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The Feed-Drum〔( GRAME Rencontre Musicales Pluridisciplinaries 2006 ) Retrieved on August 18, 2009.〕 is an imperial bass drum with a system of electronic conditioning of the skin conceived by composer Michelangelo Lupone and coproduced between CRM - Centro Ricerche Musicali, Rome and Istituto Gramma in L'Aquila. Through the principle of feed-back, the signal produced by the excitation of the skin returns to the skin in the form of acoustic pressure. The result is an infinitely sustained sound. The system controls the damping of the movement of the skin, and therefore the decay rate of the sound, and permits isolation of high frequency modes by the combined action of nodes present on the skin and the amount of feed-back input energy.〔(Universidad Complutense de Madrid )〕 The design on the skin surface is a simplified map of the oscillatory modes based on the Bessel functions. The map was limited to 13 diameters and 8 nodal circles, the latter divided into even semicircles (to the left) and odd semicircles (to the right).〔(Max Planck Institut - Informatik )〕 See also Skin-Act. Image: Feed2.jpg|Map of the first 13 nodal diameters Image: Feed3.jpg|Feed-drum, first map with 13 diameters and 8 nodal circles ==Experimental Work== Although the skin of an imperial bass drum allows the excitation of a considerable number of high-frequency modes, their duration in time is not normally appreciable by the listener, apart from the timbric contribution to the attack phase of the sound. The possible variations of the mode of emission, adequate for a sufficient acoustic response of the resonator (shell), are limited and with scarce modulability. The basic frequency, obtained by the tension of the skins, upper and lower, each bound to the edges with 16 mechanical tie rods, is influenced by the non-homogeneous distribution of the tensioning forces which contributes to render complex the spectrum of the real modes.〔(Exibart )〕 Experiments were made at the Centro Ricerche Musicali - CRM in Rome〔Gran Cassa and the Adaptive Instrument Feed-Drum - Computer Music Modeling and Retrieval - Seno, Lorenzo - Lupone, Michelangelo - Spinger Verlag 2006 - ISBN 3-540-34027-0〕〔(CRM - Centro Ricerche Musicali )〕 and at the Istituto Gramma in L'Aquila with the aim of achieving these objectives: * Variation of basic frequency through application of nodal constraints to the skin * Identification of timbres on the basis of type, mode, and point of excitation * Sound modulation through glissandos, vibratos, portamento, and rhythmic micro-articulation * Continuous or step variations of the dynamics, on the basis of the type of damping applied to the skin Traditional bass drums obviously do not provide these characteristics. To explore the timbre richness of the attack phase and isolate the vibrational modes, the makers created a system to electronic manipulate the skin. Through the principle of feedback, the system returns the signal produced by the excitation of the skin back to the skin as acoustic pressure. This produces infinite prolongation of the sound. The system controls the damping the skin, and therefore the decay rate of the sound, and permits isolating high frequency modes by the combined action of the nodes present on the skin and of the amount of feed-back input energy. 〔(Springer Berlin Heidelberg )〕 The stability of the signal obtained with this conditioning system makes it possible to experiment and design on the skin surface a preliminary simplified map of the oscillatory modes based on the Bessel’s functions. The map is limited to 13 diameters and 8 nodal circles, the latter divided into even semicircles (to the left) and odd semicircles (to the right). Electronic conditioning of the instrument leaves the topology and primary acoustic features unaltered, but increases the scope of the vibrational criteria and control. This made it possible to distinguish the different pitches of various modes, to obtain the emission of long notes, which could be modulated as those emitted by a stretched string, and to adapt the acoustic energy independently of the emitted frequencies.〔(INIST/CNRS )〕 To maintain agile execution and adequate reproducibility of the phenomena, the first classification of sounds and performance techniques was limited to the use of fingers, hands and arms (Fig. 4). During the composition of ''Gran Cassa'' by Michelangelo Lupone, experiments were also made with objects of different shapes and dimensions occupying wider or multiple nodal sections. This increased the sound possibilities. However, the complexity of the vibrational phenomena required analysis of the instrument's mechanical parts to identify and reduce dispersions and non-linear contributions from vibrations of the structural materials and their combinations.〔(LMA CNRS MRS France )〕 Image: Feed4.jpg|Fig. 4 Feed-drum, one of the performance techniques for the excitation of high frequency modes Image: Feed5.jpg|Fig. 5 Feed-drum Image: Feed6.jpg|Fig. 6 Feed-back – 3 Feed-drums (2002), excerpt from the score Given these complications, it was decided to plan and realize a new instrument, the Feed-drum (Fig. 5), for the purpose of not only extending the acoustic possibilities, but also of permitting the ergonomic use of new executive techniques. In particular, the vibrational attitude was transformed by eliminating the lower skin, a decision which simplified the tuning of the instrument’s basic frequency (30 Hz) and reduced the excitation rise time in the upper modes. A synthetic membrane was applied with isotropic characteristics and high flexibility on which the previously described map was drawn, with colors that made the areas of performance more visible. The shell and the tensioning hoop were realized in steel and aluminium; in particular, the tensioning hoop was made stiffer while the height was reduced and the adhesion surface increased. The suspension system was realized in such a way as to separate the Feed-drum completely from the supporting structure on the ground; all the mechanical parts, which were in contact with one another, were separated by an intermediate layer of antivibrational material.〔( Conservatory of Music Alfredo Casella L'Aquila ) Retrieved on August 21, 2009〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Feed-Drum」の詳細全文を読む スポンサード リンク
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