Local sound field reproduction using two closely spaced loudspeakers

When only two loudspeakers are used for the reproduction of sound for a single listener, time domain simulations show that it is advantageous that the two loudspeakers are very close together. The sound field reproduced by two loudspeakers that span 10 degrees as seen by the listener is simpler, and locally more similar to the sound field generated by a real sound source, than that reproduced by two loudspeakers that span 60 degrees. The basic physics of the problem is first explained by assuming that the sound propagates under free-field conditions. It is then demonstrated that when the influence of the listener on the incident sound waves is taken into account by modeling the listener's head as a rigid sphere, the results are qualitatively the same as in the free-field case. Consequently, two closely spaced loudspeakers are capable of accurately reproducing a desired sound field, not only at the ears of the listener but also in the, vicinity of the listener's head. This result, although counter-intuitive, is very encouraging. In particular, it suggests that many low-fidelity audio systems, such as those currently supplied with most multi-media computers, can be greatly improved.