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Session D Saturday, May 12 13:30 - 18:00 hr Room C/D

Loudspeakers, Part 1

Chair: David Clark, DLC Design, Wixom, MI, USA

13:30 hr D-1
Comparison of Non-Linear Properties of Closed, Vented and Passive-Radiator
Loudspeaker Boxes
Bronislaw Zoltogorski
Wroclaw University of Technology, Wroclaw, Poland

The basic types of loudspeaker boxes have been compared with regards to non-linear distortions introduced to radiated acoustical signal. For given driver characterized by small signal parameters and additional four coefficients of Bl and stiffness non-linear models, the frequency characteristics of SPL and THD have been calculated by numerical integration of a non-linear differential equation set corresponding to the electrical equivalent circuit. The submitted MATHCAD programs enable to design the non-linear characteristics of analyzed loudspeaker system.
Printed Paper not available

14:00 hr D-2
Loudspeaker Litz Wire
Steven Hutt
Harman/Becker Automotive Systems, Martinsville, IN, USA

Studies of loudspeaker components most often concentrate on the functions that add or detract from the acoustically measurable performance aspects of loudspeakers - such as cones, suspensions, or magnet and motor assemblies. On the other hand, application of litz wire into the loudspeaker design is not well documented. Yet the litz wire has a profound impact on reliability and has a propensity to cause problems such as unacceptable extraneous noise. After a review of classical theory on the vibration of strings, bars and elasticity one will surmise that understanding the vibration of litz wire is not trivial. This paper reviews a loudspeaker case study and the ramifications of using behaved and not so well behaved litz wire.
Paper 5303

14:30 hr D-3
Line Arrays: Theory and Applications
Mark Ureda
JBL Professional, Santa Ana, CA, USA

Line arrays of loudspeakers are often employed to provide increased directivity, generally in the vertical plane. For improved performance, contemporary line arrays employ specially designed loudspeaker elements to provide a nearly continuous line source. However, even these may have ìimperfectionsî relative to a perfect line source. This paper provides mathematical models to evaluate the directivity response of line sources and to quantify the effects of certain imperfections.
Paper 5304

15:00 hr D-4
Crossover Systems in Digital Loudspeakers
Simon Busbridge (1), Yaxiong Huang (1) & Peter Fryer (2)
University of Brighton, Brighton, UK
B&W Loudspeakers, Steyning, UK

A digital loudspeaker is one that does not contain any form of embedded digital to analogue converter. From a consideration of the mathematical operations describing the digital to analogue conversion process in a digital loudspeaker, it is concluded that n identical analogue filters (where n is the number of bits) separately filtering each bit driver offers a practical alternative to digital signal processing. The implementation of a multiple driver multiple voice coil digital loudspeaker is described. The effect of component tolerances in the crossover and compatibility with the requirements of current drive are evaluated. The interactions between the motion emf, driving current and mutual coupling emfís are considered. It is concluded that this method of crossover implementation is both viable and achievable.
Paper 5305

15:30 hr D-5
Sound Directivity Control using Striped Panel Loudspeaker
Marko Antila (1), Vesa V”lim”ki (2) & Jari Kataja (1)
 VTT Automation, Tampere, Finland
 Helsinki University of Technology, Espoo, Finland

The sound radiation properties of a striped panel loudspeaker are modified in this study. The panel loudspeaker is based on Electromechanical film (EMFi) and consists of 14 individual sound radiating areas in form of narrow stripes. Each stripe can be driven individually so that the panel radiation pattern can be modified and it can be used as a directivity-controlled sound source in audio applications. The performance of the panel was analyzed using an acoustical boundary element method (BEM) model. For real-time directivity control, an algorithm was developed to process the input signals to gain appropriate radiation patterns. The measurements carried out in anechoic conditions were used to verify that the striped EMFi panel operates according to the simulations and that it produces the desired directivity pattern.
Paper 5306

16:00 hr D-6
Phase Considerations in Loudspeaker Systems
Neville Thiele
University of Sydney, Sydney, Australia

The effect of phase rotation on the reproduced quality of an audio signal is well known. However, the effect of phase rotations in the responses of individual drivers on the amplitude response of a multi-way system is often misunderstood. The paper quantifies this effect and, in showing that it is similar in nature to the better understood problem of time alignment, demonstrates how similar remedies may be applied to both effects together. It also shows how lowering the low frequency cutoff of a loudspeaker system can reduce its group delay errors in-band.
Paper 5307

16:30 hr D-7
Fast and Accurate Measurement of the Linear Transducer Parameters
Wolfgang Klippel & Ulf Seidel
Klippel, Dresden, Germany

A new measurement technique is presented for the estimation of the linear parameters of the lumped transducer model. It is based on the measurement of the electrical impedance and the voice coil displacement using a laser sensor. This technique identifies the electrical and mechanical parameters directly and dispenses with a second measurement of the driver using a test enclosure or an additional mass. Problems due to leakage of the enclosure or the attachment of the mass are avoided giving accurate and reliable results. The measurement of the displacement also allows identification of the mechanical compliance versus frequency (explaining suspension creep) which is the basis for predicting the radiated sound pressure response at low frequencies precisely. The linear parameters measured at various amplitudes are compared with the results of large signal parameter identification and the need for nonlinear transducer modeling is discussed.
Paper 5308

17:00 hr D-8
Far-Field Loudspeaker Interaction: Accuracy in Theory and Practice
Justin Baird, John Meyer & Perrin Meyer
Meyer Sound Laboratories, Berkeley, CA, USA

The "Far-Field" model of loudspeaker interaction is a widely used technique to model the sound pressure radiated from arrays of loudspeakers. We will provide a quick but thorough introduction to the mathematical foundation of the far-field model, and how the model compares, with regards to accuracy and computational efficiency, to other formulations such as series solutions and boundary element methods. We present data from a series solution of a model spherical loudspeaker, and compare this mathematical model to actual high-resolution measurements. Using this model loudspeaker, we discuss methods for calculating and measuring accurate loudspeaker far-field polar (or directivity) patterns, and we discuss how the accuracy of the far-field polar patterns affect the accuracy of the far-field model.
Paper 5309

17:30 hr D-9
Speaker Auralization - Subjective Evaluation of Nonlinear Distortion
Wolfgang Klippel
Klippel, Dresden, Germany

A new auralization technique is presented for the objective and subjective assessment of drivers in the large signal domain. Using the results of the large signal parameter identification a digital model of the particular driver is realized in a digital signal processor (DSP) to simulate the sound pressure output for any given input signal (test signal, music). This technique combines objective analysis and subjective listening test to assess the linear and distortion components in real time. This valuable tool shows the impact of each distortion component on sound quality and allows driver optimization with respect to performance, size, weight and cost.
Paper 5310

 

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