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v7.0, 20040922, me

Thursday, October 28, 9:00 am – 11:30 am

Session A LOUDSPEAKERS, Part 1

Chair: Jerry Bauck,
Cooper Bauck Corporation, Tempe, AZ, USA

9:00 am
Voice Coil Impedance as a Function of Frequency and Displacement—Mark Dodd, KEF Audio UK (Ltd.), Maidstone, Kent; UK; Wolfgang Klippel, Klippel GmbH, Dresden, Germany; Jack Oclee-Brown, KEF Audio UK (Ltd), Maidstone, Kent; UK
Recent work by Klippel and Voishvillo, et al. has shown the significance of voice coil inductance in respect to the nonlinear behavior of loudspeakers. In such work the methods used to derive distortion require the inductance to be represented by an equivalent circuit rather than the frequency domain models of Wright and Leach. A new technique for measurement of displacement and frequency dependent impedance has been introduced. Thecomplex relationship between coil impedance, frequency, and displacement has been both measured and modeled, using stationary transient FEM, with exceptional agreement. Results show that the impedance model requires that its parameters vary independently with displacement to satisfactorily describe all cases. Distortion induced by the variation of impedance with coil displacement is predicted using a lumped parameter method, this prediction is compared to measurements of the actual distortion. The possibility of using a dynamic transient FE method to predict distortion is demonstrated. The nature of the distortion is discussed.
Convention Paper 6178

9:30 am
Dynamical Measurement of Loudspeaker Suspension PartsWolfgang Klippel, Klippel GmbH, Dresden, Germany
The nonlinear stiffness K(x) and the reciprocal compliance C(x) of suspension parts (spider, surrounds, cones) and passive radiators (drones) are measured versus displacement x over the full range of operation. A dynamic, nondestructive technique is developed that excites the suspension parts pneumatically under a similar condition as operated in the loudspeaker. The nonlinear parameters are estimated from the measured displacement and sound pressure signal. This guarantees highest precision of the results as well as simple handling and short measurement time. The paper develops the theoretical basis for the new technique but also discusses the practical handling, interpretation of the results, and their reproducibility.
Convention Paper 6179

10:00 am
Modeling Acoustic Room Interaction for Pistonic and Distributed-Mode Loudspeakers in the Correlation DomainNeil Harris, New Transducers Ltd. (NXT), Huntingdon, UK
AES Convention Paper 5732 (AES 114th Convention Amsterdam, The Netherlands) presented a mesh-less, analytic 3-D solution to the problem of an acoustic source located in a nonanechoic room. By applying the inverse Fourier transform, temporal data was extracted to form a complete time and frequency domain description. This paper uses the same model to investigate the correlation properties of the acoustic radiation. Maps are produced, showing how the correlation varies with position in space. Statistical analysis suggests a possible objective classification of the diffuseness of acoustic fields by scalar quantities such as mean and standard deviation of correlation coefficient values. The distribution of correlation values is seen to follow the beta distribution quite closely.
Convention Paper 6180

10:30 am
Compensating the Acoustical Loading of Small Loudspeakers Mounted Near DesktopsAndrew Goldberg, Aki Mäkivirta, Ari Varla, Genelec Oy, Iislami, Finland
In professional audio applications, small loudspeakers are often mounted on or near (within the loudspeaker’s near field region) large solid surfaces, such as mixing consoles, desktops, and work surfaces. In approximately two-thirds of loudspeakers mounted in such a fashion, the magnitude response is compromised in a predictable and systematic way. An upward deviation of peak value 5.0 dB ± 1.5 dB centered on 141 Hz ± 31 Hz was observable in approximately 80 percent of the cases studied. An additional Room Response Control in active loudspeakers is proposed to compensate for this aberration. A statistical analysis of 89 near-field loudspeakers helps define the correction filter and quantifies the effectiveness of the fixed filter design. Use of the proposed filter in an automated response optimization algorithm for in-situ response equalization is demonstrated.
Convention Paper 6181

11:00 am
A-5 Image Source Model for Loudspeaker Enclosure
Juha Backman, Nokia, Espoo, Finland; Helsinki University of Technology, Espoo, Finland
Image source models can be applied for predicting loudspeaker enclosure interior sound fields as well as for larger spaces. The model allows very efficient analysis of the effects of driver and port placement and enclosure shape for rectangular enclosures.
Convention Paper 6182

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