Chladni meets Napoleon

Chladni belonged to those few scientists who have been able to arouse enthusiasm for their work not only in professional circles, but also in the lay public. During several journeys all over Europe Chladni demonstrated the sound figures he had discovered as well as the musical instruments invented by him. In this respect the invitation pronounced by Napoleon during a longer stay in Paris to show his experiments at the imperial court was undoubtedly a highlight. Chladni has given a personal report on this event. In this article is shall be tried to sketch Chladni's character, based on his own writings but also on comments of his contemporaries.     

Chladni's clavicylinder and some imitations

Chladni's accomplishments in the field of instrument making were until recently not nearly as well-respected as his studies on the modes of vibration of plates and rods. However, he had developed his own friction instruments based on the glass harmonica, a popular instrument of his time. The instruments, which he partially built himself, had keys, which distinguished them from the glass harmonica. Additionally, these instruments differed from traditional keyboard instruments as they enabled the crescendo and decrescendo of individual notes after the key had been struck. Although Chladni's clavicylinder fascinated audiences and prompted imitations by many instrument makers, it was largely ignored by composers and pianists and therefore never became part of standard orchestration. The Museum of Musical Instruments of the University of Leipzig features three rare examples of friction instruments which have outlasted the centuries. These instruments were built according to the Chladni principle. After a thorough analysis, including the production of individual notes, these instruments will be presented in their cultural-historical as well as their technical context, followed by a discussion of their advantages and disadvantages. These originals exhibits allow for a conclusive comprehension of Chladni's ideas and his quest for new, unusual tone colors.     

The violin: Chladni patterns,plates, shells and sounds

In this article we consider the vibrations and radiated sound of the bowed violin. The vibrations are discussed in terms of the normal modes of the instrument involving the coupled vibrations of the bowed string, the supporting bridge, the hollow shell comprising the body of the instrument and, ultimately, the acoustic modes of the performance space in which the instrument is played. We show that damping plays an important role in characterizing the normal modes in what can be distinguished as weak and strong coupling limits. The historic and modern application of Chladni pattern measurements to enhance our understanding of the acoustics and as an aid to the making of violins is highlighted, alongside the modern equivalents of experimental modal and computational finite-element analysis. The symmetry-breaking properties of the internal soundpost is shown to have a profound affect on the intensity and quality of sound radiated by the bowed instrument.     

The physics exhibition, 1971

There has been a considerable upsurge of interest in musical acoustics over the last 10 to 15 years and this article is an attempt to summarize the present position in this multidisciplinary field. It first looks at the essential physics involved, reduced to its simplest terms, goes on to consider the relationships between real musical instruments and the resonance tubes and sonometers of the old text-books on ‘sound’ and outlines the history of the subject up to the Second World War. The main section then discusses areas of current study and the relevant measurement techniques in relation to three of the main groups of musical instruments. The article concludes with a discussion of some aspects of the difficult, but all-important, subject of psycho-physics and a brief attempt to predict the future prospects for research in musical acoustics     

中国筝的声功率级测试

筝是中国古老的弹弦乐器。但迄今为止,对其声功率级一直未进行科学的测定。本文在一混响室内根据ISO及GB标准,对二十一弦筝的声功率级进行了首次测定。两位资深乐师在混响室内分别演奏各自的乐器,通过围绕乐师和乐器布置的四通道测试设备,对筝所辐射的声功率级和动态范围进行测定。测试结果表明,中国筝在以不同力度演奏单音、音阶和乐曲时所辐射的声功率级及其频率特性均有所不同。考虑到乐器演奏音阶时所辐射的声功率级及其动态范围与演奏乐曲时的声功率级接近,并且,音乐的空间感也大都在乐器以f力度演奏乐曲的强音标志乐段时最为显著,故此我们建议中国筝所辐射的声功率级用其以f力度演奏音阶时的平均声功率级表示。本文测试的两架中国筝以f力度演奏音阶时的平均声功率级为85.9dB。文中不仅首次公布了中国筝声功率级的测试结果,并且所介绍的测试方法对其它乐器声功率级测试也具有借鉴意义。民族乐器所辐射的声音性能的确定是民族音乐厅堂音质研究的基础。     

An Illustrated Guide to Relativity,by Tatsu Takeuchi

Professor Sir Charles Wheatstone, F.R.S. (1802–1875) was originally destined for a career in the manufacture of musical instruments but he was more interested in the science of acoustics. He investigated Chladni's figures, the conduction of sound in solids and the action of ‘free reed’ instruments. Subsequently he turned to the electric telegraph and made fundamental studies in electrical science, especially in measurements. His practical contributions to electrical technology include many designs of telegraph and work on motors and generators.     

An international review of laser Doppler vibrometry: Making light work of vibration measurement

In 1964, just a few years after the invention of the laser, a fluid velocity measurement based on the frequency shift of scattered light was made and the laser Doppler technique was born. This comprehensive review paper charts advances in the development and applications of laser Doppler vibrometry (LDV) since those first pioneering experiments. Consideration is first given to the challenges that continue to be posed by laser speckle. Scanning LDV is introduced and its significant influence in the field of experimental modal analysis described. Applications in structural health monitoring and MEMS serve to demonstrate LDV's applicability on structures of all sizes. Rotor vibrations and hearing are explored as examples of the classic applications. Applications in acoustics recognise the versatility of LDV as demonstrated by visualisation of sound fields. The paper concludes with thoughts on future developments, using examples of new multi-component and multi-channel instruments.     

Feedback control of acoustic musical instruments: collocated control using physical analogs

Traditionally, the average professional musician has owned numerous acoustic musical instruments, many of them having distinctive acoustic qualities. However, a modern musician could prefer to have a single musical instrument whose acoustics are programmable by feedback control, where acoustic variables are estimated from sensor measurements in real time and then fed back in order to influence the controlled variables. In this paper, theory is presented that describes stable feedback control of an acoustic musical instrument. The presentation should be accessible to members of the musical acoustics community who may have limited or no experience with feedback control. First, the only control strategy guaranteed to be stable subject to any musical instrument mobility is described: the sensors and actuators must be collocated, and the controller must emulate a physical analog system. Next, the most fundamental feedback controllers and the corresponding physical analog systems are presented. The effects that these controllers have on acoustic musical instruments are described. Finally, practical design challenges are discussed. A proof explains why changing the resonance frequency of a musical resonance requires much more control power than changing the decay time of the resonance.     

Investigation of phase coupling phenomena in sustained portion of musical instruments sound

This work investigates aperiodicities that occur in the sustained portion of a sound of musical instrument played by a human player, due to synchronous versus asynchronous deviations of the partial phases. By using an additive sinusoidal analysis, phases of individual partials are precisely extracted and their correlation statistics and coupling effects are analyzed. It is shown that various musical instruments exhibit different phase coupling characteristics. The effect of phase coupling is compared to analysis by means of higher order statistics and it is shown that both methods are closely mathematically related. Following a detailed analysis of phase coupling for various musical instruments it is suggested that phase coupling is an important characteristic of a sustained portion of sound of individual musical instruments, and possibly even of instrumental families. Interesting differences in phase deviations where found for the flute, trumpet and cello. For the cello, the effect of vibrato is examined by comparing the analysis of a closed string sound played with a natural vibrato to analysis of an open string sound that contains no vibrato. Following, a possible model for phase deviations in the cello is presented and a simulation of phase fluctuations for this model is performed.     

微纳世界的音乐之声——用低维纳米机电器件探索微观世界

纳米机电器件是具有机械运动自由度的纳米电子器件。特别有趣的是,纳米机电器件同时也构成了微纳世界的各种乐器,能够演奏出独特的音乐之声。如同宏观世界中的乐器各有各的特色,这类微纳器件在研究低维及纳米尺度的物理现象时,也展现出一些独到的潜力和优势,例如研究低维体系中的独特相变过程以及纳米材料中的力学各向异性效应等。在这些工作中,通过精密测量低维纳米材料的机械振动,即仔细倾听这些乐器所奏出的音乐之声,能够帮助研究者们观察到一些原来不易被测量的现象,进而探索新的低维物理过程和材料体系,带来新的科学发现。     

Warm string tone in acoustics

The result of a basic warm string tone in a concert hall is that the whole orchestra not only sounds extremely well balanced, but the individual instruments outside the string family sound warmer and richer, and no attention is drawn to their extraneous noises. On the basis of orchestral conducting, performing, recording, and listening experience, some conclusions are reached, and suggestions made, concerning the physical conditions that are likely to be necessary, or conductive, to attainment of warm string tone. Among the physical factors considered are the acoustic and vibratory properties of the stage itself, hall volume, shape and reverberation time, and surface materials. Emphasis is placed, in discussion of the physical and musical factors, on the ways in which the musicians themselves, during performance, interact with “the acoustics”.     

Spatial correlation and coherence in reverberant acoustic fields: Extension to microphones with arbitrary first-order directivity

Spatial correlation and coherence functions in reverberant sound fields are relevant to the acoustics of enclosed spaces and related areas. Theoretical expressions for the spatial correlation and coherence functions between signals representing the pressure and/or the components of the particle velocity vector in a reverberant sound field are established in the literature and most of these have also been corroborated with measurements [F. Jacobsen, J. Acoust. Soc. Am. 108, 204-210 (2000)]. In the present paper, these expressions are generalized to microphones of first-order directivity, whereby the directivity can be expressed in terms of pressure and pressure gradient. It is shown that the resulting spatial correlation and coherence functions can be expressed in terms of the established spatial correlation and coherence functions. The derived theoretical expression for the spatial coherence function is validated with a modeled diffuse sound field. Further, it is compared with the experimental coherence obtained from the reverberant tails of room impulse responses measured with two common surround sound microphone setups in a concert and a lecture hall.     

Manipulating Chladni Patterns of Ferromagnetic Materials by an External Magnetic Field

Ernst Chladni is called the father of acoustics for his work, which includes investigating patterns formed by vibrating plates. Understanding these patterns helps research involving standing waves and other harmonic behaviors, including studies of single electron orbits in atoms. Our experiment vibrates circular plates which result in well-known patterns. Alternatively to traditional experiments that used sand or salt, we use magnetic materials, namely iron filings and nickel powder. We then manipulate the patterns by applying a localized external magnetic field to one of the rings that moves a segment of the magnetic material in that ring to the next inner ring. The results show a significant decrease in magnetic field necessary to move the magnetic material at higher frequencies as well as a significant decrease in the magnetic field required to move the magnetic material as nickel powder is substituted for iron filings while keeping the mass constant.     

Acoustics and activity noise in school classrooms in Finland

School classrooms are learning spaces for children and workplaces where a teacher’s most important tool, his or her voice, is subjected to considerable loading. Because noise has several detrimental effects on human functioning including speech production and perception, a noiseless environment and good acoustics in classrooms are important. The main aim of this study was to investigate the classroom as a sound environment and to ascertain the effect of acoustics.     

The metre

A musical wind instrument transforms a constant pressure input from the player's mouth into a fluctuating pressure output in the form of a radiating sound wave. In reed woodwind and brass instruments, this transformation is achieved through a nonlinear coupling between two vibrating systems: the flow control valve formed by the mechanical reed or the lips of the player, and the air column contained by the pipe. Although the basic physics of reed wind instruments was developed by Helmholtz in the nineteenth century, the application of ideas from the modern theory of nonlinear dynamics has led to recent advances in our understanding of some musically important features of wind instrument behaviour. As a first step, the nonlinear aspects of the musical oscillator can be considered to be concentrated in the flow control valve; the air column can be treated as a linear vibrating system, with a set of natural modes of vibration corresponding to the standing waves in the pipe. Recent models based on these assumptions have had reasonable success in predicting the threshold blowing pressure and sounding frequency of a clarinet, as well as explaining at least qualitatively the way in which the timbre of the sound varies with blowing pressure. The situation is more complicated for brass instruments, in which the player's lips provide the flow valve. Experiments using artificial lips have been important in permitting systematic studies of the coupling between lips and air column; the detailed nature of this coupling is still not fully understood. In addition, the assumption of linearity in the air column vibratory system sometimes breaks down for brass instruments. Nonlinear effects in the propagation of high amplitude sound waves can lead to the development of shock waves in trumpets and trombones, with important musical consequences.     

Nondestructive characterization of musical pillars of Mahamandapam of Vitthala Temple at Hampi, India

This paper presents the first scientific investigation on the musical pillars of the Vitthala Temple at Hampi, India. The solid stone columns in these pillars produce audible sound, when struck with a finger. Systematic investigations on the acoustic characteristics of the musical pillars of mahamandapam (great stage) of the Vitthala Temple have been carried out. The 11 most popular pillars that produce sounds of specific musical instruments are considered for the investigations. The sound produced from these 11 most popular musical pillars was recorded systematically and different nondestructive testing techniques such as low frequency ultrasonic testing, impact echo testing, and in situ metallography were employed on the musical columns of these pillars. The peak frequencies in the amplitude spectrum of the sound produced from various columns in these pillars are correlated with the dimensional measurements and ultrasonic velocity determined using impact echo technique. The peak frequencies obtained experimentally have been found to have excellent correlation with the calculated flexural frequencies based on the dimensional measurements and ultrasonic velocities of the columns.     

Physics-based modeling techniques of a twelve-string Portuguese guitar: A non-linear time-domain computational approach for the multiple-strings/bridge/soundboard coupled dynamics

The Portuguese guitar is a pear-shaped instrument with twelve metal strings which is widely used in Portuguese traditional music. Unlike most common guitars, it has a curved top-plate and a specific violin-like bridge which is not rigidly fixed to the soundboard of the instrument. From the dynamical point of view, if the bridge transmits the strings vibrations to the instrument body in order to maximize the radiated energy, it also couples all the component parts of the instrument which therefore interact by structural coupling. This can originate various audible effects such as beating behavior and the excitation of numerous sympathetic resonances enhanced by the large number of strings of the instrument, and this is certainly why the Portuguese guitar has such distinct sound compared to other guitars. In this paper, a fully coupled time-domain model of the Portuguese guitar is developed and a series of simulations are presented to emphasize the various coupling phenomena involved in sound production. To reproduce the main musical features, the model includes the coupled dynamics of the twelve strings supported by a bridge which interact with the body of the instrument, described through Finite-Element modeling of the soundboard of a typical Portuguese guitar. Further simple models have been devised for the string/fret interaction and the pluck excitation. Since nonlinear effects are quite apparent in the behavior of string musical instruments, the string dynamics is modeled by the Kirchhoff–Carrier equations which describe large-amplitude string vibrations, and includes the coupling between both polarizations of string motion. The coupling between the strings and the soundboard at the bridge is provided by a model of the bridge kinematics, built on the basis of simple geometrical rationale, so that the two perpendicular string motions can exchange energy back and forth. By a close examination of the energy transfers between the various subsystems of the model, we first assess the correct behavior of the physical model and then examine the respective influence of the string nonlinearity and the bridge on the nonplanar motion of the string. The fully coupled model which pertains to the restricted group of studies which deals with the complete physical-based modeling of a multi-stringed instrument, captures many important phenomena observed in practice, among which the pitch glide effect and the mutual excitation of sympathetic vibrations.     

Use of focused ultrasonic receivers for remote measurements in biological tissues

The feasibility of using a focusing ultrasonic transducer as a sound pressure receiver is discussed. It is shown theoretically that, at certain angular apertures of the receiver, its output signal is proportional to the sound pressure in the field point coincident with the receiver center of curvature. The receivers of this type have been demonstrated suitable for remote measurements of field spatial distribution of plane and focused ultrasonic radiators. Data are presented on the experimental testing of focused receivers in measuring acoustic fields in water, air, and certain samples of biological tissues. The instruments are sufficiently universal and allow the measurement not only of acoustic fields, but also of temperature increments in locally heated media, as well as permit one to follow the initiation and development of ultrasonic cavitation and study nonlinear effects. The remote sensing ability and high sensitivity of focused ultrasonic receivers allow their practical use in biomedical acoustics for noninvasive measurements.     

Fourier at the heart of computer music: From harmonic sounds to texture

Beyond the scope of thermal conduction, Joseph Fourier's treatise on the Analytical Theory of Heat (1822) profoundly altered our understanding of acoustic waves. It posits that any function of unit period can be decomposed into a sum of sinusoids, whose respective contributions represent some essential property of the underlying periodic phenomenon. In acoustics, such a decomposition reveals the resonant modes of a freely vibrating string. The introduction of Fourier series thus opened new research avenues on the modeling of musical timbre—a topic that was to become of crucial importance in the 1960s with the advent of computer-generated sounds. This article proposes to revisit the scientific legacy of Joseph Fourier through the lens of computer music research. We first discuss how the Fourier series marked a paradigm shift in our understanding of acoustics, supplanting the theory of consonance of harmonics in the Pythagorean monochord. Then, we highlight the utility of Fourier's paradigm via three practical problems in analysis–synthesis: the imitation of musical instruments, frequency transposition, and the generation of audio textures. Interestingly, each of these problems involves a different perspective on time–frequency duality, and stimulates a multidisciplinary interplay between research and creation that is still ongoing.