Indonesian Wood as Material for Acoustic Guitars and Violins

Traditionally, acoustic guitars and violins are made from European woods. Spruce is most preferred for the top plate (soundboard), whereas maple, sycamore and rosewood are often used for the back plate. However, these woods are not easily available in Indonesia. In this paper, we present a study on the suitability of a selection of Indonesian woods, namely acacia, mahogany, pine, sengon and sonokembang, as materials for acoustic guitars and violins. The most important acoustical properties for selecting materials for musical instruments, i.e. the speed of sound, the sound radiation coefficient and the damping factor, were investigated. Furthermore, the performance of pine and mahogany were tested by making them into a violin and a guitar. The vibration frequency spectrum and the damping factor of the top plate were measured. The results show that the acoustical characteristics of mahogany are very close to those of maple and still quite close to those of Indian rosewood, which makes it a very suitable local material for back plates. Pine has quite similar acoustical characteristics to spruce. Although its sound radiation coefficient is slightly lower, its aesthetic appeal and workability makes pine a suitable alternative for top plates. However, instruments with pine top plates exhibit different tonal colour compared to instruments with spruce top plates, due to some differences in the vibration frequency spectrum. Furthermore, the generally higher damping factors of pine and mahogany compared to those of the European woods should be taken into account, because they affect the sustain-time of the generated sound.

Vibration Frequency Spectrum Measurement on a Hydraulic Turbine Runner Chamber for a Large Bulb Hydraulic Generator Set

The vibration is severe for a hydraulic turbine runner chamber of a large bulb hydraulic generator set. A measurement and analysis system is composed of an acceleration transducer, a charge amplifier, and a dynamic data collecting & analyzing system. It is used to test the frequency spectrum, which provide a basis for the optimization design based on the modal analysis, so that its natural frequencies can stagger these frequencies of vibration sources, the resonance does not occur and the vibration is reduced.

Mechanical-Condition Assessment of Power Transformer Using Vibroacoustic Analysis

This paper presents a method for vibroacoustic analysis of a transformer in the steady state. The standard approach to this problem has been based on analysis of the vibration frequency spectrum recorded with an accelerometer mounted on the transformer’s tank. To improve legibility of measurement results, the paper suggests the analysis method for the relative coefficient of harmonic frequency contents hnorm(f). The conducted experiment showed that high values of hnorm within a wide frequency range testify to deformation of windings and degradation of solid insulation.

A Method of Measurement and Monitoring to the Train's Vibration Frequency Spectrum-Varying Fault

In condition monitoring of train, because of load change, speed fluctuation and other effect factors, it may cause vibration frequency spectrum migration. If using the common vibration signal acquisition and spectral analysis method to this fault, there will be a result of characteristic spectral smearing, which will lead to misdiagnosis or missed diagnosis. To solve this problem, the vibration mechanism of spectrum-varying fault was discussed. This paper studies a pulse-triggered sampling method of integral periodic signal, the equal angle re-sampling method and other appropriate signal processing method. The feasibility and validity of this method and technology has been verified by the application in Liuzhou Railway Bureau .

Isospectral Euler-Bernoulli beams with continuous density and rigidity functions

Isospectral systems are those that have exactly the same free-vibration frequency spectrum with respect to a given boundary condition configuration. In this paper, seven different classes of inhomogeneous Euler-Bernoulli beams with continuous density and flexural rigidity functions are found that are analytically solvable and that are isospectral with a homogeneous beam in the clamped-clamped configuration. Of these exact solutions, one class is isospectral with the homogeneous case in all ten distinct configurations obtainable from clamped, sliding and two antiresonant end conditions, whereas another class is isospectral in the six configurations with clamped, hinged or free end conditions. A connection with inverse problems is discussed.