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Last Updated: 20060821, mei

P5 - Loudspeakers - Part 1

Friday, October 6, 8:30 am — 11:00 am

Chair: Steve Temme, Listen, Inc. - Boston, MA, USA

P5-1 Measurement and Visualization of Loudspeaker Cone VibrationWolfgang Klippel, Klippel GmbH - Dresden, Germany; Joachim Schlechter, University of Technology - Dresden, Germany
Optical measurement of loudspeaker cone vibration (scanning vibrometry) can also be accomplished by using a laser triangulation technique that is a cost effective alternative to Doppler interferometry. Since triangulation sensors provide primarily displacement, advanced signal processing is required to measure the break-up modes up to 20 kHz at sufficient signal to noise ratio. In addition to stroboscopic animation of the radiation pattern a new decomposition technique is presented for the visualization of the measured data. Radial and circular modes can be separated and the total vibration can be split into radiating and non-radiating vibration components. This kind of postprocessing reveals critical vibration modes, simplifies the interpretation, and gives indications for further improvements.
Convention Paper 6882 (Purchase now)

P5-2 An Extended Small Signal Parameter Loudspeaker Model for the Linear Array TransducerAndrew Unruh, Christopher Struck, Richard Little, Ali Jabbari, Jens-Peter Axelsson, Tymphany Corporation - Cupertino, CA, USA
The Linear Array Transducer (LAT) is a tubular form-factor loudspeaker driver technology that, to a good first approximation, can be modeled by the standard linear time invariant small signal parameter (SSP) loudspeaker circuit model. However, to understand the behavior of a LAT to a greater level of detail, the SSP model can be extended with the addition of eight additional mechanical parameters. In this paper the nature of these additional parameters in the model are explained. Further, an extended blocked impedance model is introduced that may be used with LATs or conventional loudspeakers. Additionally, the model is correlated to measurements of currently available LATs. Finally, it is shown how the LAT extended SSP model is approximated by the standard loudspeaker SSP model.
Convention Paper 6883 (Purchase now)

P5-3 An Optimized Full Bandwidth 20 Hz to 20 kHz Digitally Controlled Coaxial SourceHmaied Shaiek, ENST de Bretagne - Brest Cedex, France; Bernard Debail, Yvon Kerneis, Cabasse Acoustic Center - Plouzané, France; Jean Marc Boucher, ENST de Bretagne - Brest Cedex, France; Pierre Yves Diquelou, Cabasse Acoustic Center - Plouzané, France
This paper addresses the design considerations of the first four-ways, full-bandwidth coaxial loudspeaker system. Unlike conventional coaxial drivers, a special motor configuration has been considered in order to approach to a real coincident source. Practical constraints of moving mass element and cone shape will be exhibited with regard to the targeted sound radiation characteristics. Dedicated digital signal processing techniques will be implemented in order to optimize relevant parameters such as frequency response, directivity index, and radiation pattern of the system especially on drivers’ overlap bands. This optimization is achieved thanks to a complex weighting of the crossover filter transfer functions. The optimal weights are approached with a new routine using the gradient algorithm.
Convention Paper 6884 (Purchase now)

P5-4 Linear Phase Crossover Filter Advantages in Concert Sound Reinforcement Systems: A Practical ApproachMario Di Cola, Audio Labs Systems - Milano, Italy; Miguel T. Hadelich, Dolby Laboratories - San Francisco, CA, USA; Daniele Ponteggia, Studio Ponteggia - Terni, Italy; Davide Saronni, Audio Labs Systems - Milano, Italy
Today concert sound reinforcement systems constantly demand improved performances. The chosen crossover approach could be a key point to improve the overall speaker performances, and modern DSP offers several chances to achieve this. FIR Linear Phase Filters, one of the methods of processing that belongs strictly to digital domain, could be very useful tools. FIR Linear Phase Crossover, even though well known and studied for some time, is for practical reasons not widely applied at the moment. Practical issues in real world applications suggest mixing together FIR and IIR techniques to arrive as a more efficient and practical approach. While the result of such a combination will not provide a perfect, ideal linear phase system, the overall result will be very similar to that of a Minimum Phase system. Better transient response, increased dept and warmth, improved coverage stability if compared to standard crossover approach: these are some of the advantages that can be achieved. In this practical research, an existing DSP-based piece of equipment has been used to process some real world loudspeaker systems. This piece of equipment can perform all the required processing using mixed FIR and IIR filter techniques. The differences and the advantages in time response, phase response, directivity improvements, and increased output capability will be reported in order to compare the results. Different kinds of loudspeaker systems have been processed and analyzed setting them both for the Minimum Phase response and other All Pass responses. The results will be shown and demonstrated with the large support of real measurements results.
Convention Paper 6885 (Purchase now)

P5-5 Optimum Diaphragm and Waveguide Geometry for Coincident Source Drive UnitsMark Dodd, KEF Audio - Maidstone, Kent, UK
Coincident source loudspeakers avoid the response and directivity irregularities seen with conventional spaced drivers in the crossover region. Earlier work has shown that by placing the high frequency driver at the apex of the low frequency diaphragm the directivity of both drivers may be regularized in the crossover region. This paper describes the application of transient finite element method to explore how some simple sources interact with various boundary conditions. A novel geometry giving much-improved bandwidth and directivity is introduced. Simulated results of an idealized high frequency driver using this geometry are compared to those of an idealized direct radiating dome. The implementation of a new design incorporating this novel structure is discussed, and results from a complete design are presented.
Convention Paper 6886 (Purchase now)

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