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P13 - Loudspeakers -2
Sunday, October 9, 1:00 pm — 4:00 pm
Chair: D. B. (Don) Keele, Jr., Harman International Industries - Northridge, CA, USA
P13-1 Improving Loudspeaker Transient Response with Digital Signal Processing—David Gunness, Loud Technologies, Inc. - Whitinsville, MA, USA
The transient response of a loudspeaker represents the combined effect of a multitude of physical behaviors. Some of these behaviors are time-variant, nonlinear, or spatially variable and are not good candidates for digital correction. Others are sufficiently LTI (linear, time-invariant) and sufficiently consistent directionally to be largely correctable with specialized digital filters. In the particular case of high powered, horn-loaded loudspeakers, most of the observed transient misbehavior is the result of stable, correctable phenomena. Consequently, the transient response of such loudspeakers can be significantly improved with signal preconditioning. Measurements demonstrate the improvements that are possible.
Convention Paper 6590 (Purchase now)
P13-2 Simulation of Harmonic Distortion in Horns Using an Extended BEM Postprocessing—Michael Makarski, RWTH Aachen University - Aachen, Germany
The Boundary Element Method is a well-known tool to calculate sound radiation of horns. As the BEM is based on the linearized sound field equation, only linear properties of the sound field (frequency response, directivity, etc.) can be calculated. In addition to these linear properties, the nonlinear wave propagation in horns is of great interest. It depends mainly on the shape of the horn and the growth rate of the first narrow part. This paper describes a method to combine the pure linear method BEM with the calculation of nonlinear wave propagation in horns. Simulation and measurement results of different horns are presented and discussed. As first results indicate, this method offers a fast and accurate way to calculate nonlinear wave propagation in horns.
Convention Paper 6591 (Purchase now)
P13-3 Modal Analysis and Nonlinear Normal Modes (NNM) on Moving Assemblies of Loudspeakers—Fernando Bolaños, Acústica Beyma SA - Valencia, Spain
The most important modes for a direct acoustic radiator are the axial modes, which are axisymmetric circular modes of high coherence. Numeric modal analysis and measurement of the free and forced accelerations and displacement responses of the moving assemblies are performed to establish the main modes involved on the acoustic response. The axial modes had been identified by measurements (within the intrinsic degree of uncertainty). The experiences show evidence of clearly nonlinear normal modes (NNM), justifying the high complexity of mode finding in loudspeaker cones. Based on the axial modes, a three degrees of freedom model is proposed, where only one of the masses is externally forced. The modal analysis of a double cone speaker has been treated in short form.
Convention Paper 6592 (Purchase now)
P13-4 Finite Element Modeling of a Loudspeaker. Part 2: Applications—John Vanderkooy, University of Waterloo - Waterloo, Ontario, Canada; David Henwood, Gary Geaves, B&W Group Ltd. - Steyning, West Sussex, UK
The finite-element loudspeaker model presented in Part 1 is extended to three applications. First, we study the effect of a significant increase of the magnetic motor strength Bl on the breakup modes and other resonances of a typical driver. Approximations to the theory allow modal decomposition even when the loudspeaker voice coil is driven from a normal amplifier, showing that the modes most affected are those for which the back-emf due to voice-coil motion is strong. Second, we probe how the shape of the cone influences the resonances, breakup, and acoustic performance. Cones that flare outward have the most desirable characteristics. A final third study concerns the result of a change in the distribution of the damping and stiffness of parts of the driver, to see if useful characteristics ensue. The model is also used to investigate some aspects of measurements.
Convention Paper 6593 (Purchase now)
P13-5 Ground-Plane Constant Beamwidth Transducer (CBT) Loudspeaker Circular-Arc Line Arrays—D. B. (Don) Keele, Jr., Harman International Industries - Northridge, CA, USA; Douglas J. Button, JBL Professional - Northridge, CA, USA
This paper describes a design variation of the CBT loudspeaker line array that is intended to operate very close to a planar reflecting surface. The original free-standing CBT array is halved lengthwise and then positioned close to a flat surface so that acoustic reflections essentially recreate the missing half of the array. This halved array can then be doubled in size, which forms an array that is double the height of the original array. When compared to the original free-standing array, the ground-plane CBT array provides several advantages including: (1) elimination of floor reflections, (2) doubles array height, (3) doubles array sensitivity, (4) doubles array maximum SPL capability (5) extends vertical beamwidth control down an octave, and (6) minimizes near-far variation of SPL. This paper explores these characteristics through sound-field simulations and over-the-ground-plane measurements of three systems: (1) a conventional two-way compact monitor, (2) an experimental unshaded straight-line array, and (3) an experimental CBT Lengendre-shaded circular-arc curved-line array.
Convention Paper 6594 (Purchase now)
P13-6 A Balanced Modal Radiator (BMR)—Neil Harris, New Transducers Ltd. - Huntingdon, Cambs., UK; Graham Bank, Consultant
The goal of a practical loudspeaker that behaves like the "perfect point source" has been long sought. Mathematical analysis shows that the prototype for such a device does indeed exist, but it does not point to an obvious embodiment. Using this prototype, a practical flat diaphragm loudspeaker is developed, which has a substantially flat on-axis pressure response, as well as a smooth and extended power response. A fully-coupled FEA model is used to investigate the intrinsic characteristics of this radiator in both the mechanical and acoustical domains. Measurements from a real prototype loudspeaker illustrate the practicality of the method.
Convention Paper 6595 (Purchase now)