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Noyce Guitars
Mount Clear
Ballarat, Victoria
Australia, 3350
+61 3 5330 2244


Wood Data

Evaluating wood samples.

Two important properties of wood for instruments (and any engineering applicaton) are stiffness (modulus of elasticity, E) and density (mass per unit volume). E is the ratio of stress divided by strain which is a measure of how much a sample bends or deforms under a given load.

The ratio of longitudinal sound velocity to density where , is called acoustical admittance (reciprocal of impedance). For radiating plates, the higher the admittance the more sound energy radiated.

If we make a strip of wood as in Fig.1, then the formula for calculating the resonant frequencies of the bar is:

where the velocity , the radius of gyration .

Fig.1

The table below shows various physical properties of some forty wood samples I have tested. I have used a spreadsheet for my calculations, but using rationalised dimensions for the wood strips allows anyone to more easily derive the figures.

Furthermore, having a collection of wood strips of identical size is a great way to compare the sound they produce. By holding a piece 0.22 L from the end and striking it with a Xylophone mallet you can find the exact pitch with a strobe tuner. This then must be converted to Hz. using the Frequency to Cents book available from C.G. Conn Ltd.


The strip sizes I use are Length: 288mm x Width 34.8mm x Thickness 8.0mm.

At these dimensions the speed of sound transmission C=10 times the frequency (Hz) of the bar and the density = 105/8 x mass of sample (Kgs.per cubic metre.) This results in deriving the admittance of the sample (all measurements must be in SI units).

The results obtained are consistant with the impression gained from striking the sample with the mallet.

Sample

Grain
Angle

Pitch

Mass
(Kg)

f
(Hz)

C
(m/sec)

D
(Kg/m3)

E
(GN/m2)

C/D

Beefwood

45

E4+35

0.077

336.4

3364

962.5

10.89

3.50

Belah

70

F#4+23

0.103

375

3750

1281.25

18.02

2.97

Black Wattle (Early)

85

C#5-30

0.075

545

5450

937.5

27.85

5.81

Blackwood (Gippsland)

85

A4-15

0.058

436

4360

725

13.78

6.01

Blackwood (Otways)

85

G#4-10

0.057

412

4120

712.5

12.09

5.78

Brazillian Mahogany

90

B4+10

0.043

497

4970

537.5

13.28

9.24

Ebony

45

G#4-35

0.087

407

4070

1087.5

18.01

3.74

Gidgee

90

F4+40

0.103

357.4

3574

1287.5

16.45

2.78

Gombriera

45

A#4

0.099

466

4660

1237.5

26.87

3.77

Honduras Rosewood 1

80

C5-5

0.084

521.7

5217

1050

28.58

4.97

Honduras Rosewood 2

10

A4+50

0.084

453

4530

1050

21.55

4.31

Indian Rosewood

80

G4+45

0.071

402.5

4025

887.5

14.38

4.54

Jarrah

45

B4+5

0.075

495

4950

937.5

22.97

5.28

Jarrah Jarrah

75

F#4-35

0.064

363

3630

800

10.54

4.54

Leopard Wood

80

G4 - 40

0.067

383

3830

831.25

12.19

4.61

Mineritchie

45

F# - 28

0.070

364

3640

868.75

11.51

4.19

Mountain Ash (Fb)

90

F#4+40

0.045

378.6

3786

562.5

8.06

6.73

Myrtle

70

A#4+20

0.059

445.1

4451

737.5

14.61

6.04

Native Cherry

80

F4+10

0.061

351

3510

762.5

9.39

4.60

New Guinea Rosewood 1

80

A4+10

0.052

443

4430

650

12.76

6.82

New Guinea Rosewood 2

45

B4-15

0.051

490

4900

637.5

15.31

7.69

Norfolk Pine

50

C5+10

0.036

526

5260

450

12.45

11.69

Palm

90

B4-20

0.102

488

4880

1275

30.36

3.83

Poplar

80

B4+50

0.040

508

5080

500

12.90

10.16

Queensland Walnut

90

A4-10

0.058

437.5

4375

725

13.88

6.03

Queensland Walnut- 2

70

G4-30

0.049

385

3850

612.5

9.08

6.29

River She-Oak

80

F#-40

0.057

361.5

3615

712.5

9.31

5.07

Rock Maple

80

G#4+20

0.058

420

4200

725

12.79

5.79

Sitka Spruce

70

C5-10

0.031

520.2

5202

387.5

10.49

13.42

Wandoo

40

G#4+5

0.090

417

4170

1125

19.56

3.71

Western Red Cedar

90

B4+20

0.035

500

5000

437.5

10.94

11.43

Huon Pine

90

F4-40

0.041

341

3410

512.5

5.96

6.65

Syrian Cedar

45

B4+10

0.032

497

4970

400

9.88

12.43

Kamper

80

C5+5

0.061

525

5250

762.5

21.02

6.89

Sengon

40

A4-40

0.031

430

4300

387.5

7.16

11.10

Senu

40

B4-35

0.037

484

4840

462.5

10.83

10.46

Akasia

40

G4+10

0.049

394

3940

612.5

9.51

6.43

Sono

80

A4-20

0.060

435

4350

750

14.19

5.80

Waru

40

G4+50

0.041

403

4030

512.5

8.32

7.86