Acoustic Conversion Efficiency Research Articles

Vibrational properties of harp soundboard with respect to its multi-layered structure

The vibrational properties of a harp soundboard were investigated with respect to its multi-layered structure. The surfaces of harp soundboards are usually reinforced with veneer; however, this reduces the specific dynamic Young’s modulus (E′/ρ) and significantly increases the internal friction (Q −1) of soundboards. Since smaller E′/ρ and greater Q −1 values impart a smaller acoustic conversion efficiency, the attachment of veneer is predicted to reduce the amplitude of the sound produced, as suggested by harp makers. The vibrational properties of veneer-reinforced wood are elucidated using a multi-layered model comprising base wood, a glue layer, veneer and a varnish layer. The results of calculations suggest that a thinner veneer attached with minimal glue would increase the sound amplitude.

Nondestructive detection of the effect of drilling on acoustic performance of wood

The aim of this paper is to determine the effect of hole diameter (LR Direction) on acoustic performance indicators such as acoustic coefficient and acoustic conversion efficiency of wooden beams using flexural vibration of a free-free bar test.The drilling from 0 to 8 millimetres diameter was made exactly at the middle of the bar, on the node of the second mode of vibration. The results revealed that holes of diameter from 0 to 8 millimeters didn’t cause any sever change on acoustic coefficient and acoustic conversion efficiency when the beam was impacted on both radial and tangential surfaces. Nevertheless, these acoustic properties changed a bit when the beam was impacted on the tangential surface. Thus, the changes of the acoustic coefficient and acoustic conversion efficiency for both radial and tangential impacts were not significant, even with an 8 mm hole. Therefore, hole diameter not only didn’t cause any severe effect on acoustic coefficient and acoustic conversion efficiency but also somewhat increased their values. So, a hole having a relatively small diameter may cause improved acoustical performance of a wooden beam.

Acoustic properties in Arizona cypress logs: A tool to select wood for sounding board

In this study, variation in acoustic properties of Arizona cypress wood was monitored from pith to bark as affected by tapering of the growth ring width. Specific modulus of elasticity, acoustic coefficient, damping, and acoustic conversion efficiency were calculated. It was shown that the outer parts of the stem, close to the bark containing narrower growth rings, exhibited lower damping due to internal friction and higher sound radiation. Our finding theoretically justified the luthier craftsmen’s traditional preference toward timbers with narrow growth rings to make sounding boards in musical instruments.

Acoustic Properties of Selected Tropical Wood Species

Acoustic properties such as specific dynamic Young’s modulus (E′/γ), internal friction (Q −1) and acoustic conversion efficiency (ACE) of wood are important properties frequently examined by researchers. Vibration technique is one of the non-destructive evaluation techniques used as an alternative method for measuring the acoustic properties of wood. The objectives of this study are to determine acoustic properties of selected low density tropical wood species namely Endospermum Diadenum, Cratoxylum Arborecens, Dyera Polyphylla, Macaranga Gigantea, Commersonia Bartramia and Alstonia Pneumatophora and their suitability for making violin and guitar (acoustic instruments). The acoustic properties were determined by using free-free flexural vibration method. The results show that there are significant and good relationship between log Q −1/(E′/γ) and log E′/γ with negative gradient for each and overall wood species studied. The P-value of regression equation is less than 0.01 whereas the coefficient of determination (r 2) is in the range of 0.565 to 0.894. The mean value of E′/γ, Q −1 and ACE of wood species studied are in the range of 1.69×1010 Pa to 2.73×1010 Pa, 0.017 to 0.035 and 1.50×107 to 3.56×107 respectively. Based on the mean value of E′/γ, Endospermum Diadenum, Cratoxylum Arborescens, Macaranga Gigantea and Dyera Polyphylla are preferred for making all component of violin and guitar except for the top plate of violin. Commersonia Bartramia is preferred for making the back plate of violin and guitar, whereas Alstonia Pneumatophora is only preferred for making the back plate of violin.

Calculation method of the radiation impedance of stepped circular plate

Radiation impedance is an important parameter for evaluation of acoustic conversion efficiency of a sound and vibration system. The high power flexural vibration circular plate with stepped thickness has impartant applications in fluid, especially in air due to its large radiation area. The classical theory has difficulty in calculating the radiation impedance of the stepped circular plate due to the fact that the radiation surface is not coplanar, so the domain of integration is difficult to choose. From the point of view of radiation acoustic power, and based on superposition principle, a method is proposed to calculate the radiation impedance of a stepped circular plate in this work. As an example, calculation of the radiation impedance of a circular plate with one step is given.

Acoustic conversion efficiency

Acoustic conversion efficiency

Chemical treatment of wood for musical instruments. Part I: acoustically important properties of wood for the Ranad (Thai traditional xylophone)

The purpose of this study is to determine the important acoustic properties of wood for making Ranad bars and the resonator box. The woods used in this study were separated into two groups. The first group is the type of wood that has been used to make Ranad for centuries: Ching-Chan (Dalbergia oliveri Gamble) and Ma-Had (Artocarpus lakoocha Roxb.) for making the bars, and Ka-Nun (Artocarpus neterophylla Lamk.) out of which the resonator box is made. The second group comprises woods that are abundant in Thailand and are genetically related to the first group. The physical and mechanical properties of the woods in both groups were measured including the specific dynamic Young’s modulus (E/ρ), density (ρ), hardness (H), acoustic conversion efficiency (ACE), and sound refraction coefficients (|Γ|). The results revealed that high and consistent |Γ| were crucial factors of the Ranad bar properties in addition to E/ρ, ρ, and H. The results from measurements made on the resonator box wood revealed that high E/ρ, ACE, and high and consistent |Γ| were its crucial properties.

キリ材（Ｐａｕｌｏｗｎｉａ ｔｏｍｅｎｔｏｓａ）の伝統的用途における合目的性

Physical and mechanical properties of kiri wood (Paulownia tomentosa) were estimated from the viewpoint of rationality as the Japanese traditional uses, such as furniture, fittings, and Japanese harp. From the responses of dimension and moisture content to the humidity change, the superiority of kiri wood among many kinds of hard-woods was verified in dimensional stability and humidity-controlling function. These properties of kiri wood accord with the aptitude to the furniture and woodcrafts. Furthermore, it was supported that the vibrational properties of kiri satisfy the necessary conditions (low loss tangent and high acoustic converting efficiency) for the soundboard of stringed instruments.

Effects of Chemical Modification Reagents on Acoustic Properties of Wood

Summary The acoustic properties of several chemically modified Sitka spruce samples (Picea sitchensis Carr.) were evaluated in the longitudinal direction of wood specimens. Sitka spruce treated with glyoxal and carboxymethyl cellulose (CMC) displayed superior acoustic properties to those obtained by the other treatments. The acoustic converting efficiency (ACE) of the glyoxal-CMC treated Sitka spruce was 1.84 times of that of the untreated specimen and the specific dynamic Young's modulus (E′/r) was retained without decrement after such treatment. Changes in the tanδ of Sitka spruce treated with glyoxal and different concentrations of 1,4-butanediol were opposite. With a low concentration of 1,4-butanediol (10%), the tanδ of the treated specimen decreased as a result of the formation of crosslinked cyclic structures. The potential presence of more alkyl hydroxyl groups in the Sitka spruce, after being treated with glyoxal and a high concentration of 1,4-butanediol (20%), resulted in the increment of tanδ and the decrement of ACE. The impairment of the acoustic properties of Sitka spruce was caused by the introduction of free chains with endwise carboxylic acid groups into cell walls after the succinic anhydride treatment. Slight improvement on the ACE of Sitka spruce was achieved by the reaction with acetic anhydride and the decrease in the tanδ was about 15%, which was attributed to the partial formation of crosslinked matrix. These results revealed the improvement of the acoustic properties of chemically modified wood that was probably achieved only by the formation of network structures between wood components and reagents.

Vibrational properties of wood along the grain

The dynamic Young's modulus (E′L) and loss tangent (tan δL) along the grain, dynamic shear modulus (G′L) and loss tangent (tan δS) in the vertical section, and density (ρ) of a hundred spruce wood specimens used for the soundboards of musical instruments were determined. The relative acoustic conversion efficiency (\(\alpha ,{\text{ }}\sqrt {E'_{\text{L}} /{\kern 1pt} \rho /{\kern 1pt} \tan \delta _{\text{L}} } \)) and a ratio reflecting the anisotropy of wood (β, (E′L/G′L)(tan δS/tan δL)) were defined in order to evaluate the acoustic quality of wood along the grain. There was a positive correlation between α and β, and the variation in β was larger than that in α. It seemed logical to evaluate the acoustic quality of spruce wood by a measure of β. By using a cell wall model, those acoustic factors were expressed with the physical properties of the cell wall constituents. This model predicted that the essential requirement for an excellent soundboard is smaller fibril angle of the cell wall, which yields higher α and higher β. On the other hand, the effects of chemical treatments on the α and β of wood were clarified experimentally and analyzed theoretically. It was suggested that the α and β of wood cannot be improved at the same time by chemical treatment.

Suitability of acetylated woods for clarinet reed

The density (ϱ), dynamic Young's modulus (E), loss tangent (tanδL) in the longitudinal (L) direction, and the dynamic shear modulus (G), loss tangent (tanδS) in the LT or LR (T, tangential; R, radial) plane of woods and cane (Arundo donax L.) in air-dried and wet conditions were measured. The acoustic converting efficiency (ACE), expressed by √E/ϱ3/tanδL, and the factors of anisotropy, expressed byE/G and tanδS/tanδL, of woods were compared with those of the canes. Low-density coniferous woods had higher ACE values and were of a more anisotropic nature than the cane. These woods seemed appropriate for clarinet reed owing to their homogeneous cellular structure. The stability in vibrational properties and the anticreep properties of the woods were enhanced by the acetylation treatment. Professional clarinet players suggested that acetylated Glehn's spruce and sitka spruce were suitable for clarinet reeds.

Dependence of Vibrational Properties of Wood on Varnishing during Its Drying Process in Violin Manufacturing

The influence of varnishing for violins on the vibrational properties of wood strips was investigated during the drying process by vaporization of solvent. The changes of weight, specific dynamic Young's modulus (E/r), and loss factor (tan δ) by varnishing with natural varnish (shellac) and artificial ones (cellulose nitrate: CN) were measured and their subsequent changes were traced for 1 to 2 years. For both varnishes, though the remarkable weight decrease just after varnishing ceased after 3 to 5 months, a slight weight decrease continued even after then. The change of E/r became almost undetectable within several months, whereas the decrease of tan δ continued for a longer period. Acoustic converting efficiency (ACE) fell down drastically just after varnishing, but it recovered extending for 1 year. The recovery of ACE was more largely for shellac varnished specimen than the CN lacquered one. The frequency dependencies of E/r and tan δ changed by applying the CN lacquer, whereas those by shellac varnish did not change significantly. These results suggested the superiority of shellac varnish to CN lacquer

Use of trioxane for improvement of hygroscopic and acoustic properties of wood for musical instruments

As a reagent source for the formalization of wood, trioxane was used instead of conventional paraformaldehyde. From preliminary experiments it became apparent that trioxane depolymerizes to formaldehyde by heating in the presence of some metallic salts. Formalization of wood with trioxane was carried out under the catalysis of sulfur dioxide (SO2) along with these salts. The hygroscopic and acoustic properties were considerably improved by the treatment. Especially when the reaction was catalyzed by a combination of SO2 and Fe2(SO4)3, the antiswelling efficiency (ASE) reached nearly 70%, the specific dynamic Young's modulus (E/ϱ) in the radial direction increased about 20%, and the loss tangent (tan δ) decreased about 30% and 50% in the longitudinal and radial directions, respectively. In this case, the modulus of rupture did not appreciably decrease in the radial direction. This is comparable to the most prominent results obtained so far by SO2 catalyzed formalization with tetraoxane. It can be concluded that trioxane is very effective as a reagent source for formalization. The increase in acoustic converting efficiency, $$\sqrt {(E/\varrho ^3 )} /\tan$$ δ, of about twofold in the radial direction and decrease in hygroscopicity of more than 60% should not only enrich the sound volume of musical instruments but also stabilize their tone quality against humidity changes.

Modeling and design of transducers for electromagnetic generation of acoustics (EMAT) incorporating permeable structures

As a possible means for increasing the electrical to acoustical conversion efficiency as well as enhancing the spatial resolution, we have investigated the performance characteristics of transducers for electromagnetic generation of acoustics (EMATs) that incorporate permeable magnetic structures (permeable EMAT). Since the intent of this investigation is to develop high spatial resolution EMATs for noncontact scanning applications, what we term EMAT microscopy, the basic design guidelines differ somewhat from those employed in the design of more conventional EMATs, as used in pulse-echo applications, for example. A computer program has been developed, to calculate the magnetic fields, induced currents, and generated forces, of arbitrary candidate designs, taking into strict account the stray fields due to the induced currents in the structure itself, and the anisotropic polarization of the permeable structure. The results of our calculation on even very simple structures show that an enhancement of the electrical to acoustic conversion efficiency and spatial resolution can be achieved, although at the expense of operating bandwidth.

Noise due to Surface Turbulence on Printed-Circuit Cards

The surface turbulence produced by air moving over printed-circuit cards sets the lower limit on the acoustic noise levels of a computer cooling system. The sound power generated by two types of components mounted on printed-circuit cards was compared by measuring acoustic power levels in a 230-m3 reverberation chamber. The components were mounted on phenolic cards, 1.5×65×100 mm. Over 200 cards were installed in a flow chamber so the cooling air moved between parallel rows of cards spaced 11 mm apart. Miniature components (transistors, etc.) were mounted on one type of card; microminiaturized components were mounted on the other. The air velocity was varied up to the maximum normally encountered in air-cooled circuitry: 25 m/sec. The fraction of energy radiated as sound power to total energy of moving air stream, as well as the acoustic conversion efficiency per card, was determined for both card types.