Loïc Brancheriau

Sound quality assessment of wood for xylophone bars

Xylophone sounds produced by striking wooden bars with a mallet are strongly influenced by the mechanical properties of the wood species chosen by the xylophone maker. In this paper, we address the relationship between the sound quality based on the timbre attribute of impacted wooden bars and the physical parameters characterizing wood species. For this, a methodology is proposed that associates an analysis-synthesis process and a perceptual classification test. Sounds generated by impacting 59 wooden bars of different species but with the same geometry were recorded and classified by a renowned instrument maker. The sounds were further digitally processed and adjusted to the same pitch before being once again classified. The processing is based on a physical model ensuring the main characteristics of the wood are preserved during the sound transformation. Statistical analysis of both classifications showed the influence of the pitch in the xylophone maker judgement and pointed out the importance of two timbre descriptors: the frequency-dependent damping and the spectral bandwidth. These descriptors are linked with physical and anatomical characteristics of wood species, providing new clues in the choice of attractive wood species from a musical point of view.

Predicting Microfibril Angle in Eucalyptus Wood from Different Wood Faces and Surface Qualities Using near Infrared Spectra

The microfibril angle (MFA) of crystalline cellulose in the wood cell wall along the stem axis has major effects on stiffness and longitudinal shrinkage of wood and is of key importance to timber quality. The aims of this study were: (1) to develop partial least square (PLS) regression models for microfibril angle (measured on tangential sections by X-ray diffraction) based on NIR spectra measured on tangential and on radial surfaces; (2) to develop PLS regression models for MFA based on radial NIR spectra collected from wood surfaces of different quality; and (3) to verify the reliability of these PLS-R models by external validations. T values were recorded by X-ray diffraction on tangential sections while NIR spectra were taken on tangential and radial wood surfaces. PLS-R calibrations for MFA based on tangential NIR spectra were better (r2p = 0.72) than those using radial NIR spectra (r2p = 0.64). The key role of the chemical components and the effect of surface quality of wood on NIR spectroscopy calibrations are discussed. Considering the differences between experimental conditions, these findings showed the potential of the NIR-based models for predicting MFA in Eucalyptus wood, even using spectra taken from different wood faces and surface qualities.

Key signal and wood anatomy parameters related to the acoustic quality of wood for xylophone-type percussion instruments

Wood percussion instruments have been part of culture since the earliest human societies. In making an instrument, the practical experience of musical instrument makers ensures its acoustic quality, especially with respect to selecting the most suitable wood species. The aim of this study was thus to gain further insight into the relationship between the physical properties and the perceptual classification of woods to be used in xylophone-type percussion instruments. A xylophone maker perceptually classified 58 tropical wood species, most of which are not usually used for musical instruments. Dynamic tests were then performed to record radiated signals. Key signal parameters pertaining to the acoustic quality of the material were extracted. Relationships between perceptual classifications, signal parameters, and wood anatomical characteristics were thus analyzed. It has been shown that percussive acoustic quality of wood, as determined empirically by the xylophone maker, can first be related to the temporal damping of the fundamental frequency. The samples tested in this study were not musically tuned; this could explain why no frequency descriptor was relevant. However, a draft anatomical portrait of a good acoustic wood could be drawn up. The organization of wood components in the tested species highlighted the importance of the regularity and homogeneity of the anatomical structures. The axial parenchyma seems to be the key trait. It should be paratracheal, and not very abundant if possible. The rays are another important feature; they should be short, structurally homogeneous, and not very numerous.

Resonance and near infrared spectroscopy for evaluating dynamic wood properties

Dynamic longitudinal (L) and transversal (T) tests based on wood resonance were performed on Eucalyptus specimens measuring 410 mm × 25 mm × 25 mm to obtain the dynamic elastic modulus (EL and ET), the first resonance frequency (f1L), the loss tangent (tan δT) and the specific modulus (E′L and E′T). Such dynamic traits and the air-dry density of wood were correlated by partial least squares (PLS) regressions to the near infrared (NIR) spectra measured in the central position of the longitudinal–radial surfaces. The statistics of the validation models for E, E′ and f1L ranged from 0.72 to 0.81 while the calibrations for loss tangent presented lower r2v (0.38), but promising RPD (ratio of performance to deviation) values (1.88). The key role of chemical wood components in the NIR-based calibrations for dynamic properties of wood is discussed. The association of the NIR spectroscopy and resonance techniques appears to be a rapid, low-cost and precise way to evaluate the visco-elastic properties of woods.

Literature review of acoustic and ultrasonic tomography in standing trees

Key messageHigh-resolution imaging is possible if high-frequency sensors are used together with a signal-processing and inversion algorithm that is well suited to a low signal-to-noise ratio and the effect of wood anisotropy.AbstractWood is a biological growth medium, and given that standing trees adapt themselves in their growth to environmental conditions, their material properties vary with age. These changes result in variations that are far more complex than anisotropy. Wood quality and intraspecific variability can thus be studied to gain an understanding of the development mechanisms of trees, and this can be useful for clonal selection and the management of tree communities. A number of techniques are available to determine wood properties in standing trees, but the signal-processing approaches currently used are not always robust and do not always provide the image resolution needed in the particular cases of acoustic or ultrasonic tomography. This review paper thus aims to present important aspects that should be taken into account when using tomography techniques and addresses a number of open problems. A brief review of current non-destructive wood imaging techniques is initially presented followed by a comparison of the protocols, methods and models used in acoustic and ultrasonic tomography. The devices cited were studied in terms of measurement systems and signal processing. The analysis aimed to highlight and analyze the advantages and disadvantages of each device and describe challenges and trends. The effect of various parameters is discussed: frequency, signal-to-noise ratio, number of sensors and inversion algorithm. General conclusions are then drawn in relation to future signal-processing work in the acoustic and ultrasonic tomography of standing trees.

Rapid prediction of shrinkage and fibre saturation point on teak (Tectona grandis) wood based on near-infrared spectroscopy

Abstract• Dimensional stability, along with the natural durability and colour of the wood, is one of the most important characteristics of teak used as timber. However, it is very time-consuming to take measurements of this kind. For the purposes of selection for the production of improved varieties, the number of samples to be measured rapidly exceeds the capacity of a traditional laboratory.• Near-infrared spectroscopy, based on a set of reference data, is a tool enabling many of the chemical properties of wood to be predicted and the number of laboratory measurements to be reduced exponentially. The issue here is a question of checking the effectiveness of NIRS tool to build models and predict the shrinkage and fibre saturation point of teak wood from Togo.• The results show the possible use of NIRS to measure the dimensional stability of teak wood and that it is appropriate to choose the type of wood and type of surface to be measured by NIRS. The best prediction models for radial and tangential shrinkage and fibre saturation point give R2 values of 0.72, 0.83 and 0.87 respectively with ratios of performance deviation of 1.8, 2.4 and 2.8.• Consequently, after verification on other sets of teak samples, which may or may not be included in the prediction model, NIRS can be used to predict shrinkage and fibre saturation point values accurately for a large number of samples, making it possible to include these characteristics in the selection criteria for classifying wood and high throughput phenotyping.Résumé• La stabilité dimensionnelle avec la durabilité naturelle et la couleur du bois, est l’une des plus importantes caractéristiques pour le teck utilisé en bois d’œuvre. Néanmoins, les mesures de ce caractère sont longues et coûteuses en temps. Pour les besoins de la sélection pour la production de variétés améliorées, le nombre d’échantillons à mesurer devient vite supérieur aux capacités d’un laboratoire traditionnel.• La spectroscopie proche infrarouge, sur la base d’un jeu de données de références, est un outil qui permet de prédire de nombreuses propriétés chimiques du bois et de réduire le nombre de mesures de laboratoire de façon exponentielle. La question ici est de vérifier l’efficacité de l’outil NIRS pour construire des modèles et prédire les retraits et le point de saturation des fibres du bois de teck provenant de plantations du Togo.• Les résultats démontrent la possible utilisation de la SPIR pour mesurer la stabilité dimensionnelle du bois de teck et qu’il a y lieu de choisir le type de bois et le type de face que l’on mesure par SPIR. Les modèles de prédiction pour les retraits radial et tangentiel et le point de saturation des fibres montrent des R2 de 0,72, 0,83, 0,87 respectivement avec des rapports d’efficacité de 1,8, 2,4 et 2,8.• En conséquence, et après vérification sur d’autres jeux d’échantillons de teck, qu’il conviendra ou non d’intégrer dans le modèle de prédiction, la SPIR permet de prédire des valeurs de retrait et de PSF avec efficacité pour un grand nombre d’échantillons rendant possible l’intégration de ces caractères dans les critères de sélection pour le classement des bois et pour le phénotypage à grande échelle.

Ultrasonic tomography of green wood using a non-parametric imaging algorithm with reflected waves

Abstract• Ultrasonic computed tomography in reflection was used to assess the integrity of green wood. Qualitative reflectivity images were obtained from back-scattered measurements by reflection tomography, like ultrasound in medical applications.• The reconstruction algorithm was designed using, in particular, a linear approximation of the forward problem (Born approximation) and based on the assumption that a transversal cross section of wood is isotropic. The experimental device was composed of only one rotating emitter—receiver transducer to record and compute the projections. In this specific case, a tomographic projection was directly associated with a recorded signal. The qualitative aspect of this imaging technique was validated by performing a numerical simulation and tested on a small diameter green wood (Picea abies) log.• The images obtained were geometrically accurate considering the internal inclusions. It was, however, not possible in the simulation to differentiate the object shape from the background (coupling medium) because the reflectivity value associated with the object was too low. The image obtained with the spruce sample mainly showed the position of the bark as indicated by a very high contrast area. The proportion of transmitted energy was, however, sufficient to reconstruct the artificial inclusion within the sample.Résumé• L’imagerie tomographique ultrasonore en réflexion a été employée pour évaluer l’intégrité de bois à l’état vert. La tomographie en réflexion a permis d’obtenir des images qualitatives de réflectivité à partir de mesures rétro — diffusées analogues à l’échographie en médecine.• L’algorithme de reconstruction était conçu en utilisant notamment une approximation linéaire du problème direct (l’approximation de Born) et en supposant que la section transverse du bois était isotrope. Le dispositif expérimental était composé d’un seul transducteur émetteur — récepteur en rotation pour enregistrer et calculer les projections. Dans ce cas spécifique, une projection tomographique était directement associée au signal enregistré. L’aspect qualitatif de cette technique d’imagerie a été validé en effectuant une simulation numérique et a été testé sur un rondin de faible diamètre à l’état vert (Picea abies).• Les images obtenues étaient géométriquement justes en se référant aux inclusions internes. Il n’a cependant pas été possible lors de la simulation de discriminer l’objet de l’arrière plan (milieu couplant) en raison de la trop faible valeur de réflectivité associée à l’objet. L’image obtenue avec l’échantillon d’épicéa a principalement montré la position de l’écorce marquée par un très fort contraste. La proportion d’énergie transmise a cependant été suffisante pour reconstruire l’inclusion artificielle à l’intérieur de l’échantillon.

Internal friction measurement of tropical species by various acoustic methods

A batch of 54 tropical species was analyzed using free-vibration and forced-released vibration tests. The free-vibration tests were conducted by bending and compression using nylon thread or elastic thread as supports. The wood species used cover a broad spectrum of density values and were obtained from the CIRAD wood collection. Samples were stabilized at a mean moisture content of 11.1%. The goals of the study were (a) to observe the effects of nylon or elastic supports on the measurement of vibration damping, (b) to compare the damping measurements obtained through free vibration in bending and in compression, (c) to understand the relationship between temporal damping and internal friction based on free-vibration and forced-vibration bending tests, and (d) to observe the effect of frequency on bending free-vibration damping on a rosewood specimen (Dalbergia sp., Madagascar). In this study we were able to demonstrate that (a) the type of support has a significant influence on the measurement of the temporal damping, (b) the temporal damping measurements obtained during bending free vibration are linearly linked to those obtained during compression vibration, (c) the expression of internal friction ηV according to temporal damping α was identical during compression and bending free vibration: ηV = α/(πf), and (d) changes in temporal damping α according to frequency f can be modeled in the form α = β1f2 - β2f4. This form is theoretically justified as the first-order form obtained from the generalized differential equation of linear viscoelasticity.

Correlations among microfibril angle, density, modulus of elasticity, modulus of rupture and shrinkage in 6-year-old "Eucalyptus urophylla × E. grandis"

The cellulose microfibril angle (MFA) in the cell wall is known to have major effects on wood stiffness and shrinkage. However, its influence on juvenile wood traits is not fully understood, especially in Eucalyptus. The aim of this study was to evaluate the relationships among MFA, density (ρ), dynamic modulus of elasticity (E), modulus of rupture (MOR), and shrinkage (δ) in 6-year-old Eucalyptus urophylla × E. grandis. Small clear specimens (L 410 mm x R 25 mm x T 25 mm) were cut from central boards for the determination of E and MOR. Cubic samples (25 mm³) were removed after the dynamic and static tests to evaluate ρ and δ. MFA was finally measured by X-ray diffraction on small strips coming from the cubic samples. A quasi-absence of statistical link was found for MFA - δ and MFA - ρ (R²<0.20). The parameter ρ/MFA was used to estimate E (R²=0.66) and MOR (R²=0.37). In a next step, the additive and interaction effects were investigated using multiple linear regressions with a forward selection method. The property E was found to be linked only with the additive effects of ρ and 1/MFA (R²=0.76). The additive and interaction effects were all significant for MOR (R²=0.54). This study showed that a general model including both additive and interaction effects should be used for the prediction of the modulus of elasticity and the modulus of rupture.

Application of ultrasonic tomography to characterize the mechanical state of standing trees (Picea abies)

Wood is a biological growth medium. It is orthotropic with longitudinal, radial and tangential axes. Furthermore, standing trees adapt themselves to environmental growth conditions, and their material properties vary with age. These changes result in variations that are much more complex than anisotropy. Studying wood quality and intraspecific variability is useful for clonal selection and for the genetic improvement of plantations. In this study, two logs of Picea abies underwent transmission tomography. The mean diameter was 16 cm (26-year-old tree) and the moisture content was 22%. The effect of the presence of bark and artificial defects was investigated. The tomographic device was specifically built for tree imaging. The imaging process was automatic with 900 ultrasonic acquisitions in 40 minutes (emission at 55 kHz with 5 periods of square wave form). The main conclusions were: speed near the bark is higher than in the centre because of the existence of juvenile wood combined with the moisture content gradient (moisture content lower near the bark). Likewise, damping near the bark is lower than in the centre. A significant relationship was observed between slowness and attenuation (R2 = 0.50); when the speed increased, damping decreased. No clear effect of the presence of bark was shown on the tomographic images. The bark was thin (3 to 5 mm thick) compared to the wavelength (26 mm). The 10, 20 and 50 mm artificial holes were clearly visible on the tomographic images. However, quantitative tomography does not enable the precise location of defects.