3) Vibration Characteristics of Brass Instrument Bells
John M. Bowsher - Department of Physics, University of Surrey
Peter S. Watkinson - Institute of Sound and Vibration Research, The University, Southampton, Hants, SO9 5NH, England
This paper was a preliminary study of the vibratory properties of the mathematical structures of the trombone bell. Using the finite element technique it is possible to calculate the response of the modes when these are excited acoustically. One important conclusion from this vibration analysis is that a mode is excited in proportion to its degree of asymmetry. This implies that those properties of the bell which lead to asymmetry modes are initially important. In the case of the trombone the cross braces are of major importance but other factors, such as a non-circular section, may play a role.
4) Transformations Introduced into the Brass-Instrument Sound Spectrum by the Use of Mutes
René Causse, Benny Sluchin - Institut de Recherche et de Coordination Acoustique/Musique (IRCAM), 31, rue Saint-Merri, 75004 Paris, France
Mutes not only attenuate the sound of brass instruments, they also transform and modify its sound-spectrum content and its directivity. This paper dealt only with those transformations introduced into the external spectrum by different instruments in the family. First, results were given of the directivity of different mutes. The external spectrum depends very much on the place where the sound is recorded. A simple method (for the middle of the spectrum) was then described for studying these transformations and the results obtained were then presented.
5) Acoustic Study of Multiphonic Emission in Brass Instruments
Michèle Castellengo - CNRS, Acoustic Laboratory, University of Paris VI, 4, Place Jussieu, 75005 Paris, France
René Causse, Benny Sluchin - IRCAM
The so-called “normal” emission of a wind instrument consists in maintaining a given partial. The resulting sound is periodic. “Multiphony” occurs when it is possible to identify several pitches in the emission of a note being maintained. It usually corresponds to the production of several non-harmonic partials. The phenomena described are common to all brass instruments and consist of a purely labial emission (with no voice). On a given partial the player “decentres” the sound while maintaining air pressure in his mouth. Multiphonic emission gives the impression of a “rolled” sound and is closely related to the initial partial. The multiphony phenomenon was then explained thoroughly: it depends purely on the frequency relationship between the two adjacent partials, the one corresponding to the mode of emission and the one immediately below. An analysis was presented and the problem of perception discussed.