Method for improving the acoustic properties of spruce resonance wood

Abstract

In a method for improving the acoustic properties of spruce resonance wood for musical instruments at least one resonance wood blank is subjected to a treatment with Physisporinus vitreus under controlled, sterile conditions. The previously sterilized resonance wood blank is immersed into a liquid medium enriched with fungus myecelium and kept therein in the dark for an exposure time and finally sterilized, wherein during the exposure time a temperature of 18 to 26 C. and a relative humidity of approximately 60 to approximately 80% are maintained. Due to the fact that the liquid medium contains nanofibrillated cellulose (NFC) in an amount of 200 to 300 g per liter, a reproducible, uniform improvement of the acoustic properties of the resonance wood free from local defects is ensured.

Claims

1. A method for improving acoustic properties of spruce resonance wood for musical instruments comprising: subjecting at least one resonance wood blank to a treatment with Physisporinus vitreus under controlled, sterile conditions to produce a sterilized resonance wood blank, wherein the previously sterilized resonance wood blank is immersed in a liquid medium enriched with fungus myecelium, kept therein in a dark environment for an exposure time and is subsequently sterilized, wherein during the exposure time a temperature of 18 to 26 C. and a relative humidity of approximately 60 to approximately 80% are maintained and wherein the liquid medium contains nanofibrillated cellulose (NFC) in an amount of 200 to 300 g per liter.

2. The method according to claim 1, wherein the treatment is carried out with Physisporinus vitreus EMPA 642.

3. The method according to claim 1, wherein during the exposure time a temperature of 21 C. to 23 C. and a relative humidity of approximately 65 to approximately 75% are maintained.

4. The method according to claim 1, wherein the exposure time is chosen in such manner that the resonance wood fulfils the following strength values: a module for bending longitudinally to the fiber of at least 7 GPa; a compressive strength longitudinally to the fiber of at least 24 N/mm.sup.2; and a compressive strength transversely to the fiber of at least 3 N/mm.sup.2.

5. The method according to claim 1, wherein the exposure time is 4 to 6 months.

6. The method according to claim 1, wherein the liquid medium has been obtained by incubation of an NFC-containing nutrient medium inoculated with Physisporinus vitreus under controlled pH conditions.

7. The method according to claim 1, wherein the sterilization of the resonance wood blank is carried out with ethylene oxide.

8. The method according to claim 1, wherein the method results in an increase in color index E* defined in the color space (L*, a*, b*) by at least 14.

9. The method according to claim 1, wherein the method results in a color change of the wood in form of a color distance E* defined in color space (L*, a*, b*) of at least 11.

10. An improved spruce resonance wood for musical instruments which is produced by the method according to claim 1, wherein, compared to untreated resonance wood, sound emission in the longitudinal direction is increase by at least 20% and damping in the longitudinal direction is increased by at least 25%.

11. A musical instrument comprising at least one resonance plate made of improved spruce resonance wood according to claim 10.

12. The method according to claim 2, wherein during the exposure time a temperature of 21 C. to 23 C. and a relative humidity of approximately 65 to approximately 75% are maintained.

13. The method according to claim 2, wherein the exposure time is chosen in such manner that the resonance wood fulfils the following strength values: a module for bending longitudinally to the fiber of at least 7 GPa; a compressive strength longitudinally to the fiber of at least 24 N/mm.sup.2; and a compressive strength transversely to the fiber of at least 3 N/mm.sup.2.

14. The method according to claim 4, wherein the exposure time is chosen in such manner that the resonance wood fulfils the following strength values: a module for bending longitudinally to the fiber of at least 10 GPa; a compressive strength longitudinally to the fiber of at least 34 N/mm.sup.2; and a compressive strength transversely to the fiber of at least 4.2 N/mm.sup.2.

15. The method according to claim 13, wherein the exposure time is chosen in such manner that the resonance wood fulfils the following strength values: a module for bending longitudinally to the fiber of at least 10 GPa; a compressive strength longitudinally to the fiber of at least 34 N/mm.sup.2; and a compressive strength transversely to the fiber of at least 4.2 N/mm.sup.2.

16. The method according to claim 2, wherein the exposure time is 4 to 6 months.

17. The method according to claim 3, wherein the exposure time is 4 to 6 months.

18. The method according to claim 4, wherein the exposure time is 4 to 6 months.

19. The improved spruce resonance wood of claim 10, wherein, compared to untreated resonance wood, the sound emission in the longitudinal direction is increase by at least 24% and the damping in the longitudinal direction is increased by at least 29%.

20. The musical instrument of claim 11, wherein the musical instrument is a stringed instrument.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Examples of the invention will henceforth be described in more detail by reference to the drawings, which show:

(2) FIG. 1 gel electrophoretic separation of the RAPD fragments using primer 08/9328; the samples are labeled with assay numbers (table 1), the negative control (no template DNA) is designated N; the DNA molecular weight marker used was a 100 bp ladder (M);

(3) FIG. 2 mass losses in wood samples after 12 months of incubation with Physisporinus vitreus: raw density .sub.R (bars) and mass loss m (line with squares) for three different types of wood;

(4) FIG. 3 (a) example of the relaxation of stress in the wood as a function of time; (b) photograph of a wood sample before and after microbending load;

(5) FIG. 4 stress relaxation as a function of deformation under load in freshly cut wood (control), in fungus-treated spruce wood and in old wood samples (Testore, Rougemont);

(6) FIG. 5 increase of the acoustic radiation in the longitudinal direction in wood samples after 12 months incubation with Physisporinus vitreus;

(7) FIG. 6 increase of the damping property in longitudinal direction in wood samples after 12 months incubation with Physisporinus vitreus;

(8) FIG. 7 change in the total color (green) and brightness (gray) of resonance wood (a) and lumber (b) after different durations (4-12 months) of the fungus treatment or storage time; (c) freshly cut wood (top), 12-month fungus-treated samples (middle), old wood samples from Rougemont (bottom);

(9) FIG. 8 color distance E* of resonance wood (open circles) and lumber (filled circles) after different durations (4-12 months) of the fungus treatment compared to the untreated condition; the dashed line shows the color distance of an old wood sample (Rougemont) compared to a freshly cut sample of the same type of wood; and

(10) FIG. 9 qualitative comparison of FT-IR spectral absorption for untreated wood (control), 12-month fungus-treated wood and old wood (Testore and Rougemont) at different wavenumbers. At a wavenumber of 1508 and 1738 cm.sup.1, peak values were measured (dashed lines).

MODES FOR CARRYING OUT THE INVENTION

(11) Molecular Biological Determination of the Fungus Species

(12) For the molecular biologic determination of Physisporinus vitreus, a clone-specific primer was designed and synthesized. As a result, a sensitivity of 10.sup.5 can be achieved in a real-time polymerase chain reaction (real-time PCR, real-time PCR). The detection of P. vitreus by the use of species-specific primers in combination with fungus DNA extraction techniques directly from wood is considerably simplified, since in carrying out such identification a normal standard PCR followed by gel electrophoresis is sufficient. The time requirement for this process is a few hours, which therefore is much faster and more effective compared to the conventional method because one can avoid production of pure cultures. Moreover, the risk of extraneous contamination during sampling is significantly minimized by the use of the specific primer pair.

(13) For detecting the presence and penetration depth of P. vitreus, small samples were taken from the interior of the wood under sterile conditions and transferred to nutrient media in accordance with the conventional method. Subsequently, the samples were incubated in the climate chamber for several days and examined for mycelial growth of the fungus. The identifying features consisted of macroscopic and microscopic characteristics of the mycelium. This procedure requires several days up to weeks and involves risks of extraneous contamination, which make a (re-) identification of P vitreus more difficult. Molecular biological methods which were developed for the characterization of fungus species in the 1980's may serve as an alternative to this time-consuming process (Schmidt and Moreth, 2006).

(14) In order to meet the above-mentioned quality criteria of a reliable identification method, strain-specific primers were constructed for the conclusive detection of the fungus species P. vitreus. In table 1 the fungus species used in these studies are listed. The DNA extraction for the molecular biological studies was carried out using the Extract-N-Amp Plant PCR Kit from the company Sigma Aldrich according to the manufacturer's instructions.

(15) TABLE-US-00001 TABLE 1 Fungus species used Fungus species Isolate-No. Origin 1 Physisporinus lineatus CBS 701.94 Centraalbeureau voor Schimmelcultures 2 Physisporinus ulmarius CBS 186.60 Centraalbeureau voor Schimmelcultures 3 Physisporinus laetus CBS 101079 Centraalbeureau voor Schimmelcultures 4 Physisporinus sanguilentum CBS 193.76 Centraalbeureau voor Schimmelcultures 5 Physisporinus vinctus CBS 153.84 Centraalbeureau voor Schimmelcultures 6 Physisporinus rigidus CBS 160.64 Centraalbeureau voor Schimmelcultures 7 Physisporinus vitreus EMPA 642 BFH-Hamburg 8 Physisporinus vitreus EMPA 643 Albert-Ludwigs-Universitt Freiburg 9 Physisporinus vitreus EMPA 674 BFH-Hamburg 10 Physisporinus vitreus EMPA 675 BFH-Hamburg 11 Physisporinus vitreus EMPA 676 Centraalbeureau voor Schimmelcultures

(16) In the first step, a RAPD (Randomly Amplified Polymorphic DNA) PCR was carried out for strain differentiation of the fungus species used. By using very short oligonucleotide primers, specific DNA band patterns are generated by PCR in this method and used for differentiation. These are some of the most common methods for carrying out a quick kinship analysis and identifying different isolates of a species (Schmidt and Moreth, 1998; Schmidt and Moreth, 2006). In total, DNA samples from 11 fungus species (table 1) were amplified with 10 random 10mer primers, and the electrophoretically separated band patterns were evaluated (FIG. 1).

(17) For the development of a specific primer pair for P. vitreus, the ITS1-5,8S-ITS2 region of the fungus species used was first amplified by means of the ITS 1/ITS 4 primer combination of White et al. (1990) using a thermocycler of the company Biometra. Ribosomal DNA (rDNA) was the target region of the primers used. It consists, inter alia, of coding gene segments 18S-, 5.8S- and 28S rRNA (in fungus species and other eukaryotes) that are conservative (Schmidt and Moreth, 2006). These three coding gene segments are separated from each other by highly variable introns, the Internal Transcribed Spacers (ITS1 and ITS2).

(18) The PCR products thus obtained were then commercially purified and sequenced (Synergene, Zrich). The sequence of the ITS region of P. vitreus 642 has been deposited in the international database EMBL (Accession No. FM202494). Due to the species specificity of the ITS region, the sequence of P. vitreus 642 was used to isolate short DNA sequences (20 bases) that occur exclusively in the fungus species P. vitreus by means of the program Clustal X and the Basic Local Alignment Search Tool (Primer-BLAST) of the National Center for Biotechnology Information (NCBI, http://www.ncbi.nlm.nih.gov/tools/primer-blast/). These short DNA sequences were synthesized (Microsynth) and used as a P. vitreus-specific primer pair. Thus, P. vitreus is no longer distinguished solely by a band pattern, but by a species-specific PCR in which only DNA from P. vitreus, for which the primer pair was constructed, allows the generation of a PCR product of 426 base pairs. This evaluation or differentiation is unambiguous because it produces only either a positive or a negative result (Schmidt and Moreth, 2000; Schmidt and Moreth, 2006).

(19) Deposition of Biological Material

(20) A sample of the above-mentioned strain Physisporinus vitreus EMPA 642 has been successfully deposited on Oct. 16, 2015 with the Centraalbureau voor Schimmelcultures Fungal Biodiversity Centre (CBS-KNAW), Uppsalalaan, 3584 CT, Utrecht, The Netherlands, an approved depository facility (International Depository Authority (IDA)) according to Budapest Treaty since 1981. The deposited material has been assigned accession number FM202494 on Oct. 23, 2015.

EXAMPLES

(21) 1. Cultivation of Fungus Species

(22) For cultivation of fungus species, Physisporinus vitreus (EMPA strain no. 642 or 643) was pre-cultivated on a suitable, sterile malt agar culture medium in Petri dishes ( 9 cm). As soon as the culture medium was completely overgrown by the fungus mycelium of P. vitreus (after about 12 to 16 days), about 2 g of sterile spruce sawdust (particle size <2 mm) was placed in the middle of the medium in each Petri dish under sterile conditions. After a further 4 to 6 weeks, the sawdust substrate, completely grown through with P. vitreus, was used to inoculate the liquid medium.

(23) 1.1 Composition of the Nutrient Substrate

(24) Malt extract 40 g/liter

(25) Agar (pure) 25 g/liter

(26) 1.2 Incubation Conditions

(27) 22 C. and 705% rel. humidity (in the dark)

(28) 1.3 Preparation of Liquid Medium

(29) A nanofibrillated cellulosic nutrient medium has proven to be a particularly suitable liquid medium for the cultivation of P. vitreus on the basis of preliminary experiments.

(30) 2. Composition of the Nutrient Medium

(31) In tap water with 10% spruce wood extract.sup.1): .sup.1) Spruce wood extract (about 200 g spruce wood sawdust in 1 liter of tap water boiled for 30 minutes; left to stand at room temperature for 24 hours and filtered off) 300 g of nanofibrillated cellulose/liter 5.0 g malt extract/liter 7.1 g KCI/liter

(32) 2.1 Inoculation of the Liquid Medium

(33) 1200 ml of nanofibrillated cellulose-containing liquid medium was sterilized in a steam autoclave for 20 to 30 minutes at 121 C. and inoculated with about 100 ml fungus species containing liquid medium culture (with the same composition) (not older than 8 weeks) or, in case of the inoculation of a first liquid medium culture, with fresh sawdust particles grown through fungus species (about 1 to 2 g) as described in paragraph 2 with P. vitreus.

(34) 2.2 Incubation

(35) The Incubation of the nanofibrillated cellulose-containing liquid medium was carried out under sterile conditions with P. vitreus in a bioreactor under controlled pH conditions (pH adjusted to 6.8 to 7.2, optionally under controlled oxygen supply). The rotational speed of the stirrer was adjusted to low. Alternatively, the nutrient medium can also be produced as a standing or shaked culture in suitable Erlenmeyer flasks with cotton stoppers on a horizontal shaker (50 u/min) for 4 to 8 weeks in a climatic chamber in the dark at 22 C. and 705% relative humidity.

(36) 3. Fungus Treatment of Spruce Wood

(37) The introduction of the fungus containing liquid medium and the actual exposure time or fungus treatment of the spruce wood (violin cover boards made of spruce wood) was carried out under sterile conditions in a specially prepared incubator.

(38) 3.1 Construction of the Incubator

(39) The incubator consists of a heat-resistant container made of plastic (PPC) with internal dimensions of 554 mm354 mm141 mm (supply source: WEZ Kunststoffwerk AG, CH-5036 Oberentfelden; Art. Nr. 6413.007) and a corresponding, modified cover plate made of sight glass. In this incubator, there were situated two treatment containers made of stainless steel which were adapted in their dimensions and shape to the resonance wood blanks (violin cover) to be treated and appropriately inserted holders (support devices) each with a corresponding filling tube with 3 to 4 outlet apertures, which are connected to a pipe system (made of heat-resistant material) and an inlet valve within the incubator container. This construction allows to fill the fungus-containing liquid medium into the incubator under sterile conditions.

(40) 3.2 Preparations Before Introducing the Liquid Medium

(41) The two resonance wood blanks to be treated (for a violin cover) were introduced in the appropriate support devices within treatment containers made of stainless steel. The total amount of the fungus containing liquid medium subsequently required for filling can be reduced by optionally filling a few glass beads as placeholders (volume displacer) in the lower part of the treatment container.

(42) The filling pipes were connected to the inlet valves within the incubator.

(43) The incubator was tightly closed with a cover plate (made of sight glass) and the entire container including the resonance wood blanks placed therein was sterilized under low heat action, e.g. by means of ionizing radiation.

(44) 3.3 Introduction of the Fungus Containing Liquid Medium

(45) The incubator previously sterilized and equipped with the resonance wood blanks (violin covers) to be treated was subjected to a 10% reduced pressure (about 100 mbar) under sterile conditions. Due to the reduced pressure in the incubator, the fungus containing liquid medium can be fed via the filling tube into the treatment container with the resonance wood blanks under sterile conditions via the previously also sterilized plastic tubes and valves, which are directly connected to the bioreactor or to a shaked or standing culture.

(46) As soon as the resonance wood blanks are uniformly covered with a layer of fungus containing liquid medium having a thickness of about 5 to 10 mm (detectable through the sight glass of the cover plate), the supply line was stopped and the supply tubes were emptied. The incubator was then vented to normal pressure by means of a valve provided with a sterile microfilter and incubated as a whole in a suitable air conditioning cabin for the intended fungus treatment (exposure time).

(47) 3.4 Incubation of Freshly Cut, Fungus-Treated and Old Spruce Wood Samples

(48) Twin samples with dimensions of 122.5150 mm (radialtangentiallongitudinal) taken from a red spruce tree (Picea abies L.). The tree was felled in autumn 2009 in the Sufers region. The raw density of the wood was 370 kg/m.sup.3 with a relative wood humidity of 65%. The wood samples had narrow tree rings and the resonance wood could be assigned to the quality grading master fine. A few wood samples were used as untreated controls, the others were incubated with P. vitreus in the dark at 22 C. and 70% relative humidity. For the purpose of comparative studies, old wood samples were taken from a cello (year of construction 1700, violin maker Catenes) and from a beam of a historic house in Rougemont (dated 1756, Switzerland) which was used for the construction of a cello. At a relative humidity of 65%, the raw density of the wood samples of Testore and Rougemont was 410 and 456 kg/m.sup.3. Moreover, twin samples of narrow- and wide-ringed wood were examined before and after fungus treatment. Moreover, samples of wide- and narrow-ringed wood were prepared.

(49) Of all the wood samples, preparations with a cutting thickness of 0.06 mm, a length of 15 mm and a width of 1.5 mm were produced with a rotation microscope before and after the treatment. The incubator including the wood samples surrounded by the fungus containing, nanofibrillated-cellulose-containing liquid medium was incubated for the required exposure time (fungus treatment) in a suitable air conditioning cabin at 22 C. (and 705% relative humidity) for 12 months. In intervals of 2 to 4 weeks, fresh, oxygen-rich air was supplied under sterile conditions through the valve with the sterile microfilter. After a 12-month incubation period, the wood samples were cleaned and then sterilized with ethylene oxide. From each sample variant, a minimum of 5 replicates were tested in a micromechanical measuring device for determining the stress relaxation. Subsequently, the samples were analyzed in a Fourier Transform Infrared (FT-IR) Spectrometer and by means of Dynamic Water Vapor Sorption (DVS).

(50) 4. Sampling and Post-Treatment of the Modified Wood

(51) After the fungus treatment, the incubator is opened. The fungus-treated wood samples laying in the treatment container were removed from the nanofibrillated cellulosic liquid medium that was completely intermingled with fungus myecelium and were carefully cleaned mechanically (with a metal spatula) from superficially adhering mycelium.

(52) 4.1 Drying of the Spruce Wood After the Fungus Treatment

(53) The freshly removed, fungus-modified resonance wood blanks (violin covers) have a relatively high water content, in some cases more than 150 to 250%, and have to be subsequently dried gently to avoid cracking (ring peeling).

(54) For this purpose, the spruce boards were initially stored in a climate chamber (20 C.) and with 80% relative humidity (eventually previously in a container with a xylene-containing atmosphere to prevent the growth of mold fungus) and were then successively dried down over a period of several weeks in a climate chamber at 65% and later at 50% relative humidity.

(55) 4.2 Sterilization of the Fungus-Treated Resonance Wood Blanks

(56) After drying and prior to the processing of the fungus-modified resonance wood blanks for instrument making, they may optionally be sterilized, e.g. with ionizing radiation (under low heat action).

(57) 5. Mass Losses in Fungus-Treated Wood

(58) The raw density .sub.R of the various wood samples before and after the fungus treatment is shown in FIG. 2. The average mass loss m of the fungus-treated wood samples is 3.3%0.9%. From FIG. 2 it can be seen that with declining raw density of the wood the mass losses decrease. The highest mass losses were found in the high-quality resonance wood (low raw density), the lowest mass losses were found in the inferior wood (high raw density).

(59) 6. Stress Relaxation in Fungus-Treated Wood

(60) Micromechanical investigations were carried out under bending load according to Burgert et al (2003). The thickness of the wood samples was determined in the middle and on the sides of the samples with a micrometer caliper. The width and the length (10 mm) were measured with a transmitted light brightfield microscope. The samples were loaded with a maximum load of 50 N and the experiments were carried out at a speed of 1 m/s (FIG. 3). At certain load levels, the motor was turned off for 120 seconds in order to measure the stress relaxation. The relative stress relaxation was calculated as follows:

(61) $\frac{{}_0-{}_t}{{}_0}$

(62) wherein .sub.0 is the initial tension and .sub.t is the tension after 120 seconds relaxation.

(63) In FIG. 4 the stress relaxation of freshly cut wood (control), fungus-treated wood and old wood is compared. The stress relaxation was calculated from the reduction between the initial and the effective stress after 2 minutes. Although a certain scatter of the measured data was found (coefficient of determination: R=0.6-0.82), it is undoubtedly evident that the fungus-treated wood has a higher stress relaxation than freshly cut wood.

(64) The time-dependent mechanical behavior of a material such as e.g. the stress relaxation allows conclusions to be drawn about the size and reorientation of important cell elements at different temporal and spatial levels (Cosgrove 1993). In the micromechanical stress relaxation tests, a gradual decrease was observed, which presumably results from the reorientation of various cell wall constituents in the wood. We suspect that there is a reorientation of the wood fibers that are connected to each other by the middle lamella, wherein the delay results from the incorporation of the cellulosic fibrils into the amorphous matrix of hemicellulose and lignin. The differences in the relaxation behavior between freshly cut wood, fungus-treated wood and old wood suggest that a material degradation takes place at the submicroscopic level, which is mainly due to the degradation of lignin and hemicellulosis. This results in a stress relaxation in the wood (Khler et al, 2002; Sedighi Gilani and Navi 2007). The degradation of the cell wall matrix (hemicellulose and lignin) around the embedded cellulose fibrils in turn has an influence on the vibration properties or changes the damping properties of the wood (Noguchi et al. 2012).

(65) 7. Sound Emission and Damping

(66) The most important acoustic properties that are used for the selection of resonance wood for musical instruments are the damping (tan ) and the sound emission (R). High-quality resonance wood has a high sound emission (R). R describes how strongly the vibrations of a body are damped due to the sound emission. On the other hand, the damping of the sound describes any kind of reduction of the sound intensity, which does not necessarily have to be associated with a reduction of the sound energy, for example by divergence, i.e. by a spread of the sound energy over a larger area. Both properties were examined on untreated controls and on fungus-treated wood. The vibration characteristics of wood samples were measured before and after fungus treatment (as described under 5.4) at a relative moisture content of 65%. The results show that both the sound emission and the damping significantly increase in the fungus-treated wood (FIG. 5-6).

(67) 8. Color Measurements

(68) The color measurements were carried out on wood samples with a tristimulus colorimeter (Konica Minolta) at wavelengths between 360 to 740 nm. The device allows for a non-contact measurement of brightness and color at a measuring angle of 1. The color coordinates were determined for fungus-treated and freshly cut wood and the color index was calculated as follows:
E*={square root over ((L*).sup.2+(a*).sup.2+(b*).sup.2)}
wherein L* defines the brightness from 0 (black) to 100 (white) while a* defines the ratio of red (+60) to green (60) and b* the ratio of yellow (+60) to blue (60).

(69) FIG. 7 shows the color index E*.sub.ab and the brightness L* for freshly cut and for fungus-treated resonance wood (a) and lumber (b) after 4 to 12 months. As the duration of the fungus treatment increases, the color index increases while the brightness decreases. In the original state, an E* index of 29.9 (0.8) was found for freshly cut resonance wood (a) and lumber (b) (FIG. 7a-b). After 12 months of fungus treatment, there was an increase in the E* index by 44.5 (1.2) for fungus-treated resonance wood (FIG. 7a) and by 41.6(0.6) for fungus-treated lumber (FIG. 7b).

(70) From an aesthetic point of view, a high color index (E*) is advantageous in violin making, since the wood has an older color appearance after the fungus treatment. Comparative studies with color measurements on old wood samples (Rougemont from 1756, Switzerland) have shown a color index E*=37.2 and a brightness index L*=73.7.

(71) However, the color changes of interest here are usually described not only by the change of the value of E*, which is by definition the length of a vector in the color space spanned by L*, a* and b*. Of informative value is, in particular, also the length of the change vector E*, which connects the color point (L.sub.0*, a.sub.0*, b.sub.0*) before color change with the color point (L.sub.1*, a.sub.1*, b.sub.1*) after color change:
E*={square root over ((L*.sub.1L*.sub.0).sup.2+(a*.sub.1a*.sub.0).sup.2+(b*.sub.1b*.sub.0).sup.2)}

(72) The quantity E* is also called color distance. In FIG. 8 there is shown the time course of the color distance E* of resonance wood (open circles) and lumber (filled circles) after different durations (4 to 12 months) of the fungus treatment compared to the untreated state. For comparison, the dashed line shows the color distance of an old wood sample (Rougemont) compared to a freshly cut sample of the same wood species.

(73) 9. FT-IR Analyses

(74) FIG. 9 shows the FT-IR spectra of fungus-treated wood and of freshly cut wood and also of old wood (Testore and Rougemont) in the region 1800-800 cm.sup.1, wherein the absorption at 1508 cm.sup.1, that originates from the aromatic ring vibration (CC) of lignin, has been normalized. In the old wood, there is a significant increase in the lignin polysaccharide ratio at a wavenumber of 1738 cm.sup.1, which results from the degradation of hemicellulose (Garcia Esteban et al. 2006, Nagyvary et al. 2006, Ganne-Chdeville et al. 2012). Similar degradation processes were found by means of FT-IR also on the fungus-treated wood. The measurements showed that the absolute values at wavenumbers 818, 589 and 1051, which are representative of hemicellulose and lignin, were reduced. Although the degradation processes of the polysaccharides and lignin are not identical under the fungus treatment and with natural aging, it can be assumed that the physical properties and the sorption behavior, and also the swelling and shrinkage behavior, respectively, are similar to those of freshly cut wood.

(75) Compared to freshly cut wood, FTIR analyses revealed significant changes in the ratio of lignin/polysaccharides in fungus-treated and old wood (Lehringer et al. 2011; Sedighi Giliani et al. 2014a; Sedighi Gilani et al. 2014b). A significant difference was the lower proportion of hemicellulose in old wood. Qualitative studies confirm that both lignin and hemicellulose are degraded at different rates during the delignification of the wood (Lehringer et al. 2011). Although the degradation processes of lignin and hemicellulose after selective delignification and natural aging are not identical, it can be assumed that their composition differs significantly from freshly cut wood. Presumably, the different composition of freshly cut wood has an influence on the interaction with moisture, e.g. sorption dynamics, moisture capacity and structural stability of the material. These changes will also have an impact on the wood anatomy and the supermolecular structure of the cell walls, which in turn have a significant impact on the vibromechanical properties of the wood. Studies show that increasing anatomical homogeneity of the wood structure has advantageous influences on the vibration properties, bending stiffness and damping of the wood (Jakiela et al., 2008, Stoel and Borman, 2008).

(76) When water molecules penetrate into the lignified cell wall, they are absorbed by the surfaces of the cellulose microfibrils and the matrix consisting of lignin and hemicellulose. The absorption of water molecules via the hydroxyl groups between the wood polymers results in a reduction in flexural rigidity of hemicellulose and lignin in the cell wall, which affects the vibration and mechanical properties of the material. The damping of the wood is significantly increased with increasing relative humidity (Hunt and Gril 1996, Sedighi Gilani et al 2014b), which has a negative effect on the resonance properties of the wood. The degradation of hemicellulose in old and fungus-treated wood reduces the influence of moisture sorption on vibration and mechanical properties of the material (mechano-sorptivity). This finding has recently been confirmed in wood incubated with P. vitreus (Sedighi Gilani et al 2014 b). Another consequence of the lignin and hemicellulose degradation in the cell walls is the increased exposition of the crystalline cellulose and improved sorption stability of the wood. Compared to freshly cut wood, an accelerated diffusion process of water molecules could be shown on old and fungus-treated wood by means of dynamic sorption tests (Sedighi Gilani et al 2014 b).

(77) It is likely that higher material stability during a moisture exchange with the atmosphere will improve the reliability of the vibration properties and the time-dependent mechanical properties of the wood, e.g. stress relaxation and creep behavior (Hunt and Gril 1996).

(78) The method of fungal wood modification described herein leads to a temporal reduction in the stress relaxation of the material under various mechanical stress conditions (e.g. tuning) and physical stress conditions (e.g. air humidity fluctuations), which is of critical importance for the stability and resonance quality of musical instruments that are produced from wood. The striking similarities between naturally aged and fungus-treated wood show that the fungus treatment is a valuable wood modification process for the accelerated aging of resonance wood. The success of a fungus-treated violin in the blind test at the Osnabrck Baumpflegetagen in 2009 is very likely attributable to the similarity of mechanical and hygroscopic stability of fungus-treated and old wood.

REFERENCES

(79) Anon. (2009) The biotech Stradivarius. Nature Biotechnology News 28: 6. Barlow C Y, Edwards P P, Millward G R, Raphael R A, Rubio D J. (1988) Wood treatment used in Cremonese instruments. Nature 332: 313. Bucur V. (2006) Acoustics of wood, 2nd edn. Berlin, Germany: Springer Series in Wood Science Springer, Heidelberg 407 S. Burckle L, Grissino-Mayer H D. (2003) Stradivaris, violins, tree rings, and the Maunder Minimum: a hypothesis. Dendrochronologia 21:41-45. Burgert I, Frhmann K, Keckes J, Fratzl P, Stanzl-Tschegg S E. (2003) Microtensile Testing of Wood Fibers Combined with videoextensometry for efficient Strain Detection. Holzforschung 57: 661-664 1. Bryne E., Lausmaa J, Ernstsson M, Englund F, Wallinder M E P. (2010) Ageing of modified wood. Part 2: Determination of surface composition of acetylated, furfurylated, and thermally modified wood by XPS and ToF-SIMS. Holzforschung 64:305-313. Cosgrove D J. (1993) Wall extensibility: its nature, measurement and relationship to plant cell growth. New Phytol 124:1-23. Dimigen H, Dimigen E. (2014) Zum Alterungsverhalten von Tonholz Holztechnologie 1:16-21. Esper J, Cook E R, Schweingruber F H. (2002) Low-frequency signals in long tree-ring chronologies for reconstructing past temperature variability. Science 295: 2250-2252. Ebrahimzadeh P R, Kubat D G. (1993) Effects of humidity changes on damping and stress relaxation in wood. J Mater Sci 28: 5668-5674. Ganne-Chdeville C, skelnen A S, Froidevaux J, Hughes M, Navi P. (2012) Natural and artificial ageing of spruce wood as observed by FTIR-ATR and UVRR spectros-copy. Holzforschung 66:163-170 Garcia Esteban L, Fernandez F G, Casasus A G, De Palacios P, Gril J. (2006) Comparison of the hygroscopic behaviour of 205-year-old and recently cut juvenile wood from Pinus sylvestris L. Ann For Sci 63: 309-317 Gug R. (1991) Choosing resonance wood. The Strad 102: 60-64. Hunt D G, Gril J. (1996) Evidence of a physical ageing phenomenon in wood. J Mater Sci Lett 15:80-92 Holz D. (1966) Untersuchungen an Resonanzhlzern. 1. Mitteilung: Beurteilung von Fichtenresonanzhlzern auf der Grundlage der Rohdichteverteilung and der Jahrringbreite. Archiv fr Forstwesen 15: 1287-1300. Jakiela S, Bratasz L, Kozlowski R. (2008) Numerical modeling of moisture movement and related stress field in lime wood subjected to changing climate conditions. Wood Sci. Technol. 42, 21-37. Kataoka Y, Kiguchi M. (2001) Depth profiling of photo-induced degradation in wood by FT-IR microspectroscopy, J Wood Sci 47:325-327. Khler L, Spatz H C. (2002) Micromechanics of plant tissues beyond the linear-elastic range, Planta, 215: 33-40 Lehringer C, Koch G, Adusumalli R B, Mook W M, Richter K, Militz H. (2011) Effect of Physisporinus vitreus on wood properties of Norway spruce. Part 1: aspects of delignification and surface hardness. Holzforschung 65:711-719 Matsuo M, Yokoyama M, Umemura K, Sugiyama J, Kawai S, Gril J, Kubodera S, Mitsutani T, Ozaki H, Sakamoto M, Imamura M. (2011) Aging of wood: analysis of color changes during natural aging and heat treatment. Holzforschung 65:361-368. Meyer H G. (1995) A practical approach to the choice of tone wood for the instruments of the violin family. Catgut Acoustical Society Journal 2: 9-13. Mller H A. (1986) How violin makers choose wood and what this procedure means from a physical point of view. In: Hutchins C M, ed. Research Papers in Violin Acoustics: 1975-1993, volume 1. Woodbury, N.Y., USA: Acoustical Society of America, paper 92. Nagyvary J, DiVerdi J A, Owen O I, Dennis Tolley H. (2006) Wood used by Stradivari and Guarneri. Nature 444, 565. Noguchi T, Obataya, E, Ando K. (2012) Effects of aging on the vibrational properties of wood. Journal of Cultural Heritage 13: 21-25. Ono T, Norimoto M. (1983) Study on Young's modulus and internal friction of wood in relation to the evaluation of wood for musical instruments. Japan Journal of Applied Physics 22: 611-614. Ono T, Norimoto M. (1984) On physical criteria for the selection of wood for sound-boards of musical instruments. Rheol Acta 23: 652-656. Pfriem A, Eichelberger K, Wagenfhr A. (2007) Acoustic properties of thermally modified spruce for use of violins. J Violin Soc Am 21:102-111. Roth K. (2009) Das chemische Geheimnis der Geigenvirtuosen Mit Stradivari, Kunstsaiten and Kolophonium. Chem. Unserer Zeit 43: 168-181. Schleske M. (1998) On the acoustical properties of violin varnish. Catgut Acoustical Society Journal 3: 15-24. Schmidt, O, MORETH, U. (1998). Characterization of indoor rot fungi by RAPD analysis. Holzforschung 52: 229-233. Schmidt, O. Moreth, U. (2000). Species-specific priming PCR in the rDNA-ITS region as a diagnostic tool for Serpula lacrymans. Mycol. Research 104: 69-72. Schmidt, O. Moreth, U. (2006) Molekulare Untersuchungen an Hausfulepilzen. Zeitschrift fr Mykologie 72:137-152. Schwarze F W M R, Lonsdale D, Mattheck C. (1995) Detectability of wood decay caused by Ustulina deusta in comparison with other tree-decay fungi. European Journal of Forest Pathology 25: 327-341. Schwarze F W M R, Spycher M, Fink S. (2008) Superior wood for violinswood decay fungi as a substitute for cold climate. New Phytologist 179: 1095-1104. Sedighi Gilani M, Navi P. (2007) Experimental observations and micromechanical modeling of successive-damaging phenomenon in wood cells tensile behavior. Wood Sci Technol, 41(1): 69-85. Sedighi Gilani, M., Boone, M. N., Mader, K., Schwarze, F. W. M. R. (2014). Synchrotron X-ray micro-tomography imaging and analysis of wood degraded by Physisporinus vitreus and Xylaria longipes Journal of Structural Biology 187: 149-157. Sedighi Gilani, M., Tingaut P., Heeb M., Schwarze, F. W. M. R. (2014). Influence of moisture on the vibro-mechanical properties of bio-engineered wood. Journal of Material Science. 49: 7679-7687. Spycher M. (2008) The application of wood decay fungi to improve the acoustic properties of resonance wood for violins. PhD thesis. Freiburg, Germany: Albert-Ludwigs-Universitt Freiburg. Spycher M, Schwarze F W M R, Steiger R. (2008) Assessment of resonance wood quality by comparing the physical and histological properties. Wood Science and Technology 42, 325-342. Stoel B C, Borman T M. (2008) Comparison of Wood Density between Classical Cremonese and Modern Violins. PLoS ONE 3: 1-7. Topham T J, McCormick M D. (2000) A dendrochronological investigation of stringed instruments of the Cremonese School (1666-1757) including The Messiah violin attributed to Antonio Stradivari. Journal of Archaeological Science 27: 183-192. Wagenfhr A, Pfriem A, Eichelberger K. (2005a) Der Einfluss einer thermischen Modifikation von Holz auf im Musikinstrumentenbau relevante Eigenschaften. Teil I: spezielle anatomische und physikalische Eigenschaften. Holztechnologie 46: 36-42. Wagenfhr A, Pfriem A, Eichelberger K. (2005b.) Der Einfluss einer thermischen Modifikation von Holz auf im Musikinstrumentenbau relevante Eigenschaften. Teil 2: technologische Eigenschaften, Herstellung und Prfung von Musikinstrumentenbauteilen. Holztechnologie 47: 39-43. Wegst U G K. (2006) Wood for sound. American Journal of Botany 93: 1439-1448. White T J, Bruns T, Lee S, Taylor J. (1990) Amplification and direct sequencing of fungal ribosomal RNA genes for phylogenetics. In: PCR Protocols: a Guide to Methods and Applications (eds Innis M A, Gelfand D H, Sninsky J J, White T J), pp. 315-321. Academic Press, San Diego, Calif. Windeisen E, Bachle H, Zimmer B, Wegener G. (2009) Relations between chemical changes and mechanical properties of thermally treated wood 10th EWLP, Stockholm, Sweden, Aug. 25-28, 2008. Holzforschung 63:773-778. Yano H, Kajita H, Minato K. (1994) Chemical treatment of wood for musical instruments. Journal of the Acoustical Society of America 96: 3380-3391.