Mihailo Kolundzija

Publications associées (16)

Baffled Circular Loudspeaker Array With Broadband High Directivity

Christof Faller, Mihailo Kolundzija, Martin Vetterli

Super-directional loudspeaker arrays can be used to achieve high directivity in a limited low-frequency range. As opposed to microphone arrays, the distance between the loudspeakers has to be relatively large, resulting in aliasing starting at relatively low frequencies. On the other hand, mounting a loudspeaker on a rigid baffle (e.g., a rigid cylinder or sphere) increases its directivity with frequency. Using super-directional array techniques at low frequencies and leveraging loudspeakers' increased directivity at high frequencies enables achieving high directivity both at low and high frequencies. The design of baffled circular loudspeaker arrays and an improved beamforming procedure for achieving high directivity in a broad frequency range is described.

2010

Chargement

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Gradient based microphone arrays, the horizontal sound field's plane wave decomposition, and the corresponding circular harmonics decomposition are reviewed. Further, a general relation between directivity patterns of the horizontal sound field gradients and the circular harmonics of any order is derived. Based on this relation, a number of example differential microphone arrays are analyzed, including arrays capable of approximating the sound pressure gradients necessary for obtaining the circular harmonics up to order three.

2010

Chargement

Design and Limitations of Non-Coincidence Correction Filters for Soundfield Microphones

Christof Faller, Mihailo Kolundzija

The tetrahedral microphone capsule arrangement in a Soundfield microphone captures a so-called A-format signal which is then converted to a corresponding B-format signal. The phase differences between the A-format signal channels due to non-coincidence of the microphone capsules cause errors in the corresponding B-format signals and linear combinations thereof. Various strategies for designing B-format non-coincidence correction filters are compared and limitations are discussed.

2009

Chargement

Designing Practical Filters For Sound Field Reconstruction

Christof Faller, Mihailo Kolundzija, Martin Vetterli

Multichannel sound field reproduction techniques, such as Wave Field Synthesis (WFS) and Sound Field Reconstruction (SFR), define loudspeaker filters in the frequency domain. However, in order to use these techniques in practical systems, one needs to convert these frequency-domain characteristics to practical and efficient time-domain digital filters. Additional limitation of SFR comes from the fact that it uses a numerical matrix pseudoinversion procedure, where the obtained filters are sensitive to numerical errors when the system matrix has a high condition number. This paper describes physically-motivated modifications of the SFR approach that allow for mitigating conditioning problems and frequency-domain loudspeaker filter smoothing that allows for designing short time-domain filters while maintaining high sound field reproduction accuracy. It also provides comparisons of sound field reproduction accuracy of WFS and SFR using the obtained discrete-time filters.

2009

Chargement

Sound Field Reconstruction: An Improved Approach For Wave Field Synthesis

Christof Faller, Mihailo Kolundzija, Martin Vetterli

Wave field synthesis (WFS) is a prevalent approach to multiple-loudspeaker sound reproduction for an extended listening area. Although powerful as a theoretical concept, its deployment is hampered by practical limitations due to diffraction, aliasing, and the effects of the listening room. Reconstructing the desired sound field in the listening area, accounting for the medium propagation characteristic, is another approach termed as sound field reconstruction (SFR). It is based on the essential band-limitedness of the sound field, which enables a continuous matching of the reconstructed and the desired sound field by their matching on a discrete set of points spaced below the Nyquist distance. We compare the two approaches in a common single-source free-field setup, and show that SFR provides improved sound field reproduction compared to WFS in a wide listening area around a defined reference line.

2009

Chargement

Spatio-Temporal Gradient Analysis of Differential Microphone Arrays

Christof Faller, Mihailo Kolundzija, Martin Vetterli

The literature on gradient and differential microphone arrays makes a distinction between the two types, and nevertheless shows how both types can be used to obtain the same directional responses. A more theoretically sound rationale for using delays in differential microphone arrays has not yet been given. This paper presents a gradient analysis of the sound field viewed as a spatio-temporal phenomenon, and gives a theoretical interpretation of the working principles of gradient and differential microphone arrays. It shows that both types of microphone arrays can be viewed as devices for approximately measuring spatio-temporal derivatives of the sound field. Furthermore, it also motivates the design of high-order differential microphone arrays using the aforementioned spatio-temporal gradient analysis.

2009

Chargement