A digital loudspeaker produces a quantized sound field directly from a digital stimulus without a digital to analogue converter. Reproduction accuracy improves if the conversion is done as late as possible in the audio chain. This paper assesses the relative merits of the two currently competing technologies, digital transducer arrays and multiple voice coils, as well as possible alternatives, by considering the underlying principles. The requirements for crossovers and drive electronics are discussed, and the performance of prototype systems is reported. Methods to extend the present manufacturability to 16 bits include the use of semiconductor mass fabrication techniques in the case of arrays and applications of over-sampling and noise shaping. In the latter case the psychoacoustic implications must be understood.
Convention Paper 5518

09:30 h
E2 Suspension Bounce as a Distortion Mechanism in Loudspeakers with a Progressive Stiffness – Don Keele, Jr., Ryan Mihelich, Harman/Becker Automotive Systems, Martinsville, IN, USA

The stiffness of a progressive suspension is fairly constant for small excursions and then gets progressively stiffer for larger excursions. When the moving assembly enters the region of increasing stiffness, forces are generated that rapidly reverse its motion much the same as when a bouncing ball hits the ground. Contrary to the common wisdom that predicts a squared-off displacement waveform, the bouncing-ball analogy predicts that the displacement waveform will be turned into a triangle wave. Under some conditions, the moving assembly will repetitively bounce at a frequency tens of times higher than the excitation frequency with acoustic output that exhibits high-level harmonics several times higher in amplitude and frequency than the fundamental. Time-domain simulations and experiments are presented to illustrate the effects.
Convention Paper 5519

10:00 h
E3 Radiation Impedance of Cones at High Frequencies – Joerg Panzer, NXT - New Transducers Ltd., Huntingdon, UK

The cavity of concave diaphragms causes a typical variation of the radiation impedance, which has an effect on the performance of the speaker system in the frequency range where the wavelength is comparable with the dimension of the diaphragm. This paper investigates the radiation impedance and its effects on the sound pressure response of the whole driver with the help of a circular symmetric boundary element method for the infinite baffle. The electrical and mechanical properties of the electro dynamical driver are modeled with lumped elements. An approximation for the wide band radiation impedance of cone type diaphragms is given and compared to the exact results from the BEM.
Convention Paper 5520

10:30 h
E4 The Application of FEM to the Analysis of Loudspeaker Motor Thermal Behavior – Mark Dodd, Celestion Int Ltd & KEF Audio (UK), Ipswich, UK

A simple 2D Finite element method (FEM) may be applied within the thermal domain to analyze the behavior of systems where fluid flow is not a significant factor. FEM’s ability to analyze problems with arbitrary geometric form makes it a powerful alternative to the lumped element approach for modeling loudspeakers. Applying suitable boundary conditions, and using modified material properties, it is possible to model the thermal behavior of a loudspeaker motor with FEM. This approach minimizes errors due to fluid flow and includes heat radiation to the environment. The FEM technique is applied to a new driver topology with external frame and magnet. Static thermal FEM results are compared to those obtained from the driver by measurement. The material properties for air were derived from experimental results. A separate model, including the full mechanical structure of the coil, is used to derive its bulk thermal properties thus allowing a more efficient solution.
Convention Paper 5521

11:00 h
E5 Vented Box Geometry and Low-Frequency Reproduction: The Aerodynamical Approach - Jean-Dominique Polack, Jean-Pierre Morkerken, Guillaume Pellerin, Benjamin Parzy, Laboratoire d'Acoustique Musicale, Paris, France

To-day, low frequency reproduction with loudspeakers in vented box is limited by two factors: the volume of the box, and non-linear airflow through the vent. We propose a novel approach that takes into account aerodynamical parameters, leading to original profiles and an improved functioning of the vented box. For example, under certain alignment conditions, there exists a second cut-off frequency below the first one, localized on the lower impedance hump. Using this lower cut-off frequency and an adapted vent profile makes it possible to radiate frequencies around 40 Hz with box volumes smaller than 1 liter and small drivers. A prototype will be demonstrated.
Convention Paper 5522