Multizone Soundfield Reproduction Using Ambisonics

Ambisonics system is based on the theory that soundfield can be decomposed or reconstructed by a series of spherical harmonics. Ambisonics is one of the classic methods about soundfield reproduction, and it can provide a same sound environment to each listener without fixed audience orientation. However, Ambisonics can not provide different soundfiled for different types of listeners or different audience orientations. Multizone soundfield reproduction is a technology with the purpose of providing an individual sound environment to each listener without physical isolations or the use of headphones. There are many potential applications such as surround sound systems in exhibition centers, and personal loudspeaker systems in the shared office space, quiet zones in a noisy environment, etc. In this paper, we present an in-depth analysis of reproducing multizone soundfield based on Ambisonics, and three-dimensional(3D) multizone soundfield reproduction in reverberant environments.The main work of this paper is embodied as follows:(1) The 3D multizone soundfield reproduction based on Ambisonics is deeply studied. Based on several single zone soundfield reproduction methods including mode matching approach, simple source approach and continuous loudspeaker array hypothesis approach, a general expression of the loudspeaker driving signal is derived, which can reproduce the sound field effectively. The inverse problem that leads to unstable solutions due to the ill-conditioning of matrix always exist when deriving the loudspeaker driving signal is taken into account in this paper. The genetic algorithm is introduced and applied to the solution of the inverse problem in order to obtain stable solutions and to reduce soundfield reproduction error.(2) Spatial multizone soundfield reproduction is an extension of single zone soundfield reproduction. Multizone soundfield reproduction can provide different soundfiled for different types of listeners or different audience orientation. Based on the in-depth analysis of Ambisonics, a method of reproducing 3D multizone soundfield using a single spherical loudspeaker array is proposed. A set of equivalent global soundfield coefficients is achieved based on the addition theorem for spherical Bessel functions. The complicated multizone soundfield reproduction problem can be translated into a reproduction of single zone soundfield. By applying the driving signal to the corresponding loudspeakers, the target 3D multizone soundfield in free-field can be accurately reproduced.(3) A method for reproducing a desired 3D multizone soundfield in reverberant environments using a single spherical loudspeaker array is proposed. Based on the addition theorem for spherical Bessel functions, the desired global soundfield is derived by translating local desired soundfield to a single global coordinate system. The optimal least-squares solutions for the loudspeaker driving signal that minimize the reproduction error are derived by the modal space approach. A practical method to precisely measure the acoustic transfer function(ATF) between each loudspeaker and the reproduction region is proposed. By applying the driving signal to the corresponding loudspeakers, the target 3D multizone soundfield in reverberant environments can be accurately reproduced.