Home HomeUwe J. Hansen, Indiana State University (U.S.A.)
All pitched musical instruments rely on resonances in some form for frequency selection and amplification. In most percussion instruments, string instruments and string keyboard instruments a membrane, the instrument body or a sound board is largely responsible for radiation from the instrument. The normal modes of these structures thus have a significant influence on the sound heard by an audience. Among the techniques used to study such normal modes are near field mapping, holographic interferometry, electronic speckle interferometry, computer animated modal analysis and theoretical finite element methods. These techniques will be discussed and illustrated with examples on Handbells, Guitars, Piano Sound Boards and Caribbean Steel Pans.
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TOPHervey Bagot, Bagot Bellfoundries (Australia)
The Western bell has a 1000-year history of development as a musical in-strument. The technical improvements in that time have been a mixture of serendipity and science. An historical overview is given in this presentation, and some current problems and research mentioned. About the year 1000 case bronze bells for use in belltowers began a development from the cylindrical shape borrowed from the East. From then to the present day seven important stages can be seen: (1) movement to a new (flared) shape which would give an identifiable musical note by about year 1200; (2) appreciation of the design laws for bells in a musical scale (without resort to mechanical tuning by 1500; (3) understanding the vibrational complexities of the bells, leading to the possibility of harmonic tuning before 1700; (4) description (without understanding) of the modal content of the bell by 1950; (5) revelation of the physical significance of the vibrational modes by 1980; (6) building on the past to design and modify bells, using the mathematical and computational tools now available - from 1980; (7) improving understanding of correct voicing of bells to good effect -- also in our day.
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Uwe J. Hansen, Indiana State University (U.S.A.)
Thomas D Rossing, Northern Illinois University (U.S.A.)
Since the SV IV review report on modal analysis studies in steel pans a relatively complete survey of normal modes of a tenor steel pan has been conducted using electronic speckle interferometry. Like holographic interferometry, this technique relies on the time average of comparisons of quasistationary images in the extremal positions of normal mode motion. Computer image processing techniques enable contrast enhancement and close to real time interference pattern observation. A number of interference patterns associated with particular note section normal modes will be shown to illustrate mode patterns, linear coupling and amplitude dependent nonlinear coupling between note sections.
sv970368.pdf (Scanned) TOPRiduan Osman, University of Sydney (Australia)
The application of binaural recordings for the comparisons and assessments of the acoustic quality of music rooms and concert halls are discussed. Correctly made binaural recordings can provide easy and precise subjective comparisons and ranking of the acoustic quality of music rooms and concert halls without enduring the disadvantages of relying on the subjects' acoustic memory. A review of the types of dummy heads, microphone locations, the resulting binaural recordings that can achieved and equalisation required are carried out. The various methods of binaural recording reproduction, using headphones and loudspeakers, for presentation to the listening subjects are discussed and methods of subjective assessments of binaural recordings made in music rooms and concert hall are recommended.
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Suhashini Shankar, University of Technology, Sydney (Australia)
Suzanne Hogg, University of Technology, Sydney (Australia)
The number and nature of the mechanisms of pitch discrimination in the human ear is not clearly understood. To deepen our understanding of the mechanism involved in perceiving pitch, we have used the auditory model of Meddis and Hewitt (1991). We optimised the parameters and measured the jnd of the model for sinusoidal stimulus. Comparison of our experimental findings on the mechanism of pitch discrimination, reported earlier, and the performance of the model indicates the single mechanism operating in discriminating pitch.
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Lucile Rossi, University of Corsica (France)
G. Girolami, University of Corsica (France)
The aim of this paper is to present a study of the evolution of partials in polyphonic piano sounds. The identification of polyphonic sounds usually takes place in the frequency domain and works on a small number of partials, but a common problem in most of the identification methods is octave errors. In this paper, the authors consider the identification of polyphonic piano sound signals, that is, several notes played simultaneously from the same keyboard instrument. The evolution in time and frequency of the partials and the distribution of their energy are interesting to investigate in order to use them to identify the notes. For example, the amplitude of the partials could be used to distinguish the case of overlapping repeated notes. Thus the case of a note (N1) played twO times with a short delay between the notes [N1+short delay+N1] is difficult to separate from the case [N1 long+short delay+N2], when note N2 is played during N1s decay. In order to treat these and similar difficult situations, this paper presents a study of the evolution of the partials of different piano notes, which can be used when deriving general identification methods for polyphonic piano signals.
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M.H. van Houten, Eindhoven University of Technology (The Netherlands)
A.J.G. Schoofs, Eindhoven University of Technology (The Netherlands)
D.H. van Campen, Eindhoven University of Technology (The Netherlands)
The decay rates of the different partials of a vibrating bell are an important characteristic of the bell's sound spectrum. These decay rates are caused by material damping of the bell structure and acoustic damping due to the surrounding air. Designing new bells, bell founders would like to know the damping of the different partials before they cast a bell since casting a new bell is expensive and time consuming. However, the damping can only be determined accurately experimentally after a bell is cast. Numerical methods (FEM/BEM) can give an estimation of the damping values. To gain a better understanding of the damping behavior of bells, modal measurements were carried out on four different bells to obtain the eigenfrequencies and the material and acoustic damping values of the partials. The results were compared with the results from fast numerical analyses methods utilizing axisymmetric Fourier elements in circumferential direction for both the structural and acoustic analyses. Some characteristic features of the damping values of bells are obtained and the comparison of experimental and numerical results shows that the damping values for most of the seven lowest partials can be predicted fast within 30% of the measured values.
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Katherine A. Legge, La Trobe University (Australia)
J. Petrolito, La Trobe University (Australia)
The transverse modes generated when a uniform beam is struck between its two supports are not harmonic. In order to tune the beam so that at least the lowest of these modes are harmonically reIated, parabolic arches are cut on the underside of the beams. The actual dimensions of the undercut are an empirical design determined by tradition, and relate the subtleties of the sound produced with those favoured by the human ear. The current paper takes a very general approach to the problem. Finite element analysis is used to determine the optimal undercut required to tune the beam. However no assumption is made regarding the shape of the cut beyond ensuring that material is not added and that the structure remains a single beam. An optimisation approach is then used to calculate the profile of the beam to satisfy the prescribed frequencies. The calculated profile depends on the optimisation criterion specified. The paper will present a variety of profiles for which the optimization criteria vary from ease of modelling to ease of construction. The results often do not resemble the traditional cut.
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