Thursday, September 29, 4:00 pm — 6:00 pm (Rm 403A)
Mark Gander, JBL Professional/Harman International - Northridge, CA, USA
P6-1 Measurement of the Frequency and Angular Responses of Loudspeaker Systems Using Radiation Modes—Maryna Sanalatii, Laboratoire de Mécanique et d'Acoustique UPR CNRS - Marseille, France; Université du Maine, UMR CNRS - Le Mans cedex 9, France; Philippe Herzog, CNRS-LMA - Marseille, France; Manuel Melon, Université du Maine - Le Mans cedex 9, France; Régine Guillermin, Laboratoire de Mécanique et d'Acoustique UPR CNRS - Marseille, France; Jean-Christophe Le Roux, Centre de Transfert de Technologie du Mans - Le Mans, France; Nicolas Poulain, Centre de Transfert de Technologie du Mans - Le Mans, France
In this paper the ”radiation mode” (RM) method is applied to the measurement of the frequency response and directivity pattern of two loudspeaker systems. This approach is based on solving the discretized Helmholtz equation on the source boundaries to obtain an efficient expansion suitable to represent any field radiated by a source. Bookshelf and column systems have been tested. Results obtained with the proposed method are then compared to the ones given by two other methods: measurement in an anechoic room and boundary element computation based on the scanning of the membrane velocity. Results show a good agreement between the different methods. Pros and cons of the different approaches are then discussed as well as the possibility to use the ”radiation mode” method in non-anechoic rooms.
Convention Paper 9615 (Purchase now)
P6-2 Vandermonde Method for Separation of Nonlinear Orders and Measurement of Linear Response—Russell H. Lambert, Harman International - Salt Lake City, UT, USA
The Vandermonde matrix method for separation of nonlinear components and full-power linear response measurement is analyzed in this paper. This technique involves making several measurements of a nonlinear system (a woofer or horn system for example) at different gains and applying the inverse Vandermonde gain matrix to the vector of outputs. The Vandermonde matrix method does more than just return the linear response, as it more generally separates all of the nonlinear orders breaking difficult nonlinear system estimation tasks into more tractable problems, one for each Volterra kernel. Quantitative measures for the degree of nonlinear order separation are proposed. The Vandermonde matrix order separation method is analyzed for noise robustness and gain spacing sensitivity and found to be a useful and practical tool for audio measurements.
Convention Paper 9616 (Purchase now)
P6-3 Fluid Dynamics Analysis of Ported Loudspeakers—Juha Backman, Genelec Oy - Iisalmi, Finland; Microsoft Mobile - Espoo, Finland
The small-signal performance of ported loudspeakers is described in an excellent way by traditional models, such as lumped parameters, waveguide models, or numerical solutions of the acoustic wave equation. However, the acoustic models are clearly insufficient to predict the nonlinear behavior of ported enclosures. This paper presents the results of a computational fluid dynamics analysis of an unlined ported enclosure, focusing on the behavior around the tuning frequency. The results indicate that the vortex formation around the port ends has a significant effect already at a relatively low flow velocities and that the transient behavior of the vortex field can differ from that predicted by the acoustical solution.
Convention Paper 9617 (Purchase now)
P6-4 Compression Drivers’ Phasing Plugs—Alexander Voishvillo, JBL/Harman Professional Solutions - Northridge, CA, USA
Most of compression drivers have phasing plugs with annular slots. Existing theories give recommendations for positioning of annular slots to suppress air resonances in compression chamber. However, interaction of diaphragm’s mechanical resonances with the compression chamber’s air resonances makes the problem very complex and a general theoretical solution hardly exists. New approach, based on certain empirical assumptions, is proposed and explained. New phasing plugs have slots of a “meandering” shape that provide effective “averaging” of high-frequency acoustical signal received from different parts of compression chamber. The method is applicable to drivers having domes, cones, and annular diaphragms. Other aspects of the design such as efficiency, compression ratio, and difference between air resonances in dome and annular compression chambers are discussed.
Convention Paper 9618 (Purchase now)