66.0 9.9 5.6
Pecan 735 8100 11.93 94.5 54.1 13.6 5.5
African Padauk 745 8760 11.72 116.0 56.0 7.6 5.3
Keruing (Apitong) 745 6170 15.81 115.2 61.4 16.3 6.2
White Oak 755 5990 12.15 0.369 102.3 50.8 16.3 5.3 31.6
Black siris 760 7260 11.8 96.4 56.1 12.3 5.2
Black Locust 770 7560 14.14 133.8 70.3 10.2 5.6
Tzalem 780 6230 13.10 88.3 9.5 5.3
Plum 795 6900 10.19 88.4 4.5
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 (Shedua, Amazique) 825 5900 18.60 140.3 64.2 12.1 5.8
Yellowheart 825 7950 16.64 115.9 69.5 12.0 5.4
East Indian Rosewood 830 10870 11.50 114.4 59.7 8.5 4.5
Canarywood 830 6750 14.93 131.6 67.2 8.4 5.1
Brazilian Rosewood 835 12410 13.93 135.0 67.2 8.5 4.9
Partridgewood 835 7960 18.17 127.5 64.1 12.3 5.6
Pignut Hickory 835 9520 15.59 138.6 63.4 17.5 5.2
Indian Laurel 855 10390 12.46 101.4 56.7 13.2 4.5
Osage Orange 855 11640 11.64 128.6 64.7 9.2 4.3
Bocote 855 8950 12.19 114.4 59.4 11.6 4.4
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
Panga Panga 870 7310 15.73 131.2 75.1 10.5 4.9
Leopardwood 885 9560 19.91 50.2 11.5 5.4
Bubinga 890 10720 18.41 168.3 75.8 13.9 5.1
Purpleheart (Amaranth) 905 11190 20.26 151.7 83.7 10.6 5.2
Gonçalo Alves 905 9640 16.56 117.0 74.2 11.2 4.7
Jatoba 910 11950 18.93 155.2 81.2 12.1 5.0
Santos Mahogany 915 10680 16.41 148.7 80.6 10.0 4.6
Madagascar Rosewood 935 12080 12.01 165.7 76.6 10.3 3.8
Macacauba (Granadillo) 950 12030 19.6 148.6 80.7 7.2 4.8
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 (Pernambuco) 980 12540 17.55 179.4 13.3 4.3
Chechen 990 10010 10.8
Mora (Nato) 1015 10230 19.24 155.5 82.4 17.7 4.3
Curapay 1025 16150 18.04 193.2 94.4 12.0 4.1
Honduran Rosewood 1025 9790 22.00 4.5
Pau Rosa 1030 13080 17.10 166.2 92.8 10.7 4.0
Bloodwood 1050 12900 20.78 174.4 98.7 11.7 4.2
Bulletwood (Massaranduba) 1080 13920 23.06 192.2 89.2 16.8 4.3
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
Ipê 1100 15620 22.07 177.0 93.8 12.4 4.1
Macassar Ebony 1120 14140 17.35 157.2 80.2 - 3.5
Katalox (Mexican Royal Ebony) 1150 16260 25.62 193.2 105.1 11.2 4.1
Snakewood 1210 16900 23.2 195 119 10.7 3.6
Lignum Vitae 1260 19510 14.09 127.2 84.1 14.0 2.7
African Blackwood (Grenadilla) 1270 16320 17.95 213.6 72.9 7.7 3.0
Carbon-fiber/Epoxy 1600 135 0.30 1500 1200 0 5.7 334
Common flat glass 2530 74 0 2.1
Aluminum Alloy 2700 68 0.33 0 1.9 172
Steel Alloy 8000 200 0.30 0 0.6 495

Carbon-fiber/Epoxy, glass, aluminum, and steel added for comparison, since they are sometimes used in musical instruments.

Density is measured at 12% moisture content of the wood, i.e. air at 70 °F and 65% relative humidity.[8] Most professional luthiers will build at 8% moisture content (45% relative humidity), and such wood would weigh less on average than that reported here, since it contains less water.

Data comes from the Wood Database,[9] except for 𝜈LR, Poisson's ratio, which comes from the Forest Product Laboratory, United States Forest Service, United States Department of Agriculture.[10] 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.[11] 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 coefficient is defined[12] as:

where is flexural modulus in Pascals (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 and plate vibrations. The flexural rigidity of an isotropic plate is:

where is flexural 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 describes the rigidity in one orientation. For example, if we use 𝜈LR, then we get the rigidity when bending on the longitudinal axis (with the grain), as would be usual for an instrument's top. This is typically 10 to 20 times the cross-grain rigidity for most species.

The value for shown in the table was calculated using this formula and a thickness of 3.0mm=0.118″, or a little less than 1/8".

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 flexural 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).

Read more about mechanical properties in Wood for Guitars.[13]

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 (Some instruments require large pieces of suitable wood)

Sources

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,[14][15] 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.[16] 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,[17] dating from the violins of Antonio Stradivari to the piano soundboards of the contemporary maker Fazioli.

Preparation

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.[18] Some luthiers prefer further seasoning for several years. Wood for instruments is typically used at 8% moisture content (which is in equilibrium with air at 45% relative humidity). This is drier than usually produced by kilns, which is 12% moisture content (65% relative humidity). If an instrument is kept at a humidity that is significantly lower than that at which it was built, it may crack. Therefore, valuable instruments must be contained in controlled environments to prevent cracking, especially cracking of the top.

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. Guitar builders using torrefied soundboards claim improved tone, similar to that of an aged instrument. Softwoods such as Spruce, Cedar, and Redwood, which are commonly used for guitar soundboards, are easier to torrefy than hardwoods, such as Maple.

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 (heat and humidity). However, while engineering tests of the ThermoWood method indicated increased resistance to humidity, they also showed a significant reduction in strength (ultimate breaking point), while stiffness (flexural modulus) remained the same or was slightly reduced.[19][20] Although the reduction in strength can be controlled by reducing the temperature of the process, the manufacturer recommends not using its product for structural purposes. However, it is perhaps possible to compensate for this loss of strength in guitars by using carbon-fiber stiffeners in necks and increased bracing in tops.

References

  1. ^ Mottola, R.M. (1 January 2020). Mottola's Cyclopedic Dictionary of Lutherie Terms. LiutaioMottola.com. p. 165. ISBN 978-1-7341256-0-3.
  2. ^ The Acoustic Guitar Guide, p63
  3. ^ "Music to your ears: CITES CoP18 moves towards strengthened regulations for tropical trees, as well as cautions exemptions for rosewood musical instruments". CITES.
  4. ^ "Saving the Music Tree". Smithsonian Magazine. Retrieved 2017-11-07.
  5. ^ "Alternate Woods - Jeffrey R Elliott - Guitars hand crafted by Jeffrey Elliott". Elliottguitars.com. Retrieved 2016-11-05.
  6. ^ Mottola, R.M. (20 October 2021). Building the Steel String Acoustic Guitar. Amazon Digital Services LLC - Kdp. ISBN 978-1-7341256-1-0.
  7. ^ Gore / Gilet (2016). Contemporary Acoustic Guitar Design and Build. Australia: Trevor Gore. pp. 4–50. ISBN 978-0-9871174-2-7.
  8. ^ "Average Dried Weight | The Wood Database". Retrieved 2022-03-13.
  9. ^ "The Wood Database". The Wood Database.
  10. ^ "Wood Handbook: Chapter 5: Mechanical Properties of Wood" (PDF). Forest Product Laboratory. 2021.
  11. ^ "Dimension Shrinkage". The Wood Database.
  12. ^ Wegst, Ulrike (October 2006). "Wood for Sound". American Journal of Botany. 93 (10): 1439–1448. doi:10.3732/ajb.93.10.1439. PMID 21642091.
  13. ^ Gore, Trevor (2011-05-23). Wood for Guitars. Proceedings of Meetings on Acoustics. Vol. 12. p. 035001. doi:10.1121/1.3610500.
  14. ^ "Acoustic Guitar Central: Recycled Tonewoods". Michelettiguitars.com. Retrieved 2016-11-05.
  15. ^ "Adrian Lucas. Luthier Interview. MP3. | Guitarbench Magazine". Guitarbench.com. 2009-02-10. Retrieved 2016-11-05.
  16. ^ "The Lucky Strike Redwood. Tonewood profile. | Guitarbench Magazine". Guitarbench.com. 2009-11-04. Retrieved 2016-11-05.
  17. ^ See article posted by National Public Radio: [1], as well as the web site of Ciresa, a tonewood company based in the Fiemme Valley.
  18. ^ "Tonewood in the Making". Archived from the original on 2011-05-03. Retrieved 2011-04-12.
  19. ^ "ThermoWood Handbook" (PDF). International ThermoWood Association.
  20. ^ "Comparison of different techniques of thermal modification, regarding the improvement of acoustical properties of resonant soundboard material Scientific Report by order of Pacific Rim Tonewoods Inc". ResearchGate. Retrieved 2021-08-16.