WAVE FIELD SYNTHESIS: FROM RESEARCH TO APPLICATIONS Karlheinz Brandenburg, Sandra Brix and Thomas Sporer Fraunhofer IDMT & Ilmenau Technical University Langewiesener Str. 22, 98693 Ilmenau, Germany Phone: +49 3677 69-4341, Fax: +49 3677 69-4399, E-mail: bdg@idmt.fraunhofer.de Web: www.idmt.fraunhofer.de ABSTRACT Wave Field Synthesis can dramatically increase the quality of sound reproduction. To create new vir- tual rooms with realistic ambience within any listen- ing space, new ideas for room simulation and virtual acoustics are needed. The work originally started at Delft Technical University (TU Delft) is now contin- ued at a number of research locations. The paper will introduce the basic techniques, show the require- ments for a number of real world applications and give an overview of current research topics. The ap- plications scenarios include cinemas, concert halls and all kinds of music performances (indoor and out- door). 1. INTRODUCTION The history of spatial sound reproduction began originally with the stereophonic reproduction by us- ing the concept of the acoustic curtain (many micro- phones wired 1:1 with many loudspeakers) at the Bell Laboratories. Research conducted by Blumlein resulted in channel reduction down to basically three channels, but due to long-time practical limitations only two channel stereo was applicable. Looking at further evolution from two-channel stereophony over quadrophony to 5.1, there are limitations which have not been overcome since the early days of Blumlein. The reproduction system quality depends strongly on the properties of the reproduced sound field and on psychoacoustic effects (phantom sources). Besides phantom sources and problems that come with them (no precise source positioning, no precise source localization, etc.) the well-known existence of a “sweet spot” represents a limit of best spatial impression and immersion in a reproduction room. There have been many efforts to solve these prob- lems especially at universities, but all these investi- gations did not achieve economic impact. In the late 90 th the 3D audio profile of the MPEG-4 standard prepared the field for a significant step forward. Since the beginning of 2001 universities, research institutes and companies joined their efforts in the development of 3D audio. The EU-project called CARROUSO [1] has developed key technologies for recording, encoding, transmitting, decoding and ren- dering a sound field in an efficient way at highest perceived quality. Important key components for these technologies were the Wave-Field-Synthesis (WFS) as a new way of reproducing sound and MPEG-4 codecs. WFS was invented at the TU Delft in Holland and has been demonstrated in academic environments successfully in the past [2, 3]. Due to its high computational complexity it has not found broad application until today. The progress in mi- croelectronics with decreasing costs of computing power made the first application in the professional market possible. In February 2003 Fraunhofer IDMT implemented a large WFS array in the Ilmenau cin- ema and new applications for WFS technology are around the corner. 2. BASIC THEORY Wave-Field-Synthesis (WFS) is based on the wave theory concept of Huygens: All points on a wave front serve as individual point sources of spherical secondary wave fronts. This principle is applied in acoustics by using a large number of small and closely spaced loudspeakers (loudspeaker arrays) (Figure 1). Each loudspeaker in the array is fed with a corresponding driving signal calculated by means of algorithms based on the Kirchhoff- Helmholtz integrals and Rayleighs representation theorems [4]. 1369