Abstract
Increasing demand for resonance spruce has led to gradual depletion of resources in traditional areas. Consequently, to meet the need for raw material to manufacture musical instruments, sorting has become the key operation of exploitation. This study was completed on the largest Romanian resonance wood resource, to maximize outputs of flitches for violin, cello, and double bass instruments by optimizing traditional requirements regarding quality of raw material with its current level. Ten resonance spruces were felled and gradually turned into semi-manufactured musical instruments. The material was analysed for defects in all stages of conversion. The frequency of zero defective samples was 60%. Evolution of defects along the trees indicated the tree section from 1 m to 12 m above the ground for musical instruments manufacturing. Output in terms of flitches ranged from one tree to another: between 19 and 32% if calculated from logs volume, and between 13 and 30% if calculated from volume of the standing trees. The results advocated for relaxing traditional requirements on resonance logs, at least regarding buttress and knottiness. Thus, recommendations are made, from the perspective of increasing efficiency, on the admissibility of defects and size diversification of musical instruments.
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Musical Instrument Lumber Recovery from Romanian Resonance Spruces
Cristian Teofil Albu,a Florin Dinulică,b Szilard Bartha,c,* Maria Magdalena Vasilescu,b Cristian Cornel Tereșneu,b and Ioana Andra Vlad d
Increasing demand for resonance spruce has led to gradual depletion of resources in traditional areas. Consequently, to meet the need for raw material to manufacture musical instruments, sorting has become the key operation of exploitation. This study was completed on the largest Romanian resonance wood resource, to maximize outputs of flitches for violin, cello, and double bass instruments by optimizing traditional requirements regarding quality of raw material with its current level. Ten resonance spruces were felled and gradually turned into semi-manufactured musical instruments. The material was analysed for defects in all stages of conversion. The frequency of zero defective samples was 60%. Evolution of defects along the trees indicated the tree section from 1 m to 12 m above the ground for musical instruments manufacturing. Output in terms of flitches ranged from one tree to another: between 19 and 32% if calculated from logs volume, and between 13 and 30% if calculated from volume of the standing trees. The results advocated for relaxing traditional requirements on resonance logs, at least regarding buttress and knottiness. Thus, recommendations are made, from the perspective of increasing efficiency, on the admissibility of defects and size diversification of musical instruments.
Keywords: Cello; Double bass; Knots; Lumber recovery; Norway spruce; Resin pockets; Strings; Tree butress; Violin
Contact information: a: Gurghiu Forestry High Scool, Gurghiu, 547295 Romania; b: Department of Forest Engineering, Forest Management Planning and Terrestrial Measurements, Transilvania University of Brașov, Brașov, 500123 Romania; c: Department of Forestry and Forest Engineering, University of Oradea, Bihor, 410048 Romania; d: Department of Food Engineering, University of Oradea, Bihor, 410048 Romania; *Corresponding author: barthaszilard10@yahoo.com
INTRODUCTION
Over time, wood has ennobled the existence of humanity in all aspects thereof: family, professional, artistic, spiritual, etc., and it remains the preferred material for musical instruments manufacturing (Bucur 2006; Wegst 2006). For this purpose, it must have an architecture that ensures the undistorted and, at the same time, amplified transmission of sound emitted by the strings (Kolneder 1998). This architecture develops under certain conditions, and not all trees or tree species can provide such material, which is called “resonance wood” (Domont 2000). Its texture strives towards perfection in terms of fineness and regularity. This explains the multiple set of qualitative restrictions imposed on the raw material (Table 1). Given the environmental constraints plus physiological and genetic determinism, the likelihood of a tree to meet all these requirements simultaneously is low, and the wood that satisfies them is recognized as being the most valuable on Earth (Schmidt-Vogt 1981).
Table 1. Criteria for Selecting Spruce Wood for Manufacturing Strings Instruments Top Plate
The defects invoked (Table 1) have a detrimental effect on the vibrational properties (Norimoto et al. 1983; Brémaud 2006; Brémaud et al. 2013) via elasticity properties (Kuprevicius et al. 2013). Stem structural defects, e.g., eccentricity, sweep, twisting, and fluting, enhance the internal stresses (Mattheck and Kubler 1997) and can result in degradation when the timber is dried or sawn.
The continuous decrease of wood quality in the last century, from which the spruce is not excepted (Rozenberg and Cahalan 1997), as well as increasing pressure on high-quality wood resources (Zaițev 1969), make it difficult to find resonance spruce in forests once famous for it (Holz 1967; Rădulescu 1969). To produce musical instruments, it is now possible to use less-pruned, root-swelled stems, which therefore have higher knottiness and content of latewood and compression wood (Ille 1975; Albu 2010). However, the knots must be grouped into whorls, the distance between whorls must exceed the length of flitches for the violin (Krzysik 1968; Albu 2010), and the compression wood and biological attacks must be concentrated in the area lacking acoustic expectation (Grapini and Constantinescu 1968; Dinulică et al. 2015).
Under these circumstances, the role of sorting in the selection and processing of raw material has greatly increased, especially with the sorters’ financial bonus for increasing yield of resonance flitches (Krzysik 1968). Through this research, the authors proposed (a) to determine the output of musical instruments from the current resonance spruce stands in the Romanian Carpathians, by an accurate and judicious sorting, and (b) to find ways to improve the output. To this end, the authors proceeded to: (1) find and measure all visible defects, starting with logs and ending with flitches, and (2) optimize the cutting pattern in relation to the quality of material and the demand to maximize output.
EXPERIMENTAL
To quantify the output of musical instruments, the raw material was tracked from the standing timber to the flitches stored for seasoning (Fig. 1).
Fig. 1. Flowchart of the study
Materials
The raw material came from a spruce stand with resonance wood from the eastern chain of the Romanian Carpathians (Table 2), sheltered in the caldera of a former volcano (Reghin, Romania). The forest site is protected from wind, and the volcanic substrate, which is unique for spruce resonance (Domont 2000), supports a constant soil moisture regime, and balanced nutrition for spruce trees (Albu 2010). The sampled trees aged up to 240 years (Table 2) and they came exclusively from natural forests.
Table 2. Resource Characterization
Resource Sampling and Processing
Ten trees, whose phenotype corresponded to the established portrait of resonance spruce, were selected (Geambașu 1995; Zugliani and Dotta 2009a). The chosen trees were mechanically felled during the inactive vegetative season, to avoid the flow of sap and to minimize resin content (Schelleng 1982), during a temperature ranging between 3 °C to 5 °C and with a layer of snow, to avoid cracking when felling.
The felled trees were trimmed and cut according to the position of the critical defects for resonance wood (curvature, knots, and biological attacks). The measurement of defects followed the requirements of EN 1310 (1997). Eighteen logs complied with the qualitative requirements outlined in Table 1 and were further converted into flitches for musical instruments (Tables 3 and 4), at the premises of Gliga Company (Reghin, Romania), one of the largest producers of bowed string instruments in Europe. Logs had lengths that ranged between 8.2 m to 12.6 m and small-end diameters of 15 cm to 46 cm without bark.
Table 3. Technological Flow when Converting Resonance Wood into Logs
Table 4. Technological Flow when Converting Logs into Flitches for Musical Instruments
Pair flitches were calibrated to the dimensions required for the cello, and they were glued and pressed on the peripheral edge, then the outline of the instrument plate was shaped using the template.
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| Fig. 2. Snapshot from the quarter splitting | Fig. 3. Measurements of wood features: KA – cutting angle of the knot,
KD – maximum diameter of a knot, Kd – minimum diameter of a knot, KIA – length of the intergrown area, LK – length of the loose knot, KL – length of knot, WDF – width of deflected fibre area, RPL – length of resin pocket, RPW – width of resin pocket, and RPT- thickness of resin pocket |
Methods
Data acquisition
In the logs with resonance wood and in the discs, all visible qualitative characteristics were measured (Table 5). The eccentricity was measured at the butt end of the logs (Richter 2015), and the ovality at the small end. The highest value measured in the log was retained for the ring shake.
For resonance lumber, the defects measured were the knots and resin pockets (Table 5), which were the only ones allowed for cutting musical instrument flitches (Tables 3 and 4).
To not disrupt the technological flow from the factory, measurements on wood defects in flitches were performed only on the cello ones (62 pairs of flitches). The measurements were performed on both radial and tangential sides.
Because the knots usually have an elliptical section, the diameter was averaged from their values on minor and major axes (Table 5). The ellipticity of the knot was calculated as a dimensionless ratio between its extreme diameters. The knots produce the local distortion of the annual rings, which was why the authors measured near the knot and the width of the affected area, which was further related to the diameter of the knot that resulted in the following variable: influence of the knot area ratio.
For the pair flitches, the mirror pockets were measured at both flitches, and the resulting values were used to reconstruct the 3D geometry of the sectioned pocket.
Thus, the length and thickness of the original pocket were assimilated to the maximum sizes of the measurements from the pair pockets, and the width of the original pocket resulted from the addition of the width of the pair pockets and the addition of the wood cutting thickness (the thickness of the blade plus the double set of the saw). In this study, the cut of the band saw used was 3 mm.
Table 5. Measuring the Wood Qualitative Features
Data analyses were performed using Statistica 12.0 software (StatSoft, Inc., Tulsa, OK, USA).
Kruskall-Wallis test and t test were used to check the significance of the differences in defects size between the values of ordinal variables.
Computing the Lumber Recovery
The recovery of musical instruments flitches (in this case: violins, violas, cello, and double bass) was calculated in two variants, dividing the cumulative volume of the instruments obtained either by the log volume input or the volume of the standing trees (Eq. 1 and Eq. 2, respectively), as follows,
(1)
where RFRFL is the resonance flitches recovery factor from logs (%), FV is the total volume of logged flitches (m3), and LV is the total volume of logs (m3) and,
(2)
where RFRFT is the resonance flitches recovery factor from standing trees (%), FV is the total volume of logged flitches (m3), and TV is the total volume of standing trees (m3). The total volume of the flitches was calculated by multiplying the volume of the flitches corresponding to each instrument with the number of samples obtained for the respective instrument and then by summing the values. The volume of the standing timber was calculated using Eq. 3 (Leahu 1994; Giurgiu et al. 2004; Vasilescu et al. 2017),
(3)
where VT is the volume of the tree (m3), DBH is the diameter at breast height (m), TH is the tree height (m), and f is the false form factor of the spruce tree (Giurgiu et al. 1972).
The recovery was calculated separately for each felled tree.
RESULTS AND DISCUSSION
Log Shape Defects
The log sample was quite heterogeneous in terms of qualitative characteristics subject to analysis (Table 6), even if they originated in biometrically similar trees. Log roundness corresponded to most of the first grade requirements of softwood. The extreme values of the ovality were recorded in the butt-end of the felled trees (which would be rectified before sawing), and, accidentally, in the wood from the base of the crown.
Table 6. Basic Statistic of Resonance Log Qualitative Features
The eccentricities that exceeded the first grade threshold were only 8% of the measurements that also belonged to the butt end of the felled trees. Measurements showed a logarithmic decay of both the ovality and the eccentricity (Fig. 4). Starting already with 1 m from the felling section of the trees, both defects dropped below the first quality threshold. This result fueled the distrust of the luthiers with respect to the base stem (Hutchins 1978). Additionally, the eccentricity was a strong indication of the internal tensions of the wood, which could be released after felling by cracking.
Fig. 4. Variation of the ovality and eccentricity along the resonance spruce trees
The timber obtained by radial cutting of the logs with pronounced eccentricity had fibre deviations, with negative acoustic implications. To mitigate these negative effects, the authors recommend that the quartering or halving of logs should follow the position of the pith. In the past, raw material with moderately eccentric pith was used only for the musical instrument keyboard (Albu 2010).
Approximately 70% of the buttress values exceeded the limit required on spruce wood first grade, which is 10 cm (SR 1294 1993). The forest site and rooting conditions forced the spruce trees to fortify the trunk base, with inevitable effects in terms of stem shape and of the wood architecture. The resonance spruces ensured their stability in the wind through 3 to 5 counterforts (Geambașu 1995). The buttress wood had an irregular structure, and consequently the timber cut from this wood had an anomalous grain (Fig. 5). In this study, tree buttresses occupied the first 0.5 m to 0.8 m of the butt-log (Table 6), which were actually removed from the technological flow of musical instruments manufacturing. It was more efficient to remove the buttress when trimming the logs than to remove the distorted fibre area from the lumber. Because all the trees felled in this study were finally processed into musical instruments, the authors support the relaxation of restrictions on buttress on the first grade spruce (SR 1294 1993) by accepting root-swelled trees, if there are objective acoustic arguments and the length of the root-swelling is reasonable.
Six of the 18 resonance logs had a ring-shake, with a relative diameter of 3% to 13%, which meant that they occupied the core of the trees. This wood was not used in making musical instruments. Considering an average width of 4 cm to 10 cm of the central area without acoustic qualities (Albu 2010), it turned out that ring-shakes sizing up to 20% of the diameter of the wood could be accepted in the case of resonance logs. If they occurred outside the juvenile wood, the partial ring-shakes could be accepted in terms of resonance, provided they appear at one end of the sample that otherwise does not show any other defects. The cutting model will be adapted so that the ring-shake is removed. The size of the ring-shake found in this study was not related to its position along the tree.