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v3.2, 20040330, ME

Session L Monday, May 10 09:00 h–12:00 h
(focus on drivers and horns)
Chair: Juha Backman, Nokia Mobile Phones, Espoo, Finland; Helsinki University of Technology, Espoo, Finland

L-1 Bit Expansion in Digital Loudspeakers with Oversampling and Noise Shaping Haihua Zhang, Simon Busbridge, University of Brighton, Brighton, East Sussex, UK; Peter Fryer, B&W Loudspeakers Ltd., Steyning, West Sussex, UK
The resolution of true digital loudspeakers is currently limited by their physical construction. Transducer arrays require 2N-1 speaklets and multiple voice coil topologies require N coils (N = the number of bits). Oversampling and noise shaping have been used to maintain resolution with fewer bits. Results are presented where the oversampled signal falls both within and outside the bandwidth of the radiator. A linear model is being developed to understand the observations. The radiator displacement shows little difference between the original and oversampled cases. It is concluded that the limited bandwidth of existing acoustical radiators is advantageous in acting as the reintegration filter. In circumstances where this is not possible the auditory system may perform this task.
L-2 Geometrical Stiffness of Loudspeaker ConesPeter Larsen, Loudsoft, Horsholm, Denmark
The frequency response of a loudspeaker cone is affected by two main factors: material parameters and geometry. While the first may be generally understood, the inherent stiffness due to the basic geometry is the subject of this paper. Using Finite Element Modeling (FEM), first a flat cone disk is analyzed followed by shallow and deep conical cones plus curved concave and convex cones. The results are extended to include softer and high damping cone materials. The cone break-up behavior and frequency response is shown to be strongly dependent on the geometrical stiffness of the cone, which should therefore be considered a very important design parameter.
L-3 A Circuit Approach to Short Circuit Ring Design for High Power WoofersLorenzo Fontanesi, Alessandro Salvini, University of Rome, Rome, Italy
Demodulation ring solutions can offer many advantages in terms of harmonic distortion reduction in high power 18-inch woofers. In this paper we show a circuit approach to evaluate the effects of aluminum short circuit rings properly shaped to improve woofer performances. To find the Laplacian force that acts on the voice coil, the proposed approach allows the partial inductance calculation method to evaluate the distribution of eddy currents into the massive ring aluminum conductors. By partitioning the conductor into cells and modeling each cell by an equivalent circuit this method can give results showing a maximum error equal to 6 percent by comparing measurements to simulations.
L-4 On the Velocity Distribution at the Interface of Horn Driver and Horn—Gottfried Behler, Michael Makarski, Aachen University, Aachen, Germany
For the numerical simulation (BEM) of horns, the sound velocity distribution at the horn throat is required as one boundary condition. It is common to use plane wave excitation even at high frequencies since the shape of the real wave front in general is unknown. The error in the simulation result (directivity / frequency response) is difficult to predict and can only be judged by measurement of the real system. To achieve accurate simulation results the specific velocity distribution of each driver is required, which must be measured at the interface between horn driver and horn. A more general approach for simulation techniques is created using modal composition. Measurements and simulations of different systems are compared to verify this method.
L-5 Determining Two-Port Parameters of Horn Drivers Using Only Electrical Measurements— Michael Makarski, Aachen University, Aachen, Germany
The basic theory and a measurement procedure for the two-port description of horn drivers and horns was presented at the 111th AES Convention in New York, 2001 (Convention Paper 5409, Behler and Makarski, “Two-Port Representation of the Connection between Horn Driver and Horn,” [JAES, Vol. 51, No. 10, 2003]). It was shown that this method is a powerful tool for the development of loudspeakers, but it suffered from the restricted frequency range of the necessary acoustical impedance measurements with the Kundt’s tube. A new method of measuring the driver’s two-port parameters is presented here, using only electrical measurements and an acoustical reference impedance. The frequency range of the two-port parameters could be extended using this method. The theoretical approach and first results are presented.
L-6 Analysis and Minimization of Unwanted Resonances in Loudspeaker Systems via FEM Techniques—Mario Di Cola1, Davide Doldi1, Marco Mocellin1, Rinaldo Grifoni2, Paolo Antinori2, Remo Orsoni2, Giogio Santarelli2
Audio Labs Systems—LiSA Design Workgroup, Milan, Italy
Proel S.p.A., Sant’Omero (TE), Italy
High output loudspeaker systems, particularly horn-loaded loudspeaker systems, are often severely affected by unwanted structural resonances due to the high sound pressure locally generated. Modern high power transducers, in fact, are capable of generating very high sound pressure. This sound pressure turns out to be a great stimulus for a cabinet’s structural modes. An experimental procedure aimed at resonance minimization is shown. This method is based on FEM structural analysis techniques validated by microphone and accelerometer measurements.

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