The sound pressure and the sound velocity in the near field of a linear loudspeaker array is proposed and investigated from a mathematical point of view. Four different piston models, employing circular, elliptical and (two different models of) rectangular pistons, are explicitly calculated and closed-form solutions using higher transcendental functions are provided. As a representative overview of results, near field directional diagrams for different frequencies, different distances of the field point, as well as for varying phases of signal, are shown. Based on these results some optimization methods for phases of signal, loudspeaker geometry and array geometry are developed.
Convention Paper 5608

09:30 h
R2 Intensity Measurements of the Acoustic Emission from a DML Panel – Elena Prokofieva¹, Kirill Horoshenkov¹, Neil Harris² - ¹University of Bradford, Bradford, UK; ²NXT Ltd, Huntingdon, UK

An experimental investigation is reported into the effects of a porous layer on the radiated sound intensity from distributed mode loudspeakers (DMLs). For an unbaffled panel, the results suggest that attaching an absorbent layer behind the panel leads to a smoothing of the spectra of sound intensity. When a specially developed enclosure was used, an improvement in the low frequency response of DML panel was observed. The inclusion of a porous layer in this enclosure further reduced the fluctuations of the emitted sound spectra, and smoothed the resonance peaks in the low frequency range.
Convention Paper 5609

10:00 h
R3 Distributed Mode Loudspeaker Arrays – Lee Copley, Mark Avis, Trevor Cox, University of Salford, Salford, UK

The usefulness of Distributed Mode Loudspeakers (DMLs) in arrays has been investigated. The design goal is an array that evenly distributes energy over a hemi-disc. A model has been developed to predict trends of DML array radiation and compared with measurements. This model enables the performance of established array technologies to be tested. When several DML panels are positioned in an array, spatial aliasing results, as would be expected. Conventional array techniques, such as number theory modulation, can improve the radiation characteristics. Complete omni directionality is not achieved.
Convention Paper 5610

10:30 h
R4 Multichannel Inverse Filtering of Distributed Mode Loudspeakers for Wavefield Synthesis – Etienne Corteel¹, Ulrich Horbach², Renato Pellegrini² - ¹IRCAM, Paris, France; ²Studer Prof. Audio AG, Regensdorf, Switzerland

A new filter design method to synthesize the wave field of a given virtual source in a horizontal plane is presented. The reproduction of the wave field is performed by a novel “multi-exciter” distributed mode loudspeaker, which contains a special array of transducers, attached on a single panel. Below the spatial aliasing frequency, the diffuse behavior of the panel as well as the individual directional characteristics of the transducers are taken into account accurately. Above that corner frequency, a modified design procedure is proposed, which employs energy considerations and spatial averaging. A number of such modules can be cascaded to a system, which allows true spatial audio reproduction over a large listening area.
Convention Paper 5611

11:00 h
R5 Diffuse Signal Processing and Acoustic Source Characterization for Applications in Synthetic Loudspeaker Arrays – Malcolm Hawksford¹, Neil Harris² - ¹University of Essex, Colchester, UK; ²New Transducers Limited, Huntingdon, UK

Active diffuse loudspeaker arrays can be implemented by incorporating a distribution of small radiating elements each characterized by processes that embed a unique diffuse impulse response. The properties of synthetic diffuse impulses are investigated both individually and collectively and algorithmic generation techniques presented. The diffuse properties of such synthetic arrays are confirmed both by polar response descriptors and spatial correlation techniques.
Convention Paper 5612