Reproduction of binaural signals through loudspeakers

Binaural signals are sound recordings that are picked up, either by miniature microphones in the ears of humans, or - more conveniently - by built-in microphones in the ears of manikins. A very authentic sound reproduction can be achieved with binaural recordings, including the correct spatial experience, e.g. regarding the perception of direction and distance. When binaural recordings are reproduced, it is crucial that the recordings from the right ear are heard by the right ear only, and that the recordings from the left ear are heard by the left ear only. For this reason headphones are usually used for the reproduction, because they by nature have a perfect channel separation. If one listens to the sound by means of loudspeakers, the signals are mixed in the room, and both loudspeakers are heard with both ears. It is possible to use loudspeakers, though, if electronic compensation is provided for the signal that reaches the left ear from right loudspeaker and vice versa. This so-called crosstalk cancellation is extremely sensitive to several parameters in the physical setup, such as reflections from the surroundings and the listener's exact position. The use of small angles between the loudspeakers (sometimes denoted stereo-dipole) reduces the sensitivity on some points, but, in return, it increases the demands for the system on other points (e.g. the power handling capacity at low frequencies). If the listener makes small head turns - which we often do inadvertently -, the loudspeaker angle has a significant impact on the localization. The project has so far (till the end of 2002) primarily been a theoretical pilot project for a possible larger initiative for examination of possibilities and limitations for loudspeaker reproduction of binaural signals. Some of the results have, though, been tested in student projects.