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Session F Sunday, May 13 9:00 - 13:00 hr Room C/D

Loudspeakers, Part 2

Chair: Neville Thiele, University of Sydney, Sydney, Australia

9:00 hr F-1
SSAVV: A Loudspeaker Systems Simulation Software
Juan G█mez-Alfageme & Manuel Recuero-Lopez
Universidad Polit╚cnica de Madrid, Madrid, Spain

The software we will describe allows the study and analysis of direct radiation loudspeaker systems of one or multiple ways and with different configurations in the woofer one, by means of computer simulation, based on electro-acoustical analogous circuits. This program allows simulating the electrodynamic loudspeaker behavior from the electrical, mechanical and acoustical point of view, and could get information about different variables frequency response.
Paper 5318

9:30 hr F-2
Horn's Directivity Related to the Pressure Distribution at their Mouth: Part 2
Mario Di Cola, Davide Doldi (1) & Davide Saronni (2)
Politecnico di Milano, Milan, Italy
(2) Independent System Engineer, Milan, Italy

The directional properties of horn devices are governed by the wave frontÝs shape presented at the mouth. An analysis of the sound pressure distribution across the horn's mouth that we call Pressure Distribution Mapping could certainly be helpful to understand how the wave front is shaped there. Moreover, this could help to understand what happen in some particular circumstances. For example midrange beaming or high frequency mouth diffraction phenomena are two well known obstacles to overcome designing a broad band constant directivity horn. The method forwarded by us in the previous work is here extended to some different cases and improved in the data processing. The results that come out of such analysis will be shown through graphic illustrations. Presented will be the results obtained performing measurements upon real devices correlated to traditional directivity plots as well.
Paper 5319

10:00 hr F-3
Verification of an Approach for Transient Structural Simulation of Loudspeakers incorporating Damping
Gary Geaves (1), Jon Moore (1), David Henwood (2) & Peter Fryer (1)
 B&W Loudspeakers, Steyning, UK
 University of Brighton, Brighton, UK

An approach for simulating transient structural wave propagation in loudspeakers is described. The Finite Element Method is used for spatial discretization and the Laplace transform for the time solution. The accuracy of the spatial discretization is verified by simulating the acoustic frequency response of a loudspeaker and comparing the results with measured data. A damping model is introduced that approximates standard hysteretic damping and yet can be used directly in both the time and frequency domains. The overall approach is verified by comparing laser measured and simulated results of the transient structural response of a loudspeaker to an impulse-like excitation. Finally, structural energy is plotted and discussed.
Paper 5320

10:30 hr F-4
Series-Type Passive Crossover Networks. Part 1: First and Less-Than-Second Order Crossovers
Umberto Nicolao (1) & Francesco Maffioli (2)
(1) Consultant, Santorso, Italy
(2) Politecnico di Milano, Milan, Italy

Although there is no question that the implementation of a parallel crossover network represents the most useful and flexible approach to the electro-acoustical transducer matching in a loudspeaker system, there is also no doubt that series-type crossover networks can provide the designer with some interesting features. Unfortunately, the conventional formulae are restricted to the case where the impedance loads, representing the drivers, are equal to each other, therefore limiting the application range. This work is intended to explore in more detail the series crossover network topology, presenting more general formulae and showing the advantages and disadvantages with respect to a parallel solution. In this paper, first to ýless-than-secondţ order circuit realizations will be considered.
Paper 5321

11:00 hr F-5
Electronically Controlled Loudspeaker Arrays without Side Lobes
Johan van der Werff
Peutz & Associates, Nijmegen, The Netherlands

It is possible to arrange loudspeakers in such a way that only one lobe emits from the array. This lobe can have an arbitrary beam width and to a certain extent an arbitrary beam shape. Because of this control over the beam, narrow beam widths can be made where wave fronts travel coherently 200 meters or more. It is possible now to cover an area below and in front of the array from almost zero to 200 meters with even direct-sound distribution of +/- 3 dB, where the frequency response is only dependant on the transducer used and the air absorption. This eliminates the coloration-effects due to side or grating lobes.
Paper 5322

11:30 hr F-6
Listening Test Results from a New Digital Loudspeaker/Room Correction Systems
Lars Johansen (1) & Per Rubak (2)
 Aalborg University, Aalborg, Denmark
 Engineering College of Aarhus, Aarhus, Denmark

A new three band loudspeaker/room correction system has been designed in order to reveal what room acoustic properties and psychoacoustic relations are necessary and sufficient to consider. Most parameters are variable, and the system is designed to enable real-time implementation. A small scale listening test has revealed that even when operating on high-end audio equipment and employing a well damped listening room, improvements in reproduction quality can be achieved. Also in a listening position far away from the optimal and corrected one, some improvement is observed.
Paper 5323

12:00 hr F-7
The Effect of Porous Materials on the Acoustic Response of DML Panels
Elena Prokofieva (1), Kirill Horoshenkov (1) & Neil Harris (2)
 University of Bradford, Bradford, UK
 New Transducers Limited, Huntingdon, UK

This work investigates experimentally the effect a porous layer on the acoustic response of distributed mode loudspeakers (DMLs), which are manufactured under license from NXT plc. The experiments were carried out in an anechoic chamber. The results suggest that a porous layer between a rigid base and a DML panel can considerably alter the acoustic emission in the near-field and in the far-field. This is typically illustrated by a reduction in the level of fluctuations in the emitted acoustic pressure spectra. These fluctuations are normally associated with interference between the sound emitted by the front surface of the speaker and by that emitted from the back. The results also suggest that the interference pattern in the air gap is altered by the porous layer, so that some individual resonances in the acoustic pressure spectra which inevitably occur between the rigid base and the vibrating plate can appear suppressed. A numerical simulation was carried out to model this effect.
Paper 5324

12:30 hr F-8
Design Principles for Symmetrical Band-Pass Loudspeaker Systems of Sixth and Eighth Order
Andrzej Dobrucki & Grzegorz Matusiak
Wroclaw University of Technology, Wroclaw, Poland

A denominator of a transfer function of a symmetrical band-pass loudspeaker system can be presented as a product of three or four second order polynomials. Every polynomial can represent the denominator of the transfer function of an electrical filter. The product of remaining polynomials forms the denominator of the transfer function of a non-symmetrical loudspeaker system. Then, various combinations of these polynomials give various possibilities of realization of the entire system.
Paper 5325

 

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