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:

Contents

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

Mechanical properties of tonewoods

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

Wood speciesρ

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 1503003.710.22919.611.68.533.28.8
Paulownia 28013304.3837.820.76.414.1
Northern White Cedar 35014205.520.33744.827.37.211.314.0
King Billy Pine [7] 3505.8069.011.6
Sugi (Japanese Cedar)36014207.6536.428.010.512.8
Western Red Cedar 37015607.660.37851.731.46.812.320.1
Obeche 38019106.6960.829.38.711.0
Engelmann Spruce 38517409.440.42262.231.511.012.925.8
Black Cottonwood 38515608.7658.631.012.412.4
Sugar Pine 40016908.210.35656.630.87.911.321.2
Eastern White Pine 40016908.5559.333.18.211.6
Norway Spruce 40516809.7063.035.512.912.0
American

Basswood (Linden, Lime)

415182410.070.36460.032.615.811.926.1
Coast Redwood 41520008.410.36061.739.26.910.821.7
Black Willow 41519206.9753.828.313.99.9
White Fir 415214010.2466.939.69.812.0
Noble Fir 415182011.1774.439.512.412.5
Sitka Spruce 425227011.030.37270.038.211.512.028.8
White Spruce 42521409.0759.632.613.710.9
Okoume 43017908.4775.036.212.210.3
Red Spruce (Adirondack)435218010.7666.033.611.811.4
Western White Pine 435187010.070.32966.934.811.811.125.4
California Red Fir 435222010.2371.537.311.411.1
Butternut 43521808.1455.935.210.69.9
White Poplar 44018208.900.34465.0NA8.410.222.7
Red Alder 45026209.5267.640.112.610.2
Yellow Poplar 455240010.900.31869.738.212.710.827.3
Catalpa 46024508.3564.818.97.39.3
Port Orford Cedar 465262011.350.37884.841.910.110.629.8
Primavera 46531707.8170.540.48.68.8
Western Hemlock 465240011.240.48577.937.312.410.633.1
Spanish Cedar 47026709.1270.840.410.29.4
Australian Red Cedar (Toona)48531309.2271.536.110.89.0
Swamp Ash 481-538
European Alder (Black Alder)49528908.9975.942.211.08.6
Alaskan Yellow Cedar 49525809.7976.643.59.29.0
Douglas Fir 510276012.170.29286.247.911.69.629.9
Bald Cypress 51522709.930.33873.143.910.58.525.2
Silver Maple 53031107.8661.436.012.07.3
Mediterranean Cypress 53524905.2844.65.9
Kauri (Agathis)540323011.8786.642.311.38.7
Black Ash 545378011.0086.941.215.28.2
American Sycamore 54534309.7969.037.114.17.8
Bigleaf Maple 545378010.0073.841.011.67.9
Sweetgum 545378011.310.32586.243.615.88.428.5
Anigre 550438010.9583.047.711.88.1
Limba (Korina)555299010.4986.245.410.87.8
Black Cherry 560423010.300.39284.849.011.57.727.4
Cerejeira 560351010.8872.943.58.37.9
Queensland Maple 560362010.8381.047.015.07.9
American Elm 56036909.2481.438.114.67.3
Western Larch 575369012.900.35589.752.614.08.233.2
Avodiré 575518011.13106.251.711.37.7
Lacewood 5803740
Honduran Mahogany 590402010.060.31480.846.67.57.025.1
Monkeypod 60040107.965.739.96.06.1
Cuban Mahogany 60041209.3174.443.38.06.6
Peruvian Walnut 60042507.8177.045.211.46.0
Red Elm 600383010.2889.743.913.86.9
Red Maple 610423011.310.43492.445.112.67.131.4
Black Walnut 610449011.590.495100.752.312.87.134.5
Koa 610518010.3787.048.712.46.8
Sycamore Maple (EU)61546809.9298.155.012.36.5
California Black Oak 62048406.7659.438.910.25.3
Nyatoh 620476013.3796.054.48.77.5
Oregon Myrtle 63556508.4566.938.911.95.7
English Walnut 640541010.81111.550.213.06.4
Green Ash 640534011.4097.248.812.56.6
Australian Blackwood 640518014.82103.641.011.97.5
African Mahogany (Khaya)640476010.6091.049.010.06.4
Redheart 640538010.3298.746.210.66.3
Claro Walnut (California Black Walnut)640503010.7
Norway Maple 645451010.60115.059.06.3
Teak 655474012.2897.154.87.26.6
Narra 655562011.8996.357.06.96.5
Iroko 66056109.3887.654.08.85.7
Sapele 670628012.04109.960.412.86.3
White Ash 675587012.000.371103.551.113.36.231.3
Dark Red Meranti (Lauan)675357012.0287.748.812.56.3
European Ash 680658012.31103.651.015.36.3
Makore 685535010.71112.657.212.45.8
Yellow Birch 690561013.860.426114.556.316.86.538.1
Pear 69073807.8083.344.113.84.9
Field Maple 690511011.80123.06.0
Red Oak 700543012.140.35099.246.813.75.931.1
Hard Maple (Sugar, Rock)705645012.620.424109.054.014.76.034.6
European Beech 710646014.31110.157.017.36.3
American Beech 720578011.86102.851.117.25.6
Afrormosia 725698011.83102.966.09.95.6
Pecan 735810011.9394.554.113.65.5
African Padauk 745876011.72116.056.07.65.3
Keruing (Apitong)745617015.81115.261.416.36.2
White Oak 755599012.150.369102.350.816.35.331.6
Black siris 760726011.896.456.112.35.2
Black Locust 770756014.14133.870.310.25.6
Tzalem 780623013.1088.39.55.3
Plum 795690010.1988.44.5
Zebrawood 805816016.37122.863.517.85.6
Ziricote 805878010.93113.163.99.84.6
Ovangkol (Shedua, Amazique)825590018.60140.364.212.15.8
Yellowheart 825795016.64115.969.512.05.4
East Indian Rosewood 8301087011.50114.459.78.54.5
Canarywood 830675014.93131.667.28.45.1
Brazilian Rosewood 8351241013.93135.067.28.54.9
Partridgewood 835796018.17127.564.112.35.6
Pignut Hickory 835952015.59138.663.417.55.2
Indian Laurel 8551039012.46101.456.713.24.5
Osage Orange 8551164011.64128.664.79.24.3
Bocote 855895012.19114.459.411.64.4
Pau Ferro 865871010.86122.460.99.94.1
Wenge 870860017.59151.780.712.95.2
Panga Panga 870731015.73131.275.110.54.9
Leopardwood 885956019.9150.211.55.4
Bubinga 8901072018.41168.375.813.95.1
Purpleheart (Amaranth)9051119020.26151.783.710.65.2
Gonçalo Alves 905964016.56117.074.211.24.7
Jatoba 9101195018.93155.281.212.15.0
Santos Mahogany 9151068016.41148.780.610.04.6
Madagascar Rosewood 9351208012.01165.776.610.33.8
Macacauba (Granadillo)9501203019.6148.680.77.24.8
Gaboon Ebony 9551370016.89158.176.319.64.4
Boxwood 9751261017.20144.568.615.84.3
Brazilwood (Pernambuco)9801254017.55179.413.34.3
Chechen 9901001010.8
Mora (Nato)10151023019.24155.582.417.74.3
Curapay 10251615018.04193.294.412.04.1
Honduran Rosewood 1025979022.004.5
Pau Rosa 10301308017.10166.292.810.74.0
Bloodwood 10501290020.78174.498.711.74.2
Bulletwood (Massaranduba)10801392023.06192.289.216.84.3
Cumaru 10851480022.33175.195.512.64.2
Cocobolo 10951414018.70158.081.37.03.8
Ipê 11001562022.07177.093.812.44.1
Macassar Ebony 11201414017.35157.280.2-3.5
Katalox (Mexican Royal Ebony)11501626025.62193.2105.111.24.1
Snakewood 12101690023.219511910.73.6
Lignum Vitae 12601951014.09127.284.114.02.7
African Blackwood (Grenadilla)12701632017.95213.672.97.73.0
Carbon-fiber/Epoxy 16001350.301500120005.7334
Common flat glass 25307402.1
Aluminum Alloy 2700680.3301.9172
Steel Alloy 80002000.3000.6495

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:

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.

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  2. The Acoustic Guitar Guide, p63
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  14. "Acoustic Guitar Central: Recycled Tonewoods". Michelettiguitars.com. Retrieved 2016-11-05.
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  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: , 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.