Simone Fontana

MEASURING IMPULSE RESPONSES CONTAINING COMPLETE SPATIAL INFORMATION

Traditional impulse response measurements did capture limited spatial information. Often just omnidirectional sources and microphones are employed. In some cases it was attempted to get more spatial information employing directive transdudcers: known examples are binaural microphones, figure‐of‐8 microphones, and directive loudspeakers. However, these approaches are not scientifically based and do not provide an easy way to process and visualize the spatial information. On the other side, psychoacoustics studies demonstrated that ‘‘spatial hearing’’ is one of the dominant factors for the acoustic quality of rooms, particularly for theatres and concert halls. Of consequence, it is necessarily to reformulate the problem entirely, describing the transfer function between a source and a receiver as a time/space filter. This requires us to ‘‘sample’’ the impulse response not only in time, but also in space. This is possible employing spherical harmonics for describing, with a predefined accuracy, the directivi...

Generation of Private Sound With a Circular Loudspeaker Array and the Weighted Pressure Matching Method

In this paper, we propose a system for private sound which is based on the weighted pressure matching method (WPMM). The aim is to design the input signals to an array of loudspeakers that allow for the synthesis of a target field defined with large amplitude variations between the so-called dark points and the listeners position. The system enables listeners to control the trade-off between directivity performance and the accuracy of reproduction of the target field at the listening position when the input energy to the array is limited. This is achieved by calculating the WPMM weight in the dark zone based on a constraint on the characteristics of the sound field in the listening zone. The system is validated for a number of predefined use-case scenarios. The results of the experiments in an anechoic environment with a circular array prototype show that listeners can control the performance trade-off in a wide frequency range. In the second part of the paper, algorithms are presented for the fast update of the input signals when the user selects a new value of the performance constraint.

A general radiation model for sound fields and nearfield acoustical holography in wedge propagation spaces

In this work an expression for the solution of the Helmholtz equation for wedge spaces is derived. Such propagation spaces represent scenarios for many acoustical problems where a free field assumption is not eligible. The proposed sound field model is derived from the general solution of the wave equation in cylindrical coordinates, using sets of orthonormal basis functions. The latter are modified to satisfy several boundary conditions representing the reflective behaviour of wedge-shaped propagation spaces. This formulation is then used in the context of nearfield acoustical holography (NAH) and to obtain the expression of the Neumann Green function. The model and its suitability for NAH is demonstrated through both numerical simulations and measured data, where the latter was acquired for the specific case of a loudspeaker on a hemi-cylindrical rigid baffle.