Acoustical properties of wood in string instruments soundboards and tuned idiophones: biological and cultural diversity

The acoustical properties of wood for instruments have mostly been studied on a few archetypal woods in Western musical instruments. The objective of this paper is to extend knowledge on the diversity in wood properties and uses in instruments from different geo-cultural areas. A wide set of data has been collected on vibrational properties of 452 species, through experiments and literature survey. Property distributions within broad categories confirm the known characteristics of softwoods, but also evidence specificities of tropical hardwoods compared to temperate-zone species. A relational database has been created to link wood properties and uses in musical instruments of the world. Two case studies on acoustically important functions in different geo-cultural areas show contrasted trends: (i) species used for xylophone bars and slit-drums in different continents all share a very low internal friction, (ii) on the contrary, the only characteristic common to soundboards' woods is a lower than average density, whereas their acoustical properties differ widely between them and with the "Western" standard in wood choice. All these materials being nevertheless adapted to their context, cultural specificities in the structure, playing mode and "sonority" preferences should also be taken into account.     

A classification of open string models

Open string models are classified using modular invariance. No good candidates for new models are found, though the existence of anE ₈ invariant model inR ^{17, 1}, a similar one inR ^{5, 1} and of a supersymmetric model inR ^{2, 1} cannot be excluded by this technique. An intriguing relation between the left moving and right moving sectors of the heterotic string emerges.     

Acoustical barrier for tonal noises

In this paper, a novel acoustical barrier based on the principle of the Helmholtz resonator is proposed for the mitigation of tonal noises and its in situ performance has been assessed in comparison with a reflecting barrier and an absorbent barrier. For a lightly damped thin-walled reflecting barrier, the energy transmitted through the barrier structure is comparable with that diffracted over the edges. The absorption treatment not only absorbs acoustical energy but also damps the barrier structure resulting in a negligible energy transmission. The results demonstrated that for tonal noises the proposed barrier is more effective than reflecting and absorbent barriers.     

保利剧院的声学设计

保利剧院是一座继承传统歌剧院的良好品质,又能适应近代各种需求的专业歌剧院,兼供自然声音乐演奏和戏剧演出,为确保剧有良好的音质,从方案阶段就开始声学设计,并贯穿于设计、施工、试用调试的全过程,从而获得了良好的音质,评价颇高,本文概要介绍保利剧院的声学设计及从中取得的经验。     

Acoustical criteria for concert hall stages

A survey of values of the inversion index (II) in a number of concert halls reveals large variations. Extreme values occur for stages of obviously quite different properties.Recent investigations have concentrated on the energy balance between direct sound energy and early reflection energy for a number of concert hall stages.Some numerical results, together with the corresponding reflectograms, are commented upon.     

BRST invariant mixed string vertex for the bosonic string

We construct a BRST invariant (N + M)-string vertex including both open and closed string states. When we saturate it with N open string and M closed string physical states it reproduces their corresponding scattering amplitude. As a particular case we obtain a BRST invariant vertex for the open-closed string transition.     

Acoustical properties of coal

A model has been proposed for bituminous coal which takes into consideration the transverse isotropic properties of coal and the effects of the nature of fluid in the pores on its acoustical properties. The predicted values were then compared with the experimental results performed on a bituminous coal slab, and good agreement was found between the predicted and experimental values, thus verifying the proposed model. The sound velocity through coal increases and the attenuation decreases as the pores become saturated with water.     

Acoustical impedance models for outdoor ground surfaces

A theory which predicts the acoustical characteristics of rigid porous materials in terms of four physical parameters is used to provide impedance versus frequency models for various types of ground surface. It is found possible to obtain tolerable agreement with measurements of surface normal impedance for grass-covered ground, bare ground and layered forest floor when measured values of flow resistivity and porosity and estimated values of the other two parameters are used. The agreement with measured acoustical data is shown to be superior to that obtainable with the single-parameter, semi-empirical model that is widely used to predict ground effect even when the single parameter is adjusted for best-fit. A low frequency/high flow resistivity approximation is derived in a form that requires the adjustment of only a single parameter when fitting impedance versus frequency data. This model predicts that the real part of the surface normal impedance, or resistance, and imaginary part, or reactance, are equal and decrease as the inverse square root of frequency. The low frequency/high flow resistivity approximation makes possible the derivation of a two-parameter impedance versus frequency model for a medium with a porosity that decreases exponentially with depth. If the two parameters are considered to be adjustable for best-fit, then some measurements of surface impedance are found to be explicable by means of such a model. The low frequency/high flow resistivity approximation is used, together with the assumption of layer thickness small compared with internal wavelength, to derive another simple two-parameter model for grounds that behave acoustically as thin hard-backed porous layers. Examples of the validity of this model are provided. Both of the two-parameter models predict values of reactance which are greater than those of resistance over the audio-frequency range. Methods of adjusting the two parameters of each model in fitting short-range excess-attenuation data are suggested as alternatives to the single-parameter method, and as the basis for predicting ground effect at long range and low frequencies.     

Acoustical characterization of perforated facings

An experimental method to estimate the acoustical parameters of perforated facings used for noise control applications is proposed. These perforating facings (also called screens) can be woven or non-woven fabrics or even micro-perforated plates (MPP). Following the work by Atalla and Sgard [J. Sound Vib. 303, 195-208 (2007)], the perforated facings are modeled as porous media composed with identical cylindrical perforations of circular cross-section. The acoustical parameters characterized with the proposed method are the radius of the perforations and the perforation rate (also named the open-porosity). These parameters are obtained from analytical expressions and a single measurement of the normal acoustic surface impedance of the perforated facing backed by an air cavity in a standing wave tube. The value of the static air flow resistivity can also be recovered with no additional assumption or measurement. In the case of a facing that contains perforations of an arbitrary shape, the radius parameter should be understood as a characteristic length of the visco-inertial dissipative effects. Results for two characterization examples (a low porosity screen and a high porosity one) are presented and discussed. Values of the estimated static air flow resistivity are compared with the results from direct measurements. Values of the predicted sound absorption coefficients are compared to the measured ones.     

Acoustical characteristics of porous materials

The diversity of porous materials is noted. However, this study is particularly relevant to the use of sound absorbent materials in architectural acoustics. The theory of sound propagation within an idealised porous material consisting of a rigid matrix through which run parallel cylindrical pores normal to the surface is reviewed. Extensions to pores of arbitrary orientation and cross-section are achieved by introducing physically-measura ble microstructural constants rather than phenomenological bulk parameters that might be frequency dependent. By comparison of several theories that account for sound propagation within an elastically-framed porous material a basis is laid for an improved formulation, that takes into account both viscosity and heat conduction.The application of various propagation theories to model the reflection and transmission of sound at porous boundaries is considered. Particular attention is paid to the common assumption of local reaction and to the adequacy of modelling the porous interface as that of a quasi-homogeneous fluid. Finally the most widely used methods of measuring acoustical characteristics of porous materials at normal and oblique incidence and of obtaining their values by empirical means are surveyed.     

Acoustical Correlates of Affective Prosody

The word "Anna" was spoken by 12 female and 11 male subjects with six different emotional expressions: "rage/hot anger," "despair/lamentation," "contempt/disgust," "joyful surprise," "voluptuous enjoyment/sensual satisfaction," and "affection/tenderness." In an acoustical analysis, 94 parameters were extracted from the speech samples and broken down by correlation analysis to 15 parameters entering subsequent statistical tests. The results show that each emotion can be characterized by a specific acoustic profile, differentiating that emotion significantly from all others. If aversive emotions are tested against hedonistic emotions as a group, it turns out that the best indicator of aversiveness is the ratio of peak frequency (frequency with the highest amplitude) to fundamental frequency, followed by the peak frequency, the percentage of time segments with nonharmonic structure ("noise"), frequency range within single time segments, and time of the maximum of the peak frequency within the utterance. Only the last parameter, however, codes aversiveness independent of the loudness of an utterance.     

Evidence for nonperturbative string symmetries

String theory appears to admit a group of discrete field transformations — calledS dualities — as exact nonperturbative quantum symmetries. Mathematically, they are rather analogous to the better-knownT duality symmetries, which hold perturbatively. In this Letter the evidence forS duality is reviewed and some speculations are presented.     

Acoustical comparison of three theaters

Three theaters, including both thrust stage and proscenium arch designs, are evaluated using acoustical measures not yet in common use. The unique characteristics of each theater are considered and include a partially covered orchestra pit and a music shell. A computer model is used to estimate the detrimental effects of excessive ceiling lighting holes.     

Momentum lattice for CHL string

We propose some analogue of the Narain lattice for CHL string. The symmetries of this lattice are the symmetries of the perturbative spectrum. We explain in this language the known results about the possible gauge groups in compactified theory. For the four-dimensional theory, we explicitly describe the action of S-duality on the background fields. We show that the moduli spaces of the six-, seven- and eight-dimensional compactifications coincide with the moduli spaces of the conjectured type IIA, M-theory and F-theory duals. We classify the rational components of the boundary of the moduli space in seven, eight and nine dimensions.